SIP servers include: * Proxy server-The proxy server is an intermediate device that receives SIP requests from a client and then forwards the requests on the client's behalf > 자유게시판

SIP servers include: * Proxy server-The proxy server is an intermediate device that receives SIP requests from a client and then forwards the requests on the client's behalf. Basically, proxy servers receive SIP messages and forward them to the next SIP server in the network. Proxy servers can provide functions such as authentication, authorization, network access control, routing, reliable request retransmission, and security.

* Redirect server-Provides the client with information about the next hop or hops that a message should take and then the client contacts the next hop server or UAS directly.

* Registrar server-Processes requests from UACs for registration of their current location. Registrar servers are often co-located with a redirect or usa proxy server.

refer: website SIP component establishes the connection with requests and responses?