Updated Development of lMS Standardization

Li Haihua

（China Academy of Telecommunications Research, MII, Beijing 100045, China）

Abstract:As the integrated core network for fixed and mobile access,the IP Multimedia Subsystem（IMS）adopts the mechanism that separates bear control from session control,as well as separates service control from session control,which greatly enhances the network capabilities.It's publicly regarded that IMS is the orientation of network evolvement and development nowadays.The international series of IMS standardizations are accomplished by the Third Generation Partnership Project（3GPP）and Telecommunications and Internet Converged Services and Protocols for Advanced Networking（TISPAN）standard organizations.This article covers the general standards of IMS by 3GPP and TISPAN,the research on the key technologies and hot issues of IMS.This includes the improvement and enhancement of core control part of IMS network,the existing problems in the interconnection and coexistence between IMS and Circuit Switching（CS）domain that are related to IMS.In addition,it includes the related research upon IMS in the Next Generation Network（NGN）R2 phase.he IPMultimedia Subsystem（IMS）is proposed by the Third Generation Partnership Project（3GPP）organization in R5,which is a general term for the logic functional entities on the network core layer that is controlled by IMS.The concept of IMS can be divided into the narrow sense and the broad sense.In the narrow sense,it refers to the logical functional entities involved in the network core controllayer in version 3GPPR5 or above.In the broad sense,it's a general term based on the IMSnetwork architecture.This article focuses on the description related to the network core control part.

The international oganizations for IMS standardization mainly include the 3GPP and Telecommunications and Internet Converged Services and Protocols for Advanced Networking（TISPAN）.The 3GPPresearches IMSfrom the mobile aspect,while TISPAN raises requirements for IMSfrom the fixed aspect.The 3GPPimproves it in a unified sense,and eventually implements the unified control upon fixed and mobile T access by IMS.

1 IMS Standardization by 3GPP

The IMSwas first introduced by the 3GPP in R5,and has been further improved in R6 and R7.The IMSR5 has been frozen since September 2002,which emphasizes on the research of IMSbasic structure,related functional entities,interactive flows between function entities,and more.The IMSR6 was frozen in March 2005.That emphasizes on the interconnection between IMSand external network including the interconnection with Circuit Switching（CS）domain,the interconnection with IP network,the interconnection with Wireless Local Area Network（WLAN）,and the supporting of various services.The IMSR6 specifies that the services are provided and controlled by the home location of IMSsubscribers.Therefore,the IMSbecomes a real operable network technology.The IMSR7 would be frozen at the end of 2006,which is more concerned with the requirements upon fixed access,and based on absorbing the research results of TISPAN,including:Fixed Broadband Access to IMS（FBI）,Circuit Switching and IMSIntegrated Services（CSI）,IMS emergency services,and more［1-2］.

2 IMS Standardization by TISPAN

The TISPAN has been in close cooperation with the 3GPPon the research of IMS,and submits proposals to the 3GPPabout the suggestion of amending IMSfrom the aspect of fixed access.Working in the similar way as the 3GPP,TISPAN issues different versions for different phases.Up to now,it has released the corresponding specifications of version R1,and is in the researching process of version R2.

（1）Phase R1

Considering the architecture,TISPAN adopts the IMSstructure defined by 3GPPR7（refer to TS.23.228 v.7.2.0）,with corresponding amendments for the particular requirements.That is,raises the Network Attachment Subsystem（NASS）and the Resource and Admission Control Subsystem（RACS）,including the architecture of the two subsystems and the interfaces between functionalentities in these subsystems;gives the mechanism to support and achieve the PSTN/ISDNEmulation Subsystem（PES）based on IMSarchitecture,and more.Considering the protocol,the interface already defined by 3GPPand TISPAN makes corresponding amendments for the particular requirements of fixed access,defines the protocol between NASSand external interfaces,and defines the protocol between RACSand external interfaces.Considering the service,TISPANdefines how to implement the supplementary services of the traditional telecommunication network in the IMSstructure.

（2）Phase R2

Presently,the R2 phase is mainly in the phase of requirement analysis,highlighting the projects of research on RACSR2,IPTV,Fixed-mobile Convergence（FMC）,home network,and the improvement of PESstructure.However,currently these projects have not made very great progress.Due to the pressures from various aspects,TISPAN has announced on the TISPAN 10Ter conference that the research on architecture can be free from the restrictions by the progress of requirement analysis,and can be gradually improved［3-4］.