Nokia 7705 - 3.2.3.3 4-Priority Scheduling

Quality of Service Guide QoS and QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 79
4. If a packet arrives at any of the queues marked for Expedited scheduling while
the scheduler is servicing a packet from a Best Effort queue, the Best Effort
scheduler finishes servicing the current packet and then the Expedited
scheduler immediately activates to service the packet in the Expedited queue. If
there are no other packets to be serviced in any of the Expedited queues, the
Best Effort scheduler resumes servicing the packets in the Best Effort queues.
If the queues are configured according to the tables and defaults described in
this guide, CoS-4 will be scheduled prior to CoS-1 among queues marked as
Best Effort.
5. After one cycle is completed across all the queues marked as Best Effort, the
next pass is started until all the packets in all the queues marked as Best Effort
are serviced, or a packet arrives to a queue marked as Expedited and is serviced
as described in step 2.
3.2.3.3 4-Priority Scheduling
4-priority scheduling combines profiled scheduling and queue-type scheduling and
applies the combination to all of the access ingress queues. The profile and
queue-type schedulers are combined and applied to all the queues to provide
maximum flexibility and scalability that meet the stringent QoS requirements of
modern network applications. See Profiled (Rate-based) Scheduling and
Queue-Type Scheduling for information on these types of scheduling.
Packets with a flow rate that is less than or equal to the CIR value of a queue are
scheduled as in-profile. Packets with a flow rate that exceeds the CIR value but is
less than the PIR value of a queue are scheduled as out-of-profile.
The scheduling cycle for 4-priority scheduling of CoS queues is shown in Figure 16.
The following basic steps apply:
1. In-profile traffic from Expedited queues is serviced in round-robin fashion up to
the CIR value. When a queue exceeds its configured CIR value, its state is
changed to out-of-profile.
2. Once all of the in-profile packets from the Expedited queues are serviced,
in-profile packets from Best Effort queues are serviced in a round-robin fashion
until the configured CIR value is exceeded. When a queue exceeds its
configured CIR value, its state is changed to out-of-profile.
3. Once all of the in-profile packets from the Best Effort queues are serviced,
out-of-profile packets from Expedited queues are serviced in a round-robin
fashion.
4. Once all of the out-of-profile packets from the Expedited queues are serviced,
the out-of-profile packets from the Best Effort queues are serviced in a
round-robin fashion.