p2p方式的IM系统开发,采用SIP/SIMPLE协议

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SOSIMPLE:ASIP/SIMPLEBasedP2P

VoIPandIMSystem

DavidA.BryanandBruceB.Lowekamp

ComputerScienceDepartmentCollegeofWilliamandMaryWilliamsburg,VA23185{bryan,lowekamp}@cs.wm.edu

Abstract—VoiceoverIP(VoIP)andInstantMessaging(IM)systemstodatehavebeeneitherhighlycentralizedornon-standardinnature.SOSIMPLEisafullydecentral-ized,standards-basedP2Pcommunicationssystemsthatreusesexistingclients.Thisdesignisbasedoncurrentlyavailableopen-sourcesoftware.Inthispaperweaddressthechallengesofdevelopingadistributedmessagingsys-temthatpreservestheadvantagesofcentralizedsystems,includingsecureauthentication.Thisapproachopensupnewopportunitiesfordecentralizedcommunicationssys-temsthatarereadilyavailableandextensible.

I.INTRODUCTION

VoiceoverIP(VoIP)andInstantMessaging(IM)areincreasinglypopularcommunicationssystemsforprivate,corporate,andacademicpurposes.Despitethispopularity,requirementsforcentralproxies,maintainedlocallyorbyathirdparty,havelimitedgrowthandplacedaburdenonusers.EffortshavebeenmadetoincorporateP2Ptechnology,buttodatethesehaveutilizednon-standardprotocolsorsystemsthatarenotfullydecentralized.

ManynetworkelementssupportingthecurrentVoIPandIMstandardprotocolsarealreadyinplace.Becauseoftheextensiveinvestmentofbothapplicationdevelop-menttimeandequipmentcosts,anewsystemshouldallowforreuseofexistingtechnology.Finally,asystemutilizingstandardprotocolswillallowmanyenhance-mentsfortheseprotocols,aswellastheconvergenceofVoIPandIM,tobeseamlesslyintegratedintoaP2Pbasedsystem.

Weproposetocombinewell-documented,standards-basedVoIPandIMtechnologieswiththeself-organizingpropertiesofanexistingP2Psystemstoforgeanopen,standards-drivensolutionthatwillallowustoleverageexistingapplicationsandequipmentWecombinetheSIP/SIMPLEfamilyofIETFstandardsforVoIPandIMwithaDistributedHashTable(DHT)P2Pproto-coltoreachthisobjective.Throughoutourdesign,we

havekeptexistingSIP/SIMPLEclientsinmind,andincorporatedcomponentstoallowthemtomakeuseoftheP2Papproachwithfewornomodi cations.Asourdesignaddsaself-organizing(SO)aspecttotheexistingSIP/SIMPLEfamily,werefertoourdesignasSOSIMPLE.

Theprimarycontributionsofthisworkare:

Creatingafully-distributed,open,P2PVoIPandIMsystem—aGnutellaforVoIPandIM.

Preservingmanyoftheadvantagesofcentral-izedapproachestoVoIPandIM—compatibilityandstandardization,extensibilitythroughhierarchi-calstructure,andreliableandcompleteresourcelocation—inadistributeddesign.

ProvidingamechanismtoconnectthissystemtoexistingSIPsystemsandthepublictelephonenet-work.

OfferingadesignthatprovidessecureidentitiesonanuntrustedP2Poverlaynetwork.

SectionIIbeginswithadiscussionofcurrentVoIP/IMarchitecturesandconcepts.ThebasicsoftheSIPandSIMPLEprotocolsarepresented,andexistingP2Pef-fortsinIM/VoIParediscussed.SectionIIIpresentstherequirementsforanopenP2PapproachtoVoIPandIM.SectionIVintroducestheSOSIMPLEarchitecture,anddiscusseshowourapproachmeetstherequirementspresentedinsectionIII.Finally,weconcludewithsomediscussionofopenquestionsandfuturework.

II.EXISTINGSOLUTIONS

A.VoIPandIMOverview

ExistingVoIPandIMsystemsneedtoprovidecapa-bilitiesforresourcelocation,sessionestablishmentandmanagement,andpresence.

Resourcelocationisprimarilyresponsibleforidenti-fyingandlocatingotheruserswhoareconnectedtothesystemsothatconversationscanbeestablished.Sessionestablishmentandmanagementallowsausertoinitiate