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SIP Language
Similarities with HTML and SMTP
SIP shares some common characteristics with HTTP and SMTP. Like the latter two,
SIP is an ASCII text-based protocol which makes it easy to read and troubleshoot. The
text below is a SIP trace that shows a user inviting another use to a session.
Users are identified by a SIP address, known as a Uniform Resource Identifier (URI).
A SIP URI is similar to an email address and is typically built around the user's phone
number or host name (e.g.,
allows users to be redirected to another phone as easily as they would be redirected to
another web page.
Types of Messages
SIP communication consists of two types of SIP messages—methods and responses.
Methods are sent from the client to the server and are used to indicate the purpose of
the request. The following six methods are part of RFC 3261.
Table B-1 RFC 3261 Methods
SIP Method
INVITE
ACK
BYE
CANCEL
REGISTER
OPTIONS
sip:[your_number]@companyA.vonage.net
Establishes a session
Confirms an INVITE request
Ends a session
Cancels establishing of a session
Registers a user with a proxy/registrar
Communicates information about the capabilities of the other side
Appendix B: SIP Overview
Description
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