Omar A. Abouabdalla

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SIP Functionality and Structure of the
Protocol

By

• Omar A. Abouabdalla
• Network Research Group
• (USM)

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What is SIP ?!
SIP or Session Initiation Protocol is an
application-level control protocol for setting
up, changing and terminating multimedia sessions
between participants on IP data networks.
SIP is a text-based protocol, similar to HTTP and
SMTP, for initiating interactive communication
sessions between users. Such sessions include
voice, video, chat, interactive games, and
virtual reality.
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When it Starts ?!

• The protocol's roots extend back to 1996.
• SIP was first developed within the Multiparty
  Multimedia Session Control (MMUSIC) working group
  at Internet Engineering Task Force (IETF).
• In 1999 SIP was approved as an official standard.
• In 1999 RFC2543 was published .
• Its real value has only recently been uncovered.

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How it Works ?!

• SIP requires the use of user data gram protocol
  (UDP), and TCP is optional.
• SIP contains its own retransmission mechanisms
  for the purpose of establishing sessions.
• Session Description Protocol (SDP), which is the
  encoded body of the SIP message contains
  information about what media types the parties
  can and will use.
• Destinations in SIP are represented with Uniform
  Resource Indicators (URI), which have the same
  format as e-mail addresses.

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SIP Advantages ?!

• It is short, simple and flexible protocol.
• It needs only a small set of messages and
  responses.
• Can run over most fixed and wireless networks.
• It uses the internet model and maps it onto
  telecom world.
• It uses email-like addresses to identify users.
• SIP address to identify users rather than the
  devices they happen to be using.

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How it Functions ?!
SIP supports five facets of establishing and
terminating multimedia communications

• User Location determination of the end system to
  be used for communication.
• User Availability determination of the
  willingness of the called party to engage in
  communications.
• User Capabilities determination of the media and
  media parameters to be used.
• Session Setup "ringing", establishment of
  session parameters at both called and calling
  party.
• Session Management including transfer and
  termination of sessions, modifying session
  parameters.

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How it Functions ?! (contd..)
SIP is a component that can be used with other
IETF protocols to build a complete multimedia
architecture.

• Real-time Transport Protocol (RTP) for
  transporting real time data.
• Real-time Streaming Protocol (RTSP) for
  controlling delivery of streaming media.
• The Media Gateway Control Protocol (MEGACO) for
  controlling gateways to Public Switched Telephone
  Network (PSTN).
• Session Description Protocol (SDP) for describing
  multimedia sessions.

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SIP Methods

• Invite - Indicates that the user is invited to a
  session.
• Ack - Used to confirm a session establishment.
• Bye - Terminates the sessions.
• Cancel - Used to cancel a pending Invite.
• Options - Used to query the server for its
  capabilities.
• Register - Used to bind a permanent address to
  the current location of the user.

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SIP Responds Codes

• 1 Informational Responses
• 100 Trying
• 180 Ringing
• 181 Call is being forwarded
• 2 Success
• 200 OK
• 3 Redirection
• 300 Multiple Choices
• 301 Moved Permanently
• 302 Moved Temporarily

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SIP Responds Codes (contd..)

• 4 Client Error
• 400 Bad Request
• 401 Unauthorized
• 482 Loop Detected
• 486 Busy Here
• 5 Server Failure
• 500 Server Internal Error
• 6 Global Failure
• 600 Busy Everywhere

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SIP Structure
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Conclusion
SIP is short, simple and flexible signaling
protocol for creating, modifying, and terminating
sessions with one or more participants.
Future work will be to bridge between SIP and
other multimedia control protocols like RSW
control protocol.
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Thank You