Cisco 7940G Руководство администратора - Страница 2

What Is Session Initiation Protocol?

Conferences can consist of two or more users and can be established using multicast or multiple unicast

sessions.

The term conference means an established session (or call) between two or more endpoints. In this

Note

document, the terms conference and call are used interchangeably.

Components of SIP

SIP is a peer-to-peer protocol. The peers in a session are called user agents (UAs). A user agent can

function in one of the following roles:

•

Typically, a SIP endpoint is capable of functioning as both a UAC and a UAS, but functions only as one

or the other per transaction. Whether the endpoint functions as a UAC or a UAS depends on the UA that

initiated the request.

From an architecture standpoint, the physical components of a SIP network can also be grouped into two

categories: clients and servers.

In addition, the SIP servers can interact with other application services, such as Lightweght Directory

Note

Access Protocol (LDAP) servers, a database application, or an eXtensible Markup Language (XML)

application. These application services provide back-end services such as directory, authentication, and

billing services.

Figure 1-1

SIP user

agents (UAs)

Cisco SIP IP Phone Administrator Guide Version 3.0

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User agent client (UAC)—A client application that initiates the SIP request.

User agent server (UAS)—A server application that contacts the user when a SIP request is received

and that returns a response on behalf of the user.

SIP Architecture

SIP

Figure 1-1

illustrates the architecture of a SIP network.

SIP proxy and

redirect servers

SIP

SIP gateway

RTP

Chapter 1

Product Overview

PSTN

Legacy PBX

OL-2206-01