When using an egress port scheduler, on which scheduling loop are orphaned queues serviced?

The Nokia 7x50 egress port scheduler uses a multi-pass process. The first two passes service user-configured queues: first, all queues operating within their Committed Information Rate (CIR), and second, all queues operating between their CIR and Peak Information Rate (PIR). Orphaned queues, which handle unclassified traffic such as routing protocols, are serviced in a separate, third pass. This pass occurs only after all configured queues have been serviced up to their PIR. The system uses a dedicated, high-priority scheduler at Level 8 for these orphaned queues to ensure critical control plane traffic is handled effectively.

A. Level 8 within CIR. This is incorrect. Orphaned queues are serviced in a distinct pass after the CIR and PIR passes for all other queues are complete.
B. Level 8 between CIR and PIR. This is incorrect. The pass for orphaned queues happens only after the "between CIR and PIR" pass has finished for all configured queues.
D. Level 1 within CIR. This is incorrect. Orphaned queues are serviced at the highest priority (Level 8), not the lowest, and it occurs after the main scheduling passes.
E. Level 1 between CIR and PIR. This is incorrect. The priority level is wrong (it's Level 8), and the scheduling pass is also incorrect.
F. Level 1, once all PIR is serviced. This is incorrect. While the timing is partially right (after PIR is serviced), the priority level is wrong. Orphaned queues use Level 8.

1. Nokia 7750 SR OS Services Architecture Guide, Release 21.10.R1, Part: Quality of Service.

Section: Port Scheduler Policies > Port Scheduler Operation: This section details the scheduling mechanism. It states, "The port scheduler allocates bandwidth to the orphan queues after the CIR and PIR passes of the port scheduler are complete. The orphan queues are served by a high-priority scheduler at priority level 8." This directly supports that orphaned queues are serviced at Level 8 after all PIR has been serviced.

2. Nokia Quality of Service Courseware (4A0-107 Student Guide).

Module: Egress Queuing and Scheduling: The official course material describes a three-pass scheduling process. It explicitly outlines the CIR pass (Levels 8-1), the PIR pass (Levels 8-1), and a final, third pass dedicated to the orphan queues, which are mapped to a scheduler at priority Level 8. This confirms the sequence and priority level described in the correct answer.