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SIP proxy

(also SIP server, Session Initiation Protocol proxy)

SIP proxy definition

A SIP proxy is a proxy that is responsible for the management of all the SIP calls in an organization’s network. A SIP proxy also takes requests from users to place and end calls. Thanks to SIP proxies, we can make calls via WiFi connections.

A SIP proxy doesn’t just enable voice calls — it also enables video calls via the internet, like FaceTime, and video calls through apps like WhatsApp, Viber, and Telegram. Another example of a service that uses SIP proxies is VoIP calls. So SIP proxies are a widely used technology.

The people or users that make calls are called SIP user agents, and they send requests for starting, changing, or ending a call session.

See also: secure connection, VoIP

SIP proxy modes

  • Stateless SIP proxy. A stateless SIP proxy is also called a basic SIP server. The job of a stateless SIP proxy is to receive and transfer information without storing it. So once a call is connected (starts ringing), the job of the stateless SIP proxy is completed.
  • Stateful SIP proxy. A stateful SIP proxy is a more complex and sophisticated version of a SIP proxy. It receives, transfers, and stores information so that users can access it later if they need to. For instance, if a call doesn’t connect, the stateful SIP server can hold onto the call and try to connect it again and again until it succeeds.