Jitter - Mitel MiVoice Business Voice Quality And Troubleshooting Manual

• amount of available bandwidth
• path that is being used through the network
• amount of traffic
For example, latency may be high during the afternoon when network usage on the site peaks.
During the period of peak network usage, the IP phone user may experience poor voice quality
on calls. Later, when network usage subsides, latency isn't a problem and voice quality on calls
is good again. Therefore, you need to perform ping tests when the voice quality issue is present
to determine if latency is the cause.
You can use a ping test to determine if network latency is causing voice quality issues between
two IP phones. See "Ping Test" on page 62 for instructions. ping delay is the time it takes for a
data packet to travel from one IP address across the network to another IP address and back
again (round-trip delay). A ping utility allows you to send a data packet from a PC to an IP
address on the network. If the packet reaches the IP address it is sent back, and the utility
displays the round-trip delay. Typically, the send and receive paths have equal delays. You can
also check the Delay time for the IP phone in the Voice Quality Statistics form of the MiVoice
Business System Administration Tool (see "Voice Quality Statistics for MiVoice IP Phones" on
page 63 for details) to determine if latency is an issue.

JITTER

Jitter is the variation in the packet delay. The major cause of jitter is network congestion. This
occurs when the amount of data arriving at a node, including the source, destination, routers,
and switches exceeds the capacity of the node to forward the data. In this case, data is stored
in a buffer queue until the node is able to forward the data. The time that the data spends in
this buffer before being forwarded is the major source of jitter.
While high quality network routers, switches, and Network Interface Cards (NICs) can generally
forward packets at the network data rate; many routers, switches, and NICs are limited in the
number packets they can forward per second. With short packets, such as VoIP packets, this
can result in network congestion at data rates significantly lower than the network bus
bandwidth.
High levels of jitter results in choppy voice quality on VoIP calls. To determine if jitter is the
cause of voice quality issues:
• Measure jitter using a network analyzer, or
• Check the Average Jitter for the IP phone in the Voice Quality Statistics form of the
MiVoice Business System Administration Tool (see "Voice Quality Statistics for MiVoice IP
Phones" on page 63 for details).
IP Network Issues
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