VG3300 series user guide
SIP ClientsSIP clients include the following:
Phones—Can act as either a UAS or UAC. Soft phones (PCs that have phone capabilities installed) and SIP IP phones can initiate SIP requests and respond to requests.
Gateways—Provide call control. Gateways provide much functionality. The most common one is a translation function between SIP conferencing endpoints and other terminal types. This function includes translation between transmission formats and between communications procedures. In addition, the gateway also translates between audio and video Codec and performs call setup and clearing on both the LAN side and the switched-circuit network side.
SIP ServersSIP servers include the following:
Proxy server—The proxy server is an intermediate device that receives SIP requests from a client and then forwards the requests on behalf of the client's. 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, 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 proxy server.