Mapping SIP Messages to QSIG Facility Messages
Question
Which SIP message element is mapped to QSIG FACILITY messages being tunneled across a SIP trunk between two Cisco IOS gateways?
Answers
Explanations
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A. B. C. D. E.Explanation.
Mapping of QSIG Message Elements to SIP Message Elements This section lists QSIG message elements and their associated SIP message elements when QSIG messages are tunneled over a SIP trunk.
" QSIG FACILITY/NOTIFY/INFO <""> SIP INFO - " QSIG SETUP <""> SIP INVITE - " QSIG ALERTING <""> SIP 180 RINGING - " QSIG PROGRESS <""> SIP 183 PROGRESS - " QSIG CONNECT <""> SIP 200 OK - " QSIG DISCONNECT <""> SIP BYE/CANCEL/4xx""6xx Response References: http://www.cisco.com/c/en/us/td/docs/ios/voice/sip/configuration/guide/15_0/sip_15_0_book/tunneling_qsig.html.
When tunnelling QSIG messages over a SIP trunk between two Cisco IOS gateways, the FACILITY message element is mapped to the SIP INFO message. Therefore, the correct answer is D. SIP INFO.
In a SIP trunk, SIP messages are exchanged between the Session Border Controllers (SBCs) or gateways of the service provider and the customer. However, in some cases, a customer may want to tunnel QSIG messages over the SIP trunk to support legacy PBX features or interoperate with non-SIP endpoints.
When QSIG messages are tunneled over a SIP trunk, the QSIG messages are encapsulated inside SIP messages. The SIP INFO message is commonly used to carry non-call-signaling information between endpoints in a SIP network. Thus, the SIP INFO message is used to carry QSIG messages in a SIP trunk.
In summary, when tunnelling QSIG messages over a SIP trunk between two Cisco IOS gateways, the FACILITY message element is mapped to the SIP INFO message.
