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 Introduction to SIP Classification of Mobility Classification of Mobility Network Layer Mobility Network Layer Mobility Application Layer (SIP-based) Mobility Application Layer (SIP-based) Mobility Conclusion Conclusion

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

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

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

Introduction to SIP (4/9) Separate signaling and media streams Separate signaling and media streams

Introduction to SIP (5/9) SIP addressing and naming SIP addressing and naming –The entities addressed by SIP are users at hosts (SIP URI: Uniform resource identifier) – -like identifier of the form User: user name or telephone number User: user name or telephone number Host: domain name or numeric network number Host: domain name or numeric network number –For example,

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

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

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

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

Classification of Mobility LayersRange Application Layer Transport Layer Network Layer MacromobilitySIPTCP-MigrateMIP MicromobilityHMSIPHAWAIICIPIDMPTIMIP

Network Layer Mobility Advantage Advantage –Retain home IP address while changing attachment point of the network –Keep tracking host location Disadvantage 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

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

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

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

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

Application Layer (SIP- based) Mobility (5/17) Pre-call Mobility 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 A large amount of the register signaling overhead Waste of the network bandwidth 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 The client simply polls the OS every few seconds Power consumption Power consumption

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

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

Application Layer (SIP- based) Mobility (8/16) The location update takes one one-way delay after the application in the MH recognizes that it has acquired a new IP address The location update takes one one-way delay 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 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 For narrowband systems, it may impose delays of several tens of milliseconds

Application Layer (SIP- based) Mobility (9/16) RTP translator intercepts the media packets and directs them to the current location of the MH RTP translator intercepts the media packets and directs them to the current location of the MH Insertion of an RTP translator reduces handoff delay to the one-way between the MH Insertion of an RTP translator reduces handoff delay to the one-way between the MH

Application Layer (SIP- based) Mobility (10/16) Session Mobility Session Mobility It allows a user to maintain a media session even while changing terminals It allows a user to maintain a media session even while changing terminals For example, 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

Application Layer (SIP- based) Mobility (11/16) Session mobility using SIP can be supported in at least three ways 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

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

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

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

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

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

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

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