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ContentĬontent-Type – description of the message body. It consists of an integer that is decremented by one at each hop. Max-Forwards -to limit the number of hops a request can make on the way to its destination. The Contact header field tells other elements where to send future requests. The CSeq number is incremented for each new request within a dialog and is a traditional sequence number.Ĭontact – SIP URI that represents a direct route to the originator usually composed of a username at a fully qualified domain name (FQDN), also IP addresses are permitted. The request cannot be fulfilled at any serverĬSeq or Command Sequence contains an integer and a method name. The server failed to fulfill an apparently valid request The request contains bad syntax and cannot be fulfilled at this server The request has been received and processing is continuingĪn ACK, to indicate that the action was successfully received, understood, and accepted.įurther action is required to process this request This is used to query a server about its capabilities This is used only for INVITE indicating that the client has received a final response to an INVITE requestĪ User Agent Client use this message to terminate the call The body of this message would include a description of the session to which the callee is being invited. Outlining the SIP Requests and Responses in tables below,Ī Client use this message to register an address with a SIP serverĪ User or Service use this message to let another user/service participate in a session. PUBLISH to push presence information to the network SUBSCRIBE, NOTIFY standardised by Event notification extension RFC 3856

MESSAGE Methods for Instant Message based services Traditional SIP headers for Call setup are INVITE, ACK and teardown are CANCEL or BYE, however with more adoption newer methods specific to services were added such as : More on SIP, its packet structure, transaction and dialogs, loose and strict record routing, location service, near and far end nating, and commonly used SIP Call flows like Redirection, forking, click to Dial – (opens in a new tab) SIP Request and Repsosnes SIP is a widely adopted application layer protocol used in VoIP calls and confernecing applciations and in IMS architeture or pure packet switched networks.