# Making an outbound call for using Amazon Chime SDK PSTN audio service
<a name="use-create-call-api"></a>

To create an outbound call, you use the [https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_CreateSipMediaApplicationCall.html](https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_CreateSipMediaApplicationCall.html) API. The API invokes the endpoint of a specified `SIP media application ID`. Customers can control the flow of the call by giving different signaling and [https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_SipMediaApplication.html](https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_SipMediaApplication.html) actions from the endpoint. 

In the event of a successful response, the API returns a 202 http status code along with a transactionId, which you can use with the [https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_UpdateSipMediaApplicationCall.html](https://docs.aws.amazon.com/chime-sdk/latest/APIReference/API_UpdateSipMediaApplicationCall.html) API to update an in-progress call.

The following diagram shows the invocations made to the AWS Lambda function endpoint for an outbound call.

![Diagram showing the programming flow for invocations made to the AWS Lambda endpoint.](http://docs.aws.amazon.com/chime-sdk/latest/dg/images/sip-api-1.png)


The endpoint configured for the SIP media application is invoked for different statuses of the outbound call. When a customer initiates a call, The Amazon Chime SDK invokes the endpoint with a `NEW_OUTBOUND_CALL` invocation event type. 

This example shows a typical invocation event for a `NEW_OUTBOUND_CALL`.

```
{
    "SchemaVersion": "1.0",
        "Sequence": 1,
        "InvocationEventType": "NEW_OUTBOUND_CALL",
        "CallDetails": {
            "TransactionId": "{{transaction-id}}",
            "AwsAccountId": "{{aws-account-id}}",
            "AwsRegion": "us-east-1",
            "SipApplicationId": "{{sip-application-id}}",
            "Participants": [
                {
                    "CallId": "{{call-id-1}}",
                    "ParticipantTag": "LEG-A",
                    "To": "+1{{xxxx}}",
                    "From": "+1{{xxxxxxx}}",
                    "Direction": "Outbound",
                    "StartTimeInMilliseconds": "{{159700958834234}}"
                }
            ]
    }
}
```

Any response for an event related AWS Lambda invocation is ignored.

When we receive a `RINGING` notification from the receiver, the Amazon Chime SDK invokes the configured endpoint again. 

This example shows a typical invocation event for `RINGING`.

```
{
    "SchemaVersion": "1.0",
        "Sequence": 1,
        "InvocationEventType": "RINGING",
        "CallDetails": {
            "TransactionId": "{{transaction-id}}",
            "AwsAccountId": "{{aws-account-id}}",
            "AwsRegion": "us-east-1",
            "SipApplicationId": "{{sip-application-id}}",
            "Participants": [
                {
                    "CallId": "{{call-id-1}}",
                    "ParticipantTag": "LEG-A",
                    "To": "+1{{xxxx}}",
                    "From": "+1{{xxxxxxx}}",
                    "Direction": "Outbound",
                    "StartTimeInMilliseconds": "{{159700958834234}}"
                }
           ]
    }
}
```

Any response for an event related AWS Lambda invocation is ignored.

If the receiver doesn't answer the call, or the call fails due to an error, Chime disconnects the call and invokes the endpoint with the `Hangup` event type. For more information about the `Hangup` event type, refer to [Ending a call using the Amazon Chime SDK PSTN audio service](case-5.md). 

If the call is answered, Chime invokes the endpoint with the `CALL_ANSWERED` action. This example shows a typical invocation event.

```
{
  "SchemaVersion": "1.0",
    "Sequence": 1,
    "InvocationEventType": "CALL_ANSWERED",
    "CallDetails": {
        ""TransactionId": "{{transaction-id}}",
            "AwsAccountId": "{{aws-account-id}}",
            "AwsRegion": "us-east-1",
            "SipApplicationId": "{{sip-application-id}}",
            "Participants": [
                {
                    "CallId": "{{call-id-1}}",
                    "ParticipantTag": "LEG-A",
                    "To": "+1{{xxxx}}",
                    "From": "+1{{xxxxxxx}}",
                    "Direction": "Outbound",
                    "StartTimeInMilliseconds": "{{159700958834234}}",
                "Status": "Connected"
            }
        ]
    }
}
```

At this point, you can return actions by responding to the invocation with an action list. If you don’t want to run any actions, respond with an empty list. You can respond with a maximum of 10 actions for each AWS Lambda invocation, and you can invoke a Lambda function 1,000 times per call. For more information about responding with sets of actions, refer to [Responding to invocations with action lists using the Amazon Chime SDK PSTN audio service](invoke-on-call-leg.md).