HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

Session Initiation Protocol (SIP) 3
Messages
 Responses—sent from the server to the client.
R
EQUESTS
RESPONSES Response messages contain numeric response codes. The SIP response code set
is partly based on HTTP response codes. There are two types of responses and
six classes, as follows:
Response Types
 Provisional (1xx class)—provisional responses are used by the
server to indicate progress, but they do not terminate SIP
transactions.
 Final (2xx, 3xx, 4xx, 5xx, 6xx classes)—final responses
terminate SIP transactions.
Classes
 1xx = Provisional—request received, continuing to process the
request.
 2xx = Success—the action was successfully received,
understood and accepted.
 3xx = Redirection—further action needs to be taken to complete
the request.
Table 1-1 Request Messages
Method Description
INVITE Initiates a call, changes call parameters (re-INVITE).
ACK Confirms a final response for INVITE.
BYE Terminates a call.
CANCEL Cancels searches and “ringing”.
OPTIONS Queries the capabilities of the other side.
REGISTER Registers with the Location Service.
INFO Sends mid-session information that does not modify the
session state.