Cisco Systems 188, 186 manual SIP Clients, SIP Servers

Chapter 1 Cisco Analog Telephone Adaptor Overview

Session Initiation Protocol (SIP) Overview

Figure 1-4 SIP Architecture

SIP proxy and redirect servers

SIP

SIP user agents

SIP		SIP
		SIP gateway
	RTP	PSTN
		Legacy PBX	72342

SIP Clients

SIP clients include:

•Gateways—Provide call control. Gateways provide many services, the most common being 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 codecs and performs call setup and clearing on both the LAN side and the switched-circuit network side.

•Telephones—Can act as either a UAS or UAC. The Cisco ATA can initiate SIP requests and respond to requests.

SIP Servers

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. 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—Receives SIP requests, strips out the address in the request, checks its address tables for any other addresses that may be mapped to the address in the request, and then returns the results of the address mapping to the client. Redirect servers provide 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.

Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator’s Guide (SIP)

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