Service Egress QoS Policies

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

• per-service egress shaping, soft-policing capabilities

• more granular, more fair 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 network can be measured. The service network statistics are a major asset to network provisioning tools.

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

To define a basic service 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. The parameters that can be configured for a queue are discussed in Network and Service QoS Queue Parameters.

Optional service egress QoS policy elements include:

• additional queues, up to a total of eight separate queues

• dot1p priority and DSCP value re-marking based on forwarding class

Each queue in a policy is associated with one or more of the supported 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 7705 SAR where each forwarding class is associated with a dedicated queue.

The forwarding class determination per service egress packet is determined at ingress. If the packet ingressed the service on the same 7705 SAR router, the service ingress classification rules determine the forwarding class of the packet. If the packet was received over a service transport tunnel, the forwarding class is marked in the tunnel transport encapsulation.

Service egress QoS policy ID 1 is reserved as the default service egress policy. The default policy cannot be deleted or changed.

The default service egress policy is applied to all SAPs that do not have another service egress policy explicitly assigned. The characteristics of the default policy are listed in Table: Default Service Egress Policy ID 1 Definition .