USSD – SIP Transfer Mechanism

Restcomm USSD Gateway supports implementation of Session Initiation Protocol (SIP) for using Unstructured Supplementary Service Data (USSD) operations for mobile initiated MMI mode over IP Multimedia Core Network Subsystem (IMS). 3GPP Specification 24.390 “Unstructured Supplementary Service Data (USSD) using IP Multimedia (IM) Core Network (CN) subsystem IMS” further explains flow of USSD over IMS leveraging SIP.

Restcomm USSD Gateway can easily be integrated with RestComm via SIP to enable developers to rapidly build voice, video, WebRTC, USSD, SMS, fax and rich messaging applications. More details about RestComm can be obtained from here

Following sections shows SIP flow and integration with RestComm. Instead of RestComm, user can easily integrate SIP phone that supports USSD.

The diagram below depicts an example message sequence for interacting with the Mobicents USSD Gateway SIP API. Belowflow assumes that third-party application sends back tree based menu.

1. When the subscriber initiates a USSD Request, the HLR sends a MAP_PROCESS_UNSTRUCTURED_SS_REQUEST to the USSD Gateway.
2. Upon receipt of the MAP_PROCESS_UNSTRUCTURED_SS_REQUEST of type Begin, USSD Gateway invokes the third-party Application through a SIP INVITE Request, carrying an XML Payload with USSD specific information. The XML Structure of this payload is explained in the sections below.
   

   <ussd-data>
       					<language>en</language>
       					<ussd-string>*123#</ussd-string>
       					<anyExt> 
          						<message-type>processUnstructuredSSRequest_Request</message-type> 
        					</anyExt> 
   					</ussd-data>

   
   The To Header of SIP INVITE Request carries MSISDN from where the USSD request is initiated.
3. The third-party Application will send SIP OK and after receiving SIP ACK, SIP Dialog is established between USSD Gateway and Application

   The third-party Application will then send SIP INFO Request, carrying an XML Payload with USSD specific information. The XML Structure of this payload is explained in the sections below.

   <ussd-data>
       					<language>en</language>
       					<ussd-string>Press 1 for SMS Credit and 2 for Call Credit</ussd-string>
       					<anyExt> 
          						<message-type>unstructuredSSRequest_Request</message-type> 
        					</anyExt> 
   					</ussd-data>

    

4. The USSD Gateway will send a MAP_UNSTRUCTURED_SS_REQUEST of type Continue to the HLR.
5. The Subscriber will receive a menu to choose from and reply. When the subscriber replies, the HLR will send aMAP_UNSTRUCTURED_SS_RESPONSE of type Continue to the USSD Gateway.
6. The USSD Gateway will send a SIP INFO Request, carrying an XML Payload, to the third-party Application in the same session. The XML Structure of this payload is explained in the sections below.

   <ussd-data>
       					<language>en</language>
       					<ussd-string>1</ussd-string>
       					<anyExt> 
          						<message-type>unstructuredSSRequest_Response</message-type> 
        					</anyExt> 
   					</ussd-data>

    

7. Based on the input from the subscriber, the third-party Application will send a final (SIP BYE Request, carrying an XML Payload) and invalidate the session.

   <ussd-data>
       					<language>en</language>
       					<ussd-string>Balance is 87 sms's</ussd-string>
       					<anyExt> 
          						<message-type>processUnstructuredSSRequest_Response</message-type> 
        					</anyExt> 
   					</ussd-data>

    

8. The USSD Gateway will send a MAP_PROCESS_UNSTRUCTURED_SS_RESPONSE of type End to the HLR. Consequently, the subscriber will receive a final response.

The diagram below depicts an example message sequence (USSD Push) for interacting with the Mobicents USSD Gateway SIP API. Below example initiate USSD Tree based menu.

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