72 System description
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.
Packet delay
Packet delayis the time between when a packet is sent and when it is
received. The total packet delay time consists of fixed and variable delay.
Variable delayis more manageable than fixed delay, as fixed delay is
dependent on network technology. Variabledelay is caused by the network
routing of packets. The IP Trunk 3.01 (and later) node must be as close
as possible to the network backbone (WAN) with a minimum number of
hops, in order to minimize packet delay and increase voice quality. ITG
provides echo cancellation, so that a one-way delayup to 200 milliseconds
is acceptable. For more information about Echo Cancellation, see "Echo
cancellation" (page 67).
Delay variation (jitter)
The amount of variation in packet delayis referred to as delay variation or
jitter. Jitter affects the ability of the receiving IP trunk card to assemble
voice packets into a continuous stream when the packetsare received at
irregular intervals.
Latency
Latency is the amount of time it takes for a discrete eventto occur.
Bandwidth
Bandwidth is a measure of information carrying capacity available for a
transmission medium. The greater the bandwidth the more information
that can be sent in a given amount of time. Bandwidth is expressed in bits
per second (bps).
Network performance utilities
Twocommon network performance utilities, Packet InterNet Groper (PING)
and Traceroute,are described in this section. Other utilities can be used to
gather information about IP Trunk3.01 (and later) network performance.
These descriptions are for referencepur poses only. Tracerouteis not part of
the IP Trunk3.01 (and later) product.
Because network conditions can vary over time, collect performance data
over a period of at least four hours. Use performance utilities to measure
network performance from each IP Trunk3.01 (and later) node to every
other IP Trunk3.01 (and later) node in the network.
Nortel Communication Server 1000
IP TrunkFundamentals
NN43001-563 02.01 Standard
Release 5.5 21 December 2007
Copyright© 2007, Nor tel Networks
.