Which two QoS features can be adjusted to improve voice traffic performance on an Aruba CX switch? (Select two)

To improve the performance of real-time, latency-sensitive traffic like voice, a two-step Quality of Service (QoS) process is typically used. First, the traffic must be identified and classified. DSCP marking (D) is a standard method for this, where voice packets are marked with a specific Differentiated Services Code Point value (e.g., EF - Expedited Forwarding) in the IP header. Second, once the traffic is classified, a policy is applied to give it preferential treatment. Priority queuing (A), also known as Strict Priority, is a scheduling mechanism that services the queue containing voice packets before all other lower-priority queues. This ensures voice traffic experiences minimal delay and jitter as it transits the switch.

B. Weighted Random Early Detection (WRED): WRED is a congestion avoidance mechanism that randomly drops packets from TCP flows to prevent queue exhaustion; it is unsuitable for UDP-based voice traffic, where packet loss is highly detrimental.
C. VLAN load balancing: This is a traffic engineering feature used to distribute traffic across multiple links, typically in a link aggregation group or via MSTP. It does not prioritize specific packet types within a single data flow.

1. ArubaOS-CX 10.12 Quality of Service Guide

Page 9

"QoS overview".

Quote/Concept: "The first step in configuring QoS is to classify the traffic to identify traffic to which QoS policies will be applied. Classification can be based on different criteria... Differentiated Services Code Point (DSCP) value in the IP packet header." This supports DSCP marking (D) as the classification method.

2. ArubaOS-CX 10.12 Quality of Service Guide

Page 10

"QoS queuing and scheduling".

Quote/Concept: "ArubaOS-CX switches support the following scheduling profiles: Strict Priority (SP) and Deficit Weighted Round Robin (DWRR)... The strict priority scheduler services queues in order from highest priority to lowest priority." This supports Priority queuing (A) as the mechanism for giving preferential treatment to classified traffic like voice.

3. ArubaOS-CX 10.12 Quality of Service Guide

Page 11

"Congestion control".

Quote/Concept: "WRED is a mechanism to avoid congestion in TCP networks... WRED is not recommended for queues that carry loss-sensitive traffic or traffic that is not TCP-based

such as voice." This confirms why WRED (B) is incorrect for voice traffic.