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Introduction to SIP

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Introduction to SIP Speaker: Min-Hua Yang Advisor: Ho-Ting Wu Date:2005/3/29 – PowerPoint PPT presentation

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Title: Introduction to SIP


1
Introduction to SIP
  • Speaker Min-Hua Yang
  • Advisor Ho-Ting Wu
  • Date2005/3/29

2
Outline
  • SIP Overview
  • SIP Architecture and Components
  • User Agent , Servers
  • SIP Messages
  • Request, Response and Headers
  • Reliability Mechanism
  • Summary

3
Outline
  • SIP Overview
  • SIP Architecture and Components
  • SIP Messages
  • Reliability Mechanism
  • Summary

4
SIP Overview(1) - History
  • SIP ( Session initiation protocol)
  • Work began in 1995
  • Developed in SIP Working Group in IETF
  • Proposed standard RFC2543, February 1999
  • New Version of SIP - RFC 3261, June 2002
  • Split from MMUSIC (Multiparty Multimedia Session
    Control), Sep. 1999

5
SIP Overview(2) - Main Functions
  • SIP is an application-layer control (signaling)
    protocol for
  • initiating sessions
  • Find the users current location
  • Carry session descriptions
  • Modifying sessions
  • Terminating sessions

6
SIP Overview(3) - What is a session?
  • Refers to an active connection between two
    computers for the purpose of communicating and
    transferring information
  • Internet telephone calls
  • multimedia conferences
  • Instant Messaging
  • However its not limited to the above

7
SIP Overview(4)
  • SIP is similar to HTTP
  • both use a request/response model
  • both are text-based
  • much of SIPs message and header field syntax
    is identical to HTTP/1.1.
  • Works independent of the underlying network
  • transmission protocol and indifferent to media

8
SIP Overview(5)
  • Scalability
  • Functionality such as proxying, redirection,
    location, or registration can reside in
    different physical servers.
  • Distributed functionality allows new processes
    to be added without affecting other components.

9
SIP Overview(6)
  • Interoperability
  • An open standard
  • Can implement to communicate with other SIP
    based products

10
SIP Overview(7)
  • Mobility
  • The user can be using a PC at work, PC at home
    ,wireless phone, IP phone, or regular phone.
  • Users must register/Update their current
    location.
  • Supports user mobility by proxying or redirecting
    requests to a users current location.
  • Proxy servers will forward calls to the users
    current location.

11
Integration with IETF Protocols
  • SIP forms only part of an overall IP telephony
    system
  • Other IETF protocol standards are used to build a
    fully functioning VoIP system.
  • example
  • RSVP - to reserve network resources.
  • RTP (Real Time Transport Protocol) - to
    transport real
  • time data
  • RTSP (Real Time Streaming Protocol) - for
    controlling
  • delivery of streaming media.
  • RTCP (Real Time Transport Control Protocol)
    provides
  • information about the quality of the
    communication.

12
Related Protocols
13
SIP Capabilities(1/2)
  • Determine location of target points Support
    address
  • resolution, name mapping, call redirection
  • Determine media capabilities SIP uses Session
  • Description Protocol (SDP) for this
  • Determine availability returns a message why
    the
  • remote party cannot be contacted
  • Establish a session between end points also
    support mid call changes, changes of media
    characteristics or codec

14
SIP Capabilities(2/2)
  • Permits interaction between devices via
  • signaling messages
  • These messages can
  • Register a user with a system
  • Invite a user to join an interactive session
  • Establish a media stream between 2 or more end
  • points
  • Terminate a session

15
Outline
  • SIP Overview
  • SIP Architecture and Components
  • SIP Messages
  • Reliability Mechanism
  • Summary

16
SIP Network Architecture
17
SIP Component User Agent
  • User Agent Client (UAC)- Initiate SIP Request
  • User Agent Server (UAS)-Accepts or rejects call
  • Phones acts as UAC or UAS
  • Implemented in Hardware or Software
  • Components
  • Includes softphones, sip ip phones

18
User Agents
19
SIP Component Proxy Server
  • Heart of SIP network that contains all service
    logic.
  • Receives SIP messages, forwards to next SIP UAS.
  • Interprets, rewrites or translates a request
    message before forwarding it.

20
Scenario with Proxy Server
21
SIP Component Redirect Server
  • Return routing information to the originating
    endpoint.
  • Does not accept or terminate calls
  • Does not initiate its own SIP request

22
Scenario with Redirect Server
23
SIP Component Registrar
  • Accept registration requests from users
  • Maintains users whereabouts at a
  • Location Server
  • Typically co-located with a proxy server
  • or a redirect server and may offer
  • location services

24
Scenario with Registrar
25
Invitation for SIP Proxy Server
26
Invitation for Redirect Server
27
SIP Addressing
  • The SIP address is identified by a SIP URL,in the
    format user_at_host.
  • Email-like identifier of the form
  • Examples of SIP URLs
  • siphostname_at_ntut.edu.tw
  • siphostname_at_192.168.10.1
  • sip14083831088_at_vovida.org

28
Outline
  • SIP Overview
  • SIP Architecture and Components
  • SIP Messages
  • Reliability Mechanism
  • Summary

29
SIP Messages
  • The message syntax is identical to
    HTTP/1.1(RFC2616).
  • Two kinds of SIP messages
  • SIP-message Request Response

30
SIP Messages - Requests
  • INVITE Initiates a call by inviting user to
    participate in session.
  • ACK - Confirms that the client has received a
    final response to an INVITE request.
  • BYE - Indicates termination of the call.
  • CANCEL - Cancels a pending request.
  • REGISTER Registers the user agent.
  • OPTIONS Used to query the capabilities of a
    server.

31
SIP Messages - Responses
  • 1xx - Informational Responses
  • 180 ringing
  • 2xx - Successful Responses
  • 200 OK
  • 3xx - Redirection Responses
  • 302 Moved Temporarily
  • 4xx - Request Failure Responses.
  • 404 Not Found
  • 5xx - Server Failure Responses.
  • 503 Service Unavailable
  • 6xx - Global Failures Responses.
  • 600 Busy Everywhere
  • All responses, except for 1XX, are considered
    final responses

32
Message Headers
  • Provide further information about the message
  • E.g.,
  • To header in an INVITE
  • The called party
  • From header
  • The calling party
  • Four main categories
  • General, Request, Response, and Entity headers

33
Header Fields
  • General Header
  • Be applied to both request and response
    messages
  • Entity Header
  • Define information about the message body
  • Request Header
  • Allow the client to pass additional information
    about
  • the request
  • Response Header
  • Allow the server to pass additional information
  • about the response

34
SIP Headers
35
SIP Headers From
  • A field required in all requests and response
    messages
  • Provides identity of requests initiator
  • Example
  • From Laura Brown ltsipLaura.Brown_at_university.comgt

36
SIP Headers To
  • Provides identity of the intended
  • recipient of the request
  • Example
  • To Bob Johnson ltsipBob.Johnson_at_company.comgt

37
SIP Headers Call-ID(1/2)
  • Provides a globally unique identifier to
  • distinguish specific invitations
  • Typically uses a 32-bit cryptographically
  • random numbers
  • Example
  • Call-ID ges456fcdw21lkfgte12ax_at_workstation1234.un
    iversity.com

38
SIP Headers Call-ID(2/2)
39
SIP Headers Contact(1/2)
  • A Contact header provides a URL where the user
    can be reached directly.
  • This feature is important because it offloads SIP
    servers that do not need to be in the signalling
    path after routing the first INVITE.
  • Example
  • Contact Bob JohnsonltsipBob_at_140.124.181.227gt

40
SIP Headers Contact(2/2)
41
SIP Header - Via
  • History of messages path through network(s)
  • Helps to prevent looping and ensures
  • replies route back to originator
  • Indicates the used transport protocol, ip
  • address and port of sender
  • Via SIP/2.0/UDP 192.168.6.215060

42
SIP Header Content-Type
  • Provides information about media type of message
    body
  • Content-Type application/sdp

43
SIP Header CSeq(1/2)
  • CSeq or command sequence
  • Needed in both request messages as well
  • as response messages
  • Need to increment this when a user with the
  • same Call-ID wants to send different SIP
  • methods or content ( Except ACK and Cancel)
  • When sending responses to requests, CSeq
  • should be the same
  • The numerical part of the Cseq is used to order
    different requests within the same session.
  • CSeq 1 INVITE

44
SIP Header CSeq(2/2)
45
An example of SIP Request
46
An example of SIP Response
47
Outline
  • SIP Overview
  • SIP Architecture and Components
  • SIP Messages
  • Reliability Mechanism
  • Summary

48
Reliable Transmission of Responses(1/2)
  • Final responses are transmitted reliably between
    server and client, using retransmissions or a
    reliable transport protocol to ensure delivery.
  • Provisional responses may either be received by
    the client or be lost in the network.

49
Reliable Transmission of Responses(2/2)
50
Reliable Transmission of Requests(1/2)
51
Reliable Transmission of Requests(2/2)
52
Outline
  • SIP Overview
  • SIP Architecture and Components
  • SIP Messages
  • Reliability Mechanism
  • Summary

53
Summary
  • SIP is gaining acceptance in the industry
  • Open Source projects are taking the lead
  • in SIP implementations
  • New generation of services are already
  • being offered
  • Staying with single a vender solution is
    currently workable
  • Interoperability between vender products is still
  • in early stages

54
Reference
  • RFC 2543(SIP/1.0)
  • RFC 3261(SIP/2.0)
  • RFC 2327(SDP)
  • Related Material provided by
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