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IP Trunk 3.01 (and later) DSP profile settings 163
The Media Card 32-port trunk card does not support Profile 3.
The DSP coding algorithm parameter sets the preferred codec of each IP
trunk card. The recommendation is to use Profile 1, and to set the preferred
codec to G.729AB with VAD/Silence Suppression with a payload setting of
30 ms. With this codec-payload combination, IP Trunk 3.01 (and later) can
deliver good QoS but loads less than 10 kbit/s per port on the intranet.
Nortel recommends that all the nodes in the IP Trunk 3.01 (and later)
network have a common preferred codec. From a network planning
perspective, this provides a predictable load on the intranet since all calls
will negotiated on one codec. If multiple preferred codecs are configured in
the network, some calls will negotiate a G.723 5.3K call successfully, while
other calls will default to the G.711A/G.711U codec when the originating
and destination codecs do not match, since this codec is available in all
three images.
Consider the effect if the IP Trunk 3.01 (and later) network results in tandem
encoding for some of the users. Too much consecutive coding and encoding
by G.729AB, G.723.1, or G.729B codecs can lower the end-to-end QoS.
To maintain an acceptable QoS on speech, Silence Suppression can be
disabled under some conditions, such as in tandem networking conditions
when some trunk facilities have excessively low audio levels.
Payload size
The IP Trunk 3.01 (and later) default payload sizes are as follows:
•
30 ms for G.729AB, G.729B, and G.723.1 codecs, and 10ms for the
G.711A-law and G.711 mu-law codecs
•
30 bytes for fax
The payload size is adjustable to 10 ms and 20 ms for the G.711A-law/G.711
mu-law and G.729AB codec series. In a site pair that experiences packet
losses, selecting a smaller payload size improves voice and fax quality,
though at the cost of a higher bandwidth use. See Table 17 "Silence
Suppression disabled TLAN Ethernet and WAN IP bandwidth usage per IP
Trunk 3.01 (and later) " (page 113).
Jitter buffer parameters (voice playout delay)
There are three parameters that control the size of the jitter buffer in the
destination IP Trunk 3.01 (and later) node.
1. Voice playout nominal delay. This can range from twice the payload size
to 10 times, subject to a maximum of 320 ms.
2. Voice playout maximum delay.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.