SIP Elements

by | Mar 4, 2010 | Non classé, SIP, Written Theory | 0 comments

Here are various elements, definitions of what you can find in SIP world:

  • User Agent (UA) : This an endpoint that can act as both an User Agent Client (UAC) and an User Agent Server (UAS), a good example is a SIP IP Phone.

  • UAC : This is a logical entity that initiates and sends requests, such as those specifiying the INVITE method. the UAC is a logigal role, so it lasts only for the duration of a SIP transaction.

  • UAS : This is an entity that responds to a SIP request by accepting, rejecting, or redirecting the request. The UAS role also lasts  only for the duration of the SIP transaction.

  • Redirect Server : This an (UA) server that provides address translation and redirects clients to alternative destination addresses. It does this by sending 3XX responses to requests.

  • Proxy Server : A SIP proxy server’s primary role is to provide routing, but it can also enforce policies, provide features, and authenticate and authorize users.

  • Registrar Server : Users are registering their current location (location service) so Registrar Server uses the information to provide a lookup service that allows SIP UA to be located.

  • Location Service : This is created by a registrar server and is populated with bindings of Address-of-records (AOR). It is a kind of user’s profiel address. This service can be used by the proxy or redirect servers to retrieve information relating to a called party’s possible locations.