VoIP (Voice over Internet Protocol) is a set of technologies that carry voice calls as streams of small IP packets instead of over dedicated circuit-switched telephone lines. A codec digitizes and compresses the audio, signaling sets up the call, and the packets travel over the same networks as other data.
Why it matters
VoIP replaced most business telephone systems and underpins many consumer calling apps. It is cheaper for long distance and lets one connection carry many calls. But voice is unusually sensitive to network quality: delay above roughly 150 ms one way, jitter, and packet loss are directly audible as echo, robotic sound or dropped words.
Example
A desk phone registers with a provider using SIP. When you dial, SIP negotiates the call, then audio flows as RTP packets, typically one every 20 ms. With the G.711 codec this uses about 64 kbit/s of audio plus packet overhead, around 80 to 90 kbit/s each direction on the wire.
Common mistakes
- Running VoIP over a congested link without QoS prioritization.
- Blocking or rewriting SIP and RTP ports in a firewall or NAT device, causing one-way audio.
- Ignoring power: unlike analog lines, IP phones stop working in a power cut unless backed up.
Related
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