Wi-Fi Multicast Traffic Reliability Metric
Short answer
B Packet error rate indicates an issue with Wi-Fi multicast traffic reliability due to the lack of MAC-layer retransmissions.
Question
Key Takeaways
The question tests the unique MAC-layer behavior of 802.11 multicast frames; the common trap is assuming throughput is the primary bottleneck for video reliability.
Wi-Fi multicast traffic lacks link-layer acknowledgments, leading to dropped frames that cannot be retransmitted. This page establishes that packet error rate is the key indicator of unreliable Wi-Fi multicast compared to wired networks.
Common mistake: Choosing throughput (C) because video requires high bandwidth, but reliability issues (dropped frames) are specifically indicated by packet error rate due to the lack of MAC-layer retransmissions for multicast.
Expert Analysis
Why the Answer Is Correct
Packet error rate (PER) is the definitive metric for unreliable Wi-Fi multicast traffic. Unlike unicast frames, 802.11 multicast and broadcast frames are transmitted without Request-to-Send/Clear-to-Send (RTS/CTS) protection and without Acknowledgments (ACKs). Because the access point never receives an ACK, it cannot retransmit lost multicast frames at the MAC layer, leading directly to a high packet error rate when collisions or interference occur.
Why the Other Options Are Wrong
Throughput (C) measures the volume of data successfully delivered over time, but it does not directly measure reliability or packet loss; a network can have high throughput yet still drop critical multicast packets. Latency (D) and jitter (A) are timing metrics. Because multicast frames are not retransmitted, their latency and jitter might actually be lower than unicast traffic that requires retransmissions, even though the stream becomes unreliable due to missing frames.
Community Comment Notes
Some learners argue for throughput, as Bandito noted: "If the coverage is good, than I suggest, there is not enough throughput." However, others correctly identify that interference causes packet errors without retransmission, as 55f2ace explained: "A source of interference can cause packet errors that interrupt a voice or video stream." Rododendron2 also supports this by pointing out that "foreign interference and packer errors" are the real-world culprits for multicast unreliability.
Exam Strategy
When evaluating multicast reliability over Wi-Fi, always remember that 802.11 multicast lacks MAC-layer ACKs and retransmissions. Focus on metrics that reflect frame loss (packet error rate) rather than bandwidth (throughput) or timing (latency/jitter).
Community Votes
50% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 4 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 4
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Bandito 👍 4 Answered CIf the coverage is good, than I suggest, there is not enough throughput.
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Jonycici 👍 2 Answered BThroughput is indeed an important performance metric, but it doesn’t specifically indicate issues with multicast traffic reliability.
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55f2ace 👍 1 Answered BA source of interference can cause packet errors that interrupt a voice or video stream. As packets are lost, they can be retransmitted and delayed, increasing latency and jitter. Other factors like poor radio frequency (RF) coverage, high channel utilization, and excessive collisions can also impede good data throughput and integrity.
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Rododendron2 👍 1 Answered BB) packet error rate is my choice here ... if wifi network is designed for video over wifi, it shall be designed as well for throughput... and wifi throughput is really rarely issue ... so in real world more likely foreign interference and packer errors
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