3Com 3CRWX120695A, Configuration Manual

Page: 402 / 728

402 C
HAPTER
19: C
ONFIGURING AND
M
ANAGING
S
ECURITY
ACL
S
General Guidelines 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.