© Struggling in pa schoolJul 31, 2017 · SIP Message Codes and Its Meaning. SIP message responses are maintained in an Internet Assigned Numbers Authority (IANA) list called Session Initiation Protocol (SIP) Parameters. They always begin with a response code. These Response Code are divided in following categories:
SIP employs design elements similar to the HTTP request and response transaction model. Each transaction consists of a client request that invokes a particular method or function on the server and at least one response. SIP reuses most of the header fields, encoding rules and status codes of HTTP, providing a readable text-based format. SIP Requests are answered with SIP responses, of which there are six classes: 1xx = Informational responses, such as 180 (ringing). 2xx = Success responses. 3xx = Redirection responses.