SIP requests are the codes used by Session Initiation Protocol for communication. To complement them there are SIP Responses, which generally indicate whether this request succeeded or failed, and in the latter case, why it failed.
SIP requests| Request name | Description | Defined in |
|---|
| INVITE | Indicates a client is being invited to participate in a call session. | RFC 3261 |
| ACK | Confirms that the client has received a final response to an INVITE request. | RFC 3261 |
| BYE | Terminates a call and can be sent by either the caller or the callee. | RFC 3261 |
| CANCEL | Cancels any pending request. | RFC 3261 |
| OPTIONS | Queries the capabilities of servers. | RFC 3261 |
| REGISTER | Registers the address listed in the To header field with a SIP server. | RFC 3261 |
| PRACK | Provisional acknowledgement. | RFC 3262 |
| SUBSCRIBE | Subscribes for an Event of Notification from the Notifier. | RFC 3265 |
| NOTIFY | Notify the subscriber of a new Event. | RFC 3265 |
| PUBLISH | Publishes an event to the Server. | RFC 3903 |
| INFO | Sends mid-session information that does not modify the session state. | RFC 6086 |
| REFER | Asks recipient to issue SIP request (call transfer.) | RFC 3515 |
| MESSAGE | Transports instant messages using SIP. | RFC 3428 |
| UPDATE | Modifies the state of a session without changing the state of the dialog. | RFC 3311 |
