Nortel Networks NN43001-563 - Manual (Page 117)

Factors that effect the real-time capacity 117
The circuit-switched path between the tromboned trunks is connected
by the time switch on the Media Card 32-port trunk card. There is no
voice quality degradation due to delay or multiple transcoding since
the speech path does not pass through the IP Trunk codecs and
packetization/depacketization. The tromboned trunks are busy for the
duration of the call.
• Both IP Trunks are on the same ITG-Pentium 24-port trunk card running
IP Trunk 3.01 (and later).
The media path between the tromboned trunks is connected by
the IP loopback route on the ITG-Pentium 24-port trunk card.
Voice quality degradation may occur due to delay and multiple
transcoding since the speech path passes through both codecs and
packetization/depacketization. The tromboned trunks are busy for the
duration of the call.
• The two IP Trunks are on different IP Trunk cards.
The media path between the tromboned trunks is connected by the
TLAN network interface route between the two IP Trunk cards. Voice
quality degradation may occur due to delay and multiple transcoding
since the speech path passes through both codecs and
packetization/depacketization. The tromboned trunks are busy for the
duration of the call.
TAT as a method of Improving Voice Quality in a VoIP network
In a purely TDM network, TAT provides a method of eliminating the
unnecessary use of trunking resources.
In a VoIP network, there are three primary benefits of TAT.
1. As in a TDM network, TAT eliminates tromboning of trunks and frees up
valuable trunking resources.
2. TAT provides a method of reducing bandwidth requirements, which can
be crucial over a slow WAN link. If TAT is not used, a tromboned call
using a G.729 codec can theoretically use 60-70Kbps on a WAN link.
By using TAT, bandwidth can be reduced to zero for a tromboned call.
3. TAT improves voice quality. If a call is tromboned using a G.729 codec,
multiple transcodings can diminish voice quality. Since each transcoding
introduces errors for a G.729 codec, the goal is to eliminate as many
hops as possible. TAT provides the means to accomplish this.
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.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.