Qsig Tunneling; Implementation - AudioCodes Mediant 1000 User Manual

11.2

QSIG Tunneling

The gateway supports QSIG tunneling over SIP according to <draft-elwell-sipping-qsig-
tunnel-03>. 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 / different QSIG PBX) to communicate
with each other over an IP network. Tunneling is supported for 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 (QSIG SIP QSIG). The advantage of tunneling over QSIG 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.

11.2.1 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 gateway adds a Content-Disposition header
in the following format:
Content-Disposition: signal; handling=required.
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.
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.
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 gateways, and the parameter ISDNDuplicateQ931BuffMode to
128 (duplicate all messages) (both parameters are described in 'ISDN and CAS
Interworking-Related Parameters' on page 343).
SIP User's Manual 480
Mediant 1000
Document #: LTRT-83302