Nortel Networks NN43001-563 - Manual (Page 118)

118 ITG engineering guidelines
2. Telephone A at Site 1 calls Telephone B at Site 2. Telephone B answers
the call and decides to transfer the call to Phone C which is located at
Site A.
3. Telephone C answers the call transferred from Telephone B at Site 2.
4. After the call has been answered by Telephone C, Site B sends a TAT
Invoke message to Site A. Site B only sends a TAT Invoke message if the
Tromboned Trunks belong to the same D-Channel and Customer. If a
customer has multiple DCHIP cards in their node, The first leg of the call
could be associated with one D-Channel and the second leg of the call
associated with another D-Channel. In this case, TAT will not be invoked.
To prevent problems, the following recommendations are made:
• The use of multiple DCHIPs in a node or the use of multiple IP Trunk
3.01 (and later) nodes in a system must be implemented with caution. It
can lead to poor voice quality in certain call scenarios.
• Tromboned Trunks must belong to the same customer.
• TAT must be configured in the RCAP prompt for D-Channel
Configuration. IP Trunk 3.01 (and later) Nodes at both sites must have
TAT in the RCAP of their respective D-channels.
Therefore, TAT can fail if the originating side has multiple DCHIPs configured
or multiple nodes configured in a system. TAT failure can also occur if the
recipient of the TAT Invoke message has multiple DCHIPs or IP Trunk 3.01
(and later) nodes.
If Site A in the previously described scenario had multiple DCHIPs or
multiple IP Trunk 3.01 (and later) nodes, TAT would fail. The reason is as
follows: if the call between Telephone A and Telephone B was set up using
one D-Channel and the call between Telephone B and Telephone C was set
up using another D-Channel, then the D-Channel for the first leg of the call
is not able to validate the Call Reference Value* for the second leg of the
call. This prevents TAT from being used.
*The Facility message invoking TAT is sent using the Call Reference
Value of the first call, which was from Telephone A to Telephone B. The
TAT Invoke includes the Call Reference Value of the second call, which
was Telephone B transferring the call to Telephone C.
TAT versus TRO
Nortel recommends that both Trunk Route Optimization (TRO) and TAT be
implemented with IP Trunk 3.01 (and later) nodes.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
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