WebSocket
WebSocket is a protocol that maintains a persistent, two-way connection between a client and server. Once connected, either side can send messages without opening a new HTTP request for every exchange.
How WebSocket works
A WebSocket connection begins with an HTTP handshake and then switches to the WebSocket protocol. The client and server exchange framed text or binary messages over the open connection. Because either side can send at any time, the server does not need to wait for the client to poll before delivering an update.
The persistent connection changes the operational model. Both sides need to detect disconnections, authenticate the session, limit message sizes, and decide how to reconnect. Heartbeats can reveal a connection that appears open but no longer carries traffic. Applications also need backpressure rules so a fast sender does not overwhelm a slower receiver.
WebSocket preserves message ordering within a connection, but it does not make application events durable. If a connection drops, messages sent during the gap may be lost unless the application adds sequence tracking, acknowledgements, or replay. A reconnect is a new connection, so the client must restore any required state.
Why it matters for AI phone calls
Voice applications exchange information continuously while a caller is speaking. A persistent channel can carry audio frames, partial transcripts, timing signals, tool events, or agent responses with less request overhead than repeated REST calls. That makes WebSocket useful for interactive paths where updates need to move in both directions.
Low overhead does not guarantee a good call. Network latency, jitter, packet loss, buffering, slow downstream processing, and reconnect behavior all affect the experience. Sensitive call data also requires transport protection, session authorization, and careful logging.
WebSocket, REST, webhooks, and WebRTC solve different problems. REST fits bounded client-requested operations. Webhooks push discrete events to a server endpoint. WebSocket provides a general bidirectional message channel. WebRTC adds browser-oriented real-time media and connection negotiation. An AI phone architecture may use more than one of these, with each assigned to the part of the call flow it handles best.