The default scheduler on a Nokia 7750 SR is a two-tier hierarchical scheduler. It separates traffic into expedited and best-effort classes. Expedited queues (NC, H1, EF, H2) are serviced with strict priority over best-effort queues (L1, AF, L2, BE).

Therefore, the H1 forwarding class, being expedited, will always have its Committed Information Rate (CIR) serviced before any traffic from the best-effort AF queue is processed.

Furthermore, queues have a defined type. By default, the AF queue is a 'best-effort' type. If a network administrator decides to forward EF traffic to this queue, the queue itself will not automatically gain expedited status. It must be explicitly re-configured as an 'expedite' queue to be serviced by the high-priority scheduler.

A. The default scheduler is a two-tier hierarchical model using strict priority for expedited queues and weighted scheduling for best-effort queues, not a single-level round-robin algorithm.

B. The scheduler does not spend an equal amount of time per queue. Expedited queues are always serviced before best-effort queues, violating the principle of equal time.

D. Unclassified traffic is mapped into the Best Effort (BE) forwarding class and its corresponding queue. The BE queue itself does not schedule other "orphaned" queues.

1. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "Hierarchical Scheduling". This section details the two-tier scheduling hierarchy, stating, "The expedited scheduler queues are always served before the best-effort scheduler queues." This directly supports the reasoning for answer C.

2. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "Queue Parameters", Subsection: "Queue-Type". This subsection explains the expedite and best-effort queue types. It clarifies that a queue's type determines its scheduling priority. To change a queue from best-effort (like the default AF queue) to expedited, explicit configuration is required, which supports answer E.

3. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "Default SAP QoS Policy", Subsection: "Default Forwarding Classes and Queues". This section lists the default classification of H1 as an expedited class and AF as a best-effort class, providing the foundational information for answer C. It also shows that the default scheduling is not a simple round-robin, invalidating options A and B.