User`s guide

222 XSR User’s Guide
Configuring QoS on an Interface Chapter 10
Configuring Quality of Service
Suggestions for Using QoS on the XSR
The XSR supports QoS on all interfaces (FastEthernet/GigabitEthernet, Serial,
and Frame Relay DLCI). But, you should enable QoS only on the data path
that actually requires it (generally on lower speed Frame Relay and PPP
interfaces) because QoS is fairly processor intensive and may adversely
impact router performance.
In a typical XSR environment, QoS may be enabled on the WAN link. The
following lists two configuration scenarios:
 A standard office IP application, with no multi-media programs:
– Enable PQ or CBWFQ
 A complex office application, with multi-media applications:
– Use high Priority Queue for VoIP traffic with a cap on bandwidth
it may consume
– Use CBWFQ queue for interactive traffic - Telnet, Web access
– Use CBWFQ with RED for remaining traffic
Additionally, if the WAN link is running Frame Relay, you may also enable
generic traffic shaping on Frame Relay to specify the Committed Information
Rate (CIR), FECN and BECN options to control link throughput.
Configuring QoS on an Interface
The following example configures Class1 with these characteristics: a
minimum of 200 Kbps of bandwidth are expected to be delivered to this class
in the event of congestion, and the queue reserved for this class can enqueue
40 packets before tail drop is employed to handle additional packets.
Class2 is specified with these characteristics: a minimum of 300 Kbps of
bandwidth are expected to be delivered to this class in the event of
congestion. For congestion avoidance, RED packet drop is used, not tail drop.
The default class is configured with a maximum of 20 packets per queue
which are enqueued before tail drop is used to handle additional packets.
Begin by creating Class1 and Class2 and matching their respective parameters:
XSR(config)#class-map class1
XSR(config-cmap<class1)#match access-group 136
XSR(config)#class-map class2