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Overview
In a typical network, there are often many users and applications competing for limited system
and network resources. While resource sharing on a first-come, first-serve basis may suffice when
your network load is light, access can freeze quickly when the network gets congested. Under
these conditions, a bandwidth-hungry application (large file transfer files, emails) may devour
most of the network bandwidth, depriving applications that send small-sized packets (voice,
telnet and other interactive applications) of their fair share of bandwidth, and result in long delays
causing applications to fail.
Quality of Service (QoS) cannot magically provide all applications their requested bandwidth, but
it can help you identify your mission-critical, high priority application traffic and give it
preferential treatment (higher priority, higher bandwidth or guaranteed bandwidth) relative to
the rest of your network traffic. In this way, critical applications will work under both normal and
congested conditions while less important and time-sensitive traffic will continue to flow, perhaps
at a lower rate than expected.
Consider the following aspects of the XSR's QoS implementation:
•
QoS can be configured on LAN and/or WAN interfaces/sub-interfaces.
•
QoS is implemented as a service which can be applied on any interface at will (intuitive
configuration).
•
Packet classification is based on source/destination address, source/destination port, IP
precedence or DSCP value and is specified using ACLs, the IP precedence or DHCP fields.
•
Class-Based queuing is provided for prioritization and bandwidth sharing.
•
Up to four priority queues and 60 shared queues can be configured per policy-map.
•
Link efficiency mechanisms with interleaving for real-time traffic: Multi Class MLPPP for PPP
and FRF.12 for Frame Relay.
•
Traffic policing using Single-color, Three-rate token bucket.
•
Three buffer management strategies: tail drop, Weighted and Random Early Detection (WRED/
RED).
•
Traffic shaping per class and per policy map on the output traffic.
•
Marking the DSCP or IP precedence field of the packet.
•
Marking the 802.1P info in VLAN header.
•
Service policy can be applied on the input and/or output traffic.
•
Automatic internal prioritization of the control packets locally generated by the XSR.
Configuring Quality of Service
12
XSR User's Guide 12-1
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Table of Contents
Troubleshooting
