Minimum Bandwidth Calculations - Extreme Networks EPICenter Reference 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, use one of the following options:
Add
Remove
Remove All
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.
558
Select one or more ports in the Ports in VLAN list, and click the Add button
to move 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.
EPICenter Reference Guide