The SIP protocol defines several functional components. These functional entities can be implemented as a separate server, or the same server can perform multiple functions. VoipSwitch’s class 5 softswitch acts as:
- Proxy server — performs call routing, authentication, authorization and address resolution
- Registrar server — User Agents register their location with a registrar server, which places that information into a location database. A registrar server responds to location requests from other servers.
- Location server — This server maintains the location database for registered User Agents.
- Back-to-back user agent (B2BUA) — This server acts as a User Agent server and client at the same time. It terminates the signaling from the calling client and then initiates signaling to the called party. B2BUAs are allowed to change the content of requests, giving them more control over the call parameters.
- Presence server — This server gathers presence information from Presentities and subscription information from Watchers, and sends status notifications.