Voice over Wireless LAN Solution Guide v1.0 December 2005
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Figure 17: ERS 5510/5520 performing packet classification
These deployment options are presented strictly for the sake of discussion concerning the
capabilities of the ERS 5510/5520 given possible locations within various networks. Because the
ERS 5520 has PoE ports, and the ERS 5510 does not, only an ERS 5520 can provide Interface A
to AP 2330s. Given a particular real-world network, implement the recommendations below if the
ERS 5510/5520 is directly connected to any of the devices at the specified interfaces.
2.5.3.1 Prioritizing/marking CAPP
For an ERS 5510/5520 connected to a WSS 2300 at Interface B, you can use a prioritization
approach similar to that used for the ES family products. That is specifically to have the WSS
2300 mark all voice and data traffic, leaving only the control traffic unmarked. A filter on the ERS
5510/5520 can be designed to identify all remaining CAPP traffic that has no DSCP marking and
mark it as 0x30 (110000) corresponding to the CS6 class.
Configure an ERS 5520 connected to an AP2330 at Interface A to mark all traffic with DSCP
value of 0x2e (101110) corresponding to the EF class. The easiest way to accomplish this is by
marking all traffic ingressing on the interface.
The ERS 5510/5520 can implement an alternative classification scheme using the offset filtering
capabilities. This feature is particularly useful at Interface A because the AP is not capable of
marking packets when WMM is disabled. An offset filter can be used to identify SVP buried within
the CAPP protocol and mark the outer CAPP packet. You might be able to use similar offset
filters to identify and mark control traffic and other data and multimedia. However, discussion of
the exact offsets and bit patterns to match are beyond the scope of this document.
2.5.3.2 Prioritizing/marking interswitch (WSS 2300) traffic
The classification techniques for an ERS 5510/5520 at Interface B with respect to inter-WSS
traffic do not differ from the ES. The marking behavior should also follow as described for the ES.
2.5.3.3 Prioritizing/marking SVP
The ERS 5510/5520 does not have the same restriction on user-defined IP protocol numbers,
and therefore the recommended filtering criteria at Interface B to identify SVP is to use an IP
classifier that matches IP protocol 119. The ERS 5510/5520 must then mark the DSCP value as
0x2e.