IMT-2000 Network Architecture

vToshio Shimoe vTakamichi Sano (Manuscript received May 31, 2002)

International Mobile Telecommunication-2000 (IMT-2000) is a third-generation mobile communication system. It has been established as an international standard to realize advanced services and also overcome the performance limitations of the telephone and data communication services that are based on existing second-generation mobile communication systems (i.e., Personal Digital Cellular [PDC], cdmaOne, and Glo- bal Systems for Mobile communications [GSM]). This paper outlines the services recommended in IMT-2000 and describes the base station systems, switching systems, and various servers of the IMT-2000 network architecture. This paper also describes the packet processing mechanism and the tech- niques for constructing IMT-2000 networks. Finally, this paper describes the technologies related to intelligent networks (IN), which provide additional, highly advanced services.

1. Introduction the future. Mobile telephone and data transmission ser- International Mobile Telecommunication- vices are mainly provided by the 2000 (IMT-2000) is a new, third-generation mobile second-generation mobile systems that are the network being discussed at international stan- domestic standards worldwide. In Japan, the dards organizations to overcome the weak points major digital mobile networks are based on the of second-generation mobile networks. IMT-2000 Personal Digital Cellular (PDC) system. On the is expected to consist of multi-vendor networks other hand, a mobile telecommunication service and to advance the standardization of the inter- vender has started a commercial service based on face between the functional elements of networks. the cdmaOne system, which is a North America IMT-2000 networks can be functionally clas- standard. In other countries, mobile networks are sified into Core Networks (CNs), Radio Access constructed with one of two systems. One is the Networks (RANs), Intelligent Networks (INs), and Global Systems for Mobile (GSM) communications other networks installed in center offices. system, which has shown the best results so far, The IMT-2000 standards are being discussed and the other is the cdmaOne system, which is by two organizations: the 3rd Generation Partner- based on the latest technology. ship Project (3GPP) and the 3rd Generation There is a limit to the data communication Partnership Project2 (3GPP2). The participants speed in second-generation mobile networks. Also, of the 3GPP are ARIB, ETSI, TI, TTA, and TTC, it has been pointed out that there is a limit to the and the participants of the 3GPP2 are ANTI, supply of high-speed IP packet services, for which ARIB, ETSI, TTA, and TTC. The 3GPP aims to there will be an explosive increase in demand in construct an IMT-2000 network based on the GSM

134 FUJITSU Sci. Tech. J., 38,2,p.134-139(December 2002) T. Shimoe et al.: IMT-2000 Network Architecture

network. On the other hand, the 3GPP2 aims to mation service using mobile networks has been develop standards for the IMT-2000 network by examined. For example, traffic information and enhancing the cdmaOne system. In the 3GPP, sightseeing guides for a specific area and naviga- IMT-2000 is referred to as the Universal Mobile tion services can be provided based on terminal Telecommunication System (UMTS) or Wideband location information. CDMA (W-CDMA). In Japan, the ARIB and TTC have advanced the domestic standardization of W- 2.2 Global service CDMA and cdma2000. A global service allows a user to communi- However, although the network configura- cate anywhere, both indoors and outdoors, tions of W-CDMA/UMTS and cdma2000 are regardless of the user’s moving speed and loca- similar, there is a difference in the packet pro- tion (e.g., city, suburb, or countryside). One of the cessing method. This paper outlines the IMT-2000 major achievements of a global service is that it networks and the differences between the two enables global roaming: that is, users can use the network technologies. same mobile terminal in any country without hav- ing to change any of its settings. 2. Services in IMT-2000 networks To realize a global service, three levels of One of the main purposes of IMT-2000 is to mobility are required: terminal mobility, user provide global roaming services. In order to offer mobility, and service mobility. Terminal mobility worldwide communication services that include means independence from the location and radio access to fixed networks and the Internet, IMT- conditions. User mobility means that any mobile 2000 is designed to connect not only land mobile terminal can be used. Service mobility means that networks but also fixed networks and satellite the service environment of the home network can mobile networks. be reproduced in another network. Another major purpose of IMT-2000 is to pro- One of the major technical issues in these vide broadband services for mobile terminals. Of global services is how to provide the high levels of course, seamless handover is required to provide security and privacy that are required. quality of service (QoS) in high-speed transfer services. The services that IMT-2000 is designed 2.3 Seamless service to provide are described below. A seamless service allows a user to connect to a conventional network and the Internet with 2.1 Multimedia communication service the same quality regardless of the wireless envi- A multimedia service offers the service qual- ronment, location, and communication service ities (transmission rate, line quality, delay time, vendor. etc.) required for voice communication and data communication (including video communication). 3. Standardization trend For example, notebook personal computers The 3GPP and 3GPP2 were established to equipped with a mobile terminal offer a service discuss the IMT-2000 from the end of 1998 to the quality that is equivalent to that offered by fixed beginning of 1999. The 3GPP makes mobile net- networks. As a result, it is now possible to access work system specifications based on the GSM the World Wide Web, e-mail, electronic commerce communications/General Packet Radio Service services (e.g., electronic bank services), and infor- (GPRS), and the 3GPP2 is based on the ANSI-41. mation services such as electronic newspapers and The standardization work of Release1999 (the education courses outdoors. 1999 edition recommendation, or R99 for short) Moreover, a highly accurate location infor- was completed by the 3GPP in December 1999.

FUJITSU Sci. Tech. J., 38,2,(December 2002) 135 T. Shimoe et al.: IMT-2000 Network Architecture

R99 basically follows the functions of GSM and to the IN in the conventional networks can be con- GPRS that have already been recommended. In nected to IMT-2000 networks. the 3GPP2, the standardization work of Release Compared to the first method, this method A was completed in December 1999. Release A requires a lower initial capital investment and basically follows the functions of cdmaOne that makes it easier to construct an IMT-2000 network. have already been recommended. However, this method requires changes to be made Both the 3GPP and 3GPP2 have included the to the conventional networks. achievement of high-speed data transfer in all of their recommendations. The speeds they recom- 4.2 Necessary nodes for construction of mend are 64 kb/s or more in circuit switching mode IMT-2000 networks1) and 384 kb/s or more in packet switching mode As mentioned above, an IMT-2000 network (2 Mb/s for a stationary terminal). basically consists of the RAN, CN, IN, and other elements (Figure 1). This section introduces each 4. Mobile network structure of these nodes in the W-CDMA/UMTS system. The migration from conventional networks 1) RAN is the most important issue for realizing IMT-2000 The RAN is a wireless network located be- mobile networks. In this section, we describe the tween the user terminal and the CN. It is architecture of IMT-2000 networks. Then, we in- composed of Radio Network Controllers (RNCs), troduce the node group needed to construct a Node-Bs, OMC-Rs, and other components. mobile network. 2) CN2) The CN is a network located between the 4.1 Realization of IMT-2000 networks RAN and another network (e.g., a Public Switched To construct IMT-2000 networks from con- Telephone Network [PSTN]). It is composed of ventional networks, network venders can use circuit switches (Mobile Switch Center [MSC]/ either of the following two network construction Gateway Mobile Switch Center [GMSC]), packet methods. switches (Serving GPRS Support System [SGSN]/ 1) New installation of IMT-2000 networks Gateway GPRS Support System [GGSN]), sub- The IMT-2000 network can be installed with- scriber databases (Home Location Register [HLR]/ out influencing conventional operating networks. Visitor Location Register [VLR]), address resolu- However, the initial capital investment required tion servers for packet processing (Domain Name to install IMT-2000 is high. Server [DNS]), and the authentication and secu- 2) Construction of IMT-2000 networks through rity centers (Authentication Center [AuC]/ effective use of existing networks. Equipment Identity Register [EIR]). In this method, the facilities of the conven- 3) IN tional networks are used as much as possible to The intelligent network is a node group for construct IMT-2000 networks economically. For achieving enhanced services (number portability, example, the RAN part of IMT-2000, including the freephone, credit card calls, etc.). It is composed voice circuit-switching, can be connected with con- of Service Control Points (SCPs). ventional core networks. As described above, the 4) Other devices standardization of the IMT-2000 network is done Some of the other IMT-2000 network compo- based on the existing networks. This method fo- nents are: cuses a lot on the usability of existing technologies. •Voice Mail System (VMS). This has voice re- Moreover, subscriber databases (e.g., the Home cording and replay functions such as an Location Register [HLR]) and the devices related answer phone. There is also a component

136 FUJITSU Sci. Tech. J., 38,2,(December 2002) T. Shimoe et al.: IMT-2000 Network Architecture

Intelligent network (IN) SCP SMSC PDC network Core network (CN)

HLR/AuC/ VMS EIR GSM network

Radio access network (RAN) PLMN PSTN MSC GMSC N-ISDN Um VLR UE lub lu RNC IP networks Node B SGSN GGSN

PDSN WAP NMS GCR Backbone network BC APL DNS

APL : Application server GMSC : Gateway mobile switching center PDC : Personal digital cellular SGSN: Serving GPRS support node AuC : Authentication center GSM : Global system for mobile PDSN: Packet data switched network SMSC: Short message center BC : Billing center HLR : Home location register PLMN: Public land mobile network UE : User equipment DNS : Domain name server MSC : Mobile switching center PSTN: Public switched telephone network VLR : Visitor location register EIR : Equipment identity register N-ISDN: Narrowband ISDN RNC : Radio network controller VMS : Voice mail system GCR : Group call register NMS : Network management system SCP : Service control point WAP : Wireless application protocol GGSN: Gateway GPRS support node

Figure 1 IMT-2000 (UMTS) network structure.

for receiving and re-sending faxes. 5.1 W-CDMA/UMTS packet processing • Short Message Center (SMSC). This compo- The specifications for the packet system of nent is used for transmitting and receiving W-CDMA/UMTS are the same as those for the character information. The SMSC can be GPRS system that has been used with conven- used, for example, to notify subscribers that tional GSM networks. Currently, mobility there is a message for them in the VMS. management of the subscriber is done using the • Group Call Register (GCR). This is a data- HLR. When the subscriber moves, the location base for group call services. information in the HLR is renewed. When the •Wireless Application Protocol (WAP) server. packet arrives, the location information in the This is a server that offers subscribers vari- HLR is referenced and the packet is transmitted ous information using the Wireless to the switch node to which the target mobile ter- Application Protocol. minal is registering (Figure 2).

5. Packet switching in IMT-2000 5.2 cdma2000 packet processing It was mentioned above that there are two Because the specifications for the packet pro- kinds of IMT-2000 systems: W-CDMA/UMTS and cessing method were not standardized in cdma2000. This section outlines the packet pro- cdmaOne, they have been standardized in its re- cessing of these two systems. placement, cdma2000. The packet processing method of cdma2000 adopts the Mobile IP system,

FUJITSU Sci. Tech. J., 38,2,(December 2002) 137 T. Shimoe et al.: IMT-2000 Network Architecture

HLR Mobile Mobile network (A) network (A) PDGN RAN PDSN RAN SGSN GGSN (HA)

(1) (2) Internet Mobile network (B) (1) Mobile network (B) PDSN Internet RAN (FA) PDGN RAN SGSN GGSN (2)

(1) The core-of-address (CoA) of mobile terminal is updated in (1) The location information in HLR is updated along with the HA along with the subscriber movement. subscriber movement. (2) Incomming packets are re-forwarded by the CoA in HA. (2) SGSN is specified by the location information in HLR. Figure 3 Figure 2 cdma2000 packet processing. UMTS packet processing.

Service Service development management which differs from the HLR system in W-CDMA/ environment system (SMS) UMTS and is being discussed by the IETF. When a user moves to a foreign network, a care-of ad- Home location Service control register (HLR) point (SCP) dress is sent from the Foreign Agent (FA) in the IN protocol Mobile (CAP/WIN) IN protocol foreign network to the Home Agent (HA) in the protocol (CAP/WIN) user’s home network. As shown in Figure 3, the (MAP) packets for a moving user are re-forwarded to the Mobile switch node Mobile switch node Service Service FA by the HA according to the care-of address. switching point switching point (SSP) (SSP) 6. Intelligent network (IN) The IMT-2000 IN is the key component for realizing a Virtual Home Environment (VHE), Other switch nodes which is a concept for providing the service motil- ities described in Section 2.2. For example, when Figure 4 roaming is done, the pre-paid card service avail- Intelligent network for mobile network. able in the home network can be made available in other networks. To realize a VHE, the intelligent network centrally manages the service logic Application Protocol (INAP) that is being recom- at a Service Control Point (SCP) and the SCP con- mended by the ITU-T/ETSI. CAMEL implements trols the Service Switching Point (SSP) to offer a part of the GSM Mobile Application Protocol the subscriber service as shown in Figure 4. (MAP) for interconnection between the SCP and The different protocols of SCP and SSP/HLR HLR and was recommended in the form of the were standardized by the 3GPP and 3GPP2. The CAMEL Application Protocol (CAP). 3GPP applied the Customized Application or Mo- On the other hand, for cdma2000 networks, bile network Enhanced Logic (CAMEL), and the the Wireless IN (WIN) was recommended. The 3GPP2 applied the Wireless Intelligent Network WIN was enhanced from the ANSI-41 MAP, which (WIN). the Telecommunication Industry Association CAMEL is based on the Intelligent Network (TIA)/Electronic Industry Association (EIA) stan-

138 FUJITSU Sci. Tech. J., 38,2,(December 2002) T. Shimoe et al.: IMT-2000 Network Architecture

dardized for the CDMA recommendations. New a Fixed Mobile Convergence (FMC), which is an operations for SCP and HLR communication were integration of fixed and mobile networks. More- recommended for the WIN. Also, the existing MAP over, a standard for all IP-based IMT-2000 systems was changed to accommodate the introduction of without circuit switching will be recommended. the WIN. IMT-2000 systems have the latent ability to form In the future, intelligent networks will occu- FMCs. py the most important positions in networks and IMT-2000 is expected to be developed as an will become indispensable for offering a seamless infrastructure with new functions and services service in mobile and also fixed networks. Intel- such as high-speed IP communication over mo- ligent networks integrate the functions of the bile terminals and service portability realized service control and management and can provide through the use of intelligent networks. various services between different networks. On the other hand, several issues remain: for example, how to guarantee global roaming be- 7. Conclusion tween W-CDMA/UMTS and cdma2000 systems. NTT DoCoMo,Inc. has constructed an IMT- These remaining issues must be solved so that 2000 network based on the UMTS system and IMT-2000 can develop as the infrastructure of a began IMT-2000 services in May 2001. For the truly global standard. Fujitsu will enhance the network, Fujitsu developed a Base Transceiver functions of IMT-2000 based on the appropriate Station for Node-B, an RNC, and a Mobile Multi- international standards. media Switching node (MMS) for the CN. Fujitsu’s systems efficiently integrate circuit switching and References packet switching services by using ATM and 1) H. Yumiba et al.: Overview of IMT-2000 Net- Switched Virtual Connection (SVC) systems. work Systems. (in Japanese), NTT DoCoMo We are convinced that mobile networks will Tech. Journal, 6, 4, p.8-13 (1999). become major parts of the access networks of the 2) K. Yamamoto et al.: Core Network Technol- 21st century. Communication networks are ex- ogies. NTT DoCoMo Tech. Journal, 3, 3, pected to develop into a new type of network, called p.16-30 (2001).

Toshio Shimoe received the M.S. de- Takamichi Sano received the B.S. de- gree in Communication Engineering gree in Control and System Engineer- from Tohoku University, Sendai, Japan ing from Tokyo Institute of Technology, in 1978. He joined Fujitsu Laboratories Tokyo, Japan in 1974. He joined Fujitsu Ltd., Kawasaki, Japan in 1978, where Ltd., Kawasaki, Japan in 1974, where he was engaged in research and de- he has been engaged in research and velopment of digital switching systems development of digital switching sys- and photonic switching technologies. In tems, ISDN switching systems, mobile 1991, he joined Fujitsu Ltd., Kawasaki, switching systems (IMT-2000), and Japan, where he has been engaged in mobile Internet communication sys- research and development of asynchro- tems. nous transfer mode switching systems and mobile switching systems.

FUJITSU Sci. Tech. J., 38,2,(December 2002) 139