Nortel Networks NN43001-563 TATas a method of Improving Voice Quality in a VoIP network

116 ITG engineering guidelines

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 Trunksare on the same Media Card 32-port trunk card running

IP Trunk3.01 (and later).

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 Trunkcodecs and

packetization/depacketization. The tromboned trunks are busy for the

duration of the call.

•Both IP Trunksare on the same ITG-Pentium 24-port tr unk card running

IP Trunk3.01 (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 mayoccur 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 Trunksare 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 multipletranscoding

since the speech path passes through both codecs and

packetization/depacketization. The tromboned trunks are busy for the

duration of the call.

TATas a method of Improving Voice Quality in a VoIP network

In a purely TDM network, TATprovides a method of eliminating the

unnecessary use of trunking resources.

In a VoIPnetwork, there are three primar y 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 WANlink. If TATis 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 fora trombonedcall.

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. TATprovides the means to accomplish this.

Nortel Communication Server 1000

IP TrunkFundamentals

NN43001-563 02.01 Standard

Release 5.5 21 December 2007