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
Requirements for MPLS CoS
To use the MPLS CoS feature, your network must run these Cisco IOS features:
• CEF switching in every MPLS-enabled router
• MPLS
• ATM functionality
Also, the IGX must have:
• Appropriate switch software associated with Cisco IOS software
• Appropriate firmware loaded in the associated UXM cards
Tip For information on switch software, Cisco IOS software, and card firmware compatibility, see the
Compatibility Matrix at http://www.cisco.com/kobayashi/sw-center/sw-wan.shtml.
MPLS CoS in an IP+ATM Network
In IP+ATM networks, MPLS uses predefined sets of labels for each service class, so switches
automatically know which traffic requires priority queuing. A different label is used per destination to
designate each service class (see Figure 10-8).
There can be up to four labels per IP source-destination. Using these labels, core LSRs implement
class-based WFQ to allocate specific amounts of bandwidth and buffer to each service class. Cells are
queued by class to implement latency guarantees.
On a Cisco IP+ATM LSR, the weights assigned to each service class are relative, not absolute. The
switch can therefore borrow unused bandwidth from one class and allocate it to other classes according
to weight. This scenario enables very efficient bandwidth utilization. The class-based WFQ solution
ensures that customer traffic is sent whenever unused bandwidth is available, whereas ordinary ATM
VCs drop cells in oversubscribed classes even when bandwidth is available.
Figure 10-8 Multiple LVCs for IP QoS Services
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CAR:
bandwidth
policy
CAR:
packet
classification
WRED
43
44
45
46
Class-based
queuing
Edge router ATM core
Discard packets
that exceed
CAR limits
Discard packets
that exceed
WRED limits
Packet
Packet Packet Packet
MPLS ATM LSR
Applies queuing,
bw control, and
other ATM CoS
differentiated
services
ATM cells, up
to four labels per IP
source-destination,
corresponding
to four CoS
Cisco IGX