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How to control and steer calls with Call Automation

Call Automation uses a REST API interface to receive requests for actions and provide responses to notify whether the request was successfully submitted or not. Due to the asynchronous nature of calling, most actions have corresponding events that are triggered when the action completes successfully or fails. This guide covers the actions available for steering calls, like CreateCall, Transfer, Redirect, and managing participants. Actions are accompanied with sample code on how to invoke the said action and sequence diagrams describing the events expected after invoking an action. These diagrams help you visualize how to program your service application with Call Automation.

Call Automation supports various other actions to manage call media and recording that have separate guides.

As a prerequisite, we recommend you to read these articles to make the most of this guide:

  1. Call Automation concepts guide that describes the action-event programming model and event callbacks.
  2. Learn about user identifiers like CommunicationUserIdentifier and PhoneNumberIdentifier used in this guide.

For all the code samples, client is CallAutomationClient object that can be created as shown and callConnection is the CallConnection object obtained from Answer or CreateCall response. You can also obtain it from callback events received by your application.

var client = new CallAutomationClient("<resource_connection_string>"); 

Make an outbound call

You can place a 1:1 or group call to a communication user or phone number (public or Communication Services owned number). When calling a PSTN endpoint, you also need to provide a phone number that is used as the source caller ID and shown in the call notification to the target PSTN endpoint. To place a call to a Communication Services user, you need to provide a CommunicationUserIdentifier object instead of PhoneNumberIdentifier.

Uri callbackUri = new Uri("https://<myendpoint>/Events"); //the callback endpoint where you want to receive subsequent events 
var callerIdNumber = new PhoneNumberIdentifier("+16044561234"); // This is the Azure Communication Services provisioned phone number for the caller  
var callThisPerson = new CallInvite(new PhoneNumberIdentifier("+16041234567"), callerIdNumber); // person to call
CreateCallResult response = await client.CreateCallAsync(callThisPerson, callbackUri);

When making a group call that includes a phone number, you must provide a phone number that is used as a caller ID number to the PSTN endpoint.

Uri callbackUri = new Uri("https://<myendpoint>/Events"); //the callback endpoint where you want to receive subsequent events 
var pstnEndpoint = new PhoneNumberIdentifier("+16041234567");
var voipEndpoint = new CommunicationUserIdentifier("<user_id_of_target>"); //user id looks like 8:a1b1c1-...
var groupCallOptions = new CreateGroupCallOptions(new List<CommunicationIdentifier>{ pstnEndpoint, voipEndpoint }, callbackUri)
{
    SourceCallerIdNumber = new PhoneNumberIdentifier("+16044561234"), // This is the Azure Communication Services provisioned phone number for the caller
};
CreateCallResult response = await client.CreateGroupCallAsync(groupCallOptions);

The response provides you with CallConnection object that you can use to take further actions on this call once it's connected. Once the call is answered, two events are published to the callback endpoint you provided earlier:

  1. CallConnected event notifying that the call has been established with the callee.
  2. ParticipantsUpdated event that contains the latest list of participants in the call. Sequence diagram for placing an outbound call.

In the case where the call fails, you will receive a CallDisconnected and CreateCallFailed event with error codes for further troubleshooting (see this page for more information on Call Automation error codes).

Connect to a call (in preview)

Connect action enables your service to establish a connection with an ongoing call and take actions on it. This is useful to manage a Rooms call or when client applications started a 1:1 or group call that Call automation isn't part of. Connection is established using the CallLocator property and can be of types: ServerCallLocator, GroupCallLocator, and RoomCallLocator. These IDs can be found when the call is originally established or a Room is created, and also published as part of CallStarted event.

To connect to any 1:1 or group call, use the ServerCallLocator. If you started a call using GroupCallId, you can also use the GroupCallLocator.

Uri callbackUri = new Uri("https://<myendpoint>/Events"); //the callback endpoint where you want to receive subsequent events
CallLocator serverCallLocator = new ServerCallLocator("<ServerCallId>");
ConnectCallResult response = await client.ConnectCallAsync(serverCallLocator, callbackUri);

To connect to a Rooms call, use RoomCallLocator which takes RoomId. Learn more about Rooms and how Call Automation API can be used to manage ongoing Rooms call.

Uri callbackUri = new Uri("https://<myendpoint>/Events"); //the callback endpoint where you want to receive subsequent events
CallLocator roomCallLocator = new RoomCallLocator("<RoomId>");
ConnectCallResult response = await client.ConnectCallAsync(roomCallLocator, callbackUri);

A successful response provides you with CallConnection object that you can use to take further actions on this call. Two events are published to the callback endpoint you provided earlier:

  1. CallConnected event notifying that you successfully connect to the call.
  2. ParticipantsUpdated event that contains the latest list of participants in the call.

At any point after a successful connection, if your service is disconnected from this call you will be notified via a CallDisconected event. Failure to connect to the call in the first place results in ConnectFailed event.

Sequence diagram for connecting to call.

Answer an incoming call

Once you've subscribed to receive incoming call notifications to your resource, you will answer an incoming call. When answering a call, it's necessary to provide a callback url. Communication Services post all subsequent events about this call to that url.

string incomingCallContext = "<IncomingCallContext_From_IncomingCall_Event>"; 
Uri callBackUri = new Uri("https://<myendpoint_where_I_want_to_receive_callback_events"); 

var answerCallOptions = new AnswerCallOptions(incomingCallContext, callBackUri);  
AnswerCallResult answerResponse = await client.AnswerCallAsync(answerCallOptions);
CallConnection callConnection = answerResponse.CallConnection; 

The response provides you with CallConnection object that you can use to take further actions on this call once it's connected. Once the call is answered, two events are published to the callback endpoint you provided earlier:

  1. CallConnected event notifying that the call has been established with the caller.
  2. ParticipantsUpdated event that contains the latest list of participants in the call.

Sequence diagram for answering an incoming call.

Reject a call

You can choose to reject an incoming call as shown below. You can provide a reject reason: none, busy or forbidden. If nothing is provided, none is chosen by default.

string incomingCallContext = "<IncomingCallContext_From_IncomingCall_Event>"; 
var rejectOption = new RejectCallOptions(incomingCallContext); 
rejectOption.CallRejectReason = CallRejectReason.Forbidden; 
_ = await client.RejectCallAsync(rejectOption); 

No events are published for reject action.

Redirect a call

You can choose to redirect an incoming call to another endpoint without answering it. Redirecting a call removes your application's ability to control the call using Call Automation.

string incomingCallContext = "<IncomingCallContext_From_IncomingCall_Event>"; 
var target = new CallInvite(new CommunicationUserIdentifier("<user_id_of_target>")); //user id looks like 8:a1b1c1-... 
_ = await client.RedirectCallAsync(incomingCallContext, target); 

To redirect the call to a phone number, construct the target and caller ID with PhoneNumberIdentifier.

var callerIdNumber = new PhoneNumberIdentifier("+16044561234"); // This is the Azure Communication Services provisioned phone number for the caller
var target = new CallInvite(new PhoneNumberIdentifier("+16041234567"), callerIdNumber);

No events are published for redirect. If the target is a Communication Services user or a phone number owned by your resource, it generates a new IncomingCall event with 'to' field set to the target you specified.

Transfer a participant in call

When your application answers a call or places an outbound call to an endpoint, that endpoint can be transferred to another destination endpoint. Transferring a 1:1 call removes your application from the call and hence remove its ability to control the call using Call Automation. The call invite to the target will display the caller ID of the endpoint being transferred. Providing a custom caller ID is not supported.

var transferDestination = new CommunicationUserIdentifier("<user_id>"); 
var transferOption = new TransferToParticipantOptions(transferDestination) {
    OperationContext = "<Your_context>",
    OperationCallbackUri = new Uri("<uri_endpoint>") // Sending event to a non-default endpoint.
};
// adding customCallingContext
transferOption.CustomCallingContext.AddVoip("customVoipHeader1", "customVoipHeaderValue1");
transferOption.CustomCallingContext.AddVoip("customVoipHeader2", "customVoipHeaderValue2");

TransferCallToParticipantResult result = await callConnection.TransferCallToParticipantAsync(transferOption);

When your application answers a group call or places an outbound group call to an endpoint or added a participant to a 1:1 call, an endpoint can be transferred from the call to another destination endpoint, except call automation endpoint. Transferring a participant in a group call removes the endpoint being transferred from the call. The call invite to the target will display the caller ID of the endpoint being transferred. Providing a custom caller ID is not supported.

// Transfer User
var transferDestination = new CommunicationUserIdentifier("<user_id>");
var transferee = new CommunicationUserIdentifier("<transferee_user_id>"); 
var transferOption = new TransferToParticipantOptions(transferDestination);
transferOption.Transferee = transferee;

// adding customCallingContext
transferOption.CustomCallingContext.AddVoip("customVoipHeader1", "customVoipHeaderValue1");
transferOption.CustomCallingContext.AddVoip("customVoipHeader2", "customVoipHeaderValue2");

transferOption.OperationContext = "<Your_context>";
transferOption.OperationCallbackUri = new Uri("<uri_endpoint>");
TransferCallToParticipantResult result = await callConnection.TransferCallToParticipantAsync(transferOption);

// Transfer PSTN User
var transferDestination = new PhoneNumberIdentifier("<target_phoneNumber>");
var transferee = new PhoneNumberIdentifier("<transferee_phoneNumber>"); 
var transferOption = new TransferToParticipantOptions(transferDestination);
transferOption.Transferee = transferee;

// adding customCallingContext
transferOption.CustomCallingContext.AddSipUui("uuivalue");
transferOption.CustomCallingContext.AddSipX("header1", "headerValue");

transferOption.OperationContext = "<Your_context>";

// Sending event to a non-default endpoint.
transferOption.OperationCallbackUri = new Uri("<uri_endpoint>");

TransferCallToParticipantResult result = await callConnection.TransferCallToParticipantAsync(transferOption);

The sequence diagram shows the expected flow when your application places an outbound call and then transfers it to another endpoint.

Sequence diagram for placing a 1:1 call and then transferring it.

Add a participant to a call

You can add a participant (Communication Services user or phone number) to an existing call. When adding a phone number, it's mandatory to provide a caller ID. This caller ID is shown on call notification to the participant being added.

// Add user
var addThisPerson = new CallInvite(new CommunicationUserIdentifier("<user_id>"));
// add custom calling context
addThisPerson.CustomCallingContext.AddVoip("myHeader", "myValue");
AddParticipantsResult result = await callConnection.AddParticipantAsync(addThisPerson);

// Add PSTN user
var callerIdNumber = new PhoneNumberIdentifier("+16044561234"); // This is the Azure Communication Services provisioned phone number for the caller
var addThisPerson = new CallInvite(new PhoneNumberIdentifier("+16041234567"), callerIdNumber);
// add custom calling context
addThisPerson.CustomCallingContext.AddSipUui("value");
addThisPerson.CustomCallingContext.AddSipX("header1", "customSipHeaderValue1");

// Use option bag to set optional parameters
var addParticipantOptions = new AddParticipantOptions(new CallInvite(addThisPerson))
{
    InvitationTimeoutInSeconds = 60,
    OperationContext = "operationContext",
    OperationCallbackUri = new Uri("uri_endpoint"); // Sending event to a non-default endpoint.
};

AddParticipantsResult result = await callConnection.AddParticipantAsync(addParticipantOptions); 

To add a Communication Services user, provide a CommunicationUserIdentifier instead of PhoneNumberIdentifier. Caller ID isn't mandatory in this case.

AddParticipant publishes a AddParticipantSucceeded or AddParticipantFailed event, along with a ParticipantUpdated providing the latest list of participants in the call.

Sequence diagram for adding a participant to the call.

Cancel an add participant request

// add a participant
var addThisPerson = new CallInvite(new CommunicationUserIdentifier("<user_id>"));
var addParticipantResponse = await callConnection.AddParticipantAsync(addThisPerson);

// cancel the request with optional parameters
var cancelAddParticipantOperationOptions = new CancelAddParticipantOperationOptions(addParticipantResponse.Value.InvitationId)
{
    OperationContext = "operationContext",
    OperationCallbackUri = new Uri("uri_endpoint"); // Sending event to a non-default endpoint.
}
await callConnection.CancelAddParticipantOperationAsync(cancelAddParticipantOperationOptions);

Remove a participant from a call

var removeThisUser = new CommunicationUserIdentifier("<user_id>"); 

// remove a participant from the call with optional parameters
var removeParticipantOptions = new RemoveParticipantOptions(removeThisUser)
{
    OperationContext = "operationContext",
    OperationCallbackUri = new Uri("uri_endpoint"); // Sending event to a non-default endpoint.
}

RemoveParticipantsResult result = await callConnection.RemoveParticipantAsync(removeParticipantOptions);

RemoveParticipant will publish a RemoveParticipantSucceeded or RemoveParticipantFailed event, along with a ParticipantUpdated event providing the latest list of participants in the call. The removed participant is omitted from the list.
Sequence diagram for removing a participant from the call.

Hang up on a call

Hang Up action can be used to remove your application from the call or to terminate a group call by setting forEveryone parameter to true. For a 1:1 call, hang up terminates the call with the other participant by default.

_ = await callConnection.HangUpAsync(forEveryone: true); 

CallDisconnected event is published once the hangUp action has completed successfully.

Get information about a call participant

CallParticipant participantInfo = await callConnection.GetParticipantAsync(new CommunicationUserIdentifier("<user_id>"));

Get information about all call participants

List<CallParticipant> participantList = (await callConnection.GetParticipantsAsync()).Value.ToList(); 

Get latest info about a call

CallConnectionProperties callConnectionProperties = await callConnection.GetCallConnectionPropertiesAsync();