Nortel Networks NN43001-563 - Manual (Page 71)

Quality of Service 71
The Type of Service (ToS) bits in the IP packet header can affect how
efficiently data is routed through the network. For further information on
ToS, see
"Type of Service" (page 76) .
Packet jitter related to latency affects the quality of real-time IP
transmissions. For good voice quality, the IP trunk card reassembles the
voice packets in an ordered continuous speech stream and plays them out
at regular intervals despite varying packet arrival times.
The user configures a required QoS for the IP Trunk 3.01 (and later) node in
TM 3.1. The QoS value determines when calls fallback to alternate facilities
due to poor performance of the data network. The QoS value is between 0.0
and 5.0, where 0.0 means never fallback to alternate facilities and 5 means
fallback to alternate facilities unless the voice quality is perfect. When the
QoS for outgoing calls, as measured by the Leader card, falls below the
configured value, calls fallback to alternate facilities. Once the QoS rises
above the configured value, all new outgoing calls are routed through the
IP network.
QoS is measured for each remote gateway. For example, if a given Leader
has three remote leaders in its dialing plan table, it performs three QoS
measurements and calculations (one per remote gateway).
Since IP trunks use the same port for both voice and fax, the same QoS
thresholds apply for both voice and fax calls. Network requirements for fax
are more stringent than for voice. Fax protocols, such as T.30, are more
sensitive to transmission errors than the human ear.
Quality of Service parameters
Quality of Service for both voice and fax depends on end-to-end network
performance and available bandwidth. A number of parameters determine
the ITG voice QoS over the data network.
Packet loss
Packet loss is the percentage of packets sent that do not arrive at their
destination. Packet loss is caused by transmission equipment problems
and congestion. Packet loss can also occur when packet delays exceed
configured limits and the packets are discarded. In a voice conversation,
packet loss is heard as gaps in the conversation. Some packet loss, less
than five percent, can be acceptable without too much degradation in
voice quality. Sporadic loss of small packets can be more acceptable than
infrequent loss of large packets.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.