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H323 IP Telephone Installation Page 16
15-601046 Issue 16a (15 March 2010)IP Office Release 6
1.8 Network Assessment
· WARNING: A Network Assessment is Mandatory
When installing H323 IP phones on an IP Office system, it is assumed by Avaya that a network assessment has
been performed. If a support issue is escalated to Avaya, Avaya may request to see the results of the network
assessment and may refuse to provide support if a suitable network assessment was not performed.
Current technology allows optimum network configurations to deliver VoIP with voice quality close to that of the public
phone network. However, few networks are optimum and so care should be taken assessing the VoIP quality achievable
across a customer network.
Not every network is able to carry voice transmissions. Some data networks have insufficient capacity for voice traffic or
have data peaks that will impact voice traffic on occasion. In addition, the usual history of growing and developing
networks by integrating products from many vendors makes it necessary to test all the network components for
compatibility with VoIP traffic.
A network assessment should include a determination of the following:
· A network audit to review existing equipment and evaluate its capabilities, including its ability to meet both current
and planned voice and data needs.
· A determination of network objectives, including the dominant traffic type, choice of technologies and setting voice
quality objectives.
· The assessment should leave you confident that the network will have the capacity for the foreseen data and voice
traffic, and can support H323, DHCP, TFTP and jitter buffers in H323 applications.
The network assessment targets are:
· Latency: Less than 180ms for good quality. Less than 80ms for toll quality.
This is the measurement of packet transfer time in one direction. The range 80ms to 180ms is generally acceptable.
Note that the different audio codecs used each impose a fixed delay caused by the codec conversion as follows:
· G711: 20ms.
· G723a: 80ms.
· G729: 40ms.
· Packet Loss: Less than 3% for good quality. Less than 1% for toll quality.
Excessive packet loss will be audible as clipped words and may also cause call setup delays.
· Jitter: Less than 20ms.
Jitter is a measure of the variance in the time for different packets in the same call to reach their destination.
Excessive jitter will become audible as echo.
· Duration: Monitor statistics once every minute for a full week.
The network assessment must include normal hours of business operation.