Avaya BCM 2.0 IP Telephony Manual de usuario descargar pdf (Pagina 31)

Engineering guidelines 31

P0911590 Issue 02 Enterprise Edge 2.0 IP Telephony Configuration Guide

If QoS levels of some or all routes fall short of being “Good”, the installer or

administrator needs to evaluate options and costs for upgrading the intranet. Further

network analysis on page 31 provides guidelines for reducing one-way delay. The

evaluation often requires a link upgrade, a topology change, or implementation of

QoS in the network.

The installer or administrator can opt for keeping costs down, and accept a Fair QoS

level for the time for a selected route. A calculated trade-off in quality requires the

installer or administrator monitor the QoS level, reset needs with the end users, and

respond to user feedback.

Further network analysis

This section describes actions possible actions to examine the sources of delay and

error in the intranet. This section and Implementing QoS in IP networks on page 34

discuss several methods for reducing one-way delay and packet loss. The key

methods are:

• Reduce link delay

• Reducing hop count

• Adjust the jitter buffer size

• Setting IP telephony QoS objectives.

Components of delay

End-to-end delay is the result of many delay components. The major components

of delay are as follows:

Propagation delay

Propagation delay is the result of the mileage and the medium of links moved

across. Within a country, the one-way propagation delay over terrestrial lines is

under 18 ms. Within the U.S., the propagation delay from coast-to-coast is under 40

ms. To estimate the propagation delay of long-haul and trans-oceanic circuits, use

the rule of thumb of 1 ms per 100 terrestrial miles.

If a circuit goes through a satellite system, estimate each hop between earth stations

to adds 260 ms to the propagation delay.

Serialization delay

The serialization delay is the time it takes to transmit the voice packet one bit at a

time over a WAN link. The serialization delay depends on the voice packet size and

the link bandwidth, and is the result of the following formula:

IP packet size in bytes

serialization delay in ms = 8 X

link bandwidth in kbit/s

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Avaya BCM 2.0 IP Telephony Manual de usuario Pagina 31