ISC2 CC Network Security Practice Question
Which transport layer protocol is used by voice over IP (VoIP) applications that require low latency and can tolerate some packet loss?
⚠ Common exam trap
The trap is equating reliability with quality—candidates pick TCP because it is 'reliable,' but for real-time voice, reliability via retransmission is actually harmful, and UDP's speed and loss tolerance win.
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
✓
UDP
UDP is connectionless and has no retransmission, ordering, or congestion-control overhead, which minimizes latency—exactly what VoIP needs. It tolerates some packet loss because voice codecs can interpolate or conceal minor gaps, and retransmitting lost voice packets would arrive too late to be useful anyway.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ICMP
Why it's wrong here
ICMP is a network-layer control and error-reporting protocol, not a transport protocol, and carries no ports or sessions for voice streams. It is tempting because ping tests often verify VoIP path quality, but ICMP would be the right tool for reachability diagnostics, not for carrying real-time audio.
- ✗
SCTP
Why it's wrong here
SCTP is a transport protocol offering multi-streaming and multi-homing, but VoIP endpoints and gateways almost universally use RTP over UDP, and SCTP support is rare in voice stacks. It would suit telephony signalling transport in some carrier networks, not the media stream itself.
- ✗
TCP
Why it's wrong here
TCP's retransmission and congestion control introduce delay and jitter when packets are lost, which voice cannot tolerate. It is tempting because TCP guarantees delivery, but that guarantee is exactly the problem for real-time audio; TCP suits file transfers and web traffic where reliability outweighs latency.
- ✓
UDP
Why this is correct
UDP is connectionless and omits retransmission, handshaking and ordering overhead, so it delivers the low latency VoIP requires. Its tolerance of packet loss suits real-time voice, where retransmitting delayed packets would harm call quality more than dropping them.
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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 ISC2 exam blueprint
This CC practice question is part of Courseiva's free ISC2 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 CC exam.