User`s manual

SIP User's Manual 500 Document #: LTRT-83303
Mediant 1000 & Mediant 600
11.2 QSIG Tunneling
The device supports QSIG tunneling over SIP according to IETF draft 'Tunnelling of QSIG
over SIP' (draft-elwell-sipping-qsig-tunnel-03) and the ECMA-355/ISO/IEC 22535 standard.
This method enables all QSIG messages to be sent as raw data in corresponding SIP
messages using a dedicated message body. This mechanism is useful for two QSIG
subscribers (connected to the same or different QSIG PBX) to communicate with each
other over an IP network. Tunneling is supported in both directions (Tel-to-IP and IP-to-
Tel).
The term tunneling means that messages are transferred ‘as is’ to the remote side without
being converted (QSIGÆSIPÆQSIG). The advantage of tunneling over QSIG-to-SIP
interworking is that by using interworking, QSIG functionality can only be partially achieved.
When tunneling is used, all QSIG capabilities are supported, whereas the tunneling
medium (the SIP network) does not need to process these messages.
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 device adds a Content-Disposition header in
the following format:
Content-Disposition: signal; handling=required.
 Call setup (originating device): The QSIG SETUP request is encapsulated in the
SIP INVITE message without being altered. After the SIP INVITE request is sent, the
device doesn’t encapsulate the subsequent QSIG message until a SIP 200 OK
response is received. If the originating device receives a 4xx, 5xx, or 6xx response, it
disconnects the QSIG call with a ‘no route to destination’ cause.
 Call setup (terminating device): After the terminating device 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.
 Mid-call communication: After the SIP connection is established, all QSIG
messages are encapsulated in SIP INFO messages.
 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 devices, and the parameter ISDNDuplicateQ931BuffMode to
128 (duplicate all messages) (both parameters are described in ''ISDN and CAS
Interworking-Related Parameters'' on page 348).