diff --git a/api/current.txt b/api/current.txt
index 77d261e..705a0d3 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -39196,10 +39196,10 @@
     method public void onStateChanged(android.telecom.Call, int);
     method public void onVideoCallChanged(android.telecom.Call, android.telecom.InCallService.VideoCall);
     field public static final int HANDOVER_FAILURE_DEST_APP_REJECTED = 1; // 0x1
-    field public static final int HANDOVER_FAILURE_DEST_INVALID_PERM = 3; // 0x3
-    field public static final int HANDOVER_FAILURE_DEST_NOT_SUPPORTED = 2; // 0x2
-    field public static final int HANDOVER_FAILURE_DEST_USER_REJECTED = 4; // 0x4
-    field public static final int HANDOVER_FAILURE_ONGOING_EMERG_CALL = 5; // 0x5
+    field public static final int HANDOVER_FAILURE_NOT_SUPPORTED = 2; // 0x2
+    field public static final int HANDOVER_FAILURE_ONGOING_EMERG_CALL = 4; // 0x4
+    field public static final int HANDOVER_FAILURE_UNKNOWN = 5; // 0x5
+    field public static final int HANDOVER_FAILURE_USER_REJECTED = 3; // 0x3
   }
 
   public static class Call.Details {
diff --git a/telecomm/java/android/telecom/Call.java b/telecomm/java/android/telecom/Call.java
index 2341f03..e82bd99 100644
--- a/telecomm/java/android/telecom/Call.java
+++ b/telecomm/java/android/telecom/Call.java
@@ -873,42 +873,76 @@
         /**
          * @hide
          */
-        @IntDef({HANDOVER_FAILURE_DEST_APP_REJECTED, HANDOVER_FAILURE_DEST_NOT_SUPPORTED,
-                HANDOVER_FAILURE_DEST_INVALID_PERM, HANDOVER_FAILURE_DEST_USER_REJECTED,
-                HANDOVER_FAILURE_ONGOING_EMERG_CALL})
+        @IntDef(prefix = { "HANDOVER_" },
+                value = {HANDOVER_FAILURE_DEST_APP_REJECTED, HANDOVER_FAILURE_NOT_SUPPORTED,
+                HANDOVER_FAILURE_USER_REJECTED, HANDOVER_FAILURE_ONGOING_EMERG_CALL,
+                HANDOVER_FAILURE_UNKNOWN})
         @Retention(RetentionPolicy.SOURCE)
         public @interface HandoverFailureErrors {}
 
         /**
          * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when the app
-         * to handover the call rejects handover.
+         * to handover the call to rejects the handover request.
+         * <p>
+         * Will be returned when {@link Call#handoverTo(PhoneAccountHandle, int, Bundle)} is called
+         * and the destination {@link PhoneAccountHandle}'s {@link ConnectionService} returns a
+         * {@code null} {@link Connection} from
+         * {@link ConnectionService#onCreateOutgoingHandoverConnection(PhoneAccountHandle,
+         * ConnectionRequest)}.
+         * <p>
+         * For more information on call handovers, see
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)}.
          */
         public static final int HANDOVER_FAILURE_DEST_APP_REJECTED = 1;
 
         /**
-         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when there is
-         * an error associated with unsupported handover.
+         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when a handover
+         * is initiated but the source or destination app does not support handover.
+         * <p>
+         * Will be returned when a handover is requested via
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)} and the destination
+         * {@link PhoneAccountHandle} does not declare
+         * {@link PhoneAccount#EXTRA_SUPPORTS_HANDOVER_TO}.  May also be returned when a handover is
+         * requested at the {@link PhoneAccountHandle} for the current call (i.e. the source call's
+         * {@link Details#getAccountHandle()}) does not declare
+         * {@link PhoneAccount#EXTRA_SUPPORTS_HANDOVER_FROM}.
+         * <p>
+         * For more information on call handovers, see
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)}.
          */
-        public static final int HANDOVER_FAILURE_DEST_NOT_SUPPORTED = 2;
+        public static final int HANDOVER_FAILURE_NOT_SUPPORTED = 2;
 
         /**
-         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when there
-         * are some permission errors associated with APIs doing handover.
+         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when the remote
+         * user rejects the handover request.
+         * <p>
+         * For more information on call handovers, see
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)}.
          */
-        public static final int HANDOVER_FAILURE_DEST_INVALID_PERM = 3;
-
-        /**
-         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when user
-         * rejects handover.
-         */
-        public static final int HANDOVER_FAILURE_DEST_USER_REJECTED = 4;
+        public static final int HANDOVER_FAILURE_USER_REJECTED = 3;
 
         /**
          * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when there
          * is ongoing emergency call.
+         * <p>
+         * This error code is returned when {@link #handoverTo(PhoneAccountHandle, int, Bundle)} is
+         * called on an emergency call, or if any other call is an emergency call.
+         * <p>
+         * Handovers are not permitted while there are ongoing emergency calls.
+         * <p>
+         * For more information on call handovers, see
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)}.
          */
-        public static final int HANDOVER_FAILURE_ONGOING_EMERG_CALL = 5;
+        public static final int HANDOVER_FAILURE_ONGOING_EMERG_CALL = 4;
 
+        /**
+         * Handover failure reason returned via {@link #onHandoverFailed(Call, int)} when a handover
+         * fails for an unknown reason.
+         * <p>
+         * For more information on call handovers, see
+         * {@link #handoverTo(PhoneAccountHandle, int, Bundle)}.
+         */
+        public static final int HANDOVER_FAILURE_UNKNOWN = 5;
 
         /**
          * Invoked when the state of this {@code Call} has changed. See {@link #getState()}.
@@ -1049,6 +1083,10 @@
         /**
          * Invoked when Call handover from one {@link PhoneAccount} to other {@link PhoneAccount}
          * has completed successfully.
+         * <p>
+         * For a full discussion of the handover process and the APIs involved, see
+         * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+         *
          * @param call The call which had initiated handover.
          */
         public void onHandoverComplete(Call call) {}
@@ -1056,8 +1094,12 @@
         /**
          * Invoked when Call handover from one {@link PhoneAccount} to other {@link PhoneAccount}
          * has failed.
+         * <p>
+         * For a full discussion of the handover process and the APIs involved, see
+         * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+         *
          * @param call The call which had initiated handover.
-         * @param failureReason Error reason for failure
+         * @param failureReason Error reason for failure.
          */
         public void onHandoverFailed(Call call, @HandoverFailureErrors int failureReason) {}
     }
@@ -1237,7 +1279,7 @@
      * Instructs this {@link #STATE_RINGING} {@code Call} to answer.
      * @param videoState The video state in which to answer the call.
      */
-    public void answer(int videoState) {
+    public void answer(@VideoProfile.VideoState int videoState) {
         mInCallAdapter.answerCall(mTelecomCallId, videoState);
     }
 
@@ -1451,16 +1493,65 @@
      * by {@code toHandle}.  The videoState specified indicates the desired video state after the
      * handover.
      * <p>
-     * A handover request is initiated by the user from one app to indicate a desire
-     * to handover a call to another.
+     * A call handover is the process where an ongoing call is transferred from one app (i.e.
+     * {@link ConnectionService} to another app.  The user could, for example, choose to continue a
+     * mobile network call in a video calling app.  The mobile network call via the Telephony stack
+     * is referred to as the source of the handover, and the video calling app is referred to as the
+     * destination.
+     * <p>
+     * When considering a handover scenario the device this method is called on is considered the
+     * <em>initiating</em> device (since the user initiates the handover from this device), and the
+     * other device is considered the <em>receiving</em> device.
+     * <p>
+     * When this method is called on the <em>initiating</em> device, the Telecom framework will bind
+     * to the {@link ConnectionService} defined by the {@code toHandle} {@link PhoneAccountHandle}
+     * and invoke
+     * {@link ConnectionService#onCreateOutgoingHandoverConnection(PhoneAccountHandle,
+     * ConnectionRequest)} to inform the destination app that a request has been made to handover a
+     * call to it.  The app returns an instance of {@link Connection} to represent the handover call
+     * At this point the app should display UI to indicate to the user that a call
+     * handover is in process.
+     * <p>
+     * The destination app is responsible for communicating the handover request from the
+     * <em>initiating</em> device to the <em>receiving</em> device.
+     * <p>
+     * When the app on the <em>receiving</em> device receives the handover request, it calls
+     * {@link TelecomManager#acceptHandover(Uri, int, PhoneAccountHandle)} to continue the handover
+     * process from the <em>initiating</em> device to the <em>receiving</em> device.  At this point
+     * the destination app on the <em>receiving</em> device should show UI to allow the user to
+     * choose whether they want to continue their call in the destination app.
+     * <p>
+     * When the destination app on the <em>receiving</em> device calls
+     * {@link TelecomManager#acceptHandover(Uri, int, PhoneAccountHandle)}, Telecom will bind to its
+     * {@link ConnectionService} and call
+     * {@link ConnectionService#onCreateIncomingHandoverConnection(PhoneAccountHandle,
+     * ConnectionRequest)} to inform it of the handover request.  The app returns an instance of
+     * {@link Connection} to represent the handover call.
+     * <p>
+     * If the user of the <em>receiving</em> device accepts the handover, the app calls
+     * {@link Connection#setActive()} to complete the handover process; Telecom will disconnect the
+     * original call.  If the user rejects the handover, the app calls
+     * {@link Connection#setDisconnected(DisconnectCause)} and specifies a {@link DisconnectCause}
+     * of {@link DisconnectCause#CANCELED} to indicate that the handover has been cancelled.
+     * <p>
+     * Telecom will only allow handovers from {@link PhoneAccount}s which declare
+     * {@link PhoneAccount#EXTRA_SUPPORTS_HANDOVER_FROM}.  Similarly, the {@link PhoneAccount}
+     * specified by {@code toHandle} must declare {@link PhoneAccount#EXTRA_SUPPORTS_HANDOVER_TO}.
+     * <p>
+     * Errors in the handover process are reported to the {@link InCallService} via
+     * {@link Callback#onHandoverFailed(Call, int)}.  Errors in the handover process are reported to
+     * the involved {@link ConnectionService}s via
+     * {@link ConnectionService#onHandoverFailed(ConnectionRequest, int)}.
      *
      * @param toHandle {@link PhoneAccountHandle} of the {@link ConnectionService} to handover
      *                 this call to.
-     * @param videoState Indicates the video state desired after the handover.
+     * @param videoState Indicates the video state desired after the handover (see the
+     *               {@code STATE_*} constants defined in {@link VideoProfile}).
      * @param extras Bundle containing extra information to be passed to the
      *               {@link ConnectionService}
      */
-    public void handoverTo(PhoneAccountHandle toHandle, int videoState, Bundle extras) {
+    public void handoverTo(PhoneAccountHandle toHandle, @VideoProfile.VideoState int videoState,
+            Bundle extras) {
         mInCallAdapter.handoverTo(mTelecomCallId, toHandle, videoState, extras);
     }
 
diff --git a/telecomm/java/android/telecom/ConnectionService.java b/telecomm/java/android/telecom/ConnectionService.java
index 2ea7e65..09e7f709 100644
--- a/telecomm/java/android/telecom/ConnectionService.java
+++ b/telecomm/java/android/telecom/ConnectionService.java
@@ -2219,12 +2219,50 @@
     }
 
     /**
-     * Called by Telecom on the initiating side of the handover to create an instance of a
-     * handover connection.
+     * Called by Telecom to request that a {@link ConnectionService} creates an instance of an
+     * outgoing handover {@link Connection}.
+     * <p>
+     * A call handover is the process where an ongoing call is transferred from one app (i.e.
+     * {@link ConnectionService} to another app.  The user could, for example, choose to continue a
+     * mobile network call in a video calling app.  The mobile network call via the Telephony stack
+     * is referred to as the source of the handover, and the video calling app is referred to as the
+     * destination.
+     * <p>
+     * When considering a handover scenario the <em>initiating</em> device is where a user initiated
+     * the handover process (e.g. by calling {@link android.telecom.Call#handoverTo(
+     * PhoneAccountHandle, int, Bundle)}, and the other device is considered the <em>receiving</em>
+     * device.
+     * <p>
+     * This method is called on the destination {@link ConnectionService} on <em>initiating</em>
+     * device when the user initiates a handover request from one app to another.  The user request
+     * originates in the {@link InCallService} via
+     * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+     * <p>
+     * For a full discussion of the handover process and the APIs involved, see
+     * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+     * <p>
+     * Implementations of this method should return an instance of {@link Connection} which
+     * represents the handover.  If your app does not wish to accept a handover to it at this time,
+     * you can return {@code null}.  The code below shows an example of how this is done.
+     * <pre>
+     * {@code
+     * public Connection onCreateIncomingHandoverConnection(PhoneAccountHandle
+     *     fromPhoneAccountHandle, ConnectionRequest request) {
+     *   if (!isHandoverAvailable()) {
+     *       return null;
+     *   }
+     *   MyConnection connection = new MyConnection();
+     *   connection.setAddress(request.getAddress(), TelecomManager.PRESENTATION_ALLOWED);
+     *   connection.setVideoState(request.getVideoState());
+     *   return connection;
+     * }
+     * }
+     * </pre>
+     *
      * @param fromPhoneAccountHandle {@link PhoneAccountHandle} associated with the
      *                               ConnectionService which needs to handover the call.
-     * @param request Details about the call which needs to be handover.
-     * @return Connection object corresponding to the handover call.
+     * @param request Details about the call to handover.
+     * @return {@link Connection} instance corresponding to the handover call.
      */
     public Connection onCreateOutgoingHandoverConnection(PhoneAccountHandle fromPhoneAccountHandle,
                                                          ConnectionRequest request) {
@@ -2232,12 +2270,46 @@
     }
 
     /**
-     * Called by Telecom on the receiving side of the handover to request the
-     * {@link ConnectionService} to create an instance of a handover connection.
+     * Called by Telecom to request that a {@link ConnectionService} creates an instance of an
+     * incoming handover {@link Connection}.
+     * <p>
+     * A call handover is the process where an ongoing call is transferred from one app (i.e.
+     * {@link ConnectionService} to another app.  The user could, for example, choose to continue a
+     * mobile network call in a video calling app.  The mobile network call via the Telephony stack
+     * is referred to as the source of the handover, and the video calling app is referred to as the
+     * destination.
+     * <p>
+     * When considering a handover scenario the <em>initiating</em> device is where a user initiated
+     * the handover process (e.g. by calling {@link android.telecom.Call#handoverTo(
+     * PhoneAccountHandle, int, Bundle)}, and the other device is considered the <em>receiving</em>
+     * device.
+     * <p>
+     * This method is called on the destination app on the <em>receiving</em> device when the
+     * destination app calls {@link TelecomManager#acceptHandover(Uri, int, PhoneAccountHandle)} to
+     * accept an incoming handover from the <em>initiating</em> device.
+     * <p>
+     * For a full discussion of the handover process and the APIs involved, see
+     * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+     * <p>
+     * Implementations of this method should return an instance of {@link Connection} which
+     * represents the handover.  The code below shows an example of how this is done.
+     * <pre>
+     * {@code
+     * public Connection onCreateIncomingHandoverConnection(PhoneAccountHandle
+     *     fromPhoneAccountHandle, ConnectionRequest request) {
+     *   // Given that your app requested to accept the handover, you should not return null here.
+     *   MyConnection connection = new MyConnection();
+     *   connection.setAddress(request.getAddress(), TelecomManager.PRESENTATION_ALLOWED);
+     *   connection.setVideoState(request.getVideoState());
+     *   return connection;
+     * }
+     * }
+     * </pre>
+     *
      * @param fromPhoneAccountHandle {@link PhoneAccountHandle} associated with the
      *                               ConnectionService which needs to handover the call.
      * @param request Details about the call which needs to be handover.
-     * @return {@link Connection} object corresponding to the handover call.
+     * @return {@link Connection} instance corresponding to the handover call.
      */
     public Connection onCreateIncomingHandoverConnection(PhoneAccountHandle fromPhoneAccountHandle,
                                                          ConnectionRequest request) {
@@ -2247,11 +2319,15 @@
     /**
      * Called by Telecom in response to a {@code TelecomManager#acceptHandover()}
      * invocation which failed.
-     * @param request Details about the call which needs to be handover.
-     * @param error Reason for handover failure as defined in
-     *              {@link android.telecom.Call.Callback#HANDOVER_FAILURE_DEST_INVALID_PERM}
+     * <p>
+     * For a full discussion of the handover process and the APIs involved, see
+     * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}
+     *
+     * @param request Details about the call which failed to handover.
+     * @param error Reason for handover failure.  Will be one of the
      */
-    public void onHandoverFailed(ConnectionRequest request, int error) {
+    public void onHandoverFailed(ConnectionRequest request,
+            @Call.Callback.HandoverFailureErrors int error) {
         return;
     }
 
diff --git a/telecomm/java/android/telecom/TelecomManager.java b/telecomm/java/android/telecom/TelecomManager.java
index 7e89745..fe29f3a 100644
--- a/telecomm/java/android/telecom/TelecomManager.java
+++ b/telecomm/java/android/telecom/TelecomManager.java
@@ -1786,8 +1786,25 @@
     }
 
     /**
-     * Called from the recipient side of a handover to indicate a desire to accept the handover
-     * of an ongoing call to another {@link ConnectionService} identified by
+     * Called by an app to indicate that it wishes to accept the handover of an ongoing call to a
+     * {@link PhoneAccountHandle} it defines.
+     * <p>
+     * A call handover is the process where an ongoing call is transferred from one app (i.e.
+     * {@link ConnectionService} to another app.  The user could, for example, choose to continue a
+     * mobile network call in a video calling app.  The mobile network call via the Telephony stack
+     * is referred to as the source of the handover, and the video calling app is referred to as the
+     * destination.
+     * <p>
+     * When considering a handover scenario the <em>initiating</em> device is where a user initiated
+     * the handover process (e.g. by calling {@link android.telecom.Call#handoverTo(
+     * PhoneAccountHandle, int, Bundle)}, and the other device is considered the <em>receiving</em>
+     * device.
+     * <p>
+     * For a full discussion of the handover process and the APIs involved, see
+     * {@link android.telecom.Call#handoverTo(PhoneAccountHandle, int, Bundle)}.
+     * <p>
+     * This method is called from the <em>receiving</em> side of a handover to indicate a desire to
+     * accept the handover of an ongoing call to another {@link ConnectionService} identified by
      * {@link PhoneAccountHandle} destAcct. For managed {@link ConnectionService}s, the specified
      * {@link PhoneAccountHandle} must have been registered with {@link #registerPhoneAccount} and
      * the user must have enabled the corresponding {@link PhoneAccount}.  This can be checked using
@@ -1811,7 +1828,8 @@
      * @param videoState Video state after the handover.
      * @param destAcct The {@link PhoneAccountHandle} registered to the calling package.
      */
-    public void acceptHandover(Uri srcAddr, int videoState, PhoneAccountHandle destAcct) {
+    public void acceptHandover(Uri srcAddr, @VideoProfile.VideoState int videoState,
+            PhoneAccountHandle destAcct) {
         try {
             if (isServiceConnected()) {
                 getTelecomService().acceptHandover(srcAddr, videoState, destAcct);
diff --git a/telecomm/java/android/telecom/VideoProfile.java b/telecomm/java/android/telecom/VideoProfile.java
index e0e3a08..90ed36f 100644
--- a/telecomm/java/android/telecom/VideoProfile.java
+++ b/telecomm/java/android/telecom/VideoProfile.java
@@ -62,6 +62,7 @@
     @Retention(RetentionPolicy.SOURCE)
     @IntDef(
             flag = true,
+            prefix = { "STATE_" },
             value = {STATE_AUDIO_ONLY, STATE_TX_ENABLED, STATE_RX_ENABLED, STATE_BIDIRECTIONAL,
                     STATE_PAUSED})
     public @interface VideoState {}