Nortel 1000 Description, Installation And Operation Manual page 158

Page 158 of 644
553-3001-363 Standard 2.00
ITG engineering guidelines
• Tromboned Trunks must belong to the same customer.
• TAT must be set 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 Networks recommends that both Trunk Route Optimization (TRO)
and TAT be implemented with IP Trunk 3.01 (and later) nodes.
TRO functions in a different manner than TAT. TRO is invoked before the
call has been answered. TAT is invoked once the call has been answered. To
reduce the number of trunks being used due to call redirection by CFNA,
Hunt, or Forward all Calls, configure TRO in the RDB. TRO must be enabled
at all sites.
If Telephone A at Site 1 calls Telephone B at Site 2, and Telephone B
forwards a call using CFNA to Telephone C at Site 3, then TRO must be
enabled at Sites 1 and 2. If TRO is enabled at both sites, Site 2 will drop out,
freeing up the trunk, and only trunks on Site 1 and 3 are used. This reduces
the number of trunks in use, conserves bandwidth, and improves voice
quality.
September 2004