SIP is a core protocol for initiating, managing, and terminating sessions over the internet including voice, video, and text. SIP uses various entities like user agents, proxy servers, and registrars to set up sessions between one or more participants using unicast or multicast communications. SIP defines request and response message types for functions like registration, inviting participants, and terminating calls.

1. SIP introduction

2. Introduction
SIP is the core protocol for initiating, managing
and terminating sessions in the Internet
These sessions may be text, voice, video or a
combination of these
SIP sessions involve one or more participants and
can use unicast or multicast communication.

3. SIP entities
User Agent
• User Agent Client
• User Agent Server
Proxy Server
Redirect server
Registrar
Gateway
Session border controller

4. SIP Message Types (Requests)
REGISTER
INVITE
ACK
BYE
CANCEL
OPTIONS
INFO
PRACK (Provisional Response Acknowledgement)

5. SIP Message Types (Responses)
• Request received and being processed.Provisional (1xx)
• The action was successfully received, understood, and
accepted.Success (2xx)
• Further action needs to be taken (typically by sender) to
complete the request.Redirection (3xx)
• The request contains bad syntax or cannot be fulfilled at the
server.Client Error (4xx)
• The server failed to fulfill an apparently valid request.Server Error (5xx)
• The request cannot be fulfilled at any server.Global Failure (6xx)

6. Call example

7. Links
Free SIP server software
• https://www.3cx.com/ip-pbx/
Free online SIP server
• ??????
HTML 5 sip client
• http://sipml5.org/

8. Issues and terms
• SIP trunking
• Soft-Swtching