Nortel Networks NN43001-563 - Manual (Page 116)

116 ITG engineering guidelines
Trunk Anti-Tromboning (TAT) and Trunk Route Optimization (TRO)
considerations
Trunk Anti-Tromboning (TAT) was designed to remove tromboning trunks
after a call was answered by a third party. Anti-Tromboning can occur in the
following scenarios.
• If a call is re-directed due to call forward or hunt, trunks are torn down
after the third party answers.
• Tromboning trunks are removed due to call modification, such as
transfer or conference, after the third party answers the call and the call
modification is completed.
• For calls entering the private network on CO trunks, the private network
trunks being tromboned due to call modification or call redirection are
removed.
The removal of trunks in the previous scenarios frees resources that would
be otherwise tied up due to tromboning. Therefore, a customer can reduce
the call blocking caused by excessive trunk tromboning. This feature works
in a PRI, ISL, and VNS network.
TAT enhancement
IP Trunk 3.01(and later) introduces an improved TAT validation check
that greatly reduces the number of valid anti-tromboning cases for which
TAT is blocked. The check works by comparing the H.323 Gateway
Endpoint ID (EPID) that allows TAT to optimize trunk connections in all valid
anti-tromboning cases. The EPID is the MAC address of an H.323 Gateway
host, such as an IP Trunk card or Signaling Server.
As a fallback TAT validation mechanism, IP Trunk 3.01 (and later) uses the
IP Trunk 3.01 validation check of comparing called and calling numbers. IP
Peer in CS 1000 Release 2.0, IP Trunk 3.01, BCM 3.0.1, and BCM 3.5 do
not support the new TAT validation check comparing EPIDs. Therefore,
when interoperating with these systems, IP Trunk 3.01 (and later) falls back
to the IP Trunk 3.01 (and later) TAT validation mechanism of comparing
called and calling numbers. This results in the blocking of the TAT operation
in several valid anti-tromboning cases, as previously discussed.
When tromboning of IP Trunks occurs due to limited TAT operation with CS
1000 Release 2.0 and BCM 3.5, BCM and IP Peer use H.245 signaling to
the IP Trunk 3.01 (and later) node to establish a direct media path between
the two tromboned IP Trunks. There are three cases of direct media path
connection between two tromboned IP Trunks (trunk channels) when
interoperating with BCM and IP Peer:
• Both IP Trunks are on the same Media Card 32-port trunk card running
IP Trunk 3.01 (and later).
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.