Polycom 4300T - Manual (Page 58)

User Guide V 2 IU 4300T Converged Network Appliance
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3. Specify the upstream and downstream bandwidth of your WAN link
4. Enter the WAN Downstream Bandwidth in Kbps.
5. Enter the WAN Upstream Bandwidth in Kbps.
Optionally enable priority IP addresses
VoIP traffic from devices that use the VoIP ALG function (phones, video
stations, softphones on Pcs, etc.) are already marked as high priority and do
not need to be manually configured in this list. This list is used to prioritize
voice traffic from trunk interfaces of IP PBXs or other high priority devices that
do not use the VoIP ALG function of the 4300T.
>> Enter the IP address of other high priority devices in the priority IP
Addresses box.
You can enter individual IP addresses or a range using by appending a “-“
character to the last octet. For example, 10.10.10.2-5 would specify
10.10.10.2, 10.10.10.3, 10.10.10.4 and 10.10.10.5 as voice devices.
Enable CAC
The 4300T uses CAC to limit the number of active voice calls over the WAN
link. This is necessary because a typical installation uses a ratio of 1:2 or 1:4
active voice calls to voice devices on the assumption that 50% or 25% of all
users are on the phone at the same time. These ratios are guidelines only and
at times the number of concurrent calls may exceed the amount of WAN
bandwidth available to process the calls. In this instance existing phone calls
will experience poor quality or be dropped all together. To prevent this from
occurring a typical voice installation will set a threshold for the maximum
number of concurrent voice calls supported by the WAN access link. New call
requests in excess of this threshold will receive the equivalent of a “fast busy”
and the WAN link will not become oversubscribed.
For IP Centrex installations the maximum number of concurrent voice calls is
usually configured in the 4300T by enabling CAC. When the 4300T is
deployed in IP PBX applications the maximum number of concurrent calls
could be configured in the IP PBX. If the PBX is responsible for this setting you
do not need to configure CAC in the 4300T. Please check with your IT
administrator to determine if this is the case.
Note For FT1/T1/E1 links the upstream and downstream bandwidths will always be the
same value (the link is full-duplex).
Warning Care must be taken to ensure that the IP addresses entered do not include data
devices such as PCs or workstations. Traffic from these devices will be placed in
the priority voice queue internal to the 4300T and burst up to full line rate. This will
starve actual voice devices by consuming priority bandwidth and result in dropped
calls, busy signals & poor voice quality.