Cisco 10000 Series Configuration Manual page 707

Chapter 19 Configuring Quality of Service for PVC Bundles
ATM PVC Selection
Figure 19-2 ATM VC Bundle
VC 1
IP
Precedence
ATM PVC bundle management allows you to define an ATM PVC bundle and add PVCs to it. Each PVC
of a bundle has its own ATM traffic class and ATM traffic parameters. You can apply attributes and
characteristics to discrete PVC bundle members or you can apply them collectively at the bundle level.
Using PVC bundles, you can create differentiated service by flexibly distributing IP precedence levels
or Multiprotocol Label Switching (MPLS) experimental (EXP) levels over the different PVC bundle
members. You can map a single level or a range of levels to each discrete PVC in the bundle, thereby
enabling individual PVCs in the bundle to carry packets marked with different precedence or MPLS EXP
levels. You can use weighted random early detection (WRED) to further differentiate service across
traffic that has different IP precedence or MPLS EXP levels, but that uses the same PVC in a bundle.
To determine which PVC in the bundle to use to forward a packet to its destination, the ATM PVC bundle
management software matches precedence levels or MPLS EXP levels between packets and PVCs (see
Figure 19-3). IP traffic is sent to the next hop address for the bundle because all PVCs in a bundle share
the same destination, but the PVC used to carry a packet depends on the value set for that packet in the
IP precedence bits or the MPLS EXP bits of the type of service (ToS) byte of its header. The ATM PVC
bundle management software matches the IP precedence or MPLS EXP level of the packet to the IP
precedence or MPLS EXP value or range of values assigned to a PVC, sending the packet out on the
appropriate VC.
The ATM PVC bundle management software also allows you to configure how traffic is redirected when
the PVC the packet was matched to goes down. Figure 19-3 shows how the ATM PVC bundle
management software determines which PVC bundle member to use to carry a packet and how WRED
is used to differentiate traffic on the same VC. In the figure PVC selection is based on IP precedence
levels, but it can also be based on MPLS EXP levels.
Cisco 10000 Series Router Quality of Service Configuration Guide
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