Application-Layer Mobility UsiApplication-Layer Mobility Using SIPng SIPHenning Schulzrinne, Elin WedlundHenning Schulzrinne, Elin WedlundMobile Computing and Communications Review, Volume 4, NumbeMobile Computing and Communications Review, Volume 4, Number 3r 3

Presenter: Presenter: 許啟裕許啟裕Date: 2005/5/10Date: 2005/5/10

OutlineOutline Introduction to SIPIntroduction to SIP Classification of MobilityClassification of Mobility Network Layer MobilityNetwork Layer Mobility Application Layer (SIP-based) Application Layer (SIP-based)

MobilityMobility ConclusionConclusion

Introduction to SIP Introduction to SIP (1/9)(1/9) A A powerful alternativepowerful alternative to H.323 to H.323 More More flexibleflexible, , simplersimpler Easier to implement advanced Easier to implement advanced

featuresfeatures Better to support of intelligent user Better to support of intelligent user

devicesdevices Transport independenceTransport independence (UDP, TCP, (UDP, TCP,

or SCTP)or SCTP)

Introduction to SIP Introduction to SIP (2/9)(2/9) Developed in SIP working Group Developed in SIP working Group

in IETFin IETF– Work Work began 1995began 1995– Sep. 1999 splitSep. 1999 split from from MMUSICMMUSIC

MMultiparty ultiparty MuMultimedia ltimedia SSessessiion on CControlontrol– Proposed standard Proposed standard RFC 2543RFC 2543, ,

February 1999February 1999– New version of SIP – RFC 3261, New version of SIP – RFC 3261, June June

20022002

Introduction to SIP Introduction to SIP (3/9)(3/9) SIP is an SIP is an application-layerapplication-layer signalingsignaling protocolprotocol HTTP-likeHTTP-like, “request-response”, “request-response”

– EstablishEstablish, , modifymodify, and , and terminateterminate multi multimedia sessions.media sessions. SIP+SIP+(Session Description Protocol)(Session Description Protocol)SSDPDP

Introduction to SIP Introduction to SIP (4/9)(4/9) SeparateSeparate signalingsignaling and and mediamedia streams streams

Introduction to SIP Introduction to SIP (5/9)(5/9) SIP addressing and namingSIP addressing and naming

– The entities The entities addressed addressed by SIP are by SIP are users at hostusers at hostss (SIP (SIP URIURI: : UUniform niform rresource esource iidentifier)dentifier)– Email-likeEmail-like identifier of the form user@host identifier of the form user@host

UserUser: : user nameuser name or or telephone numbertelephone number HostHost: : domain namedomain name or or numeric network numbernumeric network number

– For example,For example, m9356020m9356020@npust.edu.tw@npust.edu.tw 09441688880944168888@@npust.edu.twnpust.edu.tw Charles@Charles@140.127.1.200140.127.1.200

Introduction to SIP Introduction to SIP (6/9)(6/9) SIP defines a number of logical SIP defines a number of logical

entities, namelyentities, namely– User agentsUser agents– Redirect serversRedirect servers– Proxy serversProxy servers– RegistrarsRegistrars

Introduction to SIP Introduction to SIP (7/9)(7/9) User agentUser agent

– User AgentUser Agent Client Client - - InitiateInitiate SIP SIP requestrequest– User AgentUser Agent Server Server - - AcceptsAccepts or or rejectsrejects call call

Introduction to SIP Introduction to SIP (8/9)(8/9) Redirect ServerRedirect Server

– Redirect server Redirect server usesuses a a database or database or location servicelocation service to to look up a userlook up a user

Introduction to SIP Introduction to SIP (9/9)(9/9) Proxy ServerProxy Server

– Handle requestsHandle requests or or forwardforward requests to other s requests to other serverservers– Can be used for call forwarding, time-of-day reCan be used for call forwarding, time-of-day reouting, or follow-me servicesouting, or follow-me services

Classification of Classification of MobilityMobilityLayersLayers

RangeRangeApplication Application Layer Layer

Transport Transport Layer Layer

Network Network LayerLayer

MacromobilitMacromobilityy SIP SIP TCP-TCP-Migrate Migrate

MIP MIP

MicromobilitMicromobilityy HMSIP HMSIP HAWAIIHAWAIICIPCIP

IDMPIDMPTIMIP TIMIP

Network Layer MobilityNetwork Layer Mobility AdvantageAdvantage

– RetainRetain home home IP addressIP address while while changing changing attachment pointattachment point of the network of the network

– Keep tracking Keep tracking host locationhost location DisadvantageDisadvantage

– Difficult to deployDifficult to deploy, ISP has to provide home , ISP has to provide home agentagent

– Need to Need to modify convention IP stackmodify convention IP stack– Add Add 8-20 bytes overhead8-20 bytes overhead each packet each packet– Cannot supportCannot support session, service and session, service and

personal mobilitypersonal mobility

Application Layer (SIP-Application Layer (SIP-based) Mobility (1/16)based) Mobility (1/16) AdvantageAdvantage

– Ease to deployEase to deploy– SupportSupport session, service, personal, and session, service, personal, and terminal mobilityterminal mobility– Network transparentNetwork transparent

DisadvantageDisadvantage– A A large amountlarge amount of of signaling overheadsignaling overhead– RTPRTP does does notnot support support QoSQoS

Application Layer (SIP-Application Layer (SIP-based) Mobility (2/16)based) Mobility (2/16) In this paper, In this paper, four types mobilityfour types mobility

have been defined.have been defined.– TerminalTerminal Mobility Mobility– SessionSession Mobility Mobility– ServiceService Mobility Mobility– PersonalPersonal Mobility Mobility

Application Layer (SIP-Application Layer (SIP-based) Mobility (3/16)based) Mobility (3/16) Terminal MobilityTerminal Mobility

– Terminal Terminal altersalters the the attachment pointattachment point of of the network.the network.

– Two scenarios have to been concernedTwo scenarios have to been concerned Pre-callPre-call: Mobile host (MH) : Mobile host (MH) acquiresacquires a a newnew

addressaddress prior to receivingprior to receiving or or makingmaking a a callcall Mid-callMid-call: : MHMH is movingis moving and and sending sending

another another INVITE requestINVITE request to the to the correspondent host (CH)correspondent host (CH)

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

Application Layer (SIP-Application Layer (SIP-based) Mobility (5/17)based) Mobility (5/17) Pre-call MobilityPre-call Mobility

– The MH The MH simply re-registerssimply re-registers with its home with its home registrar each time it obtains a new IP registrar each time it obtains a new IP addressaddress

A A large amountlarge amount of the of the register signaling overheadregister signaling overhead WasteWaste of the of the network bandwidthnetwork bandwidth

– The only The only difficult partdifficult part there is the ability there is the ability to to detectdetect, at the , at the application layerapplication layer, when , when IPIP has has changedchanged..

The client simplyThe client simply polls polls the the OSOS every few seconds every few seconds Power consumptionPower consumption

Application Layer (SIP-Application Layer (SIP-based) Mobility (6/16)based) Mobility (6/16) PagingPaging, for , for MH power conservationMH power conservation, ,

can also be implemented in SIPcan also be implemented in SIP This work assumes that This work assumes that proxiesproxies are are

organized hierarchicallyorganized hierarchically E.g.E.g.

– With a proxy for each wireless network, With a proxy for each wireless network, region, cell cluster and base stationregion, cell cluster and base station

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

Application Layer (SIP-Application Layer (SIP-based) Mobility (8/16)based) Mobility (8/16) The The location updatelocation update takes takes one one-wayone one-way

delaydelay after the application in the MH after the application in the MH recognizes that it has acquired a new IP recognizes that it has acquired a new IP addressaddress

For For wideband accesswideband access, the , the delay is delay is probably equalprobably equal to to propagation delaypropagation delay plus a few millisecondsplus a few milliseconds

For For narrowband systemsnarrowband systems, it may impose , it may impose delays of several tens of millisecondsdelays of several tens of milliseconds

Application Layer (SIP-Application Layer (SIP-based) Mobility (9/16)based) Mobility (9/16) RTP translatorRTP translator interceptsintercepts the the

media packets and media packets and directsdirects them them toto the the current location of the MHcurrent location of the MH

Insertion of an RTP translator Insertion of an RTP translator reducesreduces handoff delayhandoff delay to the one- to the one-way between the MHway between the MH

Application Layer (SIP-Application Layer (SIP-based) Mobility (10/16)based) Mobility (10/16) Session MobilitySession Mobility It It allowsallows a a useuser to r to maintainmaintain a a media media

sessionsession even while changing terminals even while changing terminals For example,For example,

– A caller may want A caller may want continue a sessioncontinue a session begun on a begun on a mobile devicemobile device on the on the desktop desktop pcpc when when enterenter her her officeoffice

– A A user user may also want to may also want to move partsmove parts of a of a sessionsession, e.g., if he has specialized devices , e.g., if he has specialized devices for audio and video, such as a for audio and video, such as a video video projectorprojector, , video wallvideo wall or or speakerphonespeakerphone

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

– In the simplest approach, In the simplest approach, using new INVusing new INVITE requestITE request..– One mechanism for such configuration One mechanism for such configuration could be MGCP or could be MGCP or MegacoMegaco– Two better solutions, namely Two better solutions, namely third-partthird-party call controly call control or the or the REFER mechanismREFER mechanism

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

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

Application Layer (SIP-basApplication Layer (SIP-based) Mobility (14/16)ed) Mobility (14/16) Personal MobilityPersonal Mobility It It allowsallows to to addressaddress a a single usersingle user

located located at different terminalsat different terminals by by the same logical addressthe same logical address

Both Both 1-to-n1-to-n (one address many (one address many potential terminal) and potential terminal) and m-to-1m-to-1 (many addresses reaching one (many addresses reaching one terminal) mapping are usefulterminal) mapping are useful

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

Application Layer (SIP-basApplication Layer (SIP-based) Mobility (16/16)ed) Mobility (16/16) Service MobilityService Mobility It It allowsallows users to users to maintainmaintain accessaccess

to their to their servicesservices even while even while moving or changing devices and moving or changing devices and network service providersnetwork service providers

For instance, For instance, usersusers will likely will likely wantwant to to maintainmaintain include their include their speed speed dial listsdial lists, , address booksaddress books, and so , and so on on in Voice-over-IP environmentin Voice-over-IP environment..

ConclusionConclusion Application-layer mobilityApplication-layer mobility can can

either either partially replacepartially replace or or complement network-layer mobilitycomplement network-layer mobility

SIP-based mobilitySIP-based mobility can be used to can be used to provide provide all all common common forms offorms of mobilitymobility, including , including terminalterminal, , personalpersonal, , serviceservice, and , and sessionsession mobilitymobility

Thank you for your Thank you for your attentionattention