42 IMS White Paper Acronyms PDAPersonal Digital Assistant PDFPolicy Decision Function PDSPacket Data Subsystem PDSNPacket Data Service Node POTSPlain Old Telephone Service PSTNPublic Switched Telephone Network PLMNPublic land Mobile Network QoSQuality of Service RANRadio Access Network RADIUSRemote Authentication Dial In User Service RFRating Function RTPReal-Time Transport Protocol RTCPRTP Control Protocol SBCSession Border Controller SCCPSignaling Connection Control Part SCFSession Charging Function SCIMService Capability Interaction Manager SCPService Control Point S-CSCFServing Call Session Control Function S-CSCFServing CSCF SCTPStream Control Transmission Protocol SCFService Control Function SCPService Control Point SCSService Capability Server SDOStandards Development Organization SDPSession Description Protocol