Boots CS-1000 Manual do Utilizador descarregar pdf (Página 113)

Notes

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Zones are an artificial mechanism to control

the number of calls made on a VoIP

network. The concept is often referred to as

Call Admission Control or CAC. CAC is

necessary to prevent too many calls

affecting call quality. In a TDM network this

cannot occur as each call has its own

dedicated circuit but in packet telephony we

are sharing bandwidth and hence issues can

occur.

If the 2 phones in zone A call each other thy

have plenty of Intra zone bandwidth so the

call can proceed. The system will deduct an

amount of bandwidth equivalent to the calls

usage from the Zone whilst the call is in

place, and add it back when the call clears.

Thus if there is insufficient bandwidth to

allow the call it will be refused protecting the

quality of other calls.

In the diagram the 2 zones have a low speed

link between them of 512K. IntraZone calls

will be fine but InterZone calls to Zone 1 will

be more restricted.

The Strategy for calls allows us to choose a

suitable codec depending on the call type. In

the diagram we have selected BQ (Best

Quality) for Intra Zone calls which will result

in the G711 codec being used and

consequently more bandwidth. However for

InterZone calls we have selected BB (Best

Bandwidth) which means a higher

compression codec using less bandwidth will

be selected if available. This will usually be

G.729 and VAD (Voice activity Detection)

may also be selected to save even more

bandwidth allowing more calls to use the link

at the same time.

CS 1000 Rel 7.5 16/04/2013

Copyright Amlex Associates Ltd

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