What does VoIP stand for?
VoIP stands for Voice over Internet Protocol. Carrying phone calls as IP packets instead of over circuit-switched lines. Calls are set up with SIP and the voice travels in RTP; they are sensitive to latency and jitter, so QoS and often a separate voice VLAN are standard.
VoIP carries telephone calls as data packets on an IP network instead of on dedicated telephone lines. Two things travel separately. Signalling, usually SIP, sets the call up: it finds the other party, makes the phone ring and agrees how the audio will be encoded. The audio itself then flows as a stream of small RTP packets. Voice tolerates very little delay, or variation in delay, so networks give it priority with QoS and often place the phones in a voice VLAN of their own.
VoIP in practice: an example
An office moves its desk phones onto the data network. Calls sound fine until the nightly backup starts, when voices break up. The switches were treating voice packets like any other traffic. After the phones are moved to a voice VLAN and QoS marks their packets for priority, calls stay clear during the backup.
What VoIP is confused with
VoIP vs SIP: what is the difference?
VoIP is the whole idea of voice on IP networks. SIP is one protocol inside it, the one that sets up and ends calls. The audio travels in RTP.
VoIP vs PSTN: what is the difference?
The public switched telephone network is the traditional telephone system, which reserves a circuit for each call. VoIP sends the same call as packets over a shared data network, and gateways connect the two.
Which exams cover VoIP?
VoIP is on the official CompTIA acronym list for two of the four exams covered here.
- Network+ N10-009: on the acronym list, not tied to one objective. Listed there as “Voice over IP”.
- A+ 220-1201 and 220-1202: 220-1201 5.0 (Hardware and Network Troubleshooting).
Each number is a CompTIA exam objective and the name in brackets is its domain. The exam puts the term in a scenario; it does not ask you to recite the expansion.
Check yourself: two practice questions
Written by CertSprint for this page. They are not taken from any exam.
1. Callers on a VoIP system hear choppy audio whenever large file transfers run. Which network feature addresses this?
- Quality of service that prioritizes voice traffic
- A longer DHCP lease
- A larger DNS cache
- Disabling spanning tree
Show the answer
A. Quality of service that prioritizes voice traffic. Voice needs low delay and jitter. QoS lets switches and routers forward voice packets ahead of bulk traffic when a link is busy.
2. In a VoIP call, which protocol carries the voice itself?
- RTP
- SIP
- DNS
- SNMP
Show the answer
A. RTP. SIP only sets the call up and ends it. The audio is carried in Real-time Transport Protocol packets.
Sources: NIST SP 800-58, Security Considerations for Voice Over IP Systems; RFC 3261: SIP: Session Initiation Protocol; RFC 3550: RTP: A Transport Protocol for Real-Time Applications. The acronym and its expansion come from CompTIA's official acronym lists, linked from each exam glossary above. The explanation, example and questions are CertSprint's own, checked against these sources on 12 November 2026.