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