Server User Manual

Factors that effect the real-time capacity 117
TAT call Scenario
The following call scenario helps to understand TAT.
1. Site 1 and Site 2 both have an IP Trunk 3.01 (or later) node installed. IP
Trunk 3.01 (and later) is used for trunking between the two sites.
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.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 02.01 Standard
Release 5.5 21 December 2007
Copyright © 2007, Nortel Networks
.