Nortel Networks NN43001-563 Payload size, Jitter buffer parameters (voice playoutdelay)

162 ITG engineering guidelines

•Proﬁle 3: G.711, G.729B, Fax

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/SilenceSuppression 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 Trunk3.01 (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.

Tomaintain an acceptable QoS on speech, Silence Suppression can be

disabled under some conditions, such as in tandem networking conditions

when some trunk facilities have excessivelylow audio levels.

Payload size

The IP Trunk3.01 (and later) default payload sizes are as follows:

•30 ms for G.729AB, G.729B, and G.723.1 codecs, and 10ms forthe

G.711A-law and G.711 mu-law codecs

•30 bytes for fax

The payloadsize 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 Table17 "Silence

Suppression disabled TLAN Ethernet and WAN IP bandwidth usage per IP

Trunk3.01 (and later) " (page 113).

Jitter buffer parameters (voice playoutdelay)

There are three parameters that control the size of the jitter buffer in the

destination IP Trunk3.01 (and later) node.

1. Voiceplayout nominal delay. This can range from twice the payload size

to 10 times, subject to a maximum of 320 ms.

Nortel Communication Server 1000

IP TrunkFundamentals

NN43001-563 02.01 Standard

Release 5.5 21 December 2007