Specifications

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Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
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Chapter 10 Cisco IGX 8400 Series IP Service
IP Service—Functional Overview
MPLS CoS on the IGX
This section describes MPLS CoS with the use of the Cisco IGX 8410, 8420, and 8430 ATM label switch
router (ATM LSR). MPLS CoS is also supported in networks using the URM as a LSC.
Note The URM does not support MPLS CoS when configured as an LSR, and networks using URM-LSRs
cannot run MPLS CoS across those network segments containing the URM-LSR.
The MPLS CoS feature enables network administrators to provide differentiated types of service across
an MPLS switching network. Differentiated service satisfies a range of requirements by supplying the
specific type of service specified for each packet by its CoS service can be specified in different
ways—for example, through use of the IP precedence bit settings in either IP packets or in source and
destination addresses.
The MPLS CoS feature can be used optionally with MPLS virtual private networks. MPLS CoS can also
be used in any MPLS switching network.
In supplying differentiated service, MPLS CoS offers packet classification, congestion avoidance, and
congestion management. Table 10-7 lists these functions and how they are delivered.
MPLS CoS lets you duplicate Cisco IOS IP CoS (Layer 3) features as closely as possible in MPLS
switching devices, including label switching routers (LSRs), edge LSRS, and ATM label switching
routers (ATM LSRs). MPLS CoS functions map nearly one-for-one to IP CoS functions on all interface
types.
For additional information, refer to Cisco router and MPLS-related Cisco IOS documentation (see the
“Cisco IOS Software Documentation” section on page ix).
Table 10-7 CoS Services and Features
Service CoS Function Description
Packet
classification
Committed access rate
(CAR). Packets are
classified at the edge of
the network before
labels are assigned.
CAR uses the type of service (TOS) bits in the IP header to
classify packets according to input and output transmission
rates. CAR is often configured on interfaces at the edge of a
network in order to control traffic into or out of the network.
You can use CAR classification commands to classify or
reclassify a packet.
Congestion
avoidance
Weighted random early
detection (WRED).
Packet classes are
differentiated based on
drop probability.
WRED monitors network traffic, trying to anticipate and
prevent congestion at common network and internetwork
bottlenecks. WRED can selectively discard lower priority
traffic when an interface begins to get congested. It can also
provide differentiated performance characteristics for
different classes of service.
Congestion
management
Weighted fair queuing
(WFQ). Packet classes
are differentiated based
on bandwidth and
bounded delay.
WFQ is an automated scheduling system that provides fair
bandwidth allocation to all network traffic. WFQ classifies
traffic into conversations and uses weights (priorities) to
determine how much bandwidth each conversation is
allocated, relative to other conversations.