3com WX2200 3CRWX220095A User Manual

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ONFIGURING

 

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ANAGING

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ECURITY

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3Com recommends that you follow these guidelines for any wireless VoIP 
implementation:

„

Ensure end-to-end priority forwarding by making sure none of the 
devices that will forward voice traffic resets IP ToS or Diffserv values to 
0. Some devices, such as some types of Layer 2 switches with basic 
Layer 3 awareness, reset the IP ToS or Diffserv value of untrusted 
packets to 0. 

MSS uses IP ToS values to prioritize voice traffic. For example, when a 
MAP receives traffic from its WX switch, the MAP classifies the traffic 
based on the IP ToS value in the IP header of the tunnel that is carrying 
the traffic. By default, the WX switch marks egress traffic for priority 
forwarding only if WMM is enabled and only if the ingress traffic was 
marked for priority forwarding. If another forwarding device in the 
network resets a voice packet’s priority by changing the IP ToS or 
Diffserv value to 0, the WX does not reclassify the packet, and the 
packet does not receive priority forwarding on the MAP.

„

For WMM-capable devices, leave WMM enabled. 

„

For SVP devices, change the QoS mode to svp. You also need to 
disable IGMP snooping, and configure an ACL that marks egress 
traffic from the voice VLAN with CoS value 7.

 

(See “Enabling SVP 

Optimization for SpectraLink Phones” on page 404 for complete 
configuration guidelines.) 

For other types of non-WMM devices, you do not need to change the 
QoS mode, but you must configure an ACL to mark the traffic’s CoS 
value. This section shows examples for configuring VoIP for devices 
that use TeleSym.

Table 35 shows how WMM priority information is mapped across the 
network. When WMM is enabled in MSS, WX switches and MAPs 
perform these mappings automatically.