Communications and Networking by John Cowley

Author:John Cowley
Language: eng
Format: epub
Publisher: Springer London, London

Method

Description

INVITE

Request that a session be created

ACK

Acknowledge that a session has been created

BYE

Request that a session be terminated

CANCEL

Cancel a request that is pending

REGISTER

Register a user’s location (URL)

OPTIONS

Query a host to find out its capabilities

For VoIP sessions, SIP works as follows. Callers and callees are identified by SIP addresses, which are URLs such as ‘sip: [email protected]’. A SIP caller first locates a server and then sends a SIP request (an invitation). A SIP request may reach the callee directly. Otherwise, it may be redirected or may start off a chain of new SIP requests, which are carried out by proxy servers (intermediary systems involved in call set-up). Users are able to register their location with SIP location servers. Interaction between a SIP server and clients is illustrated in Fig. 7.26.

Fig. 7.26Interaction between a SIP server and clients

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