ABSTRACT
Project.Background............................................................................................. 114 The.Components.................................................................................................. 115
Requirements.............................................................................................. 117 The.Call.Session.Control.Functions......................................................... 118
SER.IMS.Extensions........................................................................ 119 Proxy-CSCF..................................................................................... 121 Interrogating.CSCF......................................................................... 122 Serving.CSCF.................................................................................. 123
Home.Subscriber.Server............................................................................ 124 Working.with.the.Open.IMS.Core.................................................................... 125 A.Real.Reference.Implementation?................................................................... 127 Outlook.................................................................................................................. 129 References............................................................................................................. 130
Back.in.2003,.when.we.started.our.research.work.on.the.IP.Multimedia.Subsystem. (IMS),.we.had. the.big. challenge.of.finding.a. suitable. solution. that. would.enable.us. to. route.and.process. session. initiation.protocol. (SIP). signaling.in.conformance.with.the.IMS.standards.(at.that.time.3GPP.release.5. [1]).at.an.affordable.cost.for.a.research.and.development.(R&D).institution.. Although. we. found.many.open. source. projects. focused.on. Internet. Engineering.Task.Force.(IETF).SIP.topics,.we.sadly.did.not.find.any.with.a.specific.emphasis.and.direction.on.IMS..Add.to.this.the.fact.that.we.had.a.long. legacy.in.developing.SIP.prototypes.at.Fraunhofer.FOKUS,.and.we.started. doing.our.own.development.
