220-1101 Question 448
Single answerJitterA small office reports that cloud-based VoIP calls sound choppy and words sometimes arrive out of order, especially in the afternoon when large file uploads are running. A technician tests the network and finds that average bandwidth is sufficient and packet loss is minimal, but packet arrival times vary significantly. Which issue is MOST likely causing the voice quality problem?
- A
High jitter on the network connection
- B
Incorrect DNS resolution for the VoIP server
- C
A duplex mismatch causing complete network failure
- D
Insufficient storage space on the users' workstations
Show answer and explanation
Correct answer: A
Explanation
The key clue is that bandwidth is sufficient, packet loss is minimal, and packet arrival times vary significantly. That combination indicates jitter, which is a common cause of poor-quality VoIP and video conferencing performance on busy networks. In practice, jitter often increases during congestion, such as when large uploads compete with time-sensitive traffic. CompTIA A+ Core 1 expects candidates to recognize common network symptoms and match them to the correct issue. Best practices for reducing jitter include prioritizing voice traffic with QoS, reducing network congestion, and using stable wired connections where possible. General networking guidance from vendors such as Cisco and Microsoft consistently identifies low latency, low packet loss, and low jitter as important requirements for real-time voice traffic.
- A. Correct.
Correct. Jitter is the variation in packet arrival time. Real-time applications such as VoIP are especially sensitive to inconsistent packet timing because audio packets must arrive in a steady sequence to be played back smoothly. Even when bandwidth is adequate and packet loss is low, high jitter can cause choppy audio, gaps, and out-of-order voice delivery.
- B. Incorrect.
Incorrect. DNS resolution problems would more likely prevent the VoIP client from connecting to the service or cause intermittent registration issues, not specifically create choppy audio during active calls when packet timing is the measured problem.
- C. Incorrect.
Incorrect. A duplex mismatch can create collisions, retransmissions, and poor performance, but the option states it is causing complete network failure, which does not match the scenario. The network is still functioning, and the test results specifically point to variable packet timing rather than a total link outage.
- D. Incorrect.
Incorrect. Workstation storage capacity does not affect packet arrival timing across the network in a way that would explain VoIP audio breaking up during periods of network congestion. This is a plausible distractor for general performance issues, but it is not relevant to jitter.