CallAndBridge - Amazon Chime SDK
Call flows

CallAndBridge

Creates an outbound call to a PSTN phone number, or to a SIP trunk configured as an Amazon Chime SDK Voice Connector or Amazon Chime SDK Voice Connector Group, and then bridges it with an existing call leg. You use PSTN when calling a phone number, and AWS when calling a SIP trunk.

An existing call leg can be an outbound call leg created by using the CreateSIPMediaApplicationCall API, or an inbound leg created by a SIP rule that invokes the AWS Lambda function with a NewInboundCall event. When you implement a CallAndBridge action to a Voice Connector or Voice Connector Group endpoint, you must specify the Amazon Resource Number (ARN) of the Voice Connector or Voice Connector Group.

You can also add custom SIP headers to outbound call legs and AWS Lambda functions. Custom headers allow you to pass values such as floor numbers and zip codes. For more information about custom headers, refer to Using SIP headers.

The following example code shows a typical action that bridges to a PSTN endpoint.

{
    "SchemaVersion": "1.0",
    "Actions": [{
            "Type": "CallAndBridge",
            "Parameters": {
                "CallTimeoutSeconds": 30,
                "CallerIdNumber": "e164PhoneNumber", // required            
                "Endpoints": [{
                    "BridgeEndpointType": "PSTN", // required
                    "Uri": "e164PhoneNumber", // required                       
                }],
            }
        }
    ]
}

The following example shows a typical action that uses a Voice Connector or Voice Connector Group, plus a custom SIP header.

{
   "SchemaVersion":"1.0",
   "Actions":[
      {
         "Type":"CallAndBridge",
         "Parameters":{
            "CallTimeoutSeconds":30,
            "CallerIdNumber": "e164PhoneNumber", // required
            "RingbackTone": { // optional
                    "Type": "S3",
                    "BucketName": "s3_bucket_name",
                    "Key": "audio_file_name"
                },
            "Endpoints":[
               {
                  "BridgeEndpointType":"AWS", // enum type, required                                  
                  "Arn":"arn:aws:chime:us-east-1:0123456789101:vc/abcdefg1hijklm2nopq3rs" //VC or VCG ARN, required for AWS endpoints
                  "Uri":"ValidString", // required, see description below  
               }
            ],
            "SipHeaders": { 
                "x-String":"String"
            }
         }
      }
   ]
}
CallTimeoutSeconds

Description – The interval before a call times out. The timer starts at call setup

Allowed values – Between 1 and 120, inclusive

Required – No

Default value – 30

CallerIdNumber

Description – A number belonging to the customer, or the From number of the A Leg

Allowed values – A valid phone number in the E.164 format

Required – Yes

Default value – None

Endpoints

Description – The endpoints of a call

Allowed values:

  • BridgeEndpointType – AWS for Voice Connectors and Voice Connector Groups, otherwise PSTN.

  • Arn – The ARN of a Voice Connector or Voice Connector Group. Only required when you use AWS as the BridgeEndpointType.

  • Uri – The URI value depends on the type of endpoint.

    For PSTN endpoints, the URI must be a valid E.164 phone number.

    For AWS endpoints, the URI value sets the user part of the Request-URI. You must use Augmented Backus-Naur Format. Required length: between 1 and 30, inclusive. Use the following values: a-z, A-Z, 0-9, &, =, +, $, /, %, -, _, !, ~, *, (,), (.)

    The host value of the Request-URI is derived from the Inbound routes of the target Voice Connector. The following example shows a CallAndBridge action with an AWS endpoint.

    {
   "SchemaVersion":"1.0",
   "Actions":[
      {
         "Type":"CallAndBridge",
         "Parameters":{
            "CallTimeoutSeconds":30,
            "CallerIdNumber": "+18005550122",
            "Endpoints":[
               {
                  "BridgeEndpointType":"AWS",                                   
                  "Arn":"arn:aws:chime:us-east-1:0123456789101:vc/abcdefg1hijklm2nopq3rs", 
                  "Uri":"5550"   
               }
            ],
            "SipHeaders": { 
                "x-String":"String"
            }
         }
      }
   ]
}

    For more information about Inbound routes and Voice Connectors, refer to Editing Amazon Chime SDK Voice Connector settings.

Required – Yes

Default value – None

SipHeaders

Description – Enables you to pass additional values. Use only with the AWS endpoint type.

Allowed values – Valid SIP header

Required – No

Default value – None

The following example shows a successful CallAndBridge action that uses a PSTN endpoint:

{
   "SchemaVersion": "1.0",
   "Sequence": 3,
   "InvocationEventType": "ACTION_SUCCESSFUL",
   "ActionData": {
      "Type": "CallAndBridge",
      "Parameters": {
         "CallTimeoutSeconds": 30,
         "CallerIdNumber": "e164PhoneNumber",
         "Endpoints":[
            {
               "BridgeEndpointType": "PSTN",
               "Uri": "e164PhoneNumber"               
            }
         ],
         "CallId": "call-id-1"
      }
   },
   "CallDetails":{
      .....
      .....
      "Participants":[
         {
            "CallId": "call-id-1",
            "ParticipantTag": "LEG-A",
            .....   
            "Status": "Connected"
         },
         {
            "CallId": "call-id-2",
            "ParticipantTag": "LEG-B",
            .....
            "Status": "Connected"
         }
      ]
   }
}

The following example shows a failed CallAndBridge action.

{
   "SchemaVersion": "1.0",
   "Sequence":2,
   "InvocationEventType": "ACTION_FAILED",
      "ActionData":{
      "Type": "CallAndBridge",
      "Parameters":{
         "CallTimeoutSeconds": 30,
         "CallerIdNumber": "e164PhoneNumber",
         "Endpoints": [
            {
               "BridgeEndpointType": "PSTN",
               "Uri": "e164PhoneNumber"           
            }
         ],
         "CallId": "call-id-1"
      },
      "ErrorType": "CallNotAnswered",
      "ErrorMessage": "Call not answered"
   },
   "CallDetails":{
      .....
      .....
      "Participants":[
         {
            "CallId": "call-id-1",
            "ParticipantTag": "LEG-A",
            .....   
         }
      ]
   }
}

Call flows

The CallAndBridge action provides a different call signaling and audio experience for an existing call leg, depending on the parameters and whether the leg is connected.

The following diagram shows show the call flows with different parameters when an inbound call leg A is already connected.

The flow of an answered call through the CallAndBridge action.

The following diagram shows the call flow for an unanswered call.

The flow of a call through the CallAndBridge action.
Additional Details

Remember these facts about the CallAndBridge action.

  • CallTimeoutSeconds – This timer starts when the SIP invitation is sent on the B-Leg. You can set a desired target value, but this value can be ignored by upstream carriers.

  • CallerIdNumber – This phone number must belong to the customer, or be the From number of an A-Leg.

  • Hang-up behavior and edge cases – If one call leg hangs up, the other call leg does not automatically hang up the call. When a Hangup event is sent to the AWS Lambda function, the remaining leg must be disconnected independently. If a call leg is left hanging, the call is billed until it is hung up. For example, the following scenario may lead to unexpected charges:

    • You try to bridge to a destination phone number. The destination is busy and sends the call straight to voicemail. From the Audio Service's perspective, going to voicemail is an answered call. The A-Leg hangs up, but the B-Leg continues listening for the voicemail message. While the B-Leg listens, you get billed.

    • As a best practice, use the AWS Lambda function, or the party on the other end of the call, to hang up each call leg independently.

  • Billing – You're billed for the following when using CallAndBridge:

    • Active call minutes for each call leg created (A-Leg, B-Leg, etc.) to the PSTN.

    • Audio Service usage minutes.

See working examples on GitHub: