Sample Call Flow:

Image Sourced from Amazon Web Services

Steps shown in diagram:

• The Amazon Chime SDK PSTN audio service receives a call to a phone number that is provisioned in a SIP rule.

• The PSTN audio service fetches the associated SIP media application and invokes the associated Lambda function with a NEW_INBOUND_CALL event (LEG-A).

• The Lambda function returns a list of actions, including PlayAudioAndGetDigits, which instructs the PSTN Audio service to answer the call, play an audio file to the caller, and collect the DTMF digits entered by the caller.

• The PSTN Audio service answers the call, plays an audio prompt, and collects DTMF digits input by the caller.

• The PSTN Audio service invokes the Lambda function with the DTMF digits input. The Lambda function uses the AWS SDK to create an Amazon Chime SDK meeting and a meeting attendee.

• Once the AWS SDK returns a MeetingId and AttendeeId, the Lambda function returns an action to join the call to the Amazon Chime SDK Meeting (LEG-B).

• A Real-time Transport Protocol (RTP) session is established between the caller from the public switched telephone network (PSTN) and the Amazon Chime Media service.

• When the PSTN caller hangs up, the PSTN Audio service invokes the Lambda function with a HANGUP event, and the Lambda function deletes the attendee.

Building a PSTN call answering system with the Amazon Chime SDK, Amazon Lex and Amazon Polly:

Image sourced from Amazon Web Services

This diagram is a stellar example of integrating multiple Amazon Web Services together to create a more functional product. 

The services utilized in this demo are:

• Amazon Chime SDK PSTN Audio service
• AWS Lambda
• Amazon Simple Cloud Storage (S3)
• Amazon Lex
• Amazon Polly

SIP Trunking Using AWS Voice Connecter:

Amazon Chime Voice Connector offers a pay-as-you-go SIP trunking service. This allows individuals to make or receive  calls with their phone systems that are both secure and don’t cost a ton. Since the Amazon Chime Voice Connector is pay-as-you-go, it is an inexpensive alternative to other service provider SIP trunks as well as ISDN and PRIs. Users can enable both inbound and outbound calling. Since the Amazon Chime Voice Connector is on the AWS network, it delivers a high quality calling experience in any AWS region. The service supports any US phone number with low-cost calling to over 115 countries. Users pay a monthly charge, as well as for minutes per call. There are no upfront fees, no concurrent call path charges, no commitments, and no contracts required. Amazon Chime Voice Connector uses your current internet connection or Amazon Direct Connect without requiring dedicated fixed-bandwidth data circuits.

Here are some more features of the Amazon Chime Voice Connector:

Call routing with Amazon Chime SDK:

Image sourced from Amazon Web Services

How the set up works:

1. Answers the call and plays a welcome prompt
2. Uses the From: parameter (Caller ID) in the NEW_INBOUND_CALL payload to fetch the associated account ID from a DynamoDB table.
3. If the Caller ID has an associated account, it plays a prompt and requests the caller to key in ‘1’ for sales or ‘2’ for support.
4. If the Caller ID has no associated account ID, the caller will be asked to enter their account ID using their keypad.
5. The entered account ID will be stored in DynamoDB.
6. The DynamoDB update then triggers the createWav Lambda function to create a wav file of the account ID using the Amazon Polly text to speech service.  The resulting .wav file is stored in an S3 bucket that will be accessed by the emulatorSMA Lambda function.
7. The incoming call is then transferred to the phone number corresponding to the caller’s selection (‘1’ – salesPhoneNumber or ‘2’ – supportPhoneNumber. The Calling Number of the call to the emulator is the original calling number.

When the transferred call arrives on a phone number associated with the emulatorSMA, it will perform the following steps:

1. Using the From: parameter (Caller ID) in the NEW_INBOUND_CALL payload, fetch the associated account ID.
2. Play the account number back to the caller from the S3 bucket and hang-up.

Conclusion

AWS Chime SDK is a simple to use, but complex in design that developers across the world can utilize. Chime SDK makes building communication platforms within applications a breeze, and the fact that it is built on AWS, makes it reliable and sleek. While we couldn’t cover everything that AWS Chime SDK has to offer, we went over some of the basics as to why it should be a tool in your toolbox as a developer. 

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