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220-1201 A company deploys a new VoIP phone system Practice Question
A company deploys a new VoIP phone system. Users report that calls are choppy and sometimes drop. The network uses a single flat subnet with no QoS. What is the most likely cause?
⚠ Common exam trap
The trap is that candidates chase physical-layer causes (cabling, duplex) or DNS, but the scenario explicitly states 'no QoS' — the exam expects you to connect real-time voice sensitivity to the absence of prioritization.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
There is no Quality of Service (QoS) configured.
VoIP is real-time and delay-sensitive, so without QoS, voice packets compete equally with bulk data and suffer jitter, latency, and packet loss that manifest as choppy audio and dropped calls. QoS marking (DSCP EF for voice) and priority queuing on switches and routers ensure voice traffic is serviced first. On a flat subnet with no QoS, congestion directly degrades call quality.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The VoIP phones have incorrect DNS settings.
Why it's wrong here
Incorrect DNS settings would prevent the VoIP phone from resolving the hostname of its SIP server or call manager into an IP address. This critical failure means the phone cannot register with the system or initiate any calls whatsoever. Choppy audio, however, indicates that a call has already been successfully established and is actively transmitting voice data, implying that initial server resolution and registration were successful.
- ✗
The switch ports are set to half-duplex.
Why it's wrong here
Setting switch ports to half-duplex forces devices to transmit or receive data, but not both simultaneously, leading to frequent collisions when both ends attempt to communicate. While collisions cause significant retransmissions and degraded performance, which could manifest as choppy audio, modern network devices and VoIP systems almost universally operate in full-duplex mode. This misconfiguration is less common than network congestion or lack of QoS as a primary cause for intermittent choppy audio in a newly deployed system.
- ✓
There is no Quality of Service (QoS) configured.
Why this is correct
Without Quality of Service (QoS) configured, real-time voice packets are treated with the same priority as all other data traffic on the network. This means voice packets can be delayed or dropped when competing with less time-sensitive data, especially during periods of network congestion. The resulting latency, jitter, and packet loss are precisely what cause the characteristic choppy audio and dropped calls experienced in VoIP systems.
- ✗
The Ethernet cables are Cat5 instead of Cat6.
Why it's wrong here
Standard Cat5 Ethernet cables are fully capable of supporting Fast Ethernet (100 Mbps) and often Gigabit Ethernet (1000 Mbps) over typical office distances, providing ample bandwidth for multiple concurrent VoIP calls. A single VoIP call typically requires less than 100 kbps of bandwidth, making Cat5 more than sufficient for the data rate. Therefore, the cable category itself is highly unlikely to be the cause of choppy audio, which points more towards network congestion or prioritization issues rather than insufficient physical layer capacity.
Visual reference
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Related to this question
Learn chapter
Troubleshoot: Audio Issues
Key term
Voice over IP
Voice over IP (VoIP) is a technology that lets you make phone calls using an internet connection instead of a traditional telephone line.
Key term
Packet
A packet is a small unit of data that is sent over a network, containing both the actual data and control information for delivery.
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Same concept, more angles
1 more way this is tested on 220-1201
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A customer complains that their VoIP phone intermittently drops calls and has poor audio quality. The phone is connected to a switch port that also carries data traffic for a nearby workstation. What is the most likely cause?
medium- A.The switch port is set to half-duplex.
- B.The network cable is too long.
- ✓ C.Quality of Service (QoS) is not configured on the switch port.
- D.The phone’s firmware is outdated.
Why C: QoS is the most likely cause because VoIP traffic is highly sensitive to latency, jitter, and packet loss, and when voice and data share a switch port without QoS, data bursts can delay or drop voice packets. Configuring QoS (e.g., LLQ or priority queuing) ensures voice RTP packets are marked EF (DSCP 46) and serviced ahead of best-effort data. This directly addresses the intermittent call drops and poor audio quality described.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.