Minimum Bandwidth Calculations - Extreme Networks EPICenter Software Installation Manual

Voice over IP Manager
• Egress Port Selection: The QoS Settings page also displays every port in the VLAN in one of the two
lists in the Egress Port Selection portion of the window. You use these lists to designate the ports that
should be used as the egress port on each device in the VLAN. Egress ports are used to route VoIP
traffic from the IP phone ports (ingress ports) to the Call Manager or PBX, either directly or via
trunk ports between other switches in the VLAN. You should designate at least one port on each
switch in the VLAN as an egress port in order for VoIP to function over the VLAN. You can
designate as many egress ports as you need.
To designate egress ports, do the following:
— Select one or more ports in the Ports in VLAN list, and click the Add button
them to the Selected Egress Ports in VLAN list. You can select multiple ports by holding down
the CTRL or Shift keys while you make your selections.
— To remove ports from the Selected Egress Ports in
VLAN list, select the ports and click the Remove button
You can remove all ports from the Selected Egress
Ports in VLAN list by clicking the Remove All button
NOTE
If some of the ports in your port list are not physically present in the device (a GBIC has been
removed, for example) and those ports are not set to auto-negotiate, the port speed will be shown
as zero in the port list. If you select such a port as an egress port, this will result in the minimum
bandwidth being calculated as zero for the VLAN. If the port speed is set to auto, the calculation will
assume a port speed of 100 Mbps and will work correctly.

Minimum Bandwidth Calculations

The VoIP Manager module computes the minimum bandwidth setting for the QoS profile used for the
VoIP VLAN to ensure acceptable VoIP performance. It first computes the total bandwidth needed based
on the number of VoIP phone ports in combination with the compression rate used in the IP phones for
coding/decoding voice traffic. It then determines the minimum bandwidth as the percentage of the
egress port bandwidth that is required to support all the IP phone ports simultaneously. The minimum
bandwidth setting will never be less than 1% of the egress port's total available bandwidth. However,
there may be situations where the bandwidth calculation algorithm either overestimates or
underestimates the minimum bandwidth requirements.
If the egress port speed is set to Auto, the bandwidth calculation assumes 100 Mbps as the configured
port speed. If the port's actual speed is 1000 Mbps, the calculation may overestimate the percentage of
bandwidth required for VoIP traffic. If there are multiple egress ports running at different speeds, the
VoIP applet calculates the percentage based on the lowest port speed among the egress ports. For best
results, it is recommended that you turn auto-negotiation off and explicitly configure the speed of your
egress ports.
The VoIP Manager module calculates the minimum bandwidth requirements separately for each switch
in the VLAN. The bandwidth calculation algorithm assumes there is a one-to-one correspondence
between the number of IP phones and the number ingress ports included in the VoIP VLAN, and that
all ingress ports in the VLAN (those not designated as egress ports) are IP phone ports. However, if the
VoIP VLAN topology includes upstream switches, the ingress port may actually be a trunk port
carrying aggregated VoIP traffic. In this case, the bandwidth calculation algorithm may underestimate
the minimum bandwidth needed for the ingress port on the upstream switch.
For example, Figure 198 shows a topological representation of devices in a VoIP network. In this
illustration, IP phones are connected to 10/100Mbps ports on switch A. The VoIP VLAN also includes a
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to move
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