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osdir.com/ml/ietf.sip/2002-08/msg00040.html
Posted by crouse
osdir.com/ml/ietf.sip/2002-08/msg00040.html
Posted by crouse
SIP Messages
SIP uses plain-text messages, following the format of standard Internet text messages. This helps in troubleshooting, because it is easy to read SIP messages. However, you must understand the types of messages and their formats to successfully troubleshoot them. This section helps you with that understanding.
SIP messages are either requests or responses to a request; the function that the request invokes on a server is called a method. Several types of SIP methods exist. The original SIP specification included the following six methods. Cisco gateways can both send and receive these methods, except where noted.
* REGISTER—A UA client sends this message to inform a SIP server of its location.
* INVITE—A caller sends this message to request that another endpoint join a SIP session, such as a conference or a call. This message can also be sent during a call to change session parameters.
* ACK—A SIP UA can receive several responses to an INVITE. This method acknowledges the final response to the INVITE.
* CANCEL—This message ends a call that has not yet been fully established.
* OPTIONS—This message queries the capabilities of a server. Cisco gateways receive these methods only.
* BYE—This message ends a session or declines to take a call.
Posted by sagitraz
The diagram below illustrates a basic SIP call setup scenario, using the following messages:
• INVITE - initiates session. The session description is included in the message body. Re-INVITE is used to change session state
• ACK - confirms session establishment and can be used only with INVITE
• BYE - terminates session
• CANCEL - cancels a pending INVITE
• OPTIONS - capability inquiry
REGISTER - binds a permanent address to current location and it may convey user data.
Posted by yogendra
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