VoIP

For a century, a phone call rode a dedicated circuit: when you dialed, the network reserved a private wire-like path for your voice, end to end, for the whole call. VoIP throws that out. It digitizes your voice into a stream of small packets and ships them across the ordinary, shared, best-effort Internet — the same network that carries web pages and email — alongside everyone else's traffic. There is no reserved path; your voice packets compete for road space like all the rest. VoIP, short for Voice over IP, is simply telephone calls carried as data over an IP network.

Here is the round trip in plain steps. Your microphone's sound is sampled and compressed by a codec into a stream, chopped into small chunks (often one packet every 20 milliseconds). Each chunk is wrapped in an RTP header (carrying a timestamp and sequence number so the far end can reassemble timing and detect loss), then in UDP, then in IP, and sent. At the other end the packets arrive with varying delays; a playout buffer holds them briefly and releases them on a steady clock, lost packets are concealed, and the audio is decoded and played. Separately, before any of this, a signaling protocol such as SIP found the other party and set up the call — like dialing and ringing before talking.

Why it matters: VoIP is how almost all telephony works today, from app calls to corporate phone systems, because reusing the data network is vastly cheaper than maintaining a separate voice network. The trade-off is honest: a reserved circuit gave guaranteed quality, while VoIP inherits the Internet's best-effort nature and must fight delay, loss, and jitter with buffers and concealment. It is generally good enough because operators over-provision and because the techniques work well — but on a congested or distant link, a VoIP call can still get choppy in ways the old circuit-switched phone never did.