Nortel Networks Mediant TP-1610 SIP - Manual (Page 149)

Mediant 2000 SIP User’s Manual 8. Gateway Capabilities Description
Version 4.4 149 July 2005
8.8 TDM Tunneling
The Mediant 2000 TDM Tunneling feature allows you to tunnel groups of digital trunk spans or
timeslots (B-channels) over the IP network. TDM Tunneling utilizes the internal routing
capabilities of the Mediant 2000 (working without Proxy control) to receive voice and data
streams from TDM (1 to 16 E1/T1/J1) spans or individual timeslots, convert them into packets
and transmit them automatically over the IP network (using point-to-point or point-to-multipoint
gateway distributions). A Mediant 2000 opposite it (or several Mediant 2000 gateways, when
point-to-multipoint distributions 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 Mediant 2000.
8.8.1 Implementation
When TDM Tunneling is enabled (‘EnableTDMOverIP’ is set to 1 on the originating Mediant
2000), the originating Mediant 2000 automatically initiates SIP calls from all enabled B-channels
belonging to the E1/T1/J1 spans that are configured with the ‘Transparent’ protocol. The called
number of each call is the internal phone number of the B-channel that the call originates from.
The IP to Trunk Group routing table is used to define the destination IP address of the terminating
Mediant 2000. The terminating Mediant 2000 gateway automatically answers these calls if its
E1/T1 protocol is set to ‘Transparent’ (ProtocolType = 5) and parameter ‘ChannelSelectMode = 0’
(By Phone Number).
Note: It is possible to configure both gateways to also operate in symmetric mode. To do so, set
‘EnableTDMOverIP’ to 1 and configure the Tel to IP Routing tables in both Mediant 2000
gateways. In this mode, each gateway (after it is reset) initiates calls to the second gateway. The
first call for each B-channel is answered by the second gateway.
The Mediant 2000 monitors the established connections continuously, if for some reason one or
more calls are released, the gateway automatically reestablishes these “broken“ connections. In
addition, when a failure in a physical trunk or in the IP network occurs, the Mediant 2000
gateways reestablish the tunneling connections as soon as the network restores.
Note: It is recommended to use the keep-alive mechanism for each connection by activating
“session expires” timeout, and using Reinvite messages.
By utilizing the ‘Profiles’ mechanism (refer to Section 5.8.5 on page 55 ) 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 time-slot carrying data or signaling gets a higher priority value than a time-slot carrying
voice.
For tunneling of E1/T1 CAS trunks enable RFC 2833 CAS relay mode (CASTransportType = 1).
Figure 8-1 and Figure 8-2 show an example of ini files for two Mediant 2000 gateways
implementing TDM Tunneling for four E1 spans. Note that in this example both gateways are
dedicated to TDM tunneling.