Version 5.6
403
November 2008
SIP User's Manual
10. Tunneling Applications
10 Tunneling
Applications
This section discusses TDM and QISG tunneling, supported by the device.
10.1 TDM Tunneling
The device's TDM Tunneling feature allows you to tunnel groups of digital trunk spans or
timeslots (B-channels) over the IP network. TDM Tunneling utilizes the device's internal
routing (without Proxy control) capabilities to receive voice and data streams from TDM
(E1/T1/J1/) spans or individual timeslots, convert them into packets, and then transmit them
over the IP network (using point-to-point or point-to-multipoint device distributions). A
device opposite it (or several devices when point-to-multipoint distribution is used) converts
the IP packets back into TDM traffic. Each timeslot can be targeted to any other timeslot
within a trunk in the opposite device.
When TDM Tunneling is enabled ('Enable TDM Tunneling' parameter is set to 'Enable' on
the originating device -- refer to ''Configuring the Digital Gateway Parameters'' on page
), the originating device automatically initiates SIP calls from all enabled B-channels
belonging to the E1/T1/J1 spans that are configured with the protocol type ‘Transparent’ (for
ISDN trunks) or ‘Raw CAS’ (for CAS trunks). The called number of each call is the internal
phone number of the B-channel from where the call originates. The 'IP to Trunk Group
Routing' table (refer to ''IP to Trunk Group Routing'' on page
) is used to define the
destination IP address of the terminating device. The terminating device automatically
answers these calls if its E1/T1 protocol type is set to ‘Transparent’ (ProtocolType = 5) or
‘Raw CAS’ (ProtocolType = 3 for T1 and 9 for E1) and the parameter ChannelSelectMode
is set to 0 (By Phone Number).
Note:
It's possible to configure both devices to also operate in symmetric mode. To
do so, set EnableTDMOverIP to 1 and configure the 'Tel to IP Routing' tables
in both devices. In this mode, each device (after it's reset) initiates calls to the
second device. The first call for each B-channel is answered by the second
device.
The device continuously monitors the established connections. If for some reason, one or
more calls are released, the device automatically re-establishes these ‘broken’ connections.
In addition, when a failure in a physical trunk or in the IP network occurs, the device re-
establishes the tunneling connections when the network is restored.
Note:
It's recommended to use the keep-alive mechanism for each connection, by
activating the ‘session expires’ timeout and using Re-INVITE messages.
By utilizing the ‘Profiles’ mechanism (refer to ''Configuring the Profile Definitions'' on page
), you can configure the TDM Tunneling feature to choose different settings based on a
timeslot or groups of timeslots. For example, you can use low-bit-rate vocoders to transport
voice and ‘Transparent’ coder to transport data (e.g., for D-channel). You can also use
Profiles to assign ToS (for DiffServ) per source -- a timeslot carrying data or signaling is
assigned a higher priority value than a timeslot carrying voice.
For tunneling of E1/T1 CAS trunks, set the protocol type to 'Raw CAS' (ProtocolType = 3 /
9) and enable RFC 2833 CAS relay mode ('CAS Transport Type' parameter is set to 'CAS
RFC2833 Relay' -- refer to ''Configuring the Voice Settings'' on page
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