Service egress QoS policies

Service egress queues are implemented at the transition from the service core network to the service access network. The advantages of per-service queuing before transmission into the access network are:

• per-service egress subrate capabilities especially for multipoint services

• more granular, fairer scheduling per-service into the access network

• per-service statistics for forwarded and discarded service packets

The subrate capabilities and per-service scheduling control are required to make multiple services per physical port possible. Without egress shaping, it is impossible to support more than one service per port. There is no way to prevent service traffic from bursting to the available port bandwidth and starving other services.

For accounting purposes, per-service statistics can be logged. When statistics from service ingress queues are compared with service egress queues, the ability to conform to per-service QoS requirements within the service core can be measured. The service core statistics are a major asset to core provisioning tools.

Service egress QoS policies define egress queues and map forwarding class flows to queues. In the simplest service egress QoS policy, all forwarding classes are treated like a single flow and mapped to a single queue. To define a basic egress QoS policy, the following are required:

• a unique service egress QoS policy ID

• a QoS policy scope of template or exclusive

• at least one defined default queue

Optional service egress QoS policy elements include:

• additional queues up to a total of eight separate queues (unicast)

• dot1p/DE, DSCP, and IP precedence remarking based on forwarding class

Each queue in a policy is associated with one of the forwarding classes. Each queue can have its individual queue parameters allowing individual rate shaping of the forwarding classes mapped to the queue.

More complex service queuing models are supported in the router where each forwarding class is associated with a dedicated queue.

The forwarding class determination per service egress packet is determined either at ingress or egress. If the packet ingressed the service on the same router, the service ingress classification rules determine the forwarding class of the packet. If the packet is received on a network interface, the forwarding class is marked in the tunnel transport encapsulation. In each case, the packet can be reclassified into a different forwarding class at service egress.

Service egress QoS policy ID 1 is reserved as the default service egress policy. The default policy cannot be deleted or changed. The default access egress policy is applied to all SAPs that do not have another service egress policy explicitly assigned. Table: Default service egress policy ID 1 definition lists the characteristics of the default policy.