diff --git a/BUILD b/BUILD
index 09f53f9..0a5139d 100644
--- a/BUILD
+++ b/BUILD
@@ -180,6 +180,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/subchannel_index.h",
     "src/core/client_config/uri_parser.h",
     "src/core/compression/algorithm_metadata.h",
     "src/core/compression/message_compress.h",
@@ -311,6 +312,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/subchannel_index.c",
     "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
@@ -498,6 +500,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/subchannel_index.h",
     "src/core/client_config/uri_parser.h",
     "src/core/compression/algorithm_metadata.h",
     "src/core/compression/message_compress.h",
@@ -616,6 +619,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/subchannel_index.c",
     "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
@@ -1272,6 +1276,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/subchannel_index.c",
     "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
@@ -1440,6 +1445,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/subchannel_index.h",
     "src/core/client_config/uri_parser.h",
     "src/core/compression/algorithm_metadata.h",
     "src/core/compression/message_compress.h",
diff --git a/Makefile b/Makefile
index c53b743..51b8921 100644
--- a/Makefile
+++ b/Makefile
@@ -2345,6 +2345,7 @@
     src/core/client_config/resolvers/sockaddr_resolver.c \
     src/core/client_config/subchannel.c \
     src/core/client_config/subchannel_factory.c \
+    src/core/client_config/subchannel_index.c \
     src/core/client_config/uri_parser.c \
     src/core/compression/algorithm.c \
     src/core/compression/message_compress.c \
@@ -2688,6 +2689,7 @@
     src/core/client_config/resolvers/sockaddr_resolver.c \
     src/core/client_config/subchannel.c \
     src/core/client_config/subchannel_factory.c \
+    src/core/client_config/subchannel_index.c \
     src/core/client_config/uri_parser.c \
     src/core/compression/algorithm.c \
     src/core/compression/message_compress.c \
@@ -3197,6 +3199,7 @@
     test/cpp/util/create_test_channel.cc \
     test/cpp/util/string_ref_helper.cc \
     test/cpp/util/subprocess.cc \
+    test/cpp/util/test_credentials_provider.cc \
 
 
 LIBGRPC++_TEST_UTIL_OBJS = $(addprefix $(OBJDIR)/$(CONFIG)/, $(addsuffix .o, $(basename $(LIBGRPC++_TEST_UTIL_SRC))))
@@ -3247,6 +3250,7 @@
 $(OBJDIR)/$(CONFIG)/test/cpp/util/create_test_channel.o: $(GENDIR)/src/proto/grpc/testing/echo_messages.pb.cc $(GENDIR)/src/proto/grpc/testing/echo_messages.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.cc
 $(OBJDIR)/$(CONFIG)/test/cpp/util/string_ref_helper.o: $(GENDIR)/src/proto/grpc/testing/echo_messages.pb.cc $(GENDIR)/src/proto/grpc/testing/echo_messages.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.cc
 $(OBJDIR)/$(CONFIG)/test/cpp/util/subprocess.o: $(GENDIR)/src/proto/grpc/testing/echo_messages.pb.cc $(GENDIR)/src/proto/grpc/testing/echo_messages.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.cc
+$(OBJDIR)/$(CONFIG)/test/cpp/util/test_credentials_provider.o: $(GENDIR)/src/proto/grpc/testing/echo_messages.pb.cc $(GENDIR)/src/proto/grpc/testing/echo_messages.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.pb.cc $(GENDIR)/src/proto/grpc/testing/echo.grpc.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.pb.cc $(GENDIR)/src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.cc
 
 
 LIBGRPC++_UNSECURE_SRC = \
@@ -13050,6 +13054,7 @@
 test/cpp/util/string_ref_helper.cc: $(OPENSSL_DEP)
 test/cpp/util/subprocess.cc: $(OPENSSL_DEP)
 test/cpp/util/test_config.cc: $(OPENSSL_DEP)
+test/cpp/util/test_credentials_provider.cc: $(OPENSSL_DEP)
 endif
 
 .PHONY: all strip tools dep_error openssl_dep_error openssl_dep_message git_update stop buildtests buildtests_c buildtests_cxx test test_c test_cxx install install_c install_cxx install-headers install-headers_c install-headers_cxx install-shared install-shared_c install-shared_cxx install-static install-static_c install-static_cxx strip strip-shared strip-static strip_c strip-shared_c strip-static_c strip_cxx strip-shared_cxx strip-static_cxx dep_c dep_cxx bins_dep_c bins_dep_cxx clean
diff --git a/binding.gyp b/binding.gyp
index 59356d3..a2a64ff 100644
--- a/binding.gyp
+++ b/binding.gyp
@@ -584,6 +584,7 @@
         'src/core/client_config/resolvers/sockaddr_resolver.c',
         'src/core/client_config/subchannel.c',
         'src/core/client_config/subchannel_factory.c',
+        'src/core/client_config/subchannel_index.c',
         'src/core/client_config/uri_parser.c',
         'src/core/compression/algorithm.c',
         'src/core/compression/message_compress.c',
diff --git a/build.yaml b/build.yaml
index de741d6..cb6cb56 100644
--- a/build.yaml
+++ b/build.yaml
@@ -270,6 +270,7 @@
   - src/core/client_config/resolvers/sockaddr_resolver.h
   - src/core/client_config/subchannel.h
   - src/core/client_config/subchannel_factory.h
+  - src/core/client_config/subchannel_index.h
   - src/core/client_config/uri_parser.h
   - src/core/compression/algorithm_metadata.h
   - src/core/compression/message_compress.h
@@ -385,6 +386,7 @@
   - src/core/client_config/resolvers/sockaddr_resolver.c
   - src/core/client_config/subchannel.c
   - src/core/client_config/subchannel_factory.c
+  - src/core/client_config/subchannel_index.c
   - src/core/client_config/uri_parser.c
   - src/core/compression/algorithm.c
   - src/core/compression/message_compress.c
@@ -735,6 +737,7 @@
   - test/cpp/util/create_test_channel.h
   - test/cpp/util/string_ref_helper.h
   - test/cpp/util/subprocess.h
+  - test/cpp/util/test_credentials_provider.h
   src:
   - src/proto/grpc/testing/echo_messages.proto
   - src/proto/grpc/testing/echo.proto
@@ -745,6 +748,7 @@
   - test/cpp/util/create_test_channel.cc
   - test/cpp/util/string_ref_helper.cc
   - test/cpp/util/subprocess.cc
+  - test/cpp/util/test_credentials_provider.cc
   deps:
   - grpc++
   - grpc_test_util
@@ -2648,8 +2652,8 @@
     LDXX: clang++
     compile_the_world: true
     test_environ:
-      ASAN_OPTIONS: suppressions=tools/asan_suppressions.txt:detect_leaks=1:color=always
-      LSAN_OPTIONS: suppressions=tools/asan_suppressions.txt:report_objects=1
+      ASAN_OPTIONS: detect_leaks=1:color=always
+      LSAN_OPTIONS: suppressions=tools/lsan_suppressions.txt:report_objects=1
     timeout_multiplier: 1.5
   asan-noleaks:
     CC: clang
diff --git a/doc/load-balancing.md b/doc/load-balancing.md
new file mode 100644
index 0000000..681be02
--- /dev/null
+++ b/doc/load-balancing.md
@@ -0,0 +1,97 @@
+Load Balancing in gRPC
+=======================
+
+# Objective
+
+To design a load balancing API between a gRPC client and a Load Balancer to
+instruct the client how to send load to multiple backend servers. 
+
+# Background
+
+Prior to any gRPC specifics, we explore some usual ways to approach load
+balancing.
+
+### Proxy Model
+
+Using a proxy provides a solid trustable client that can report load to the load
+balancing system. Proxies typically require more resources to operate since they
+have temporary copies of the RPC request and response. This model also increases
+latency to the RPCs.
+
+The proxy model was deemed inefficient when considering request heavy services
+like storage. 
+
+### Balancing-aware Client
+
+This thicker client places more of the load balancing logic in the client. For
+example, the client could contain many load balancing policies (Round Robin,
+Random, etc) used to select servers from a list. In this model, a list of
+servers would be either statically configured in the client, provided by the
+name resolution system, an external load balancer, etc. In any case, the client
+is responsible for choosing the preferred server from the list. 
+
+One of the drawbacks of this approach is writing and maintaining the load
+balancing policies in multiple languages and/or versions of the clients. These
+policies can be fairly complicated. Some of the algorithms also require client
+to server communication so the client would need to get thicker to support
+additional RPCs to get health or load information in addition to sending RPCs
+for user requests.
+
+It would also significantly complicate the client's code: the new design hides
+the load balancing complexity of multiple layers and presents it as a simple
+list of servers to the client.
+
+### External Load Balancing Service
+
+The client load balancing code is kept simple and portable, implementing
+well-known algorithms (ie, Round Robin) for server selection.
+Complex load balancing algorithms are instead provided by the load balancer. The
+client relies on the load balancer to provide _load balancing configuration_ and
+_the list of servers_ to which the client should send requests. The balancer
+updates the server list as needed to balance the load as well as handle server
+unavailability or health issues. The load balancer will make any necessary
+complex decisions and inform the client. The load balancer may communicate with
+the backend servers to collect load and health information.
+
+# Proposed Architecture
+
+The gRPC load balancing approach follows the third approach, by having an
+external load balancer which provides simple clients with a list of servers.
+
+## Client
+
+When establishing a gRPC stream to the balancer, the client will send an initial
+request to the load balancer (via a regular gRPC message). The load balancer
+will respond with client config (including, for example, settings for flow
+control, RPC deadlines, etc.) or a redirect to another load balancer. If the
+balancer did not redirect the client, it will then send a list of servers to the
+client. The client will contain simple load balancing logic for choosing the
+next server when it needs to send a request.
+
+## Load Balancer
+
+The Load Balancer is responsible for providing the client with a list of servers
+and client RPC parameters. The balancer chooses when to update the list of
+servers and can decide whether to provide a complete list, a subset, or a
+specific list of “picked” servers in a particular order. The balancer can
+optionally provide an expiration interval after which the server list should no
+longer be trusted and should be updated by the balancer.
+
+The load balancer may open reporting streams to each server contained in the
+server list. These streams are primarily used for load reporting. For example,
+Weighted Round Robin requires that the servers report utilization to the load
+balancer in order to compute the next list of servers.
+
+## Server
+
+The gRPC Server is responsible for answering RPC requests and providing
+responses to the client. The server will also report load to the load balancer
+if a reporting stream was opened for this purpose.
+
+### Security 
+
+The load balancer may be separate from the actual server backends and a
+compromise of the load balancer should only lead to a compromise of the
+loadbalancing functionality. In other words, a compromised load balancer should
+not be able to cause a client to trust a (potentially malicious) backend server
+any more than in a comparable situation without loadbalancing. 
diff --git a/gRPC.podspec b/gRPC.podspec
index 036deea..d2d151b 100644
--- a/gRPC.podspec
+++ b/gRPC.podspec
@@ -184,6 +184,7 @@
                       'src/core/client_config/resolvers/sockaddr_resolver.h',
                       'src/core/client_config/subchannel.h',
                       'src/core/client_config/subchannel_factory.h',
+                      'src/core/client_config/subchannel_index.h',
                       'src/core/client_config/uri_parser.h',
                       'src/core/compression/algorithm_metadata.h',
                       'src/core/compression/message_compress.h',
@@ -328,6 +329,7 @@
                       'src/core/client_config/resolvers/sockaddr_resolver.c',
                       'src/core/client_config/subchannel.c',
                       'src/core/client_config/subchannel_factory.c',
+                      'src/core/client_config/subchannel_index.c',
                       'src/core/client_config/uri_parser.c',
                       'src/core/compression/algorithm.c',
                       'src/core/compression/message_compress.c',
@@ -492,6 +494,7 @@
                               'src/core/client_config/resolvers/sockaddr_resolver.h',
                               'src/core/client_config/subchannel.h',
                               'src/core/client_config/subchannel_factory.h',
+                              'src/core/client_config/subchannel_index.h',
                               'src/core/client_config/uri_parser.h',
                               'src/core/compression/algorithm_metadata.h',
                               'src/core/compression/message_compress.h',
diff --git a/grpc.gemspec b/grpc.gemspec
index 792222a..061b0f2 100755
--- a/grpc.gemspec
+++ b/grpc.gemspec
@@ -180,6 +180,7 @@
   s.files += %w( src/core/client_config/resolvers/sockaddr_resolver.h )
   s.files += %w( src/core/client_config/subchannel.h )
   s.files += %w( src/core/client_config/subchannel_factory.h )
+  s.files += %w( src/core/client_config/subchannel_index.h )
   s.files += %w( src/core/client_config/uri_parser.h )
   s.files += %w( src/core/compression/algorithm_metadata.h )
   s.files += %w( src/core/compression/message_compress.h )
@@ -311,6 +312,7 @@
   s.files += %w( src/core/client_config/resolvers/sockaddr_resolver.c )
   s.files += %w( src/core/client_config/subchannel.c )
   s.files += %w( src/core/client_config/subchannel_factory.c )
+  s.files += %w( src/core/client_config/subchannel_index.c )
   s.files += %w( src/core/client_config/uri_parser.c )
   s.files += %w( src/core/compression/algorithm.c )
   s.files += %w( src/core/compression/message_compress.c )
diff --git a/include/grpc++/impl/codegen/call.h b/include/grpc++/impl/codegen/call.h
index e65349d..5e450b0 100644
--- a/include/grpc++/impl/codegen/call.h
+++ b/include/grpc++/impl/codegen/call.h
@@ -272,6 +272,7 @@
 class DeserializeFunc {
  public:
   virtual Status Deserialize(grpc_byte_buffer* buf, int max_message_size) = 0;
+  virtual ~DeserializeFunc() {}
 };
 
 template <class R>
@@ -283,6 +284,8 @@
     return SerializationTraits<R>::Deserialize(buf, message_, max_message_size);
   }
 
+  ~DeserializeFuncType() override {}
+
  private:
   R* message_;  // Not a managed pointer because management is external to this
 };
diff --git a/include/grpc++/support/channel_arguments.h b/include/grpc++/support/channel_arguments.h
index a2960a7..a9ede35 100644
--- a/include/grpc++/support/channel_arguments.h
+++ b/include/grpc++/support/channel_arguments.h
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -51,7 +51,7 @@
 /// concrete setters are provided.
 class ChannelArguments {
  public:
-  ChannelArguments() {}
+  ChannelArguments();
   ~ChannelArguments() {}
 
   ChannelArguments(const ChannelArguments& other);
@@ -62,8 +62,8 @@
 
   void Swap(ChannelArguments& other);
 
-  /// Populates this instance with the arguments from \a channel_args. Does not
-  /// take ownership of \a channel_args.
+  /// Dump arguments in this instance to \a channel_args. Does not take
+  /// ownership of \a channel_args.
   ///
   /// Note that the underlying arguments are shared. Changes made to either \a
   /// channel_args or this instance would be reflected on both.
@@ -77,6 +77,9 @@
   /// Set the compression algorithm for the channel.
   void SetCompressionAlgorithm(grpc_compression_algorithm algorithm);
 
+  /// The given string will be sent at the front of the user agent string.
+  void SetUserAgentPrefix(const grpc::string& user_agent_prefix);
+
   // Generic channel argument setters. Only for advanced use cases.
   /// Set an integer argument \a value under \a key.
   void SetInt(const grpc::string& key, int value);
@@ -92,6 +95,17 @@
   friend class SecureChannelCredentials;
   friend class testing::ChannelArgumentsTest;
 
+  /// Default pointer argument operations.
+  struct PointerVtableMembers {
+    static void* Copy(void* in) { return in; }
+    static void Destroy(void* in) {}
+    static int Compare(void* a, void* b) {
+      if (a < b) return -1;
+      if (a > b) return 1;
+      return 0;
+    }
+  };
+
   // Returns empty string when it is not set.
   grpc::string GetSslTargetNameOverride() const;
 
diff --git a/include/grpc/impl/codegen/grpc_types.h b/include/grpc/impl/codegen/grpc_types.h
index ea1e96c..b11f6ff 100644
--- a/include/grpc/impl/codegen/grpc_types.h
+++ b/include/grpc/impl/codegen/grpc_types.h
@@ -68,6 +68,12 @@
   GRPC_ARG_POINTER
 } grpc_arg_type;
 
+typedef struct grpc_arg_pointer_vtable {
+  void *(*copy)(void *p);
+  void (*destroy)(void *p);
+  int (*cmp)(void *p, void *q);
+} grpc_arg_pointer_vtable;
+
 /** A single argument... each argument has a key and a value
 
     A note on naming keys:
@@ -88,8 +94,7 @@
     int integer;
     struct {
       void *p;
-      void *(*copy)(void *p);
-      void (*destroy)(void *p);
+      const grpc_arg_pointer_vtable *vtable;
     } pointer;
   } value;
 } grpc_arg;
diff --git a/include/grpc/support/avl.h b/include/grpc/support/avl.h
index 28eb5b1..2fe2d0b 100644
--- a/include/grpc/support/avl.h
+++ b/include/grpc/support/avl.h
@@ -81,11 +81,12 @@
     if key exists in avl, the new tree's key entry updated
     (i.e. a duplicate is not created) */
 GPRAPI gpr_avl gpr_avl_add(gpr_avl avl, void *key, void *value);
-/** return a new tree with key deleted */
+/** return a new tree with key deleted
+    implicitly unrefs avl to allow easy chaining. */
 GPRAPI gpr_avl gpr_avl_remove(gpr_avl avl, void *key);
 /** lookup key, and return the associated value.
     does not mutate avl.
     returns NULL if key is not found. */
 GPRAPI void *gpr_avl_get(gpr_avl avl, void *key);
 
-#endif
+#endif /* GRPC_SUPPORT_AVL_H */
diff --git a/include/grpc/support/useful.h b/include/grpc/support/useful.h
index 9f08d78..a0e76da 100644
--- a/include/grpc/support/useful.h
+++ b/include/grpc/support/useful.h
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -72,4 +72,6 @@
     0x0f0f0f0f) %                                \
    255)
 
+#define GPR_ICMP(a, b) ((a) < (b) ? -1 : ((a) > (b) ? 1 : 0))
+
 #endif /* GRPC_SUPPORT_USEFUL_H */
diff --git a/package.json b/package.json
index 0feb027..0f7f454 100644
--- a/package.json
+++ b/package.json
@@ -125,6 +125,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.h",
     "src/core/client_config/subchannel.h",
     "src/core/client_config/subchannel_factory.h",
+    "src/core/client_config/subchannel_index.h",
     "src/core/client_config/uri_parser.h",
     "src/core/compression/algorithm_metadata.h",
     "src/core/compression/message_compress.h",
@@ -256,6 +257,7 @@
     "src/core/client_config/resolvers/sockaddr_resolver.c",
     "src/core/client_config/subchannel.c",
     "src/core/client_config/subchannel_factory.c",
+    "src/core/client_config/subchannel_index.c",
     "src/core/client_config/uri_parser.c",
     "src/core/compression/algorithm.c",
     "src/core/compression/message_compress.c",
diff --git a/src/core/channel/channel_args.c b/src/core/channel/channel_args.c
index 0427ce0..bae7a90 100644
--- a/src/core/channel/channel_args.c
+++ b/src/core/channel/channel_args.c
@@ -37,6 +37,7 @@
 
 #include <grpc/census.h>
 #include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 #include <grpc/support/useful.h>
 
@@ -55,9 +56,8 @@
       break;
     case GRPC_ARG_POINTER:
       dst.value.pointer = src->value.pointer;
-      dst.value.pointer.p = src->value.pointer.copy
-                                ? src->value.pointer.copy(src->value.pointer.p)
-                                : src->value.pointer.p;
+      dst.value.pointer.p =
+          src->value.pointer.vtable->copy(src->value.pointer.p);
       break;
   }
   return dst;
@@ -94,6 +94,58 @@
   return grpc_channel_args_copy_and_add(a, b->args, b->num_args);
 }
 
+static int cmp_arg(const grpc_arg *a, const grpc_arg *b) {
+  int c = GPR_ICMP(a->type, b->type);
+  if (c != 0) return c;
+  c = strcmp(a->key, b->key);
+  if (c != 0) return c;
+  switch (a->type) {
+    case GRPC_ARG_STRING:
+      return strcmp(a->value.string, b->value.string);
+    case GRPC_ARG_INTEGER:
+      return GPR_ICMP(a->value.integer, b->value.integer);
+    case GRPC_ARG_POINTER:
+      c = GPR_ICMP(a->value.pointer.p, b->value.pointer.p);
+      if (c != 0) {
+        c = GPR_ICMP(a->value.pointer.vtable, b->value.pointer.vtable);
+        if (c == 0) {
+          c = a->value.pointer.vtable->cmp(a->value.pointer.p,
+                                           b->value.pointer.p);
+        }
+      }
+      return c;
+  }
+  GPR_UNREACHABLE_CODE(return 0);
+}
+
+/* stabilizing comparison function: since channel_args ordering matters for
+ * keys with the same name, we need to preserve that ordering */
+static int cmp_key_stable(const void *ap, const void *bp) {
+  const grpc_arg *const *a = ap;
+  const grpc_arg *const *b = bp;
+  int c = strcmp((*a)->key, (*b)->key);
+  if (c == 0) c = GPR_ICMP(*a, *b);
+  return c;
+}
+
+grpc_channel_args *grpc_channel_args_normalize(const grpc_channel_args *a) {
+  grpc_arg **args = gpr_malloc(sizeof(grpc_arg *) * a->num_args);
+  for (size_t i = 0; i < a->num_args; i++) {
+    args[i] = &a->args[i];
+  }
+  qsort(args, a->num_args, sizeof(grpc_arg *), cmp_key_stable);
+
+  grpc_channel_args *b = gpr_malloc(sizeof(grpc_channel_args));
+  b->num_args = a->num_args;
+  b->args = gpr_malloc(sizeof(grpc_arg) * b->num_args);
+  for (size_t i = 0; i < a->num_args; i++) {
+    b->args[i] = copy_arg(args[i]);
+  }
+
+  gpr_free(args);
+  return b;
+}
+
 void grpc_channel_args_destroy(grpc_channel_args *a) {
   size_t i;
   for (i = 0; i < a->num_args; i++) {
@@ -104,9 +156,7 @@
       case GRPC_ARG_INTEGER:
         break;
       case GRPC_ARG_POINTER:
-        if (a->args[i].value.pointer.destroy) {
-          a->args[i].value.pointer.destroy(a->args[i].value.pointer.p);
-        }
+        a->args[i].value.pointer.vtable->destroy(a->args[i].value.pointer.p);
         break;
     }
     gpr_free(a->args[i].key);
@@ -208,3 +258,14 @@
     return (1u << GRPC_COMPRESS_ALGORITHMS_COUNT) - 1; /* All algs. enabled */
   }
 }
+
+int grpc_channel_args_compare(const grpc_channel_args *a,
+                              const grpc_channel_args *b) {
+  int c = GPR_ICMP(a->num_args, b->num_args);
+  if (c != 0) return c;
+  for (size_t i = 0; i < a->num_args; i++) {
+    c = cmp_arg(&a->args[i], &b->args[i]);
+    if (c != 0) return c;
+  }
+  return 0;
+}
diff --git a/src/core/channel/channel_args.h b/src/core/channel/channel_args.h
index 480cc9a..b3a7c9f 100644
--- a/src/core/channel/channel_args.h
+++ b/src/core/channel/channel_args.h
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -40,6 +40,9 @@
 /* Copy some arguments */
 grpc_channel_args *grpc_channel_args_copy(const grpc_channel_args *src);
 
+/* Copy some arguments, stably sorting keys */
+grpc_channel_args *grpc_channel_args_normalize(const grpc_channel_args *a);
+
 /** Copy some arguments and add the to_add parameter in the end.
    If to_add is NULL, it is equivalent to call grpc_channel_args_copy. */
 grpc_channel_args *grpc_channel_args_copy_and_add(const grpc_channel_args *src,
@@ -85,4 +88,7 @@
 int grpc_channel_args_compression_algorithm_get_states(
     const grpc_channel_args *a);
 
+int grpc_channel_args_compare(const grpc_channel_args *a,
+                              const grpc_channel_args *b);
+
 #endif /* GRPC_INTERNAL_CORE_CHANNEL_CHANNEL_ARGS_H */
diff --git a/src/core/client_config/connector.c b/src/core/client_config/connector.c
index 1603ffb..aa34aa7 100644
--- a/src/core/client_config/connector.c
+++ b/src/core/client_config/connector.c
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -33,8 +33,9 @@
 
 #include "src/core/client_config/connector.h"
 
-void grpc_connector_ref(grpc_connector* connector) {
+grpc_connector* grpc_connector_ref(grpc_connector* connector) {
   connector->vtable->ref(connector);
+  return connector;
 }
 
 void grpc_connector_unref(grpc_exec_ctx* exec_ctx, grpc_connector* connector) {
diff --git a/src/core/client_config/connector.h b/src/core/client_config/connector.h
index b4482fa..b91eb51 100644
--- a/src/core/client_config/connector.h
+++ b/src/core/client_config/connector.h
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -81,7 +81,7 @@
                   grpc_connect_out_args *out_args, grpc_closure *notify);
 };
 
-void grpc_connector_ref(grpc_connector *connector);
+grpc_connector *grpc_connector_ref(grpc_connector *connector);
 void grpc_connector_unref(grpc_exec_ctx *exec_ctx, grpc_connector *connector);
 /** Connect using the connector: max one outstanding call at a time */
 void grpc_connector_connect(grpc_exec_ctx *exec_ctx, grpc_connector *connector,
diff --git a/src/core/client_config/subchannel.c b/src/core/client_config/subchannel.c
index 0a996a1..6599c75 100644
--- a/src/core/client_config/subchannel.c
+++ b/src/core/client_config/subchannel.c
@@ -36,16 +36,17 @@
 #include <string.h>
 
 #include <grpc/support/alloc.h>
+#include <grpc/support/avl.h>
 
 #include "src/core/channel/channel_args.h"
 #include "src/core/channel/client_channel.h"
 #include "src/core/channel/connected_channel.h"
 #include "src/core/client_config/initial_connect_string.h"
+#include "src/core/client_config/subchannel_index.h"
 #include "src/core/iomgr/timer.h"
 #include "src/core/profiling/timers.h"
 #include "src/core/surface/channel.h"
 #include "src/core/transport/connectivity_state.h"
-#include "src/core/transport/connectivity_state.h"
 
 #define INTERNAL_REF_BITS 16
 #define STRONG_REF_MASK (~(gpr_atm)((1 << INTERNAL_REF_BITS) - 1))
@@ -94,6 +95,8 @@
   struct sockaddr *addr;
   size_t addr_len;
 
+  grpc_subchannel_key *key;
+
   /** initial string to send to peer */
   gpr_slice initial_connect_string;
 
@@ -207,6 +210,7 @@
   grpc_connectivity_state_destroy(exec_ctx, &c->state_tracker);
   grpc_connector_unref(exec_ctx, c->connector);
   grpc_pollset_set_destroy(&c->pollset_set);
+  grpc_subchannel_key_destroy(exec_ctx, c->key);
   gpr_free(c);
 }
 
@@ -222,22 +226,42 @@
   return old_val;
 }
 
-void grpc_subchannel_ref(grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+grpc_subchannel *grpc_subchannel_ref(grpc_subchannel *c
+                                         GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
   old_refs = ref_mutate(c, (1 << INTERNAL_REF_BITS),
                         0 REF_MUTATE_PURPOSE("STRONG_REF"));
   GPR_ASSERT((old_refs & STRONG_REF_MASK) != 0);
+  return c;
 }
 
-void grpc_subchannel_weak_ref(grpc_subchannel *c
-                                  GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+grpc_subchannel *grpc_subchannel_weak_ref(grpc_subchannel *c
+                                              GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
   old_refs = ref_mutate(c, 1, 0 REF_MUTATE_PURPOSE("WEAK_REF"));
   GPR_ASSERT(old_refs != 0);
+  return c;
+}
+
+grpc_subchannel *grpc_subchannel_ref_from_weak_ref(
+    grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+  if (!c) return NULL;
+  for (;;) {
+    gpr_atm old_refs = gpr_atm_acq_load(&c->ref_pair);
+    if (old_refs >= (1 << INTERNAL_REF_BITS)) {
+      gpr_atm new_refs = old_refs + (1 << INTERNAL_REF_BITS);
+      if (gpr_atm_rel_cas(&c->ref_pair, old_refs, new_refs)) {
+        return c;
+      }
+    } else {
+      return NULL;
+    }
+  }
 }
 
 static void disconnect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
   grpc_connected_subchannel *con;
+  grpc_subchannel_index_unregister(exec_ctx, c->key, c);
   gpr_mu_lock(&c->mu);
   GPR_ASSERT(!c->disconnected);
   c->disconnected = 1;
@@ -276,10 +300,19 @@
   return (uint32_t)(gpr_time_to_millis(gpr_now(GPR_CLOCK_MONOTONIC)));
 }
 
-grpc_subchannel *grpc_subchannel_create(grpc_connector *connector,
+grpc_subchannel *grpc_subchannel_create(grpc_exec_ctx *exec_ctx,
+                                        grpc_connector *connector,
                                         grpc_subchannel_args *args) {
-  grpc_subchannel *c = gpr_malloc(sizeof(*c));
+  grpc_subchannel_key *key = grpc_subchannel_key_create(connector, args);
+  grpc_subchannel *c = grpc_subchannel_index_find(exec_ctx, key);
+  if (c) {
+    grpc_subchannel_key_destroy(exec_ctx, key);
+    return c;
+  }
+
+  c = gpr_malloc(sizeof(*c));
   memset(c, 0, sizeof(*c));
+  c->key = key;
   gpr_atm_no_barrier_store(&c->ref_pair, 1 << INTERNAL_REF_BITS);
   c->connector = connector;
   grpc_connector_ref(c->connector);
@@ -305,7 +338,8 @@
   grpc_connectivity_state_init(&c->state_tracker, GRPC_CHANNEL_IDLE,
                                "subchannel");
   gpr_mu_init(&c->mu);
-  return c;
+
+  return grpc_subchannel_index_register(exec_ctx, key, c);
 }
 
 static void continue_connect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
diff --git a/src/core/client_config/subchannel.h b/src/core/client_config/subchannel.h
index 57c7c9d..313e63c 100644
--- a/src/core/client_config/subchannel.h
+++ b/src/core/client_config/subchannel.h
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -48,6 +48,8 @@
 #ifdef GRPC_STREAM_REFCOUNT_DEBUG
 #define GRPC_SUBCHANNEL_REF(p, r) \
   grpc_subchannel_ref((p), __FILE__, __LINE__, (r))
+#define GRPC_SUBCHANNEL_REF_FROM_WEAK_REF(p, r) \
+  grpc_subchannel_ref_from_weak_ref((p), __FILE__, __LINE__, (r))
 #define GRPC_SUBCHANNEL_UNREF(cl, p, r) \
   grpc_subchannel_unref((cl), (p), __FILE__, __LINE__, (r))
 #define GRPC_SUBCHANNEL_WEAK_REF(p, r) \
@@ -66,6 +68,8 @@
   , const char *file, int line, const char *reason
 #else
 #define GRPC_SUBCHANNEL_REF(p, r) grpc_subchannel_ref((p))
+#define GRPC_SUBCHANNEL_REF_FROM_WEAK_REF(p, r) \
+  grpc_subchannel_ref_from_weak_ref((p))
 #define GRPC_SUBCHANNEL_UNREF(cl, p, r) grpc_subchannel_unref((cl), (p))
 #define GRPC_SUBCHANNEL_WEAK_REF(p, r) grpc_subchannel_weak_ref((p))
 #define GRPC_SUBCHANNEL_WEAK_UNREF(cl, p, r) \
@@ -79,13 +83,15 @@
 #define GRPC_SUBCHANNEL_REF_EXTRA_ARGS
 #endif
 
-void grpc_subchannel_ref(grpc_subchannel *channel
-                             GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
+grpc_subchannel *grpc_subchannel_ref(grpc_subchannel *channel
+                                         GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
+grpc_subchannel *grpc_subchannel_ref_from_weak_ref(
+    grpc_subchannel *channel GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
 void grpc_subchannel_unref(grpc_exec_ctx *exec_ctx,
                            grpc_subchannel *channel
                                GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
-void grpc_subchannel_weak_ref(grpc_subchannel *channel
-                                  GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
+grpc_subchannel *grpc_subchannel_weak_ref(grpc_subchannel *channel
+                                              GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
 void grpc_subchannel_weak_unref(grpc_exec_ctx *exec_ctx,
                                 grpc_subchannel *channel
                                     GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
@@ -146,6 +152,8 @@
     grpc_subchannel_call *subchannel_call);
 
 struct grpc_subchannel_args {
+  /* When updating this struct, also update subchannel_index.c */
+
   /** Channel filters for this channel - wrapped factories will likely
       want to mutate this */
   const grpc_channel_filter **filters;
@@ -159,7 +167,8 @@
 };
 
 /** create a subchannel given a connector */
-grpc_subchannel *grpc_subchannel_create(grpc_connector *connector,
+grpc_subchannel *grpc_subchannel_create(grpc_exec_ctx *exec_ctx,
+                                        grpc_connector *connector,
                                         grpc_subchannel_args *args);
 
 #endif /* GRPC_INTERNAL_CORE_CLIENT_CONFIG_SUBCHANNEL_H */
diff --git a/src/core/client_config/subchannel_index.c b/src/core/client_config/subchannel_index.c
new file mode 100644
index 0000000..f78a7fd
--- /dev/null
+++ b/src/core/client_config/subchannel_index.c
@@ -0,0 +1,259 @@
+//
+//
+// Copyright 2016, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//
+
+#include "src/core/client_config/subchannel_index.h"
+
+#include <stdbool.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/avl.h>
+#include <grpc/support/tls.h>
+
+#include "src/core/channel/channel_args.h"
+
+// a map of subchannel_key --> subchannel, used for detecting connections
+// to the same destination in order to share them
+static gpr_avl g_subchannel_index;
+
+static gpr_mu g_mu;
+
+struct grpc_subchannel_key {
+  grpc_connector *connector;
+  grpc_subchannel_args args;
+};
+
+GPR_TLS_DECL(subchannel_index_exec_ctx);
+
+static void enter_ctx(grpc_exec_ctx *exec_ctx) {
+  GPR_ASSERT(gpr_tls_get(&subchannel_index_exec_ctx) == 0);
+  gpr_tls_set(&subchannel_index_exec_ctx, (intptr_t)exec_ctx);
+}
+
+static void leave_ctx(grpc_exec_ctx *exec_ctx) {
+  GPR_ASSERT(gpr_tls_get(&subchannel_index_exec_ctx) == (intptr_t)exec_ctx);
+  gpr_tls_set(&subchannel_index_exec_ctx, 0);
+}
+
+static grpc_exec_ctx *current_ctx() {
+  grpc_exec_ctx *c = (grpc_exec_ctx *)gpr_tls_get(&subchannel_index_exec_ctx);
+  GPR_ASSERT(c != NULL);
+  return c;
+}
+
+static grpc_subchannel_key *create_key(
+    grpc_connector *connector, grpc_subchannel_args *args,
+    grpc_channel_args *(*copy_channel_args)(const grpc_channel_args *args)) {
+  grpc_subchannel_key *k = gpr_malloc(sizeof(*k));
+  k->connector = grpc_connector_ref(connector);
+  k->args.filter_count = args->filter_count;
+  k->args.filters = gpr_malloc(sizeof(*k->args.filters) * k->args.filter_count);
+  memcpy((grpc_channel_filter *)k->args.filters, args->filters,
+         sizeof(*k->args.filters) * k->args.filter_count);
+  k->args.addr_len = args->addr_len;
+  k->args.addr = gpr_malloc(args->addr_len);
+  memcpy(k->args.addr, args->addr, k->args.addr_len);
+  k->args.args = copy_channel_args(args->args);
+  return k;
+}
+
+grpc_subchannel_key *grpc_subchannel_key_create(grpc_connector *connector,
+                                                grpc_subchannel_args *args) {
+  return create_key(connector, args, grpc_channel_args_normalize);
+}
+
+static grpc_subchannel_key *subchannel_key_copy(grpc_subchannel_key *k) {
+  return create_key(k->connector, &k->args, grpc_channel_args_copy);
+}
+
+static int subchannel_key_compare(grpc_subchannel_key *a,
+                                  grpc_subchannel_key *b) {
+  int c = GPR_ICMP(a->connector, b->connector);
+  if (c != 0) return c;
+  c = GPR_ICMP(a->args.addr_len, b->args.addr_len);
+  if (c != 0) return c;
+  c = GPR_ICMP(a->args.filter_count, b->args.filter_count);
+  if (c != 0) return c;
+  c = memcmp(a->args.addr, b->args.addr, a->args.addr_len);
+  if (c != 0) return c;
+  c = memcmp(a->args.filters, b->args.filters,
+             a->args.filter_count * sizeof(*a->args.filters));
+  return grpc_channel_args_compare(a->args.args, b->args.args);
+}
+
+void grpc_subchannel_key_destroy(grpc_exec_ctx *exec_ctx,
+                                 grpc_subchannel_key *k) {
+  grpc_connector_unref(exec_ctx, k->connector);
+  gpr_free(k->args.addr);
+  gpr_free((grpc_channel_args *)k->args.filters);
+  grpc_channel_args_destroy((grpc_channel_args *)k->args.args);
+  gpr_free(k);
+}
+
+static void sck_avl_destroy(void *p) {
+  grpc_subchannel_key_destroy(current_ctx(), p);
+}
+
+static void *sck_avl_copy(void *p) { return subchannel_key_copy(p); }
+
+static long sck_avl_compare(void *a, void *b) {
+  return subchannel_key_compare(a, b);
+}
+
+static void scv_avl_destroy(void *p) {
+  GRPC_SUBCHANNEL_WEAK_UNREF(current_ctx(), p, "subchannel_index");
+}
+
+static void *scv_avl_copy(void *p) {
+  GRPC_SUBCHANNEL_WEAK_REF(p, "subchannel_index");
+  return p;
+}
+
+static const gpr_avl_vtable subchannel_avl_vtable = {
+    .destroy_key = sck_avl_destroy,
+    .copy_key = sck_avl_copy,
+    .compare_keys = sck_avl_compare,
+    .destroy_value = scv_avl_destroy,
+    .copy_value = scv_avl_copy};
+
+void grpc_subchannel_index_init(void) {
+  g_subchannel_index = gpr_avl_create(&subchannel_avl_vtable);
+  gpr_mu_init(&g_mu);
+}
+
+void grpc_subchannel_index_shutdown(void) {
+  gpr_mu_destroy(&g_mu);
+  gpr_avl_unref(g_subchannel_index);
+}
+
+grpc_subchannel *grpc_subchannel_index_find(grpc_exec_ctx *exec_ctx,
+                                            grpc_subchannel_key *key) {
+  enter_ctx(exec_ctx);
+
+  // Lock, and take a reference to the subchannel index.
+  // We don't need to do the search under a lock as avl's are immutable.
+  gpr_mu_lock(&g_mu);
+  gpr_avl index = gpr_avl_ref(g_subchannel_index);
+  gpr_mu_unlock(&g_mu);
+
+  grpc_subchannel *c =
+      GRPC_SUBCHANNEL_REF_FROM_WEAK_REF(gpr_avl_get(index, key), "index_find");
+  gpr_avl_unref(index);
+
+  leave_ctx(exec_ctx);
+  return c;
+}
+
+grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
+                                                grpc_subchannel_key *key,
+                                                grpc_subchannel *constructed) {
+  enter_ctx(exec_ctx);
+
+  grpc_subchannel *c = NULL;
+
+  while (c == NULL) {
+    // Compare and swap loop:
+    // - take a reference to the current index
+    gpr_mu_lock(&g_mu);
+    gpr_avl index = gpr_avl_ref(g_subchannel_index);
+    gpr_mu_unlock(&g_mu);
+
+    // - Check to see if a subchannel already exists
+    c = gpr_avl_get(index, key);
+    if (c != NULL) {
+      // yes -> we're done
+      GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, constructed, "index_register");
+    } else {
+      // no -> update the avl and compare/swap
+      gpr_avl updated =
+          gpr_avl_add(gpr_avl_ref(index), subchannel_key_copy(key),
+                      GRPC_SUBCHANNEL_WEAK_REF(constructed, "index_register"));
+
+      // it may happen (but it's expected to be unlikely)
+      // that some other thread has changed the index:
+      // compare/swap here to check that, and retry as necessary
+      gpr_mu_lock(&g_mu);
+      if (index.root == g_subchannel_index.root) {
+        GPR_SWAP(gpr_avl, updated, g_subchannel_index);
+        c = constructed;
+      }
+      gpr_mu_unlock(&g_mu);
+
+      gpr_avl_unref(updated);
+    }
+    gpr_avl_unref(index);
+  }
+
+  leave_ctx(exec_ctx);
+
+  return c;
+}
+
+void grpc_subchannel_index_unregister(grpc_exec_ctx *exec_ctx,
+                                      grpc_subchannel_key *key,
+                                      grpc_subchannel *constructed) {
+  enter_ctx(exec_ctx);
+
+  bool done = false;
+  while (!done) {
+    // Compare and swap loop:
+    // - take a reference to the current index
+    gpr_mu_lock(&g_mu);
+    gpr_avl index = gpr_avl_ref(g_subchannel_index);
+    gpr_mu_unlock(&g_mu);
+
+    // Check to see if this key still refers to the previously
+    // registered subchannel
+    grpc_subchannel *c = gpr_avl_get(index, key);
+    if (c != constructed) {
+      gpr_avl_unref(index);
+      break;
+    }
+
+    // compare and swap the update (some other thread may have
+    // mutated the index behind us)
+    gpr_avl updated = gpr_avl_remove(gpr_avl_ref(index), key);
+
+    gpr_mu_lock(&g_mu);
+    if (index.root == g_subchannel_index.root) {
+      GPR_SWAP(gpr_avl, updated, g_subchannel_index);
+      done = true;
+    }
+    gpr_mu_unlock(&g_mu);
+
+    gpr_avl_unref(updated);
+    gpr_avl_unref(index);
+  }
+
+  leave_ctx(exec_ctx);
+}
diff --git a/src/core/client_config/subchannel_index.h b/src/core/client_config/subchannel_index.h
new file mode 100644
index 0000000..095ef17
--- /dev/null
+++ b/src/core/client_config/subchannel_index.h
@@ -0,0 +1,77 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_INTERNAL_CORE_CLIENT_CONFIG_SUBCHANNEL_INDEX_H
+#define GRPC_INTERNAL_CORE_CLIENT_CONFIG_SUBCHANNEL_INDEX_H
+
+#include "src/core/client_config/connector.h"
+#include "src/core/client_config/subchannel.h"
+
+/** \file Provides an index of active subchannels so that they can be
+    shared amongst channels */
+
+typedef struct grpc_subchannel_key grpc_subchannel_key;
+
+/** Create a key that can be used to uniquely identify a subchannel */
+grpc_subchannel_key *grpc_subchannel_key_create(grpc_connector *con,
+                                                grpc_subchannel_args *args);
+
+/** Destroy a subchannel key */
+void grpc_subchannel_key_destroy(grpc_exec_ctx *exec_ctx,
+                                 grpc_subchannel_key *key);
+
+/** Given a subchannel key, find the subchannel registered for it.
+    Returns NULL if no such channel exists.
+    Thread-safe. */
+grpc_subchannel *grpc_subchannel_index_find(grpc_exec_ctx *exec_ctx,
+                                            grpc_subchannel_key *key);
+
+/** Register a subchannel against a key.
+    Takes ownership of \a constructed.
+    Returns the registered subchannel. This may be different from
+    \a constructed in the case of a registration race. */
+grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
+                                                grpc_subchannel_key *key,
+                                                grpc_subchannel *constructed);
+
+/** Remove \a constructed as the registered subchannel for \a key. */
+void grpc_subchannel_index_unregister(grpc_exec_ctx *exec_ctx,
+                                      grpc_subchannel_key *key,
+                                      grpc_subchannel *constructed);
+
+/** Initialize the subchannel index (global) */
+void grpc_subchannel_index_init(void);
+/** Shutdown the subchannel index (global) */
+void grpc_subchannel_index_shutdown(void);
+
+#endif /* GRPC_INTERNAL_CORE_CLIENT_CONFIG_SUBCHANNEL_INDEX_H */
diff --git a/src/core/iomgr/pollset_posix.h b/src/core/iomgr/pollset_posix.h
index b34bb09..5868b3f 100644
--- a/src/core/iomgr/pollset_posix.h
+++ b/src/core/iomgr/pollset_posix.h
@@ -142,6 +142,10 @@
 void grpc_remove_fd_from_all_epoll_sets(int fd);
 
 /* override to allow tests to hook poll() usage */
+/* NOTE: Any changes to grpc_poll_function must take place when the gRPC
+   is certainly not doing any polling anywhere.
+   Otherwise, there might be a race between changing the variable and actually
+   doing a polling operation */
 typedef int (*grpc_poll_function_type)(struct pollfd *, nfds_t, int);
 extern grpc_poll_function_type grpc_poll_function;
 extern grpc_wakeup_fd grpc_global_wakeup_fd;
diff --git a/src/core/security/credentials.c b/src/core/security/credentials.c
index afba007..c58574b 100644
--- a/src/core/security/credentials.c
+++ b/src/core/security/credentials.c
@@ -196,14 +196,21 @@
   return grpc_server_credentials_ref(p);
 }
 
+static int server_credentials_pointer_cmp(void *a, void *b) {
+  return GPR_ICMP(a, b);
+}
+
+static const grpc_arg_pointer_vtable cred_ptr_vtable = {
+    server_credentials_pointer_arg_copy, server_credentials_pointer_arg_destroy,
+    server_credentials_pointer_cmp};
+
 grpc_arg grpc_server_credentials_to_arg(grpc_server_credentials *p) {
   grpc_arg arg;
   memset(&arg, 0, sizeof(grpc_arg));
   arg.type = GRPC_ARG_POINTER;
   arg.key = GRPC_SERVER_CREDENTIALS_ARG;
   arg.value.pointer.p = p;
-  arg.value.pointer.copy = server_credentials_pointer_arg_copy;
-  arg.value.pointer.destroy = server_credentials_pointer_arg_destroy;
+  arg.value.pointer.vtable = &cred_ptr_vtable;
   return arg;
 }
 
diff --git a/src/core/security/security_connector.c b/src/core/security/security_connector.c
index bdccbab..b462053 100644
--- a/src/core/security/security_connector.c
+++ b/src/core/security/security_connector.c
@@ -202,12 +202,17 @@
   return GRPC_SECURITY_CONNECTOR_REF(p, "connector_pointer_arg");
 }
 
+static int connector_pointer_cmp(void *a, void *b) { return GPR_ICMP(a, b); }
+
+static const grpc_arg_pointer_vtable connector_pointer_vtable = {
+    connector_pointer_arg_copy, connector_pointer_arg_destroy,
+    connector_pointer_cmp};
+
 grpc_arg grpc_security_connector_to_arg(grpc_security_connector *sc) {
   grpc_arg result;
   result.type = GRPC_ARG_POINTER;
   result.key = GRPC_SECURITY_CONNECTOR_ARG;
-  result.value.pointer.destroy = connector_pointer_arg_destroy;
-  result.value.pointer.copy = connector_pointer_arg_copy;
+  result.value.pointer.vtable = &connector_pointer_vtable;
   result.value.pointer.p = sc;
   return result;
 }
diff --git a/src/core/security/security_context.c b/src/core/security/security_context.c
index 2068c97..a71b3bc 100644
--- a/src/core/security/security_context.c
+++ b/src/core/security/security_context.c
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -309,14 +309,19 @@
   return GRPC_AUTH_CONTEXT_REF(p, "auth_context_pointer_arg");
 }
 
+static int auth_context_pointer_cmp(void *a, void *b) { return GPR_ICMP(a, b); }
+
+static const grpc_arg_pointer_vtable auth_context_pointer_vtable = {
+    auth_context_pointer_arg_copy, auth_context_pointer_arg_destroy,
+    auth_context_pointer_cmp};
+
 grpc_arg grpc_auth_context_to_arg(grpc_auth_context *p) {
   grpc_arg arg;
   memset(&arg, 0, sizeof(grpc_arg));
   arg.type = GRPC_ARG_POINTER;
   arg.key = GRPC_AUTH_CONTEXT_ARG;
   arg.value.pointer.p = p;
-  arg.value.pointer.copy = auth_context_pointer_arg_copy;
-  arg.value.pointer.destroy = auth_context_pointer_arg_destroy;
+  arg.value.pointer.vtable = &auth_context_pointer_vtable;
   return arg;
 }
 
diff --git a/src/core/support/avl.c b/src/core/support/avl.c
index 9734c99..f378b3e 100644
--- a/src/core/support/avl.c
+++ b/src/core/support/avl.c
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -167,7 +167,7 @@
       vtable->copy_key(right->left->key),
       vtable->copy_value(right->left->value),
       new_node(key, value, left, ref_node(right->left->left)),
-      new_node(vtable->copy_key(right->key), vtable->copy_key(right->value),
+      new_node(vtable->copy_key(right->key), vtable->copy_value(right->value),
                ref_node(right->left->right), ref_node(right->right)));
   unref_node(vtable, right);
   return n;
diff --git a/src/core/surface/channel_create.c b/src/core/surface/channel_create.c
index 4d4337d..fd7e20e 100644
--- a/src/core/surface/channel_create.c
+++ b/src/core/surface/channel_create.c
@@ -172,7 +172,7 @@
   c->base.vtable = &connector_vtable;
   gpr_ref_init(&c->refs, 1);
   args->args = final_args;
-  s = grpc_subchannel_create(&c->base, args);
+  s = grpc_subchannel_create(exec_ctx, &c->base, args);
   grpc_connector_unref(exec_ctx, &c->base);
   grpc_channel_args_destroy(final_args);
   return s;
diff --git a/src/core/surface/init.c b/src/core/surface/init.c
index e3ab70d..a4a53d3 100644
--- a/src/core/surface/init.c
+++ b/src/core/surface/init.c
@@ -46,6 +46,8 @@
 #include "src/core/client_config/resolver_registry.h"
 #include "src/core/client_config/resolvers/dns_resolver.h"
 #include "src/core/client_config/resolvers/sockaddr_resolver.h"
+#include "src/core/client_config/subchannel.h"
+#include "src/core/client_config/subchannel_index.h"
 #include "src/core/debug/trace.h"
 #include "src/core/iomgr/executor.h"
 #include "src/core/iomgr/iomgr.h"
@@ -127,6 +129,7 @@
     }
     gpr_timers_global_init();
     grpc_cq_global_init();
+    grpc_subchannel_index_init();
     for (i = 0; i < g_number_of_plugins; i++) {
       if (g_all_of_the_plugins[i].init != NULL) {
         g_all_of_the_plugins[i].init();
@@ -145,6 +148,7 @@
     grpc_executor_shutdown();
     grpc_cq_global_shutdown();
     grpc_iomgr_shutdown();
+    grpc_subchannel_index_shutdown();
     census_shutdown();
     gpr_timers_global_destroy();
     grpc_tracer_shutdown();
diff --git a/src/core/surface/secure_channel_create.c b/src/core/surface/secure_channel_create.c
index dd1441a..9c04426 100644
--- a/src/core/surface/secure_channel_create.c
+++ b/src/core/surface/secure_channel_create.c
@@ -238,7 +238,7 @@
   gpr_mu_init(&c->mu);
   gpr_ref_init(&c->refs, 1);
   args->args = final_args;
-  s = grpc_subchannel_create(&c->base, args);
+  s = grpc_subchannel_create(exec_ctx, &c->base, args);
   grpc_connector_unref(exec_ctx, &c->base);
   grpc_channel_args_destroy(final_args);
   return s;
diff --git a/src/cpp/client/create_channel.cc b/src/cpp/client/create_channel.cc
index fdaa28f..76a1b31 100644
--- a/src/cpp/client/create_channel.cc
+++ b/src/cpp/client/create_channel.cc
@@ -32,7 +32,6 @@
  */
 
 #include <memory>
-#include <sstream>
 
 #include <grpc++/channel.h>
 #include <grpc++/create_channel.h>
@@ -56,13 +55,8 @@
     const ChannelArguments& args) {
   internal::GrpcLibrary
       init_lib;  // We need to call init in case of a bad creds.
-  ChannelArguments cp_args = args;
-  std::ostringstream user_agent_prefix;
-  user_agent_prefix << "grpc-c++/" << grpc_version_string();
-  cp_args.SetString(GRPC_ARG_PRIMARY_USER_AGENT_STRING,
-                    user_agent_prefix.str());
   return creds
-             ? creds->CreateChannel(target, cp_args)
+             ? creds->CreateChannel(target, args)
              : CreateChannelInternal("", grpc_lame_client_channel_create(
                                              NULL, GRPC_STATUS_INVALID_ARGUMENT,
                                              "Invalid credentials."));
diff --git a/src/cpp/common/channel_arguments.cc b/src/cpp/common/channel_arguments.cc
index 90cd513..d7faa5e 100644
--- a/src/cpp/common/channel_arguments.cc
+++ b/src/cpp/common/channel_arguments.cc
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -30,14 +30,23 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
-
 #include <grpc++/support/channel_arguments.h>
 
+#include <sstream>
+
+#include <grpc/impl/codegen/grpc_types.h>
 #include <grpc/support/log.h>
 #include "src/core/channel/channel_args.h"
 
 namespace grpc {
 
+ChannelArguments::ChannelArguments() {
+  std::ostringstream user_agent_prefix;
+  user_agent_prefix << "grpc-c++/" << grpc_version_string();
+  // This will be ignored if used on the server side.
+  SetString(GRPC_ARG_PRIMARY_USER_AGENT_STRING, user_agent_prefix.str());
+}
+
 ChannelArguments::ChannelArguments(const ChannelArguments& other)
     : strings_(other.strings_) {
   args_.reserve(other.args_.size());
@@ -62,9 +71,7 @@
         break;
       case GRPC_ARG_POINTER:
         ap.value.pointer = a->value.pointer;
-        ap.value.pointer.p = a->value.pointer.copy
-                                 ? a->value.pointer.copy(ap.value.pointer.p)
-                                 : ap.value.pointer.p;
+        ap.value.pointer.p = a->value.pointer.vtable->copy(ap.value.pointer.p);
         break;
     }
     args_.push_back(ap);
@@ -81,6 +88,31 @@
   SetInt(GRPC_COMPRESSION_ALGORITHM_ARG, algorithm);
 }
 
+// Note: a second call to this will add in front the result of the first call.
+// An example is calling this on a copy of ChannelArguments which already has a
+// prefix. The user can build up a prefix string by calling this multiple times,
+// each with more significant identifier.
+void ChannelArguments::SetUserAgentPrefix(
+    const grpc::string& user_agent_prefix) {
+  if (user_agent_prefix.empty()) {
+    return;
+  }
+  bool replaced = false;
+  for (auto it = args_.begin(); it != args_.end(); ++it) {
+    const grpc_arg& arg = *it;
+    if (arg.type == GRPC_ARG_STRING &&
+        grpc::string(arg.key) == GRPC_ARG_PRIMARY_USER_AGENT_STRING) {
+      strings_.push_back(user_agent_prefix + " " + arg.value.string);
+      it->value.string = const_cast<char*>(strings_.back().c_str());
+      replaced = true;
+      break;
+    }
+  }
+  if (!replaced) {
+    SetString(GRPC_ARG_PRIMARY_USER_AGENT_STRING, user_agent_prefix);
+  }
+}
+
 void ChannelArguments::SetInt(const grpc::string& key, int value) {
   grpc_arg arg;
   arg.type = GRPC_ARG_INTEGER;
@@ -92,13 +124,15 @@
 }
 
 void ChannelArguments::SetPointer(const grpc::string& key, void* value) {
+  static const grpc_arg_pointer_vtable vtable = {
+      &PointerVtableMembers::Copy, &PointerVtableMembers::Destroy,
+      &PointerVtableMembers::Compare};
   grpc_arg arg;
   arg.type = GRPC_ARG_POINTER;
   strings_.push_back(key);
   arg.key = const_cast<char*>(strings_.back().c_str());
   arg.value.pointer.p = value;
-  arg.value.pointer.copy = nullptr;
-  arg.value.pointer.destroy = nullptr;
+  arg.value.pointer.vtable = &vtable;
   args_.push_back(arg);
 }
 
diff --git a/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs b/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
index f77e9c6..1837f5c 100644
--- a/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
+++ b/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -71,7 +71,7 @@
         /// <returns>The interceptor.</returns>
         public static AsyncAuthInterceptor FromAccessToken(string accessToken)
         {
-            Preconditions.CheckNotNull(accessToken);
+            GrpcPreconditions.CheckNotNull(accessToken);
             return new AsyncAuthInterceptor(async (context, metadata) =>
             {
                 metadata.Add(CreateBearerTokenHeader(accessToken));
diff --git a/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
index 5c9ab04..5ba06d6 100644
--- a/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
+++ b/src/csharp/Grpc.Core/AsyncAuthInterceptor.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -61,8 +61,8 @@
         /// </summary>
         public AuthInterceptorContext(string serviceUrl, string methodName)
         {
-            this.serviceUrl = Preconditions.CheckNotNull(serviceUrl);
-            this.methodName = Preconditions.CheckNotNull(methodName);
+            this.serviceUrl = GrpcPreconditions.CheckNotNull(serviceUrl);
+            this.methodName = GrpcPreconditions.CheckNotNull(methodName);
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/CallCredentials.cs b/src/csharp/Grpc.Core/CallCredentials.cs
index a71c890..7cd41d0 100644
--- a/src/csharp/Grpc.Core/CallCredentials.cs
+++ b/src/csharp/Grpc.Core/CallCredentials.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -87,7 +87,7 @@
         /// <param name="interceptor">authentication interceptor</param>
         public MetadataCredentials(AsyncAuthInterceptor interceptor)
         {
-            this.interceptor = Preconditions.CheckNotNull(interceptor);
+            this.interceptor = GrpcPreconditions.CheckNotNull(interceptor);
         }
 
         internal override CallCredentialsSafeHandle ToNativeCredentials()
@@ -111,7 +111,7 @@
         /// <param name="credentials">credentials to compose</param>
         public CompositeCallCredentials(params CallCredentials[] credentials)
         {
-            Preconditions.CheckArgument(credentials.Length >= 2, "Composite credentials object can only be created from 2 or more credentials.");
+            GrpcPreconditions.CheckArgument(credentials.Length >= 2, "Composite credentials object can only be created from 2 or more credentials.");
             this.credentials = new List<CallCredentials>(credentials);
         }
 
diff --git a/src/csharp/Grpc.Core/CallInvocationDetails.cs b/src/csharp/Grpc.Core/CallInvocationDetails.cs
index 8228b8f..52bfbe6 100644
--- a/src/csharp/Grpc.Core/CallInvocationDetails.cs
+++ b/src/csharp/Grpc.Core/CallInvocationDetails.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -85,11 +85,11 @@
         /// <param name="options">Call options.</param>
         public CallInvocationDetails(Channel channel, string method, string host, Marshaller<TRequest> requestMarshaller, Marshaller<TResponse> responseMarshaller, CallOptions options)
         {
-            this.channel = Preconditions.CheckNotNull(channel, "channel");
-            this.method = Preconditions.CheckNotNull(method, "method");
+            this.channel = GrpcPreconditions.CheckNotNull(channel, "channel");
+            this.method = GrpcPreconditions.CheckNotNull(method, "method");
             this.host = host;
-            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
-            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
+            this.requestMarshaller = GrpcPreconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
+            this.responseMarshaller = GrpcPreconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
             this.options = options;
         }
 
diff --git a/src/csharp/Grpc.Core/CallOptions.cs b/src/csharp/Grpc.Core/CallOptions.cs
index 1fda80c..7bd95d4 100644
--- a/src/csharp/Grpc.Core/CallOptions.cs
+++ b/src/csharp/Grpc.Core/CallOptions.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -176,13 +176,13 @@
             {
                 if (propagationToken.Options.IsPropagateDeadline)
                 {
-                    Preconditions.CheckArgument(!newOptions.deadline.HasValue,
+                    GrpcPreconditions.CheckArgument(!newOptions.deadline.HasValue,
                         "Cannot propagate deadline from parent call. The deadline has already been set explicitly.");
                     newOptions.deadline = propagationToken.ParentDeadline;
                 }
                 if (propagationToken.Options.IsPropagateCancellation)
                 {
-                    Preconditions.CheckArgument(!newOptions.cancellationToken.CanBeCanceled,
+                    GrpcPreconditions.CheckArgument(!newOptions.cancellationToken.CanBeCanceled,
                         "Cannot propagate cancellation token from parent call. The cancellation token has already been set to a non-default value.");
                     newOptions.cancellationToken = propagationToken.ParentCancellationToken;
                 }
diff --git a/src/csharp/Grpc.Core/Channel.cs b/src/csharp/Grpc.Core/Channel.cs
index d8d43c7..d7a482d 100644
--- a/src/csharp/Grpc.Core/Channel.cs
+++ b/src/csharp/Grpc.Core/Channel.cs
@@ -1,5 +1,5 @@
 #region Copyright notice and license
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -68,7 +68,7 @@
         /// <param name="options">Channel options.</param>
         public Channel(string target, ChannelCredentials credentials, IEnumerable<ChannelOption> options = null)
         {
-            this.target = Preconditions.CheckNotNull(target, "target");
+            this.target = GrpcPreconditions.CheckNotNull(target, "target");
             this.options = CreateOptionsDictionary(options);
             EnsureUserAgentChannelOption(this.options);
             this.environment = GrpcEnvironment.AddRef();
@@ -117,7 +117,7 @@
         /// </summary>
         public Task WaitForStateChangedAsync(ChannelState lastObservedState, DateTime? deadline = null)
         {
-            Preconditions.CheckArgument(lastObservedState != ChannelState.FatalFailure,
+            GrpcPreconditions.CheckArgument(lastObservedState != ChannelState.FatalFailure,
                 "FatalFailure is a terminal state. No further state changes can occur.");
             var tcs = new TaskCompletionSource<object>();
             var deadlineTimespec = deadline.HasValue ? Timespec.FromDateTime(deadline.Value) : Timespec.InfFuture;
@@ -184,7 +184,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!shutdownRequested);
+                GrpcPreconditions.CheckState(!shutdownRequested);
                 shutdownRequested = true;
             }
 
@@ -221,7 +221,7 @@
 
             bool success = false;
             handle.DangerousAddRef(ref success);
-            Preconditions.CheckState(success);
+            GrpcPreconditions.CheckState(success);
         }
 
         internal void RemoveCallReference(object call)
diff --git a/src/csharp/Grpc.Core/ChannelCredentials.cs b/src/csharp/Grpc.Core/ChannelCredentials.cs
index 5d96958..03cda28 100644
--- a/src/csharp/Grpc.Core/ChannelCredentials.cs
+++ b/src/csharp/Grpc.Core/ChannelCredentials.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -183,9 +183,9 @@
         /// <param name="callCredentials">channelCredentials to compose</param>
         public CompositeChannelCredentials(ChannelCredentials channelCredentials, CallCredentials callCredentials)
         {
-            this.channelCredentials = Preconditions.CheckNotNull(channelCredentials);
-            this.callCredentials = Preconditions.CheckNotNull(callCredentials);
-            Preconditions.CheckArgument(channelCredentials.IsComposable, "Supplied channel credentials do not allow composition.");
+            this.channelCredentials = GrpcPreconditions.CheckNotNull(channelCredentials);
+            this.callCredentials = GrpcPreconditions.CheckNotNull(callCredentials);
+            GrpcPreconditions.CheckArgument(channelCredentials.IsComposable, "Supplied channel credentials do not allow composition.");
         }
 
         internal override ChannelCredentialsSafeHandle ToNativeCredentials()
diff --git a/src/csharp/Grpc.Core/ChannelOptions.cs b/src/csharp/Grpc.Core/ChannelOptions.cs
index d70673c..65e15e2 100644
--- a/src/csharp/Grpc.Core/ChannelOptions.cs
+++ b/src/csharp/Grpc.Core/ChannelOptions.cs
@@ -1,5 +1,5 @@
 #region Copyright notice and license
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -73,8 +73,8 @@
         public ChannelOption(string name, string stringValue)
         {
             this.type = OptionType.String;
-            this.name = Preconditions.CheckNotNull(name, "name");
-            this.stringValue = Preconditions.CheckNotNull(stringValue, "stringValue");
+            this.name = GrpcPreconditions.CheckNotNull(name, "name");
+            this.stringValue = GrpcPreconditions.CheckNotNull(stringValue, "stringValue");
         }
 
         /// <summary>
@@ -85,7 +85,7 @@
         public ChannelOption(string name, int intValue)
         {
             this.type = OptionType.Integer;
-            this.name = Preconditions.CheckNotNull(name, "name");
+            this.name = GrpcPreconditions.CheckNotNull(name, "name");
             this.intValue = intValue;
         }
 
@@ -118,7 +118,7 @@
         {
             get
             {
-                Preconditions.CheckState(type == OptionType.Integer);
+                GrpcPreconditions.CheckState(type == OptionType.Integer);
                 return intValue;
             }
         }
@@ -130,7 +130,7 @@
         {
             get
             {
-                Preconditions.CheckState(type == OptionType.String);
+                GrpcPreconditions.CheckState(type == OptionType.String);
                 return stringValue;
             }
         }
diff --git a/src/csharp/Grpc.Core/ContextPropagationToken.cs b/src/csharp/Grpc.Core/ContextPropagationToken.cs
index 1d899b9..c0f638f 100644
--- a/src/csharp/Grpc.Core/ContextPropagationToken.cs
+++ b/src/csharp/Grpc.Core/ContextPropagationToken.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -68,7 +68,7 @@
 
         internal ContextPropagationToken(CallSafeHandle parentCall, DateTime deadline, CancellationToken cancellationToken, ContextPropagationOptions options)
         {
-            this.parentCall = Preconditions.CheckNotNull(parentCall);
+            this.parentCall = GrpcPreconditions.CheckNotNull(parentCall);
             this.deadline = deadline;
             this.cancellationToken = cancellationToken;
             this.options = options ?? ContextPropagationOptions.Default;
diff --git a/src/csharp/Grpc.Core/Grpc.Core.csproj b/src/csharp/Grpc.Core/Grpc.Core.csproj
index 8d7d2ca..3189835 100644
--- a/src/csharp/Grpc.Core/Grpc.Core.csproj
+++ b/src/csharp/Grpc.Core/Grpc.Core.csproj
@@ -39,8 +39,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="System" />
-    <Reference Include="System.Interactive.Async, Version=1.2.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
-      <SpecificVersion>False</SpecificVersion>
+    <Reference Include="System.Interactive.Async">
       <HintPath>..\packages\Ix-Async.1.2.5\lib\net45\System.Interactive.Async.dll</HintPath>
     </Reference>
   </ItemGroup>
@@ -91,7 +90,6 @@
     <Compile Include="Internal\AsyncCallBase.cs" />
     <Compile Include="Internal\AsyncCallServer.cs" />
     <Compile Include="Internal\AsyncCall.cs" />
-    <Compile Include="Utils\Preconditions.cs" />
     <Compile Include="Internal\ServerCredentialsSafeHandle.cs" />
     <Compile Include="ServerCredentials.cs" />
     <Compile Include="Metadata.cs" />
@@ -130,6 +128,7 @@
     <Compile Include="Profiling\IProfiler.cs" />
     <Compile Include="Profiling\Profilers.cs" />
     <Compile Include="Internal\DefaultSslRootsOverride.cs" />
+    <Compile Include="Utils\GrpcPreconditions.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="Grpc.Core.nuspec" />
diff --git a/src/csharp/Grpc.Core/GrpcEnvironment.cs b/src/csharp/Grpc.Core/GrpcEnvironment.cs
index f3aa3d7..86b37b8 100644
--- a/src/csharp/Grpc.Core/GrpcEnvironment.cs
+++ b/src/csharp/Grpc.Core/GrpcEnvironment.cs
@@ -83,7 +83,7 @@
         {
             lock (staticLock)
             {
-                Preconditions.CheckState(refCount > 0);
+                GrpcPreconditions.CheckState(refCount > 0);
                 refCount--;
                 if (refCount == 0)
                 {
@@ -118,7 +118,7 @@
         /// </summary>
         public static void SetLogger(ILogger customLogger)
         {
-            Preconditions.CheckNotNull(customLogger, "customLogger");
+            GrpcPreconditions.CheckNotNull(customLogger, "customLogger");
             logger = customLogger;
         }
 
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCall.cs b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
index 7dc4490..2caba26 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCall.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
@@ -99,7 +99,7 @@
 
                 lock (myLock)
                 {
-                    Preconditions.CheckState(!started);
+                    GrpcPreconditions.CheckState(!started);
                     started = true;
                     Initialize(cq);
 
@@ -141,7 +141,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!started);
+                GrpcPreconditions.CheckState(!started);
                 started = true;
 
                 Initialize(environment.CompletionQueue);
@@ -168,7 +168,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!started);
+                GrpcPreconditions.CheckState(!started);
                 started = true;
 
                 Initialize(environment.CompletionQueue);
@@ -192,7 +192,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!started);
+                GrpcPreconditions.CheckState(!started);
                 started = true;
 
                 Initialize(environment.CompletionQueue);
@@ -217,7 +217,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!started);
+                GrpcPreconditions.CheckState(!started);
                 started = true;
 
                 Initialize(environment.CompletionQueue);
@@ -257,7 +257,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                 CheckSendingAllowed();
 
                 call.StartSendCloseFromClient(HandleHalfclosed);
@@ -297,7 +297,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(finishedStatus.HasValue, "Status can only be accessed once the call has finished.");
+                GrpcPreconditions.CheckState(finishedStatus.HasValue, "Status can only be accessed once the call has finished.");
                 return finishedStatus.Value.Status;
             }
         }
@@ -310,7 +310,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(finishedStatus.HasValue, "Trailers can only be accessed once the call has finished.");
+                GrpcPreconditions.CheckState(finishedStatus.HasValue, "Trailers can only be accessed once the call has finished.");
                 return finishedStatus.Value.Trailers;
             }
         }
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs b/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
index 81a9a40..45d4c3e 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
@@ -79,9 +79,9 @@
 
         public AsyncCallBase(Func<TWrite, byte[]> serializer, Func<byte[], TRead> deserializer, GrpcEnvironment environment)
         {
-            this.serializer = Preconditions.CheckNotNull(serializer);
-            this.deserializer = Preconditions.CheckNotNull(deserializer);
-            this.environment = Preconditions.CheckNotNull(environment);
+            this.serializer = GrpcPreconditions.CheckNotNull(serializer);
+            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer);
+            this.environment = GrpcPreconditions.CheckNotNull(environment);
         }
 
         /// <summary>
@@ -91,7 +91,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(started);
+                GrpcPreconditions.CheckState(started);
                 cancelRequested = true;
 
                 if (!disposed)
@@ -135,7 +135,7 @@
 
             lock (myLock)
             {
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                 CheckSendingAllowed();
 
                 call.StartSendMessage(HandleSendFinished, payload, writeFlags, !initialMetadataSent);
@@ -154,7 +154,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                 CheckReadingAllowed();
 
                 call.StartReceiveMessage(HandleReadFinished);
@@ -204,22 +204,22 @@
 
         protected void CheckSendingAllowed()
         {
-            Preconditions.CheckState(started);
+            GrpcPreconditions.CheckState(started);
             CheckNotCancelled();
-            Preconditions.CheckState(!disposed);
+            GrpcPreconditions.CheckState(!disposed);
 
-            Preconditions.CheckState(!halfcloseRequested, "Already halfclosed.");
-            Preconditions.CheckState(!finished, "Already finished.");
-            Preconditions.CheckState(sendCompletionDelegate == null, "Only one write can be pending at a time");
+            GrpcPreconditions.CheckState(!halfcloseRequested, "Already halfclosed.");
+            GrpcPreconditions.CheckState(!finished, "Already finished.");
+            GrpcPreconditions.CheckState(sendCompletionDelegate == null, "Only one write can be pending at a time");
         }
 
         protected virtual void CheckReadingAllowed()
         {
-            Preconditions.CheckState(started);
-            Preconditions.CheckState(!disposed);
+            GrpcPreconditions.CheckState(started);
+            GrpcPreconditions.CheckState(!disposed);
 
-            Preconditions.CheckState(!readingDone, "Stream has already been closed.");
-            Preconditions.CheckState(readCompletionDelegate == null, "Only one read can be pending at a time");
+            GrpcPreconditions.CheckState(!readingDone, "Stream has already been closed.");
+            GrpcPreconditions.CheckState(readCompletionDelegate == null, "Only one read can be pending at a time");
         }
 
         protected void CheckNotCancelled()
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
index 6752d3f..b72cbd7 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
@@ -53,7 +53,7 @@
 
         public AsyncCallServer(Func<TResponse, byte[]> serializer, Func<byte[], TRequest> deserializer, GrpcEnvironment environment, Server server) : base(serializer, deserializer, environment)
         {
-            this.server = Preconditions.CheckNotNull(server);
+            this.server = GrpcPreconditions.CheckNotNull(server);
         }
 
         public void Initialize(CallSafeHandle call)
@@ -71,7 +71,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(call);
+                GrpcPreconditions.CheckNotNull(call);
 
                 started = true;
 
@@ -108,14 +108,14 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(headers, "metadata");
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(headers, "metadata");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
 
-                Preconditions.CheckState(!initialMetadataSent, "Response headers can only be sent once per call.");
-                Preconditions.CheckState(streamingWritesCounter == 0, "Response headers can only be sent before the first write starts.");
+                GrpcPreconditions.CheckState(!initialMetadataSent, "Response headers can only be sent once per call.");
+                GrpcPreconditions.CheckState(streamingWritesCounter == 0, "Response headers can only be sent before the first write starts.");
                 CheckSendingAllowed();
 
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
 
                 using (var metadataArray = MetadataArraySafeHandle.Create(headers))
                 {
@@ -136,7 +136,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                 CheckSendingAllowed();
 
                 using (var metadataArray = MetadataArraySafeHandle.Create(trailers))
@@ -177,7 +177,7 @@
         protected override void CheckReadingAllowed()
         {
             base.CheckReadingAllowed();
-            Preconditions.CheckArgument(!cancelRequested);
+            GrpcPreconditions.CheckArgument(!cancelRequested);
         }
 
         protected override void OnAfterReleaseResources()
diff --git a/src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs b/src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs
index 9d7a990..5c75b52 100644
--- a/src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs
@@ -101,7 +101,7 @@
         {
             bool success = false;
             shutdownRefcount.IncrementIfNonzero(ref success);
-            Preconditions.CheckState(success, "Shutdown has already been called");
+            GrpcPreconditions.CheckState(success, "Shutdown has already been called");
         }
 
         private void EndOp()
diff --git a/src/csharp/Grpc.Core/Internal/CompletionRegistry.cs b/src/csharp/Grpc.Core/Internal/CompletionRegistry.cs
index 2796c95..3a293e1 100644
--- a/src/csharp/Grpc.Core/Internal/CompletionRegistry.cs
+++ b/src/csharp/Grpc.Core/Internal/CompletionRegistry.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -59,7 +59,7 @@
         public void Register(IntPtr key, OpCompletionDelegate callback)
         {
             environment.DebugStats.PendingBatchCompletions.Increment();
-            Preconditions.CheckState(dict.TryAdd(key, callback));
+            GrpcPreconditions.CheckState(dict.TryAdd(key, callback));
         }
 
         public void RegisterBatchCompletion(BatchContextSafeHandle ctx, BatchCompletionDelegate callback)
@@ -71,7 +71,7 @@
         public OpCompletionDelegate Extract(IntPtr key)
         {
             OpCompletionDelegate value;
-            Preconditions.CheckState(dict.TryRemove(key, out value));
+            GrpcPreconditions.CheckState(dict.TryRemove(key, out value));
             environment.DebugStats.PendingBatchCompletions.Decrement();
             return value;
         }
diff --git a/src/csharp/Grpc.Core/Internal/Enums.cs b/src/csharp/Grpc.Core/Internal/Enums.cs
index b0eab20..098e7c0 100644
--- a/src/csharp/Grpc.Core/Internal/Enums.cs
+++ b/src/csharp/Grpc.Core/Internal/Enums.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -72,7 +72,7 @@
         /// </summary>
         public static void CheckOk(this GRPCCallError callError)
         {
-            Preconditions.CheckState(callError == GRPCCallError.OK, "Call error: " + callError);
+            GrpcPreconditions.CheckState(callError == GRPCCallError.OK, "Call error: " + callError);
         }
     }
 
diff --git a/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs b/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
index 36b865c..e810ffc 100644
--- a/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
+++ b/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
@@ -53,7 +53,7 @@
 
         public NativeMetadataCredentialsPlugin(AsyncAuthInterceptor interceptor)
         {
-            this.interceptor = Preconditions.CheckNotNull(interceptor, "interceptor");
+            this.interceptor = GrpcPreconditions.CheckNotNull(interceptor, "interceptor");
             this.nativeInterceptor = NativeMetadataInterceptorHandler;
 
             // Make sure the callback doesn't get garbage collected until it is destroyed.
diff --git a/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs b/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
index de66759..ccf144d 100644
--- a/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
+++ b/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -78,10 +78,10 @@
             var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
-                Preconditions.CheckArgument(await requestStream.MoveNext().ConfigureAwait(false));
+                GrpcPreconditions.CheckArgument(await requestStream.MoveNext().ConfigureAwait(false));
                 var request = requestStream.Current;
                 // TODO(jtattermusch): we need to read the full stream so that native callhandle gets deallocated.
-                Preconditions.CheckArgument(!await requestStream.MoveNext().ConfigureAwait(false));
+                GrpcPreconditions.CheckArgument(!await requestStream.MoveNext().ConfigureAwait(false));
                 var result = await handler(request, context).ConfigureAwait(false);
                 status = context.Status;
                 await responseStream.WriteAsync(result).ConfigureAwait(false);
@@ -134,10 +134,10 @@
             var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
-                Preconditions.CheckArgument(await requestStream.MoveNext().ConfigureAwait(false));
+                GrpcPreconditions.CheckArgument(await requestStream.MoveNext().ConfigureAwait(false));
                 var request = requestStream.Current;
                 // TODO(jtattermusch): we need to read the full stream so that native callhandle gets deallocated.
-                Preconditions.CheckArgument(!await requestStream.MoveNext().ConfigureAwait(false));
+                GrpcPreconditions.CheckArgument(!await requestStream.MoveNext().ConfigureAwait(false));
                 await handler(request, responseStream, context).ConfigureAwait(false);
                 status = context.Status;
             }
diff --git a/src/csharp/Grpc.Core/Internal/ServerCredentialsSafeHandle.cs b/src/csharp/Grpc.Core/Internal/ServerCredentialsSafeHandle.cs
index a1d080c..a50f357 100644
--- a/src/csharp/Grpc.Core/Internal/ServerCredentialsSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/ServerCredentialsSafeHandle.cs
@@ -49,7 +49,7 @@
 
         public static ServerCredentialsSafeHandle CreateSslCredentials(string pemRootCerts, string[] keyCertPairCertChainArray, string[] keyCertPairPrivateKeyArray, bool forceClientAuth)
         {
-            Preconditions.CheckArgument(keyCertPairCertChainArray.Length == keyCertPairPrivateKeyArray.Length);
+            GrpcPreconditions.CheckArgument(keyCertPairCertChainArray.Length == keyCertPairPrivateKeyArray.Length);
             return Native.grpcsharp_ssl_server_credentials_create(pemRootCerts,
                                                                   keyCertPairCertChainArray, keyCertPairPrivateKeyArray,
                                                                   new UIntPtr((ulong)keyCertPairCertChainArray.Length),
diff --git a/src/csharp/Grpc.Core/Internal/Timespec.cs b/src/csharp/Grpc.Core/Internal/Timespec.cs
index 148d877..754be4e 100644
--- a/src/csharp/Grpc.Core/Internal/Timespec.cs
+++ b/src/csharp/Grpc.Core/Internal/Timespec.cs
@@ -141,8 +141,8 @@
         /// </summary>
         public DateTime ToDateTime()
         {
-            Preconditions.CheckState(tv_nsec >= 0 && tv_nsec < NanosPerSecond);
-            Preconditions.CheckState(clock_type == GPRClockType.Realtime);
+            GrpcPreconditions.CheckState(tv_nsec >= 0 && tv_nsec < NanosPerSecond);
+            GrpcPreconditions.CheckState(clock_type == GPRClockType.Realtime);
 
             // fast path for InfFuture
             if (this.Equals(InfFuture))
@@ -195,7 +195,7 @@
                 return Timespec.InfPast;
             }
 
-            Preconditions.CheckArgument(dateTime.Kind == DateTimeKind.Utc, "dateTime needs of kind DateTimeKind.Utc or be equal to DateTime.MaxValue or DateTime.MinValue.");
+            GrpcPreconditions.CheckArgument(dateTime.Kind == DateTimeKind.Utc, "dateTime needs of kind DateTimeKind.Utc or be equal to DateTime.MaxValue or DateTime.MinValue.");
 
             try
             {
diff --git a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
index 95a8797..e763c15 100644
--- a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
+++ b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
@@ -65,7 +65,7 @@
 
         public UnmanagedLibrary(string libraryPath)
         {
-            this.libraryPath = Preconditions.CheckNotNull(libraryPath);
+            this.libraryPath = GrpcPreconditions.CheckNotNull(libraryPath);
 
             if (!File.Exists(this.libraryPath))
             {
diff --git a/src/csharp/Grpc.Core/KeyCertificatePair.cs b/src/csharp/Grpc.Core/KeyCertificatePair.cs
index 6f69197..0fb6817 100644
--- a/src/csharp/Grpc.Core/KeyCertificatePair.cs
+++ b/src/csharp/Grpc.Core/KeyCertificatePair.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -54,8 +54,8 @@
         /// <param name="privateKey">PEM encoded private key.</param>
         public KeyCertificatePair(string certificateChain, string privateKey)
         {
-            this.certificateChain = Preconditions.CheckNotNull(certificateChain, "certificateChain");
-            this.privateKey = Preconditions.CheckNotNull(privateKey, "privateKey");
+            this.certificateChain = GrpcPreconditions.CheckNotNull(certificateChain, "certificateChain");
+            this.privateKey = GrpcPreconditions.CheckNotNull(privateKey, "privateKey");
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Marshaller.cs b/src/csharp/Grpc.Core/Marshaller.cs
index 3493d2d..5847248 100644
--- a/src/csharp/Grpc.Core/Marshaller.cs
+++ b/src/csharp/Grpc.Core/Marshaller.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -51,8 +51,8 @@
         /// <param name="deserializer">Function that will be used to deserialize messages.</param>
         public Marshaller(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
         {
-            this.serializer = Preconditions.CheckNotNull(serializer, "serializer");
-            this.deserializer = Preconditions.CheckNotNull(deserializer, "deserializer");
+            this.serializer = GrpcPreconditions.CheckNotNull(serializer, "serializer");
+            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer, "deserializer");
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Metadata.cs b/src/csharp/Grpc.Core/Metadata.cs
index 21bdf4f..aa22f84 100644
--- a/src/csharp/Grpc.Core/Metadata.cs
+++ b/src/csharp/Grpc.Core/Metadata.cs
@@ -1,5 +1,5 @@
 #region Copyright notice and license
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -179,7 +179,7 @@
 
         private void CheckWriteable()
         {
-            Preconditions.CheckState(!readOnly, "Object is read only");
+            GrpcPreconditions.CheckState(!readOnly, "Object is read only");
         }
 
         #endregion
@@ -211,10 +211,10 @@
             public Entry(string key, byte[] valueBytes)
             {
                 this.key = NormalizeKey(key);
-                Preconditions.CheckArgument(this.key.EndsWith(BinaryHeaderSuffix),
+                GrpcPreconditions.CheckArgument(this.key.EndsWith(BinaryHeaderSuffix),
                     "Key for binary valued metadata entry needs to have suffix indicating binary value.");
                 this.value = null;
-                Preconditions.CheckNotNull(valueBytes, "valueBytes");
+                GrpcPreconditions.CheckNotNull(valueBytes, "valueBytes");
                 this.valueBytes = new byte[valueBytes.Length];
                 Buffer.BlockCopy(valueBytes, 0, this.valueBytes, 0, valueBytes.Length);  // defensive copy to guarantee immutability
             }
@@ -227,9 +227,9 @@
             public Entry(string key, string value)
             {
                 this.key = NormalizeKey(key);
-                Preconditions.CheckArgument(!this.key.EndsWith(BinaryHeaderSuffix),
+                GrpcPreconditions.CheckArgument(!this.key.EndsWith(BinaryHeaderSuffix),
                     "Key for ASCII valued metadata entry cannot have suffix indicating binary value.");
-                this.value = Preconditions.CheckNotNull(value, "value");
+                this.value = GrpcPreconditions.CheckNotNull(value, "value");
                 this.valueBytes = null;
             }
 
@@ -270,7 +270,7 @@
             {
                 get
                 {
-                    Preconditions.CheckState(!IsBinary, "Cannot access string value of a binary metadata entry");
+                    GrpcPreconditions.CheckState(!IsBinary, "Cannot access string value of a binary metadata entry");
                     return value ?? Encoding.GetString(valueBytes);
                 }
             }
@@ -323,8 +323,8 @@
 
             private static string NormalizeKey(string key)
             {
-                var normalized = Preconditions.CheckNotNull(key, "key").ToLower(CultureInfo.InvariantCulture);
-                Preconditions.CheckArgument(ValidKeyRegex.IsMatch(normalized), 
+                var normalized = GrpcPreconditions.CheckNotNull(key, "key").ToLower(CultureInfo.InvariantCulture);
+                GrpcPreconditions.CheckArgument(ValidKeyRegex.IsMatch(normalized), 
                     "Metadata entry key not valid. Keys can only contain lowercase alphanumeric characters, underscores and hyphens.");
                 return normalized;
             }
diff --git a/src/csharp/Grpc.Core/Method.cs b/src/csharp/Grpc.Core/Method.cs
index 99162a7..3870076 100644
--- a/src/csharp/Grpc.Core/Method.cs
+++ b/src/csharp/Grpc.Core/Method.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -106,10 +106,10 @@
         public Method(MethodType type, string serviceName, string name, Marshaller<TRequest> requestMarshaller, Marshaller<TResponse> responseMarshaller)
         {
             this.type = type;
-            this.serviceName = Preconditions.CheckNotNull(serviceName, "serviceName");
-            this.name = Preconditions.CheckNotNull(name, "name");
-            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
-            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
+            this.serviceName = GrpcPreconditions.CheckNotNull(serviceName, "serviceName");
+            this.name = GrpcPreconditions.CheckNotNull(name, "name");
+            this.requestMarshaller = GrpcPreconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
+            this.responseMarshaller = GrpcPreconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
             this.fullName = GetFullName(serviceName, name);
         }
 
diff --git a/src/csharp/Grpc.Core/Server.cs b/src/csharp/Grpc.Core/Server.cs
index d120f95..5d0fc6b 100644
--- a/src/csharp/Grpc.Core/Server.cs
+++ b/src/csharp/Grpc.Core/Server.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -125,7 +125,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!startRequested);
+                GrpcPreconditions.CheckState(!startRequested);
                 startRequested = true;
                 
                 handle.Start();
@@ -142,8 +142,8 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(startRequested);
-                Preconditions.CheckState(!shutdownRequested);
+                GrpcPreconditions.CheckState(startRequested);
+                GrpcPreconditions.CheckState(!shutdownRequested);
                 shutdownRequested = true;
             }
 
@@ -162,8 +162,8 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(startRequested);
-                Preconditions.CheckState(!shutdownRequested);
+                GrpcPreconditions.CheckState(startRequested);
+                GrpcPreconditions.CheckState(!shutdownRequested);
                 shutdownRequested = true;
             }
 
@@ -181,7 +181,7 @@
 
             bool success = false;
             handle.DangerousAddRef(ref success);
-            Preconditions.CheckState(success);
+            GrpcPreconditions.CheckState(success);
         }
 
         internal void RemoveCallReference(object call)
@@ -197,7 +197,7 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckState(!startRequested);
+                GrpcPreconditions.CheckState(!startRequested);
                 foreach (var entry in serviceDefinition.CallHandlers)
                 {
                     callHandlers.Add(entry.Key, entry.Value);
@@ -213,8 +213,8 @@
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(serverPort.Credentials, "serverPort");
-                Preconditions.CheckState(!startRequested);
+                GrpcPreconditions.CheckNotNull(serverPort.Credentials, "serverPort");
+                GrpcPreconditions.CheckState(!startRequested);
                 var address = string.Format("{0}:{1}", serverPort.Host, serverPort.Port);
                 int boundPort;
                 using (var nativeCredentials = serverPort.Credentials.ToNativeCredentials())
diff --git a/src/csharp/Grpc.Core/ServerCredentials.cs b/src/csharp/Grpc.Core/ServerCredentials.cs
index 3c6703d..456d331 100644
--- a/src/csharp/Grpc.Core/ServerCredentials.cs
+++ b/src/csharp/Grpc.Core/ServerCredentials.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -90,11 +90,11 @@
         public SslServerCredentials(IEnumerable<KeyCertificatePair> keyCertificatePairs, string rootCertificates, bool forceClientAuth)
         {
             this.keyCertificatePairs = new List<KeyCertificatePair>(keyCertificatePairs).AsReadOnly();
-            Preconditions.CheckArgument(this.keyCertificatePairs.Count > 0,
+            GrpcPreconditions.CheckArgument(this.keyCertificatePairs.Count > 0,
                 "At least one KeyCertificatePair needs to be provided.");
             if (forceClientAuth)
             {
-                Preconditions.CheckNotNull(rootCertificates,
+                GrpcPreconditions.CheckNotNull(rootCertificates,
                     "Cannot force client authentication unless you provide rootCertificates.");
             }
             this.rootCertificates = rootCertificates;
diff --git a/src/csharp/Grpc.Core/ServerPort.cs b/src/csharp/Grpc.Core/ServerPort.cs
index 598404d..10ddcb7 100644
--- a/src/csharp/Grpc.Core/ServerPort.cs
+++ b/src/csharp/Grpc.Core/ServerPort.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -62,9 +62,9 @@
         /// <param name="credentials">credentials to use to secure this port.</param>
         public ServerPort(string host, int port, ServerCredentials credentials)
         {
-            this.host = Preconditions.CheckNotNull(host, "host");
+            this.host = GrpcPreconditions.CheckNotNull(host, "host");
             this.port = port;
-            this.credentials = Preconditions.CheckNotNull(credentials, "credentials");
+            this.credentials = GrpcPreconditions.CheckNotNull(credentials, "credentials");
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Utils/Preconditions.cs b/src/csharp/Grpc.Core/Utils/GrpcPreconditions.cs
similarity index 98%
rename from src/csharp/Grpc.Core/Utils/Preconditions.cs
rename to src/csharp/Grpc.Core/Utils/GrpcPreconditions.cs
index a8ab603..76bf04c 100644
--- a/src/csharp/Grpc.Core/Utils/Preconditions.cs
+++ b/src/csharp/Grpc.Core/Utils/GrpcPreconditions.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -38,7 +38,7 @@
     /// <summary>
     /// Utility methods to simplify checking preconditions in the code.
     /// </summary>
-    public static class Preconditions
+    public static class GrpcPreconditions
     {
         /// <summary>
         /// Throws <see cref="ArgumentException"/> if condition is false.
diff --git a/src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs b/src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs
index 26c6445..e2ad1a8 100644
--- a/src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs
+++ b/src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs
@@ -1,5 +1,5 @@
 ﻿#region Copyright notice and license
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -127,8 +127,8 @@
         {
             public Key(string host, string service)
             {
-                this.Host = Preconditions.CheckNotNull(host);
-                this.Service = Preconditions.CheckNotNull(service);
+                this.Host = GrpcPreconditions.CheckNotNull(host);
+                this.Service = GrpcPreconditions.CheckNotNull(service);
             }
 
             readonly string Host;
diff --git a/src/csharp/Grpc.IntegrationTesting/ClientRunners.cs b/src/csharp/Grpc.IntegrationTesting/ClientRunners.cs
index e9e659c..c401601 100644
--- a/src/csharp/Grpc.IntegrationTesting/ClientRunners.cs
+++ b/src/csharp/Grpc.IntegrationTesting/ClientRunners.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -58,7 +58,7 @@
         public static IClientRunner CreateStarted(ClientConfig config)
         {
             string target = config.ServerTargets.Single();
-            Grpc.Core.Utils.Preconditions.CheckArgument(config.LoadParams.LoadCase == LoadParams.LoadOneofCase.ClosedLoop);
+            GrpcPreconditions.CheckArgument(config.LoadParams.LoadCase == LoadParams.LoadOneofCase.ClosedLoop);
 
             var credentials = config.SecurityParams != null ? TestCredentials.CreateSslCredentials() : ChannelCredentials.Insecure;
             var channel = new Channel(target, credentials);
@@ -95,7 +95,7 @@
         
         public SyncUnaryClientRunner(Channel channel, int payloadSize, HistogramParams histogramParams)
         {
-            this.channel = Grpc.Core.Utils.Preconditions.CheckNotNull(channel);
+            this.channel = GrpcPreconditions.CheckNotNull(channel);
             this.payloadSize = payloadSize;
             this.histogram = new Histogram(histogramParams.Resolution, histogramParams.MaxPossible);
 
diff --git a/src/csharp/Grpc.IntegrationTesting/Histogram.cs b/src/csharp/Grpc.IntegrationTesting/Histogram.cs
index 7e7cb2c..08a674d 100644
--- a/src/csharp/Grpc.IntegrationTesting/Histogram.cs
+++ b/src/csharp/Grpc.IntegrationTesting/Histogram.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -66,8 +66,8 @@
 
         public Histogram(double resolution, double maxPossible)
         {
-            Grpc.Core.Utils.Preconditions.CheckArgument(resolution > 0);
-            Grpc.Core.Utils.Preconditions.CheckArgument(maxPossible > 0);
+            GrpcPreconditions.CheckArgument(resolution > 0);
+            GrpcPreconditions.CheckArgument(maxPossible > 0);
             this.maxPossible = maxPossible;
             this.multiplier = 1.0 + resolution;
             this.oneOnLogMultiplier = 1.0 / Math.Log(1.0 + resolution);
diff --git a/src/csharp/Grpc.IntegrationTesting/ServerRunners.cs b/src/csharp/Grpc.IntegrationTesting/ServerRunners.cs
index e8be775..9b09b9b 100644
--- a/src/csharp/Grpc.IntegrationTesting/ServerRunners.cs
+++ b/src/csharp/Grpc.IntegrationTesting/ServerRunners.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -57,7 +57,7 @@
         /// </summary>
         public static IServerRunner CreateStarted(ServerConfig config)
         {
-            Grpc.Core.Utils.Preconditions.CheckArgument(config.ServerType == ServerType.ASYNC_SERVER);
+            GrpcPreconditions.CheckArgument(config.ServerType == ServerType.ASYNC_SERVER);
             var credentials = config.SecurityParams != null ? TestCredentials.CreateSslServerCredentials() : ServerCredentials.Insecure;
 
             // TODO: qps_driver needs to setup payload properly...
@@ -83,7 +83,7 @@
 
         public ServerRunnerImpl(Server server)
         {
-            this.server = Grpc.Core.Utils.Preconditions.CheckNotNull(server);
+            this.server = GrpcPreconditions.CheckNotNull(server);
         }
 
         public int BoundPort
diff --git a/src/csharp/Grpc.IntegrationTesting/WorkerServiceImpl.cs b/src/csharp/Grpc.IntegrationTesting/WorkerServiceImpl.cs
index bb2918b..59ecebf 100644
--- a/src/csharp/Grpc.IntegrationTesting/WorkerServiceImpl.cs
+++ b/src/csharp/Grpc.IntegrationTesting/WorkerServiceImpl.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -49,7 +49,7 @@
     {
         public async Task RunServer(IAsyncStreamReader<ServerArgs> requestStream, IServerStreamWriter<ServerStatus> responseStream, ServerCallContext context)
         {
-            Grpc.Core.Utils.Preconditions.CheckState(await requestStream.MoveNext());
+            GrpcPreconditions.CheckState(await requestStream.MoveNext());
             var serverConfig = requestStream.Current.Setup;
             var runner = ServerRunners.CreateStarted(serverConfig);
 
@@ -73,7 +73,7 @@
 
         public async Task RunClient(IAsyncStreamReader<ClientArgs> requestStream, IServerStreamWriter<ClientStatus> responseStream, ServerCallContext context)
         {
-            Grpc.Core.Utils.Preconditions.CheckState(await requestStream.MoveNext());
+            GrpcPreconditions.CheckState(await requestStream.MoveNext());
             var clientConfig = requestStream.Current.Setup;
             var runner = ClientRunners.CreateStarted(clientConfig);
 
diff --git a/src/node/ext/call_credentials.cc b/src/node/ext/call_credentials.cc
index 91acb86..98696db 100644
--- a/src/node/ext/call_credentials.cc
+++ b/src/node/ext/call_credentials.cc
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -187,7 +187,8 @@
   shared_ptr<Resources> resources(new Resources);
   grpc_status_code code = static_cast<grpc_status_code>(
       Nan::To<uint32_t>(info[0]).FromJust());
-  char *details = *Utf8String(info[1]);
+  Utf8String details_utf8_str(info[1]);
+  char *details = *details_utf8_str;
   grpc_metadata_array array;
   if (!CreateMetadataArray(Nan::To<Object>(info[2]).ToLocalChecked(),
                            &array, resources)){
diff --git a/src/node/ext/node_grpc.cc b/src/node/ext/node_grpc.cc
index 654c5ae..0c71b2d 100644
--- a/src/node/ext/node_grpc.cc
+++ b/src/node/ext/node_grpc.cc
@@ -237,7 +237,8 @@
         "headerKeyIsLegal's argument must be a string");
   }
   Local<String> key = Nan::To<String>(info[0]).ToLocalChecked();
-  char *key_str = *Nan::Utf8String(key);
+  Nan::Utf8String key_utf8_str(key);
+  char *key_str = *key_utf8_str;
   info.GetReturnValue().Set(static_cast<bool>(
       grpc_header_key_is_legal(key_str, static_cast<size_t>(key->Length()))));
 }
@@ -248,7 +249,8 @@
         "metadataNonbinValueIsLegal's argument must be a string");
   }
   Local<String> value = Nan::To<String>(info[0]).ToLocalChecked();
-  char *value_str = *Nan::Utf8String(value);
+  Nan::Utf8String value_utf8_str(value);
+  char *value_str = *value_utf8_str;
   info.GetReturnValue().Set(static_cast<bool>(
       grpc_header_nonbin_value_is_legal(
           value_str, static_cast<size_t>(value->Length()))));
@@ -260,7 +262,8 @@
         "metadataKeyIsLegal's argument must be a string");
   }
   Local<String> key = Nan::To<String>(info[0]).ToLocalChecked();
-  char *key_str = *Nan::Utf8String(key);
+  Nan::Utf8String key_utf8_str(key);
+  char *key_str = *key_utf8_str;
   info.GetReturnValue().Set(static_cast<bool>(
       grpc_is_binary_header(key_str, static_cast<size_t>(key->Length()))));
 }
diff --git a/src/node/index.js b/src/node/index.js
index 7eacdc6..1c19772 100644
--- a/src/node/index.js
+++ b/src/node/index.js
@@ -56,17 +56,18 @@
 /**
  * Load a gRPC object from an existing ProtoBuf.Reflect object.
  * @param {ProtoBuf.Reflect.Namespace} value The ProtoBuf object to load.
+ * @param {Object=} options Options to apply to the loaded object
  * @return {Object<string, *>} The resulting gRPC object
  */
-exports.loadObject = function loadObject(value) {
+exports.loadObject = function loadObject(value, options) {
   var result = {};
   if (value.className === 'Namespace') {
     _.each(value.children, function(child) {
-      result[child.name] = loadObject(child);
+      result[child.name] = loadObject(child, options);
     });
     return result;
   } else if (value.className === 'Service') {
-    return client.makeProtobufClientConstructor(value);
+    return client.makeProtobufClientConstructor(value, options);
   } else if (value.className === 'Message' || value.className === 'Enum') {
     return value.build();
   } else {
@@ -77,28 +78,45 @@
 var loadObject = exports.loadObject;
 
 /**
- * Load a gRPC object from a .proto file.
- * @param {string} filename The file to load
+ * Load a gRPC object from a .proto file. The options object can provide the
+ * following options:
+ * - convertFieldsToCamelCase: Loads this file with that option on protobuf.js
+ *   set as specified. See
+ *   https://github.com/dcodeIO/protobuf.js/wiki/Advanced-options for details
+ * - binaryAsBase64: deserialize bytes values as base64 strings instead of
+ *   Buffers. Defaults to false
+ * - longsAsStrings: deserialize long values as strings instead of objects.
+ *   Defaults to true
+ * @param {string|{root: string, file: string}} filename The file to load
  * @param {string=} format The file format to expect. Must be either 'proto' or
  *     'json'. Defaults to 'proto'
+ * @param {Object=} options Options to apply to the loaded file
  * @return {Object<string, *>} The resulting gRPC object
  */
-exports.load = function load(filename, format) {
+exports.load = function load(filename, format, options) {
   if (!format) {
     format = 'proto';
   }
-  var builder;
-  switch(format) {
-    case 'proto':
-    builder = ProtoBuf.loadProtoFile(filename);
-    break;
-    case 'json':
-    builder = ProtoBuf.loadJsonFile(filename);
-    break;
-    default:
-    throw new Error('Unrecognized format "' + format + '"');
+  var convertFieldsToCamelCaseOriginal = ProtoBuf.convertFieldsToCamelCase;
+  if(options && options.hasOwnProperty('convertFieldsToCamelCase')) {
+    ProtoBuf.convertFieldsToCamelCase = options.convertFieldsToCamelCase;
   }
-  return loadObject(builder.ns);
+  var builder;
+  try {
+    switch(format) {
+      case 'proto':
+      builder = ProtoBuf.loadProtoFile(filename);
+      break;
+      case 'json':
+      builder = ProtoBuf.loadJsonFile(filename);
+      break;
+      default:
+      throw new Error('Unrecognized format "' + format + '"');
+    }
+  } finally {
+    ProtoBuf.convertFieldsToCamelCase = convertFieldsToCamelCaseOriginal;
+  }
+  return loadObject(builder.ns, options);
 };
 
 /**
diff --git a/src/node/src/client.js b/src/node/src/client.js
index b5247a6..c02c447 100644
--- a/src/node/src/client.js
+++ b/src/node/src/client.js
@@ -698,13 +698,16 @@
  * Creates a constructor for clients for the given service
  * @param {ProtoBuf.Reflect.Service} service The service to generate a client
  *     for
+ * @param {Object=} options Options to apply to the client
  * @return {function(string, Object)} New client constructor
  */
-exports.makeProtobufClientConstructor =  function(service) {
-  var method_attrs = common.getProtobufServiceAttrs(service, service.name);
+exports.makeProtobufClientConstructor =  function(service, options) {
+  var method_attrs = common.getProtobufServiceAttrs(service, service.name,
+                                                    options);
   var Client = exports.makeClientConstructor(
       method_attrs, common.fullyQualifiedName(service));
   Client.service = service;
+  Client.service.grpc_options = options;
   return Client;
 };
 
diff --git a/src/node/src/common.js b/src/node/src/common.js
index 2e6c01c..e521760 100644
--- a/src/node/src/common.js
+++ b/src/node/src/common.js
@@ -44,9 +44,20 @@
 /**
  * Get a function that deserializes a specific type of protobuf.
  * @param {function()} cls The constructor of the message type to deserialize
+ * @param {bool=} binaryAsBase64 Deserialize bytes fields as base64 strings
+ *     instead of Buffers. Defaults to false
+ * @param {bool=} longsAsStrings Deserialize long values as strings instead of
+ *     objects. Defaults to true
  * @return {function(Buffer):cls} The deserialization function
  */
-exports.deserializeCls = function deserializeCls(cls) {
+exports.deserializeCls = function deserializeCls(cls, binaryAsBase64,
+                                                 longsAsStrings) {
+  if (binaryAsBase64 === undefined || binaryAsBase64 === null) {
+    binaryAsBase64 = false;
+  }
+  if (longsAsStrings === undefined || longsAsStrings === null) {
+    longsAsStrings = true;
+  }
   /**
    * Deserialize a buffer to a message object
    * @param {Buffer} arg_buf The buffer to deserialize
@@ -55,7 +66,7 @@
   return function deserialize(arg_buf) {
     // Convert to a native object with binary fields as Buffers (first argument)
     // and longs as strings (second argument)
-    return cls.decode(arg_buf).toRaw(false, true);
+    return cls.decode(arg_buf).toRaw(binaryAsBase64, longsAsStrings);
   };
 };
 
@@ -119,19 +130,28 @@
 /**
  * Return a map from method names to method attributes for the service.
  * @param {ProtoBuf.Reflect.Service} service The service to get attributes for
+ * @param {Object=} options Options to apply to these attributes
  * @return {Object} The attributes map
  */
-exports.getProtobufServiceAttrs = function getProtobufServiceAttrs(service) {
+exports.getProtobufServiceAttrs = function getProtobufServiceAttrs(service,
+                                                                   options) {
   var prefix = '/' + fullyQualifiedName(service) + '/';
+  var binaryAsBase64, longsAsStrings;
+  if (options) {
+    binaryAsBase64 = options.binaryAsBase64;
+    longsAsStrings = options.longsAsStrings;
+  }
   return _.object(_.map(service.children, function(method) {
     return [_.camelCase(method.name), {
       path: prefix + method.name,
       requestStream: method.requestStream,
       responseStream: method.responseStream,
       requestSerialize: serializeCls(method.resolvedRequestType.build()),
-      requestDeserialize: deserializeCls(method.resolvedRequestType.build()),
+      requestDeserialize: deserializeCls(method.resolvedRequestType.build(),
+                                     binaryAsBase64, longsAsStrings),
       responseSerialize: serializeCls(method.resolvedResponseType.build()),
-      responseDeserialize: deserializeCls(method.resolvedResponseType.build())
+      responseDeserialize: deserializeCls(method.resolvedResponseType.build(),
+                                     binaryAsBase64, longsAsStrings)
     }];
   }));
 };
diff --git a/src/node/src/credentials.js b/src/node/src/credentials.js
index 710ab6d..1d73723 100644
--- a/src/node/src/credentials.js
+++ b/src/node/src/credentials.js
@@ -98,6 +98,8 @@
         message = error.message;
         if (error.hasOwnProperty('code')) {
           code = error.code;
+        } else {
+          code = grpc.status.UNAUTHENTICATED;
         }
         if (!metadata) {
           metadata = new Metadata();
@@ -116,13 +118,16 @@
 exports.createFromGoogleCredential = function(google_credential) {
   return exports.createFromMetadataGenerator(function(auth_context, callback) {
     var service_url = auth_context.service_url;
+    console.log('Service URL:', service_url);
     google_credential.getRequestMetadata(service_url, function(err, header) {
       if (err) {
+        console.log('Auth error:', err);
         callback(err);
         return;
       }
       var metadata = new Metadata();
       metadata.add('authorization', header.Authorization);
+      console.log(header.Authorization);
       callback(null, metadata);
     });
   });
diff --git a/src/node/src/metadata.js b/src/node/src/metadata.js
index 51a9f8a..33d7ea1 100644
--- a/src/node/src/metadata.js
+++ b/src/node/src/metadata.js
@@ -64,7 +64,7 @@
   if (grpc.metadataKeyIsLegal(key)) {
     return key;
   } else {
-    throw new Error('Metadata key contains illegal characters');
+    throw new Error('Metadata key"' + key + '" contains illegal characters');
   }
 }
 
@@ -79,7 +79,8 @@
           'keys that don\'t end with \'-bin\' must have String values');
     }
     if (!grpc.metadataNonbinValueIsLegal(value)) {
-      throw new Error('Metadata string value contains illegal characters');
+      throw new Error('Metadata string value "' + value +
+                      '" contains illegal characters');
     }
   }
 }
diff --git a/src/node/src/server.js b/src/node/src/server.js
index e5aadcd..0cf7ba3 100644
--- a/src/node/src/server.js
+++ b/src/node/src/server.js
@@ -737,7 +737,12 @@
  *     method implementation for the provided service.
  */
 Server.prototype.addProtoService = function(service, implementation) {
-  this.addService(common.getProtobufServiceAttrs(service), implementation);
+  var options;
+  if (service.grpc_options) {
+    options = service.grpc_options;
+  }
+  this.addService(common.getProtobufServiceAttrs(service, options),
+                  implementation);
 };
 
 /**
diff --git a/src/node/test/common_test.js b/src/node/test/common_test.js
index 08ba429..66a4205 100644
--- a/src/node/test/common_test.js
+++ b/src/node/test/common_test.js
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -42,7 +42,7 @@
 var messages_proto = ProtoBuf.loadProtoFile(
     __dirname + '/test_messages.proto').build();
 
-describe('Proto message serialize and deserialize', function() {
+describe('Proto message long int serialize and deserialize', function() {
   var longSerialize = common.serializeCls(messages_proto.LongValues);
   var longDeserialize = common.deserializeCls(messages_proto.LongValues);
   var pos_value = '314159265358979';
@@ -87,4 +87,52 @@
     assert.strictEqual(longDeserialize(serialized).sfixed_64.toString(),
                        neg_value);
   });
+  it('should deserialize as a number with the right option set', function() {
+    var longNumDeserialize = common.deserializeCls(messages_proto.LongValues,
+                                                   false, false);
+    var serialized = longSerialize({int_64: pos_value});
+    assert.strictEqual(typeof longDeserialize(serialized).int_64, 'string');
+    /* With the longsAsStrings option disabled, long values are represented as
+     * objects with 3 keys: low, high, and unsigned */
+    assert.strictEqual(typeof longNumDeserialize(serialized).int_64, 'object');
+  });
+});
+describe('Proto message bytes serialize and deserialize', function() {
+  var sequenceSerialize = common.serializeCls(messages_proto.SequenceValues);
+  var sequenceDeserialize = common.deserializeCls(
+      messages_proto.SequenceValues);
+  var sequenceBase64Deserialize = common.deserializeCls(
+      messages_proto.SequenceValues, true);
+  var buffer_val = new Buffer([0x69, 0xb7]);
+  var base64_val = 'abc=';
+  it('should preserve a buffer', function() {
+    var serialized = sequenceSerialize({bytes_field: buffer_val});
+    var deserialized = sequenceDeserialize(serialized);
+    assert.strictEqual(deserialized.bytes_field.compare(buffer_val), 0);
+  });
+  it('should accept base64 encoded strings', function() {
+    var serialized = sequenceSerialize({bytes_field: base64_val});
+    var deserialized = sequenceDeserialize(serialized);
+    assert.strictEqual(deserialized.bytes_field.compare(buffer_val), 0);
+  });
+  it('should output base64 encoded strings with an option set', function() {
+    var serialized = sequenceSerialize({bytes_field: base64_val});
+    var deserialized = sequenceBase64Deserialize(serialized);
+    assert.strictEqual(deserialized.bytes_field, base64_val);
+  });
+  /* The next two tests are specific tests to verify that issue
+   * https://github.com/grpc/grpc/issues/5174 has been fixed. They are skipped
+   * because they will not pass until a protobuf.js release has been published
+   * with a fix for https://github.com/dcodeIO/protobuf.js/issues/390 */
+  it.skip('should serialize a repeated field as packed by default', function() {
+    var expected_serialize = new Buffer([0x12, 0x01, 0x01, 0x0a]);
+    var serialized = sequenceSerialize({repeated_field: [10]});
+    assert.strictEqual(expected_serialize.compare(serialized), 0);
+  });
+  it.skip('should deserialize packed or unpacked repeated', function() {
+    var serialized = new Buffer([0x12, 0x01, 0x01, 0x0a]);
+    assert.doesNotThrow(function() {
+      sequenceDeserialize(serialized);
+    });
+  });
 });
diff --git a/src/node/test/test_messages.proto b/src/node/test/test_messages.proto
index c77a937..9b8cb87 100644
--- a/src/node/test/test_messages.proto
+++ b/src/node/test/test_messages.proto
@@ -36,3 +36,8 @@
   fixed64 fixed_64 = 4;
   sfixed64 sfixed_64 = 5;
 }
+
+message SequenceValues {
+  bytes bytes_field = 1;
+  repeated int32 repeated_field = 2;
+}
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index 976bfff..f43ac5c 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -100,6 +100,7 @@
   'src/core/client_config/resolvers/sockaddr_resolver.c',
   'src/core/client_config/subchannel.c',
   'src/core/client_config/subchannel_factory.c',
+  'src/core/client_config/subchannel_index.c',
   'src/core/client_config/uri_parser.c',
   'src/core/compression/algorithm.c',
   'src/core/compression/message_compress.c',
diff --git a/summerofcode/ideas.md b/summerofcode/ideas.md
new file mode 100644
index 0000000..0732623
--- /dev/null
+++ b/summerofcode/ideas.md
@@ -0,0 +1,4 @@
+Google Summer of Code 2016 gRPC Ideas
+=====================================
+
+(Skeleton for now.)
diff --git a/test/core/end2end/fixtures/h2_uchannel.c b/test/core/end2end/fixtures/h2_uchannel.c
index 5ab64f9..dbdd352 100644
--- a/test/core/end2end/fixtures/h2_uchannel.c
+++ b/test/core/end2end/fixtures/h2_uchannel.c
@@ -159,7 +159,7 @@
   c->base.vtable = &connector_vtable;
   gpr_ref_init(&c->refs, 1);
   args->args = final_args;
-  s = grpc_subchannel_create(&c->base, args);
+  s = grpc_subchannel_create(exec_ctx, &c->base, args);
   grpc_connector_unref(exec_ctx, &c->base);
   grpc_channel_args_destroy(final_args);
   if (*f->sniffed_subchannel) {
diff --git a/test/cpp/common/channel_arguments_test.cc b/test/cpp/common/channel_arguments_test.cc
index e010d37..a4821b4 100644
--- a/test/cpp/common/channel_arguments_test.cc
+++ b/test/cpp/common/channel_arguments_test.cc
@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -41,94 +41,141 @@
 
 class ChannelArgumentsTest : public ::testing::Test {
  protected:
+  ChannelArgumentsTest()
+      : pointer_vtable_({&ChannelArguments::PointerVtableMembers::Copy,
+                         &ChannelArguments::PointerVtableMembers::Destroy,
+                         &ChannelArguments::PointerVtableMembers::Compare}) {}
+
   void SetChannelArgs(const ChannelArguments& channel_args,
                       grpc_channel_args* args) {
     channel_args.SetChannelArgs(args);
   }
+
+  grpc::string GetDefaultUserAgentPrefix() {
+    std::ostringstream user_agent_prefix;
+    user_agent_prefix << "grpc-c++/" << grpc_version_string();
+    return user_agent_prefix.str();
+  }
+
+  void VerifyDefaultChannelArgs() {
+    grpc_channel_args args;
+    SetChannelArgs(channel_args_, &args);
+    EXPECT_EQ(static_cast<size_t>(1), args.num_args);
+    EXPECT_STREQ(GRPC_ARG_PRIMARY_USER_AGENT_STRING, args.args[0].key);
+    EXPECT_EQ(GetDefaultUserAgentPrefix(),
+              grpc::string(args.args[0].value.string));
+  }
+
+  bool HasArg(grpc_arg expected_arg) {
+    grpc_channel_args args;
+    SetChannelArgs(channel_args_, &args);
+    for (size_t i = 0; i < args.num_args; i++) {
+      const grpc_arg& arg = args.args[i];
+      if (arg.type == expected_arg.type &&
+          grpc::string(arg.key) == expected_arg.key) {
+        if (arg.type == GRPC_ARG_INTEGER) {
+          return arg.value.integer == expected_arg.value.integer;
+        } else if (arg.type == GRPC_ARG_STRING) {
+          return grpc::string(arg.value.string) == expected_arg.value.string;
+        } else if (arg.type == GRPC_ARG_POINTER) {
+          return arg.value.pointer.p == expected_arg.value.pointer.p &&
+                 arg.value.pointer.vtable->copy ==
+                     expected_arg.value.pointer.vtable->copy &&
+                 arg.value.pointer.vtable->destroy ==
+                     expected_arg.value.pointer.vtable->destroy;
+        }
+      }
+    }
+    return false;
+  }
+  grpc_arg_pointer_vtable pointer_vtable_;
+  ChannelArguments channel_args_;
 };
 
 TEST_F(ChannelArgumentsTest, SetInt) {
-  grpc_channel_args args;
-  ChannelArguments channel_args;
-  // Empty arguments.
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(0), args.num_args);
+  VerifyDefaultChannelArgs();
+  grpc::string key0("key0");
+  grpc_arg arg0;
+  arg0.type = GRPC_ARG_INTEGER;
+  arg0.key = const_cast<char*>(key0.c_str());
+  arg0.value.integer = 0;
+  grpc::string key1("key1");
+  grpc_arg arg1;
+  arg1.type = GRPC_ARG_INTEGER;
+  arg1.key = const_cast<char*>(key1.c_str());
+  arg1.value.integer = 1;
 
-  grpc::string key("key0");
-  channel_args.SetInt(key, 0);
+  grpc::string arg_key0(key0);
+  channel_args_.SetInt(arg_key0, arg0.value.integer);
   // Clear key early to make sure channel_args takes a copy
-  key = "";
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(1), args.num_args);
-  EXPECT_EQ(GRPC_ARG_INTEGER, args.args[0].type);
-  EXPECT_STREQ("key0", args.args[0].key);
-  EXPECT_EQ(0, args.args[0].value.integer);
+  arg_key0.clear();
+  EXPECT_TRUE(HasArg(arg0));
 
-  key = "key1";
-  channel_args.SetInt(key, 1);
-  key = "";
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(2), args.num_args);
-  // We do not enforce order on the arguments.
-  for (size_t i = 0; i < args.num_args; i++) {
-    EXPECT_EQ(GRPC_ARG_INTEGER, args.args[i].type);
-    if (grpc::string(args.args[i].key) == "key0") {
-      EXPECT_EQ(0, args.args[i].value.integer);
-    } else if (grpc::string(args.args[i].key) == "key1") {
-      EXPECT_EQ(1, args.args[i].value.integer);
-    }
-  }
+  grpc::string arg_key1(key1);
+  channel_args_.SetInt(arg_key1, arg1.value.integer);
+  arg_key1.clear();
+  EXPECT_TRUE(HasArg(arg0));
+  EXPECT_TRUE(HasArg(arg1));
 }
 
 TEST_F(ChannelArgumentsTest, SetString) {
-  grpc_channel_args args;
-  ChannelArguments channel_args;
-  // Empty arguments.
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(0), args.num_args);
+  VerifyDefaultChannelArgs();
+  grpc::string key0("key0");
+  grpc::string val0("val0");
+  grpc_arg arg0;
+  arg0.type = GRPC_ARG_STRING;
+  arg0.key = const_cast<char*>(key0.c_str());
+  arg0.value.string = const_cast<char*>(val0.c_str());
+  grpc::string key1("key1");
+  grpc::string val1("val1");
+  grpc_arg arg1;
+  arg1.type = GRPC_ARG_STRING;
+  arg1.key = const_cast<char*>(key1.c_str());
+  arg1.value.string = const_cast<char*>(val1.c_str());
 
-  grpc::string key("key0");
-  grpc::string val("val0");
-  channel_args.SetString(key, val);
+  grpc::string key(key0);
+  grpc::string val(val0);
+  channel_args_.SetString(key, val);
   // Clear key/val early to make sure channel_args takes a copy
   key = "";
   val = "";
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(1), args.num_args);
-  EXPECT_EQ(GRPC_ARG_STRING, args.args[0].type);
-  EXPECT_STREQ("key0", args.args[0].key);
-  EXPECT_STREQ("val0", args.args[0].value.string);
+  EXPECT_TRUE(HasArg(arg0));
 
-  key = "key1";
-  val = "val1";
-  channel_args.SetString(key, val);
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(2), args.num_args);
-  // We do not enforce order on the arguments.
-  for (size_t i = 0; i < args.num_args; i++) {
-    EXPECT_EQ(GRPC_ARG_STRING, args.args[i].type);
-    if (grpc::string(args.args[i].key) == "key0") {
-      EXPECT_STREQ("val0", args.args[i].value.string);
-    } else if (grpc::string(args.args[i].key) == "key1") {
-      EXPECT_STREQ("val1", args.args[i].value.string);
-    }
-  }
+  key = key1;
+  val = val1;
+  channel_args_.SetString(key, val);
+  // Clear key/val early to make sure channel_args takes a copy
+  key = "";
+  val = "";
+  EXPECT_TRUE(HasArg(arg0));
+  EXPECT_TRUE(HasArg(arg1));
 }
 
 TEST_F(ChannelArgumentsTest, SetPointer) {
-  grpc_channel_args args;
-  ChannelArguments channel_args;
-  // Empty arguments.
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(0), args.num_args);
+  VerifyDefaultChannelArgs();
+  grpc::string key0("key0");
+  grpc_arg arg0;
+  arg0.type = GRPC_ARG_POINTER;
+  arg0.key = const_cast<char*>(key0.c_str());
+  arg0.value.pointer.p = &key0;
+  arg0.value.pointer.vtable = &pointer_vtable_;
 
-  grpc::string key("key0");
-  channel_args.SetPointer(key, &key);
-  SetChannelArgs(channel_args, &args);
-  EXPECT_EQ(static_cast<size_t>(1), args.num_args);
-  EXPECT_EQ(GRPC_ARG_POINTER, args.args[0].type);
-  EXPECT_STREQ("key0", args.args[0].key);
-  EXPECT_EQ(&key, args.args[0].value.pointer.p);
+  grpc::string key(key0);
+  channel_args_.SetPointer(key, arg0.value.pointer.p);
+  EXPECT_TRUE(HasArg(arg0));
+}
+
+TEST_F(ChannelArgumentsTest, SetUserAgentPrefix) {
+  VerifyDefaultChannelArgs();
+  grpc::string prefix("prefix");
+  grpc::string whole_prefix = prefix + " " + GetDefaultUserAgentPrefix();
+  grpc_arg arg0;
+  arg0.type = GRPC_ARG_STRING;
+  arg0.key = const_cast<char*>(GRPC_ARG_PRIMARY_USER_AGENT_STRING);
+  arg0.value.string = const_cast<char*>(whole_prefix.c_str());
+
+  channel_args_.SetUserAgentPrefix(prefix);
+  EXPECT_TRUE(HasArg(arg0));
 }
 
 }  // namespace testing
diff --git a/test/cpp/end2end/async_end2end_test.cc b/test/cpp/end2end/async_end2end_test.cc
index a194c61..a15cbd7 100644
--- a/test/cpp/end2end/async_end2end_test.cc
+++ b/test/cpp/end2end/async_end2end_test.cc
@@ -43,6 +43,7 @@
 #include <grpc/grpc.h>
 #include <grpc/support/thd.h>
 #include <grpc/support/time.h>
+#include <grpc/support/tls.h>
 #include <gtest/gtest.h>
 
 #include "src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.h"
@@ -59,6 +60,8 @@
 using grpc::testing::EchoResponse;
 using std::chrono::system_clock;
 
+GPR_TLS_DECL(g_is_async_end2end_test);
+
 namespace grpc {
 namespace testing {
 
@@ -67,9 +70,11 @@
 void* tag(int i) { return (void*)(intptr_t)i; }
 
 #ifdef GPR_POSIX_SOCKET
-static int assert_non_blocking_poll(struct pollfd* pfds, nfds_t nfds,
-                                    int timeout) {
-  GPR_ASSERT(timeout == 0);
+static int maybe_assert_non_blocking_poll(struct pollfd* pfds, nfds_t nfds,
+                                          int timeout) {
+  if (gpr_tls_get(&g_is_async_end2end_test)) {
+    GPR_ASSERT(timeout == 0);
+  }
   return poll(pfds, nfds, timeout);
 }
 
@@ -86,21 +91,21 @@
   grpc_poll_function_type prev_;
 };
 
-class PollingCheckRegion : public PollOverride {
+class PollingOverrider : public PollOverride {
  public:
-  explicit PollingCheckRegion(bool allow_blocking)
-      : PollOverride(allow_blocking ? poll : assert_non_blocking_poll) {}
+  explicit PollingOverrider(bool allow_blocking)
+      : PollOverride(allow_blocking ? poll : maybe_assert_non_blocking_poll) {}
 };
 #else
-class PollingCheckRegion {
+class PollingOverrider {
  public:
-  explicit PollingCheckRegion(bool allow_blocking) {}
+  explicit PollingOverrider(bool allow_blocking) {}
 };
 #endif
 
-class Verifier : public PollingCheckRegion {
+class Verifier {
  public:
-  explicit Verifier(bool spin) : PollingCheckRegion(!spin), spin_(spin) {}
+  explicit Verifier(bool spin) : spin_(spin) {}
   Verifier& Expect(int i, bool expect_ok) {
     expectations_[tag(i)] = expect_ok;
     return *this;
@@ -183,6 +188,8 @@
   AsyncEnd2endTest() {}
 
   void SetUp() GRPC_OVERRIDE {
+    poll_overrider_.reset(new PollingOverrider(!GetParam()));
+
     int port = grpc_pick_unused_port_or_die();
     server_address_ << "localhost:" << port;
 
@@ -193,6 +200,8 @@
     builder.RegisterService(&service_);
     cq_ = builder.AddCompletionQueue();
     server_ = builder.BuildAndStart();
+
+    gpr_tls_set(&g_is_async_end2end_test, 1);
   }
 
   void TearDown() GRPC_OVERRIDE {
@@ -202,6 +211,8 @@
     cq_->Shutdown();
     while (cq_->Next(&ignored_tag, &ignored_ok))
       ;
+    poll_overrider_.reset();
+    gpr_tls_set(&g_is_async_end2end_test, 0);
   }
 
   void ResetStub() {
@@ -249,6 +260,8 @@
   std::unique_ptr<Server> server_;
   grpc::testing::EchoTestService::AsyncService service_;
   std::ostringstream server_address_;
+
+  std::unique_ptr<PollingOverrider> poll_overrider_;
 };
 
 TEST_P(AsyncEnd2endTest, SimpleRpc) {
@@ -1087,7 +1100,7 @@
     Verifier(GetParam()).Expect(7, true).Verify(cq_.get());
 
     // This is expected to fail in all cases i.e for all values of
-    // server_try_cancel. This is becasue at this point, either there are no
+    // server_try_cancel. This is because at this point, either there are no
     // more msgs from the client (because client called WritesDone) or the RPC
     // is cancelled on the server
     srv_stream.Read(&recv_request, tag(8));
@@ -1164,6 +1177,9 @@
 
 int main(int argc, char** argv) {
   grpc_test_init(argc, argv);
+  gpr_tls_init(&g_is_async_end2end_test);
   ::testing::InitGoogleTest(&argc, argv);
-  return RUN_ALL_TESTS();
+  int ret = RUN_ALL_TESTS();
+  gpr_tls_destroy(&g_is_async_end2end_test);
+  return ret;
 }
diff --git a/test/cpp/end2end/end2end_test.cc b/test/cpp/end2end/end2end_test.cc
index 65da71b..ce8e4d2 100644
--- a/test/cpp/end2end/end2end_test.cc
+++ b/test/cpp/end2end/end2end_test.cc
@@ -51,11 +51,11 @@
 #include "src/core/security/credentials.h"
 #include "src/proto/grpc/testing/duplicate/echo_duplicate.grpc.pb.h"
 #include "src/proto/grpc/testing/echo.grpc.pb.h"
-#include "test/core/end2end/data/ssl_test_data.h"
 #include "test/core/util/port.h"
 #include "test/core/util/test_config.h"
 #include "test/cpp/end2end/test_service_impl.h"
 #include "test/cpp/util/string_ref_helper.h"
+#include "test/cpp/util/test_credentials_provider.h"
 
 using grpc::testing::EchoRequest;
 using grpc::testing::EchoResponse;
@@ -191,12 +191,14 @@
 
 class TestScenario {
  public:
-  TestScenario(bool proxy, bool tls) : use_proxy(proxy), use_tls(tls) {}
+  TestScenario(bool proxy, const grpc::string& creds_type)
+      : use_proxy(proxy), credentials_type(creds_type) {}
   void Log() const {
-    gpr_log(GPR_INFO, "Scenario: proxy %d, tls %d", use_proxy, use_tls);
+    gpr_log(GPR_INFO, "Scenario: proxy %d, credentials %s", use_proxy,
+            credentials_type.c_str());
   }
   bool use_proxy;
-  bool use_tls;
+  const grpc::string credentials_type;
 };
 
 class End2endTest : public ::testing::TestWithParam<TestScenario> {
@@ -220,14 +222,8 @@
     server_address_ << "127.0.0.1:" << port;
     // Setup server
     ServerBuilder builder;
-    auto server_creds = InsecureServerCredentials();
-    if (GetParam().use_tls) {
-      SslServerCredentialsOptions::PemKeyCertPair pkcp = {test_server1_key,
-                                                          test_server1_cert};
-      SslServerCredentialsOptions ssl_opts;
-      ssl_opts.pem_root_certs = "";
-      ssl_opts.pem_key_cert_pairs.push_back(pkcp);
-      server_creds = SslServerCredentials(ssl_opts);
+    auto server_creds = GetServerCredentials(GetParam().credentials_type);
+    if (GetParam().credentials_type != kInsecureCredentialsType) {
       server_creds->SetAuthMetadataProcessor(processor);
     }
     builder.AddListeningPort(server_address_.str(), server_creds);
@@ -246,11 +242,10 @@
     }
     EXPECT_TRUE(is_server_started_);
     ChannelArguments args;
-    auto channel_creds = InsecureChannelCredentials();
-    if (GetParam().use_tls) {
-      SslCredentialsOptions ssl_opts = {test_root_cert, "", ""};
-      args.SetSslTargetNameOverride("foo.test.google.fr");
-      channel_creds = SslCredentials(ssl_opts);
+    auto channel_creds =
+        GetChannelCredentials(GetParam().credentials_type, &args);
+    if (!user_agent_prefix_.empty()) {
+      args.SetUserAgentPrefix(user_agent_prefix_);
     }
     args.SetString(GRPC_ARG_SECONDARY_USER_AGENT_STRING, "end2end_test");
     channel_ = CreateCustomChannel(server_address_.str(), channel_creds, args);
@@ -285,6 +280,7 @@
   TestServiceImpl service_;
   TestServiceImpl special_service_;
   TestServiceImplDupPkg dup_pkg_service_;
+  grpc::string user_agent_prefix_;
 };
 
 static void SendRpc(grpc::testing::EchoTestService::Stub* stub, int num_rpcs,
@@ -601,6 +597,25 @@
   TestBidiStreamServerCancel(CANCEL_AFTER_PROCESSING, 5);
 }
 
+TEST_P(End2endTest, SimpleRpcWithCustomeUserAgentPrefix) {
+  user_agent_prefix_ = "custom_prefix";
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  request.set_message("Hello hello hello hello");
+  request.mutable_param()->set_echo_metadata(true);
+
+  ClientContext context;
+  Status s = stub_->Echo(&context, request, &response);
+  EXPECT_EQ(response.message(), request.message());
+  EXPECT_TRUE(s.ok());
+  const auto& trailing_metadata = context.GetServerTrailingMetadata();
+  auto iter = trailing_metadata.find("user-agent");
+  EXPECT_TRUE(iter != trailing_metadata.end());
+  grpc::string expected_prefix = user_agent_prefix_ + " grpc-c++/";
+  EXPECT_TRUE(iter->second.starts_with(expected_prefix));
+}
+
 TEST_P(End2endTest, MultipleRpcsWithVariedBinaryMetadataValue) {
   ResetStub();
   std::vector<std::thread*> threads;
@@ -918,7 +933,7 @@
 
 // Takes 10s.
 TEST_P(End2endTest, ChannelStateTimeout) {
-  if (GetParam().use_tls) {
+  if (GetParam().credentials_type != kInsecureCredentialsType) {
     return;
   }
   int port = grpc_pick_unused_port_or_die();
@@ -1127,7 +1142,7 @@
  protected:
   SecureEnd2endTest() {
     GPR_ASSERT(!GetParam().use_proxy);
-    GPR_ASSERT(GetParam().use_tls);
+    GPR_ASSERT(GetParam().credentials_type != kInsecureCredentialsType);
   }
 };
 
@@ -1350,21 +1365,42 @@
   EXPECT_EQ("*.test.youtube.com", ToString(auth_ctx->GetPeerIdentity()[2]));
 }
 
+std::vector<TestScenario> CreateTestScenarios(bool use_proxy,
+                                              bool test_insecure,
+                                              bool test_secure) {
+  std::vector<TestScenario> scenarios;
+  std::vector<grpc::string> credentials_types;
+  if (test_secure) {
+    credentials_types = GetSecureCredentialsTypeList();
+  }
+  if (test_insecure) {
+    credentials_types.push_back(kInsecureCredentialsType);
+  }
+  for (auto it = credentials_types.begin(); it != credentials_types.end();
+       ++it) {
+    scenarios.push_back(TestScenario(false, *it));
+    if (use_proxy) {
+      scenarios.push_back(TestScenario(true, *it));
+    }
+  }
+  return scenarios;
+}
+
 INSTANTIATE_TEST_CASE_P(End2end, End2endTest,
-                        ::testing::Values(TestScenario(false, false),
-                                          TestScenario(false, true)));
+                        ::testing::ValuesIn(CreateTestScenarios(false, true,
+                                                                true)));
 
 INSTANTIATE_TEST_CASE_P(End2endServerTryCancel, End2endServerTryCancelTest,
-                        ::testing::Values(TestScenario(false, false)));
+                        ::testing::ValuesIn(CreateTestScenarios(false, true,
+                                                                false)));
 
 INSTANTIATE_TEST_CASE_P(ProxyEnd2end, ProxyEnd2endTest,
-                        ::testing::Values(TestScenario(false, false),
-                                          TestScenario(false, true),
-                                          TestScenario(true, false),
-                                          TestScenario(true, true)));
+                        ::testing::ValuesIn(CreateTestScenarios(true, true,
+                                                                true)));
 
 INSTANTIATE_TEST_CASE_P(SecureEnd2end, SecureEnd2endTest,
-                        ::testing::Values(TestScenario(false, true)));
+                        ::testing::ValuesIn(CreateTestScenarios(false, false,
+                                                                true)));
 
 }  // namespace
 }  // namespace testing
diff --git a/test/cpp/util/test_credentials_provider.cc b/test/cpp/util/test_credentials_provider.cc
new file mode 100644
index 0000000..1086e14
--- /dev/null
+++ b/test/cpp/util/test_credentials_provider.cc
@@ -0,0 +1,82 @@
+
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "test/cpp/util/test_credentials_provider.h"
+
+#include "test/core/end2end/data/ssl_test_data.h"
+
+namespace grpc {
+namespace testing {
+
+const char kTlsCredentialsType[] = "TLS_CREDENTIALS";
+
+std::shared_ptr<ChannelCredentials> GetChannelCredentials(
+    const grpc::string& type, ChannelArguments* args) {
+  if (type == kInsecureCredentialsType) {
+    return InsecureChannelCredentials();
+  } else if (type == kTlsCredentialsType) {
+    SslCredentialsOptions ssl_opts = {test_root_cert, "", ""};
+    args->SetSslTargetNameOverride("foo.test.google.fr");
+    return SslCredentials(ssl_opts);
+  } else {
+    gpr_log(GPR_ERROR, "Unsupported credentials type %s.", type.c_str());
+  }
+  return nullptr;
+}
+
+std::shared_ptr<ServerCredentials> GetServerCredentials(
+    const grpc::string& type) {
+  if (type == kInsecureCredentialsType) {
+    return InsecureServerCredentials();
+  } else if (type == kTlsCredentialsType) {
+    SslServerCredentialsOptions::PemKeyCertPair pkcp = {test_server1_key,
+                                                        test_server1_cert};
+    SslServerCredentialsOptions ssl_opts;
+    ssl_opts.pem_root_certs = "";
+    ssl_opts.pem_key_cert_pairs.push_back(pkcp);
+    return SslServerCredentials(ssl_opts);
+  } else {
+    gpr_log(GPR_ERROR, "Unsupported credentials type %s.", type.c_str());
+  }
+  return nullptr;
+}
+
+std::vector<grpc::string> GetSecureCredentialsTypeList() {
+  std::vector<grpc::string> types;
+  types.push_back(kTlsCredentialsType);
+  return types;
+}
+
+}  // namespace testing
+}  // namespace grpc
diff --git a/test/cpp/util/test_credentials_provider.h b/test/cpp/util/test_credentials_provider.h
new file mode 100644
index 0000000..f725305
--- /dev/null
+++ b/test/cpp/util/test_credentials_provider.h
@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_TEST_CPP_UTIL_TEST_CREDENTIALS_PROVIDER_H
+#define GRPC_TEST_CPP_UTIL_TEST_CREDENTIALS_PROVIDER_H
+
+#include <memory>
+
+#include <grpc++/security/credentials.h>
+#include <grpc++/security/server_credentials.h>
+#include <grpc++/support/channel_arguments.h>
+
+namespace grpc {
+namespace testing {
+
+const char kInsecureCredentialsType[] = "INSECURE_CREDENTIALS";
+
+// Provide channel credentials according to the given type. Alter the channel
+// arguments if needed.
+std::shared_ptr<ChannelCredentials> GetChannelCredentials(
+    const grpc::string& type, ChannelArguments* args);
+
+// Provide server credentials according to the given type.
+std::shared_ptr<ServerCredentials> GetServerCredentials(
+    const grpc::string& type);
+
+// Provide a list of secure credentials type.
+std::vector<grpc::string> GetSecureCredentialsTypeList();
+
+}  // namespace testing
+}  // namespace grpc
+
+#endif  // GRPC_TEST_CPP_UTIL_TEST_CREDENTIALS_PROVIDER_H
diff --git a/tools/distrib/check_copyright.py b/tools/distrib/check_copyright.py
index d1a34a9..99771f9 100755
--- a/tools/distrib/check_copyright.py
+++ b/tools/distrib/check_copyright.py
@@ -71,9 +71,9 @@
 # that given a line of license text, returns what should
 # be in the file
 LICENSE_PREFIX = {
-  '.c':         r'\s*\*\s*',
-  '.cc':        r'\s*\*\s*',
-  '.h':         r'\s*\*\s*',
+  '.c':         r'\s*(?://|\*)\s*',
+  '.cc':        r'\s*(?://|\*)\s*',
+  '.h':         r'\s*(?://|\*)\s*',
   '.m':         r'\s*\*\s*',
   '.php':       r'\s*\*\s*',
   '.js':        r'\s*\*\s*',
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index e49c675..84250e7 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -799,6 +799,7 @@
 src/core/client_config/resolvers/sockaddr_resolver.h \
 src/core/client_config/subchannel.h \
 src/core/client_config/subchannel_factory.h \
+src/core/client_config/subchannel_index.h \
 src/core/client_config/uri_parser.h \
 src/core/compression/algorithm_metadata.h \
 src/core/compression/message_compress.h \
@@ -930,6 +931,7 @@
 src/core/client_config/resolvers/sockaddr_resolver.c \
 src/core/client_config/subchannel.c \
 src/core/client_config/subchannel_factory.c \
+src/core/client_config/subchannel_index.c \
 src/core/client_config/uri_parser.c \
 src/core/compression/algorithm.c \
 src/core/compression/message_compress.c \
diff --git a/tools/asan_suppressions.txt b/tools/lsan_suppressions.txt
similarity index 100%
rename from tools/asan_suppressions.txt
rename to tools/lsan_suppressions.txt
diff --git a/tools/run_tests/configs.json b/tools/run_tests/configs.json
index d508c63..9d7b8a3 100644
--- a/tools/run_tests/configs.json
+++ b/tools/run_tests/configs.json
@@ -45,8 +45,8 @@
   {
     "config": "asan", 
     "environ": {
-      "ASAN_OPTIONS": "suppressions=tools/asan_suppressions.txt:detect_leaks=1:color=always", 
-      "LSAN_OPTIONS": "suppressions=tools/asan_suppressions.txt:report_objects=1"
+      "ASAN_OPTIONS": "detect_leaks=1:color=always", 
+      "LSAN_OPTIONS": "suppressions=tools/lsan_suppressions.txt:report_objects=1"
     }, 
     "timeout_multiplier": 1.5
   }, 
diff --git a/tools/run_tests/run_interop_tests.py b/tools/run_tests/run_interop_tests.py
index 76be932..df3ab90 100755
--- a/tools/run_tests/run_interop_tests.py
+++ b/tools/run_tests/run_interop_tests.py
@@ -422,7 +422,7 @@
     time.sleep(2)
 
 
-def cloud_to_prod_jobspec(language, test_case, server_host_name, 
+def cloud_to_prod_jobspec(language, test_case, server_host_name,
                           server_host_detail, docker_image=None, auth=False):
   """Creates jobspec for cloud-to-prod interop test"""
   container_name = None
@@ -441,7 +441,7 @@
   cwd = language.client_cwd
 
   if docker_image:
-    container_name = dockerjob.random_name('interop_client_%s' % 
+    container_name = dockerjob.random_name('interop_client_%s' %
                                            language.safename)
     cmdline = docker_run_cmdline(cmdline,
                                  image=docker_image,
@@ -457,7 +457,7 @@
           cmdline=cmdline,
           cwd=cwd,
           environ=environ,
-          shortname='%s:%s:%s:%s' % (suite_name, server_host_name, language, 
+          shortname='%s:%s:%s:%s' % (suite_name, server_host_name, language,
                                      test_case),
           timeout_seconds=90,
           flake_retries=5 if args.allow_flakes else 0,
@@ -575,18 +575,18 @@
     'percent': 1.0 * passed / (passed + failed)
   }
 
-# A dictionary of prod servers to test. 
+# A dictionary of prod servers to test.
 # Format: server_name: (server_host, server_host_override, errors_allowed)
 # TODO(adelez): implement logic for errors_allowed where if the indicated tests
 # fail, they don't impact the overall test result.
 prod_servers = {
-    'default': ('grpc-test.sandbox.googleapis.com', 
+    'default': ('grpc-test.sandbox.googleapis.com',
                 'grpc-test.sandbox.googleapis.com', False),
-    'gateway_v2': ('grpc-test2.sandbox.googleapis.com', 
+    'gateway_v2': ('grpc-test2.sandbox.googleapis.com',
                    'grpc-test2.sandbox.googleapis.com', True),
-    'cloud_gateway': ('216.239.32.255', 'grpc-test.sandbox.googleapis.com', 
+    'cloud_gateway': ('216.239.32.255', 'grpc-test.sandbox.googleapis.com',
                       False),
-    'cloud_gateway_v2': ('216.239.32.255', 'grpc-test2.sandbox.googleapis.com', 
+    'cloud_gateway_v2': ('216.239.32.255', 'grpc-test2.sandbox.googleapis.com',
                          True)
 }
 
@@ -720,7 +720,7 @@
           if not test_case in language.unimplemented_test_cases():
             if not test_case in _SKIP_ADVANCED + _SKIP_COMPRESSION:
               test_job = cloud_to_prod_jobspec(
-                  language, test_case, server_host_name, 
+                  language, test_case, server_host_name,
                   prod_servers[server_host_name],
                   docker_image=docker_images.get(str(language)))
               jobs.append(test_job)
@@ -728,7 +728,7 @@
       if args.http2_interop:
         for test_case in _HTTP2_TEST_CASES:
           test_job = cloud_to_prod_jobspec(
-              http2Interop, test_case, server_host_name, 
+              http2Interop, test_case, server_host_name,
               prod_servers[server_host_name],
               docker_image=docker_images.get(str(http2Interop)))
           jobs.append(test_job)
@@ -739,7 +739,7 @@
         for test_case in _AUTH_TEST_CASES:
           if not test_case in language.unimplemented_test_cases():
             test_job = cloud_to_prod_jobspec(
-                language, test_case, server_host_name, 
+                language, test_case, server_host_name,
                 prod_servers[server_host_name],
                 docker_image=docker_images.get(str(language)), auth=True)
             jobs.append(test_job)
@@ -802,7 +802,7 @@
   report_utils.render_interop_html_report(
       set([str(l) for l in languages]), servers, _TEST_CASES, _AUTH_TEST_CASES,
       _HTTP2_TEST_CASES, resultset, num_failures,
-      args.cloud_to_prod_auth or args.cloud_to_prod, args.prod_servers, 
+      args.cloud_to_prod_auth or args.cloud_to_prod, args.prod_servers,
       args.http2_interop)
 
 finally:
diff --git a/tools/run_tests/run_node.bat b/tools/run_tests/run_node.bat
index f5cf01f..ad9ca14 100644
--- a/tools/run_tests/run_node.bat
+++ b/tools/run_tests/run_node.bat
@@ -29,4 +29,4 @@
 
 set JUNIT_REPORT_PATH=src\node\reports.xml
 set JUNIT_REPORT_STACK=1
-.\node_modules\.bin\mocha.cmd --reporter mocha-jenkins-reporter src\node\test
\ No newline at end of file
+.\node_modules\.bin\mocha.cmd --reporter mocha-jenkins-reporter --timeout 8000 src\node\test
\ No newline at end of file
diff --git a/tools/run_tests/run_node.sh b/tools/run_tests/run_node.sh
index 40f61d7..178584a 100755
--- a/tools/run_tests/run_node.sh
+++ b/tools/run_tests/run_node.sh
@@ -41,10 +41,13 @@
 
 root=`pwd`
 
+test_directory='src/node/test'
+timeout=8000
+
 if [ "$CONFIG" = "gcov" ]
 then
   ./node_modules/.bin/istanbul cover --dir reports/node_coverage \
-    -x **/interop/* ./node_modules/.bin/_mocha -- --timeout 8000 src/node/test
+    -x **/interop/* ./node_modules/.bin/_mocha -- --timeout $timeout $test_directory
   cd build
   gcov Release/obj.target/grpc/ext/*.o
   lcov --base-directory . --directory . -c -o coverage.info
@@ -55,5 +58,7 @@
   echo '<html><head><meta http-equiv="refresh" content="0;URL=lcov-report/index.html"></head></html>' > \
     ../reports/node_coverage/index.html
 else
-  JUNIT_REPORT_PATH=src/node/reports.xml JUNIT_REPORT_STACK=1 ./node_modules/.bin/mocha --reporter mocha-jenkins-reporter src/node/test
+  JUNIT_REPORT_PATH=src/node/reports.xml JUNIT_REPORT_STACK=1 \
+    ./node_modules/.bin/mocha --timeout $timeout \
+    --reporter mocha-jenkins-reporter $test_directory
 fi
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index de3716b..0b3efa2 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -334,13 +334,14 @@
 
   def test_specs(self, config, args):
     return [config.job_spec(['tools/run_tests/run_ruby.sh'], None,
+                            timeout_seconds=10*60,
                             environ=_FORCE_ENVIRON_FOR_WRAPPERS)]
 
   def pre_build_steps(self):
     return [['tools/run_tests/pre_build_ruby.sh']]
 
   def make_targets(self, test_regex):
-    return ['static_c']
+    return []
 
   def make_options(self):
     return []
@@ -1197,4 +1198,3 @@
   if BuildAndRunError.POST_TEST in errors:
     exit_code |= 4
   sys.exit(exit_code)
-
diff --git a/tools/run_tests/sources_and_headers.json b/tools/run_tests/sources_and_headers.json
index c4a0774..3cdd7b4 100644
--- a/tools/run_tests/sources_and_headers.json
+++ b/tools/run_tests/sources_and_headers.json
@@ -3010,6 +3010,7 @@
       "src/core/client_config/resolvers/sockaddr_resolver.h", 
       "src/core/client_config/subchannel.h", 
       "src/core/client_config/subchannel_factory.h", 
+      "src/core/client_config/subchannel_index.h", 
       "src/core/client_config/uri_parser.h", 
       "src/core/compression/algorithm_metadata.h", 
       "src/core/compression/message_compress.h", 
@@ -3190,6 +3191,8 @@
       "src/core/client_config/subchannel.h", 
       "src/core/client_config/subchannel_factory.c", 
       "src/core/client_config/subchannel_factory.h", 
+      "src/core/client_config/subchannel_index.c", 
+      "src/core/client_config/subchannel_index.h", 
       "src/core/client_config/uri_parser.c", 
       "src/core/client_config/uri_parser.h", 
       "src/core/compression/algorithm.c", 
@@ -3548,6 +3551,7 @@
       "src/core/client_config/resolvers/sockaddr_resolver.h", 
       "src/core/client_config/subchannel.h", 
       "src/core/client_config/subchannel_factory.h", 
+      "src/core/client_config/subchannel_index.h", 
       "src/core/client_config/uri_parser.h", 
       "src/core/compression/algorithm_metadata.h", 
       "src/core/compression/message_compress.h", 
@@ -3713,6 +3717,8 @@
       "src/core/client_config/subchannel.h", 
       "src/core/client_config/subchannel_factory.c", 
       "src/core/client_config/subchannel_factory.h", 
+      "src/core/client_config/subchannel_index.c", 
+      "src/core/client_config/subchannel_index.h", 
       "src/core/client_config/uri_parser.c", 
       "src/core/client_config/uri_parser.h", 
       "src/core/compression/algorithm.c", 
@@ -4190,7 +4196,8 @@
       "test/cpp/util/cli_call.h", 
       "test/cpp/util/create_test_channel.h", 
       "test/cpp/util/string_ref_helper.h", 
-      "test/cpp/util/subprocess.h"
+      "test/cpp/util/subprocess.h", 
+      "test/cpp/util/test_credentials_provider.h"
     ], 
     "language": "c++", 
     "name": "grpc++_test_util", 
@@ -4206,7 +4213,9 @@
       "test/cpp/util/string_ref_helper.cc", 
       "test/cpp/util/string_ref_helper.h", 
       "test/cpp/util/subprocess.cc", 
-      "test/cpp/util/subprocess.h"
+      "test/cpp/util/subprocess.h", 
+      "test/cpp/util/test_credentials_provider.cc", 
+      "test/cpp/util/test_credentials_provider.h"
     ]
   }, 
   {
diff --git a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
index 3d35371..33860af 100644
--- a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
+++ b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
@@ -153,6 +153,7 @@
     <ClInclude Include="$(SolutionDir)\..\test\cpp\util\create_test_channel.h" />
     <ClInclude Include="$(SolutionDir)\..\test\cpp\util\string_ref_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\test\cpp\util\subprocess.h" />
+    <ClInclude Include="$(SolutionDir)\..\test\cpp\util\test_credentials_provider.h" />
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="$(SolutionDir)\..\src\proto\grpc\testing\echo_messages.pb.cc">
@@ -191,6 +192,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\test\cpp\util\subprocess.cc">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\test\cpp\util\test_credentials_provider.cc">
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\grpc++\grpc++.vcxproj">
diff --git a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
index 27ac675..b35ba1f 100644
--- a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
@@ -28,6 +28,9 @@
     <ClCompile Include="$(SolutionDir)\..\test\cpp\util\subprocess.cc">
       <Filter>test\cpp\util</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\test\cpp\util\test_credentials_provider.cc">
+      <Filter>test\cpp\util</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="$(SolutionDir)\..\test\cpp\end2end\test_service_impl.h">
@@ -48,6 +51,9 @@
     <ClInclude Include="$(SolutionDir)\..\test\cpp\util\subprocess.h">
       <Filter>test\cpp\util</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\test\cpp\util\test_credentials_provider.h">
+      <Filter>test\cpp\util</Filter>
+    </ClInclude>
   </ItemGroup>
 
   <ItemGroup>
diff --git a/vsprojects/vcxproj/grpc/grpc.vcxproj b/vsprojects/vcxproj/grpc/grpc.vcxproj
index b364bad..a426e41 100644
--- a/vsprojects/vcxproj/grpc/grpc.vcxproj
+++ b/vsprojects/vcxproj/grpc/grpc.vcxproj
@@ -308,6 +308,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\resolvers\sockaddr_resolver.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\uri_parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\compression\algorithm_metadata.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\compression\message_compress.h" />
@@ -468,6 +469,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\uri_parser.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\compression\algorithm.c">
diff --git a/vsprojects/vcxproj/grpc/grpc.vcxproj.filters b/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
index 7c19b8a..0b99cba 100644
--- a/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
@@ -82,6 +82,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.c">
       <Filter>src\core\client_config</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.c">
+      <Filter>src\core\client_config</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\uri_parser.c">
       <Filter>src\core\client_config</Filter>
     </ClCompile>
@@ -584,6 +587,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.h">
       <Filter>src\core\client_config</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.h">
+      <Filter>src\core\client_config</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\uri_parser.h">
       <Filter>src\core\client_config</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
index 4edcfab..2092397 100644
--- a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
+++ b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
@@ -298,6 +298,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\resolvers\sockaddr_resolver.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\uri_parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\compression\algorithm_metadata.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\compression\message_compress.h" />
@@ -446,6 +447,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\uri_parser.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\compression\algorithm.c">
diff --git a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
index 11510b5..f6e5275 100644
--- a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
@@ -85,6 +85,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.c">
       <Filter>src\core\client_config</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.c">
+      <Filter>src\core\client_config</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\client_config\uri_parser.c">
       <Filter>src\core\client_config</Filter>
     </ClCompile>
@@ -521,6 +524,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_factory.h">
       <Filter>src\core\client_config</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\client_config\subchannel_index.h">
+      <Filter>src\core\client_config</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\client_config\uri_parser.h">
       <Filter>src\core\client_config</Filter>
     </ClInclude>