V6100 and V7122 User Guide 323ImplementationQSIG messages are transferred in SIP messages in a separate Multipurpose Internet MailExtensions (MIME) body. Therefore, if a message contains more than one body (e.g., SDPand QSIG), multipart MIME must be used. The Content-Type of the QSIG tunneled messageis ‘application/QSIG’. In addition, the V7122 adds a Content-Disposition header in thefollowing format:Content-Disposition: signal; handling=required. Call setup (originating gateway):The QSIG SETUP request is encapsulated in a SIP INVITE message without beingaltered. After the SIP INVITE request is sent, the gateway doesn’t encapsulate thefollowing QSIG message until a SIP 200 OK response is received. If the originatinggateway receives a 4xx, 5xx or 6xx response, it disconnects the QSIG call with a ‘noroute to destination’ cause. Call setup (terminating gateway):After the terminating gateway receives a SIP INVITE request with a Content-Type:application/QSIG, it sends the encapsulated QSIG SETUP message to the Tel side andsends a 200 OK response (no 1xx response is sent) to IP. The 200 OK responseincludes an encapsulated QSIG CALL PROCEEDING message (without waiting for aCALL PROCEEDING message from the Tel side). If tunneling is disabled and theincoming INVITE includes a QSIG body, a 415 response is sent. Mid-call communication:After the SIP connection is established, all QSIG messages are encapsulated in SIPINFO messages. Call tear-down:The SIP connection is terminated once the QSIG call is complete. The RELEASECOMPLETE message is encapsulated in the SIP BYE message that terminates thesession.To enable QSIG tunneling set the parameter EnableQSIGTunneling to 1 on both theoriginating and terminating gateways, and the parameter ‘ISDNDuplicateQ931BuffMode’ to128 (duplicate all messages) (both parameters are described in ISDN and CAS Interworking-Related Parameters).
