User's Manual 458 Document #: LTRT-27045
Mediant 1000B Gateway & E-SBC
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-to-SIP
interworking is that by using interworking, QSIG functionality can only be partially achieved.
When tunneling is used, all QSIG capabilities are supported and 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’. The device also adds a Content-Disposition header in the
following format:
Content-Disposition: signal; handling=required.
QSIG tunneling is done as follows:
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 does not 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:
1. Open the Digital Gateway Settings page (Setup menu > Signaling & Media tab >
Gateway folder > Digital Gateway > Digital Gateway Settings), and then from the
'Enable QSIG Tunneling' drop-down list (EnableQSIGTunneling), select Enable on the
originating and terminating devices.
2. Configure the QSIGTunnelingMode parameter for defining the format of encapsulated
QSIG message data in the SIP message MIME body (0 for ASCII presentation; 1 for
binary encoding).
3. Configure the ISDNDuplicateQ931BuffMode parameter to 128 to duplicate all
messages.
4. Configure the ISDNInCallsBehavior parameter to 4096.
5. Configure the ISDNRxOverlap parameter to 0 for tunneling of QSIG overlap-dialed
digits (see below for description).
The configuration of the ISDNInCallsBehavior and ISDNRxOverlap parameters allows
tunneling of QSIG overlap-dialed digits (Tel to IP). In this configuration, the device delays
the sending of the QSIG Setup Ack message upon receipt of the QSIG Setup message.
Instead, the device sends the Setup Ack message to QSIG only when it receives the SIP
INFO message with Setup Ack encapsulated in its MIME body. The PBX sends QSIG
Information messages (to complete the Called Party Number) only after it receives the
Setup Ack. The device relays these Information messages encapsulated in SIP INFO
messages to the remote party.
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