Extreme Networks EPICenter 6.0, Reference Manual

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QoS Settings for a VoIP VLAN
EPICenter Reference Guide
559
For example, Figure 284 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
gigabit port (port 50) designated as the egress port on switch A, and two gigabit ports on upstream
switch B, with port 30 designated as an egress port. This port could be connected to a Call Manager, a
PBX, or another internetworking device. Port 29 on the upstream switch is the ingress port for the VoIP
VLAN on that switch.
Figure 284: VoIP topology example
The VoIP Manager module calculates the minimum bandwidth for each switch based on the number of
IP phone ports in the VLAN on that switch, the compression rate, and the speed of the egress port. For
switch A, the number of ingress ports does correspond to the number of IP phone connections.
However, for the upstream switch (B), the VoIP Manager module assumes that the one ingress port
(port 29) is a single IP phone port when it is actually a trunk port.
If the egress port (port 30) on the upstream switch B is configured as 1000 Mbps port (as is the case in
the example) the minimum bandwidth setting will probably be acceptable in most cases, because the
VoIP Manager module will never assign less than 1% of the bandwidth (10 Mbps for a 1000 Mbps port)
as the minimum. However, if switch A were a chassis switch that has several hundred phones
connected, the bandwidth calculation could determine that the minimum bandwidth setting for the
egress port should be 2-3%. But, based on the assumption that there is only one ingress IP phone port
(port 29) on switch B, the bandwidth calculation would determine that a 1% minimum is sufficient for
the egress port 30.
The information in Table 66 is provided to help you ensure that the minimum bandwidth setting in the
QoS profile for your VoIP VLAN is sufficient on any upstream switches.
XM_031
Egress
port 30
Egress
port 50
Ingress
port 29
Switch A
IP phone ports
Switch B
(upstream switch)
49R 49
50R 50
29 30 31 32