Polycom 4300T - Manual (Page 59)

Configuring the 4300T
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Determining the maximum number of concurrent calls
The maximum number of concurrent calls that can be supported by the WAN
access link is calculated using the following formula:
Max calls = (Maximum WAN upstream bandwidth * .85)/VoIP codec rate
where,
Maximum WAN upstream bandwidth = value entered in step D above (in
Kbps)
VoIP codec rate = 85.6Kbps for G.711 voice devices or 29.6Kbps for G.729 voice
devices.
The maximum WAN upstream bandwidth is multiplied by .85 in the formula
above to reduce the total bandwidth available for voice calls by 15%. This
reduction is necessary because the 4300T automatically reserves 15% of the
total WAN bandwidth for low priority data traffic so that it is not starved
completely. Starving data traffic completely would increase the number of
retry attempts and exacerbate congestion on the link during periods of peak
usage.
Examples
The maximum number of G.711 voice calls supported by a T1 (1.536 Kbps)
WAN is calculated as follows:
(1.536*.85)/85.6 = 15.3 or 15 total voice calls.
The maximum number of G.711 voice calls supported by a 768Kbps fractional
T1 WAN is calculated as follows:
(768*.85)/85.6 = 7.6 or 7 total voice calls
The maximum number of G.729 voice calls supported by a 256Kbps fractional
T1 WAN is calculated as follows:
(256*.85)/29.6 = 7.4 or 7 total voice calls
After determining the maximum number of voice calls CAC is enabled as
follows:
1. Select the Enable Call Admission Control checkbox.
2. Enter Maximum number of calls allowed as calculated above.
3. Press Submit.
A Closer Look at Traffic Management in the 4300T
The traffic management mechanisms provided by the 4300T are designed to
ensure high priority real-time voice and video traffic is processed before lower
priority data traffic. At the same time, bandwidth not in use by voice and
video traffic is made available so that data traffic can burst up to full line rate
making efficient use of WAN bandwidth. Traffic management mechanisms