Voice over Wireless LAN Solution Guide v1.0 December 2005
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The basic concept is to have the WSS 2300 classify and mark all data, voice, and video traffic,
with the assumption that the remaining unmarked traffic consists of control traffic. For example,
assume you are using a port-based ACL on the WSS 2300 to examine all ingress traffic on the
network port. This is traffic destined to wireless devices, which will be encapsulated in CAPP and
sent back out the network port to a DAP or to directly connected APs. Voice should be identified
and marked as CoS 6. For the WLAN Handsets 2210/11/12, do this by creating a rule that
matches IP protocol 119 (SVP). All other traffic can be marked to any desirable number as long
as it is not 6, 7, or 0. On the ES family, configure the port connected to the WSS 2300, shown in
Figure 14 as Interface B, as an untrusted port. “DSCP” values (really the ToS bits) that are
premarked by the WSS 2300 and arrive at Interface B, will be maintained upon egress from the
ES, shown as Interface D, into the DiffServ domain. Configure an additional rule for Interface B to
identify all CAPP traffic without a DSCP value and remark it with a DSCP value of 0x30 (110000)
corresponding to the Class Selector 6 (CS6) class. In addition, if CAPP is running on VLAN
tagged trunks at Interface D, you must set the 802.1p value to 7.
The remaining limitation is how to handle CAPP traffic from AP to WSS. The traffic in that
direction at Interface A will be unmarked, because the AP 2330 does not mark or classify packets
when WMM is disabled. For an ES 460-24T-PWR port connected to an AP, it is best to simply
mark all traffic ingressing on that interface with a DSCP value of 0x2e (101110) corresponding to
the expedited forwarding (EF) class.
2.5.2.2 Prioritizing/marking interswitch (WSS 2300) traffic
There are a number of protocol interactions that take place between WSS 2300s in a Mobility
Domain. When a user roams across different WSS 2300s, user information is passed between
the switches. Because this interaction serves a critical function in roaming, and because roaming
latency must be kept to an absolute minimum to maintain call quality, it is desirable to ensure that
this traffic is classified as a Network service class. Because this traffic will enter the DiffServ
domain at Interface B, the ES interface must be configured to identify and mark it as class CS6,
which has a corresponding DSCP value of 0x30. The 802.1p bit (if present) should also be set to
7.
In addition, when subnet roaming, the user traffic may be tunneled back to another WSS 2300
depending on whether the user’s subnet is local or remote. It is recommended that this tunneled
traffic be classified as a Premium service class and marked as class EF. This translates to a
DSCP value of 0x2e and an 802.1p bit value of 6. The easiest way to classify this on the ES
family at Interface B is to use source IP and destination IP address filters that match the IP
addresses of the WSS 2300 switches. The interswitch tunnel utilizes IP Protocol 0x04 for
transport just like CAPP, but this is not a possible filter criterion due to ES filter limitations.
2.5.2.3 Prioritizing/marking SVP
Handset voice traffic from the WSS 2300 to the LAN and from the LAN to the WSS 2300 at
interface B will be encapsulated in SVP. Because SVP contains voice traffic, it is recommended
that it be treated and marked as per the Premium service class. Figure 16 shows the levels of
nesting of voice traffic within SVP and CAPP. As you can see from the diagram, CAPP exists
between WSS 2300 and AP 2330 and traverses interfaces A and B. SVP is encapsulated in
CAPP, and during that leg of the path SVP is invisible to the network. SVP then traverses the
network between WSS 2300 and WTM 2245 between interfaces B and C. Native VoIP traffic is
nested within SVP and is invisible to the network over the CAPP and SVP legs of the path. Native
VoIP traffic only appears at Interface C as it reenters the DiffServ domain.