4A0-107 practice question 29 of 30

A physical port has three associated buffer pools. Which of the following buffer pool combinations is associated to a physical port?

Full set: 231 questions
Answer options
A: Access ingress, access egress, network egress Correct answer
B: Access ingress, network ingress, network egress
C: Port ingress, port egress, shared bi-directional
D: Port ingress, port egress, network egress
E: Port ingress, network ingress, network egress
Correct Answer:
A. Access ingress, access egress, network egress
Explanation

On Nokia SR OS platforms, buffer memory on a Media Dependent Adapter (MDA) is, by default, divided into three distinct pools. Since a physical port is located on an MDA, it is associated with these pools. The three pools are:
1. Access Ingress Pool: Used for traffic entering the system via ports configured in access mode.
2. Access Egress Pool: Used for traffic exiting the system via ports configured in access mode.
3. Network Pool: A combined pool for both ingress and egress traffic on ports configured in network mode. Within QoS policies, the egress portion of the Network Pool is specifically managed and referred to as the network egress pool. Therefore, the combination that correctly identifies these three fundamental buffer pools is access ingress, access egress, and network egress.

Why Incorrect

B. A single port cannot be associated with both access and network ingress pools simultaneously, as its mode is either access or network.
C. This uses generic terminology. SR OS buffer management is specifically defined by "access" and "network" port modes and their corresponding pools.
D. This uses generic, non-specific terminology and does not accurately reflect the three distinct buffer pools (access ingress, access egress, network) on an MDA.
E. This mixes generic ("Port ingress") and specific ("network ingress") terms in an inconsistent and incorrect combination.

References

1. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "Buffer Management", Subsection: "Buffer pools".

Quote/Concept: This section explicitly states, "By default, three buffer pools are created on each MDA: an access ingress pool, an access egress pool, and a network pool. The network pool is used for both ingress and egress traffic on network ports." This establishes the three-pool model.

2. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "Network QoS Policies", Subsection: "Network Queue Policy".

Quote/Concept: This section clarifies the terminology for the network pool's egress function: "The egress queues draw buffers from the network egress buffer pool." This justifies the use of "network egress" in the correct answer to represent the third pool.

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