Click the exhibit button below. A network operator has configured a network-queue policy to map forwarding classes to queues, as shown in the exhibit below. Based on the default scheduling behavior…

The correct answer is D. In-profile EF packets, then in-profile H2 and AF packets, then out-of-profile H2, AF and BE. Option D is correct because the Alcatel-Lucent 7750 SR default scheduling gives strict priority to in-profile EF packets alone first - EF is an expedited queue serviced before everything else. Next, in-profile H2 and AF are serviced together (weighted). Finally, out-of-profile…

Scheduling

Question

Click the exhibit button below. A network operator has configured a network-queue policy to map forwarding classes to queues, as shown in the exhibit below. Based on the default scheduling behavior of the Alcatel-Lucent 7750 SR, in which order will packets be serviced?

Exhibit

Options

AAll in-profile packets in round-robin, then all out-of-profile packets in biased round-robin.
BIn-profile EF packets, then in-profile H2 packets, then in-profile AF packets, then out-of- profile EF
CIn-profile EF, H2 and AF packets, then out-of-profile H2, AF and BE packets in biased round-
DIn-profile EF packets, then in-profile H2 and AF packets, then out-of-profile H2, AF and BE
EIn-profile EF and H2 packets, then in-profile AF packets, then out-of-profile H2, AF and BE

How the community answered

(30 responses)

A
13% (4)
B
3% (1)
C
7% (2)
D
77% (23)

Explanation

Option D is correct because the Alcatel-Lucent 7750 SR default scheduling gives strict priority to in-profile EF packets alone first - EF is an expedited queue serviced before everything else. Next, in-profile H2 and AF are serviced together (weighted). Finally, out-of-profile H2, AF, and BE are serviced as the lowest-priority group. Crucially, out-of-profile EF packets are dropped by default on the 7750 SR, so EF never appears in the out-of-profile service tier.

Why the distractors fail:

A is wrong because EF gets strict priority, not round-robin - treating all in-profile traffic equally ignores the EF queue's elevated status.
B is wrong because it sequences H2 and AF separately and includes "out-of-profile EF," which the 7750 SR drops by default rather than services.
C is wrong because it groups EF with H2 and AF in the first tier - EF must be serviced alone before the other in-profile classes.
E is wrong because it groups EF together with H2 in the first tier for the same reason - EF always stands alone with strict priority.

Memory tip: Use the acronym "EF Stands Alone" - Expedited Forwarding is the only class serviced in its own strict-priority tier, and its out-of-profile traffic is simply dropped (no out-of-profile EF ever gets scheduled). Everything else falls into in-profile middle-tier or out-of-profile last-tier.

Topics

#Queue Scheduling#QoS Priorities#Forwarding Classes#Profile-based Queueing

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