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fixed access networks by TISPAN andITU-T standard bodies.At present, IMS is not matureenough to be able to address theproblems that may arise in PSTNE m u l a t i o n S u b s y s t e m ( P E S ) .Moreover, there is no example of IMSbasedPES application in real world.So, in the recent two years, Softswitchwill still be the major element in thetransformation of PSTN.However, operators and vendorsin anticipation of IMS are workingdiligently to outline evolutionstrategies from Softswitch to IMS. Theuniversally approved evolution path isshown in Fig. 3.Stage 3 probably takes two to threeyears. Commercial deployment hasa long way to go before a full set ofstandards and a viable business modelare developed. Therefore, Softswitchis an impassable stage. Incumbentoperators are advised to start theirtransformation with the Softswitchapproach.Stage 4: FMC. Fixed and Mobileconvergence (FMC) is the ultimategoal of fixed network development.While GSM/CDMA networks areevolving towards mobile NGN,also known as mobile Softswitcharchitectures (R4 in 3GPP and LMSDin 3GPP2), PSTN networks are movingto the fixed network Softswitch, orfixed NGN, paving the way for FMC.In fact, FMC will take place at eachlayer of the network. For instance, atthe service layer, the unified servicedelivery platform enables simultaneousdelivery of services over fixed andmobile networks. At the access layer,◆ Softswitch (SS) can be upgraded to provide functions of the following networkelements based on the different networking situations: Call Session ControlFunction (CSCF), Media Gateway Control Function (MGCF), Access GatewayControl Function (AGCF), PSTN Emulation and Simulation Subsystem (PES/PSS).◆ Upgrade SHLR to provide the IMS HSS function, and upgrade SS or introduceIMS subsystem for multimedia service provision.◆ Upgrade SS to provide the MGCF function for full interoperability between IMSand the existing networks, upgrade SS to provide AGCF function or introduce theIMS element AGCF for PES service support, cut over part of NGN subscribersto IMS. At the beginning of IMS construction, it is recommended to deliver thenarrowband voice service through Softswitch.Fig. 3 Smooth evolution to IMSintegrated gateways support wirelesswirelineconvergence. At the core functions in each link in the new industryhuge potentials and display greatlayer, IMS provides unified control for value chain created by broadbandboth fixed and mobile networks. multimedia services. As the globalFixed network now has a slow economy is fastly growing, there is nodevelopment pace as if it entered limits to people’s demand for multimedia“the hibernation state”. However, services, content-based services andfixed operators are accelerating the bandwidth, spurring developmenttransformation process and developing of new technologies and innovativetowards multi-dimensional operations. services, which in turn stimulate userThey are expanding their voice and data demands. We have full confidence thatservice offering with the addition of the “Springtime” for fixed network willmultimedia services. They will unleash come soon.ZTE TECHNOLOGIES11