Service egress queues are implemented at the transition from the service core network to the service access network on access SAPs. The advantages of per-service queuing before transmission into the access network are the following:
per-service egress sub-rate capabilities
more granular, fairer scheduling per-service into the access network
per-service statistics for forwarded and discarded service packets
The sub-rate capabilities and per-service scheduling control are required to make multiple services per physical port possible. With egress shaping, it is possible to support more than one service per port. It prevents traffic from single service 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.
Service egress QoS policies define egress queues and map FC flows to queues. In the simplest service egress QoS policy, all FCs are treated like a single flow and mapped to a single queue.
Service egress QoS policies also define egress queues, shaping, scheduling, and remarking behavior for SAPs configured on hybrid ports. The QoS behavior for SAPs configured on hybrid ports is the same as for access SAPs configured on access ports.
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 the following:
additional queues up to a total of eight separate queues. An FC queue is shared by unicast and multipoint (BUM) traffic types mapped to that FC.
IEEE 802.1p priority value remarking based on FC
option to use IP DSCP values for marking based on FC
Each queue in a policy is associated with one of the FCs. Each queue can have individual queue parameters, allowing individual rate shaping of the FCs mapped to the queue. More complex service queuing models are supported in the router where each FC is associated with a dedicated queue. The FC per service egress packet is determined at ingress. If the packet ingressed the service on the same router, the service ingress classification rules determine the FC of the packet. If the packet is received, the FC is marked in the tunnel transport encapsulation (for example, QinQ encapsulated packet).