Atm Pvc Selection - Cisco 10000 Series Configuration Manual

ATM PVC Selection

ATM PVC Selection
The Cisco 10000 series router can forward packets to ATM bundle members based on the IP precedence
level or Multiprotocol Label Switching (MPLS) experimental (EXP) level of the packets.
The ATM PVC Bundle Enhancement—MPLS EXP-Based PVC Selection feature allows you to
configure multiple PVCs with different QoS characteristics between any pair of ATM-connected routers
and to configure a group of ATM PVCs with a single next-hop address. Packets are mapped to specific
PVCs in the bundle on the basis of the precedence value or MPLS EXP value in the type of service (ToS)
field of the IP header. Each packet is treated differently according to the QoS configured for each PVC.
The MPLS EXP-Based PVC Selection feature provides flexible PVC management within a PVC bundle
by allowing traffic assigned to a failed PVC to be redirected to an alternate PVC within the bundle. It
also allows you to configure the bundle to go down when certain PVCs go down. IP packets carrying
different types of traffic can be transported on different PVCs within the same PVC bundle.
Using MPLS-based ATM PVC selection, you can do the following:
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The Cisco 10000 series router forwards non-IP packets using the PVC that is responsible for carrying
precedence level 6 traffic. The router uses process-switching to forward locally generated packets as
follows:
1.
2.
3.
4.
Cisco 10000 Series Router Quality of Service Configuration Guide
19-4
Map a single precedence level or MPLS EXP level, or a range of precedence or MPLS EXP levels,
to each PVC in the bundle. This enables you to limit an individual PVC to carry only packets marked
with a specific precedence or MPLS EXP level, or packets marked with different precedence or
MPLS EXP levels. For unlabeled packets that do not specify a selection criteria, the router uses IP
precedence level as the default selection criteria for packet forwarding.
Configure a PVC to support unmapped traffic. If the PVC fails, the router attempts to identify an
alternate PVC. If the router cannot locate an alternate PVC, the router stops the PVC bundle.
Create differentiated service using PVC bundles by distributing MPLS EXP levels over the different
PVC bundle members.
Use Weighted Random Early Detection (WRED) to further differentiate service across traffic that
has different MPLS EXP levels.
To determine which PVC in a bundle is used to forward a specific type of traffic, the
ATM VC bundle management software matches MPLS EXP levels between packets and PVCs.
Because all PVCs in a bundle share the same destination, the router forwards IP traffic to the next
hop address for the bundle, but the PVC used to carry a packet depends on the value set for that
packet in the MPLS EXP level of the type of service (ToS) byte of its header.
The ATM PVC bundle management software matches the MPLS EXP level of the packet to the
MPLS EXP levels assigned to a PVC and sends the packet out on the appropriate PVC. The
ATM PVC bundle management software also allows you to configure how traffic is redirected if a
PVC goes down.
MPLS EXP-based PVC selection maps the IP precedence level in the IPv4 header to a PVC
configured with the same value. The three precedence bits in the type of service (ToS) byte of the
IP header defines the precedence levels for IP traffic. You can use a default PVC for all unspecified
precedence levels.
After you define an ATM bundle and add PVCs to it, you can configure attributes and characteristics
to discrete PVC bundle members, or you can apply them collectively at the bundle level. You can
apply ATM traffic shaping to each PVC within a bundle.
Chapter 19 Configuring Quality of Service for PVC Bundles
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