What is VoIP?
VoIP stands for Voice over Internet Protocol. It's the technology that turns your voice into digital data and sends phone calls over the internet, instead of over traditional copper phone lines. If you've used WhatsApp calling, a softphone or a cloud dialer, you've used VoIP.
How VoIP works
A normal phone call over the old network (the PSTN) reserves a dedicated circuit between two phones. VoIP does it differently:
- Your voice is captured and digitised — turned into a stream of numbers by a codec (a compression method like Opus or G.711).
- That stream is chopped into small data packets and sent across the internet, just like an email or a web page.
- At the other end, the packets are reassembled and converted back into sound, all within milliseconds.
Two things coordinate this: a signalling protocol (usually SIP) that sets up, rings and tears down the call, and a media protocol (usually RTP) that carries the actual audio.
What is SIP?
SIP (Session Initiation Protocol) is the "dial tone" of VoIP. It handles the request to start a call, the ringing, answering and hanging up — but not the audio itself. A "SIP trunk" is simply the VoIP equivalent of a phone line from a carrier, letting a business make and receive calls to real phone numbers over the internet.
Why businesses moved to VoIP
- Cost — calls ride your existing internet connection; no separate phone lines, and long-distance is far cheaper.
- Flexibility — agents can work from a browser, a desk phone or a mobile app, anywhere with internet.
- Features — IVR, call recording, queues, dialers and analytics are software, so they're easy to add.
- Scale — add lines and agents in software instead of running new cabling.
What you need for good VoIP quality
Because VoIP rides the internet, call quality depends on your connection. A stable connection with low latency and low jitter (variation in packet timing) matters more than raw speed — voice uses very little bandwidth. Wired or strong Wi-Fi beats a weak mobile signal, and business-grade routers can prioritise voice traffic (QoS) to keep calls crisp.
VoIP and call centers
Modern call center platforms are built entirely on VoIP. It's what makes cloud dialing, browser softphones, IVR and recording possible without any on-site phone hardware. Qallixo runs on VoIP end to end — bring your own SIP carrier and numbers, or use ours, and your agents dial from a browser. If you're curious what runs under the hood, see our comparison of Asterisk, FreeSWITCH, Kamailio and OpenSIPS.