The SIP Servlet Tutorial

SIP Requests

The following table lists the SIP requests.

Table A–1 SIP Request Methods

SIP Request 

Description 

INVITE 

A client is being invited to participate in a call. 

ACK 

The client has confirmed the INVITE request. 

BYE 

The call has been terminated by either the caller or callee. 

CANCEL 

Cancel any pending requests. 

OPTIONS 

Queries the server for its capabilities. 

REGISTER 

Registers the client with the server according to the address in the To header. 

PRACK 

Similar to ACK, but a provisional confirmation. 

SUBSCRIBE 

Subscribes the device for an event notification. 

NOTIFY 

Notifies all subscribers of an event. 

PUBLISH 

Publishes an event to a server. 

INFO 

Sends information in the middle of a session that doesn't modify the session's state. 

REFER 

Asks the client to issue a SIP request, typically a call transfer. 

MESSAGE 

Sends an instant message using SIP. 

UPDATE 

Modifies a session's state without altering the dialog state. 

For a list of all SIP requests and links to their definitions in their respective RFCs, see the SIP requests Wikipedia entry.