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Presenter: 許啟裕 Date: 2005/5/10

Application-Layer Mobility Using SIP Henning Schulzrinne, Elin Wedlund Mobile Computing and Communications Review, Volume 4, Number 3. Presenter: 許啟裕 Date: 2005/5/10. Outline. Introduction to SIP Classification of Mobility Network Layer Mobility Application Layer (SIP-based) Mobility

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Presenter: 許啟裕 Date: 2005/5/10

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  1. Application-Layer Mobility Using SIPHenning Schulzrinne, Elin WedlundMobile Computing and Communications Review, Volume 4, Number 3 Presenter: 許啟裕 Date: 2005/5/10

  2. Outline • Introduction to SIP • Classification of Mobility • Network Layer Mobility • Application Layer (SIP-based) Mobility • Conclusion

  3. Introduction to SIP (1/9) • A powerful alternative to H.323 • More flexible, simpler • Easier to implement advanced features • Better to support of intelligent user devices • Transport independence (UDP, TCP, or SCTP)

  4. Introduction to SIP (2/9) • Developed in SIP working Group in IETF • Work began 1995 • Sep. 1999 split from MMUSIC • Multiparty Multimedia Session Control • Proposed standard RFC 2543, February 1999 • New version of SIP – RFC 3261, June 2002

  5. Introduction to SIP (3/9) • SIP is an application-layersignaling protocol • HTTP-like, “request-response” • Establish, modify, and terminate multimedia sessions. • SIP+(Session Description Protocol)SDP

  6. Introduction to SIP (4/9) • Separatesignaling and media streams

  7. Introduction to SIP (5/9) • SIP addressing and naming • The entities addressed by SIP are users at hosts (SIP URI: Uniform resource identifier) • Email-like identifier of the form user@host • User: user name or telephone number • Host: domain name or numeric network number • For example, • m9356020@npust.edu.tw • 0944168888@npust.edu.tw • Charles@140.127.1.200

  8. Introduction to SIP (6/9) • SIP defines a number of logical entities, namely • User agents • Redirect servers • Proxy servers • Registrars

  9. Introduction to SIP (7/9) • User agent • User Agent Client - Initiate SIP request • User Agent Server - Accepts or rejects call

  10. Introduction to SIP (8/9) • Redirect Server • Redirect server uses a database or location service to look up a user

  11. Introduction to SIP (9/9) • Proxy Server • Handle requests or forward requests to other servers • Can be used for call forwarding, time-of-day reouting, or follow-me services

  12. Classification of Mobility

  13. Network Layer Mobility • Advantage • Retain home IP address while changing attachment point of the network • Keep tracking host location • Disadvantage • Difficult to deploy, ISP has to provide home agent • Need to modify convention IP stack • Add 8-20 bytes overhead each packet • Cannot support session, service and personal mobility

  14. Application Layer (SIP-based) Mobility (1/16) • Advantage • Ease to deploy • Support session, service, personal, and terminal mobility • Network transparent • Disadvantage • A large amount of signaling overhead • RTP does not support QoS

  15. Application Layer (SIP-based) Mobility (2/16) • In this paper, four types mobility have been defined. • Terminal Mobility • Session Mobility • Service Mobility • Personal Mobility

  16. Application Layer (SIP-based) Mobility (3/16) • Terminal Mobility • Terminal alters the attachment point of the network. • Two scenarios have to been concerned • Pre-call: Mobile host (MH) acquires a newaddressprior to receiving or making a call • Mid-call: MHis moving and sending another INVITE request to the correspondent host (CH)

  17. Application Layer (SIP-based) Mobility (4/16) • Pre-call

  18. Application Layer (SIP-based) Mobility (5/17) • Pre-call Mobility • The MH simply re-registers with its home registrar each time it obtains a new IP address • A large amount of the register signaling overhead • Waste of the network bandwidth • The only difficult part there is the ability to detect, at the application layer, when IP has changed. • The client simply polls the OS every few seconds • Power consumption

  19. Application Layer (SIP-based) Mobility (6/16) • Paging, for MH power conservation, can also be implemented in SIP • This work assumes that proxies are organized hierarchically • E.g. • With a proxy for each wireless network, region, cell cluster and base station

  20. Application Layer (SIP-based) Mobility (7/16) • Mid-call

  21. Application Layer (SIP-based) Mobility (8/16) • The location update takes one one-waydelay after the application in the MH recognizes that it has acquired a new IP address • For wideband access, the delay is probably equal to propagation delay plus a few milliseconds • For narrowband systems, it may impose delays of several tens of milliseconds

  22. Application Layer (SIP-based) Mobility (9/16) • RTP translatorintercepts the media packets and directs them to the current location of the MH • Insertion of an RTP translator reduceshandoff delay to the one-way between the MH

  23. Application Layer (SIP-based) Mobility (10/16) • Session Mobility • It allows a user to maintain a media session even while changing terminals • For example, • A caller may want continue a session begun on a mobile device on the desktop pc when enter her office • A user may also want to move parts of a session, e.g., if he has specialized devices for audio and video, such as a video projector, video wall or speakerphone

  24. Application Layer (SIP-based) Mobility (11/16) • Session mobility using SIP can be supported in at least three ways • In the simplest approach, using new INVITE request. • One mechanism for such configuration could be MGCP or Megaco • Two better solutions, namely third-party call control or the REFER mechanism

  25. Application Layer (SIP-based) Mobility (12/16) • Third-party call control

  26. Application Layer (SIP-based) Mobility (13/16) • REFER method

  27. Application Layer (SIP-based) Mobility (14/16) • Personal Mobility • It allows to address a single user located at different terminals by the same logical address • Both 1-to-n (one address many potential terminal) and m-to-1 (many addresses reaching one terminal) mapping are useful

  28. Application Layer (SIP-based) Mobility (15/16) • Personal Mobility

  29. Application Layer (SIP-based) Mobility (16/16) • Service Mobility • It allows users to maintainaccess to their services even while moving or changing devices and network service providers • For instance, users will likely want to maintain include their speed dial lists, address books, and so on in Voice-over-IP environment.

  30. Conclusion • Application-layer mobility can either partially replace or complement network-layer mobility • SIP-based mobility can be used to provide all common forms ofmobility, including terminal, personal, service, and session mobility

  31. Thank you for your attention

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