GSM switching services and protocols P3

Kiến trúc hệ thống và biểu Tổng mô tảcác mạng GSM được cấu trúc hệ thống dọc (Hình 3.1). Họ đáng kể của khu vực hành chính bao gồm ít nhất một, mà là giao cho một Trung tâm Chuyển mạch di động (MSC). Mỗi khu vực hành chính được tạo thành ít nhất một Địa điểm Diện tích (LA). Đôi khi LA cũng được gọi là khu vực truy cập. LA An bao gồm các nhóm tế bào khác nhau. Mỗi nhóm tế bào được phân công một Base Station Controller (BSC). Vì vậy đối với từng LA tồn...
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GSM switching services and protocols P3 GSM Switching, Services and Protocols: Second Edition. Jorg Eberspacher, È È Hans-Jorg Vogel and Christian Bettstetter È È Copyright q 2001 John Wiley & Sons Ltd Print ISBN 0-471-49903-X Online ISBN 0-470-84174-5 3 System Architecture and Addressing3.1 General DescriptionGSM networks are structured hierarchically (Figure 3.1). They substantially consist of atleast one administrative region, which is assigned to a Mobile Switching Center (MSC).Each administrative region is made up of at least one Location Area (LA). Sometimes theLA is also called the visited area. An LA consists of several cell groups. Each cell group isassigned to a Base Station Controller (BSC). Therefore for each LA there exists at leastone BSC, but cells of one BSC may belong to different LAs. Figure 3.1: GSM system hierarchyThe exact partitioning of the service area into cells and their organization or administrationwith regard to LAs, BSCs, and MSCs is, however, not uniquely determined and is left tothe respective network operator who thus has many possibilities for optimization. Figure3.2 shows the system architecture of a GSM Public Land Mobile Network (PLMN) withessential components. The hierarchical construction of the GSM infrastructure becomesevident again. The cell is formed by the radio area coverage of a Base Transceiver Station(BTS). Several base stations together are controlled by one BSC. The combined traf®c ofthe mobile stations in their respective cells is routed through a switch, the Mobile Switch-ing Center (MSC). Calls originating from or terminating in the ®xed network (e.g. theIntegrated Services Digital Network, ISDN [7]) are handled by a dedicated Gateway30 3 System Architecture and Addressing Figure 3.2: GSM system architecture with essential componentsMobile Switching Center (GMSC). Operation and maintenance are organized from acentral place, the Operation and Maintenance Center (OMC). Several databases are avail-able for call control and network management:² Home Location Register (HLR)² Visited Location Register (VLR)² Authentication Center (AUC)² Equipment Identity Register (EIR)For all subscribers registered with a network operator, permanent data (such as the usersservice pro®le) as well as temporary data (such as the users current location) are stored inthe HLR. In case of a call to a user, the HLR is always ®rst queried, to determine the userscurrent location. A VLR is responsible for a group of LAs and stores the data of subscriberswho are currently in its area of responsibility. This includes parts of the permanentsubscriber data which have been transmitted from the HLR to the VLR for faster access.But the VLR may also assign and store local data such as a temporary identi®cation. TheAUC generates and stores security-related data such as keys used for authentication andencryption, whereas the EIR registers equipment data rather than subscriber data.3.2 Addresses and Identi®ersGSM distinguishes explicitly between user and equipment and deals with them separately.According to this concept, which was introduced with digital mobile networks, mobileequipment and users each receive their own internationally unique identi®ers. The user3.2 Addresses and Identi®ers 31identity is associated with a mobile station by means of a personal chip card, the Subscri-ber Identity Module (SIM). This SIM usually comes in the form of a chip card, which istransferable between mobile stations. It allows to distinguish between equipment mobilityand subscriber mobility. The subscriber can register to the locally available network withhis or her SIM card on different mobile stations, or the SIM card could be used as a normaltelephone card in the ®xed telephone network. However, he or she cannot receive calls on®xed network ports, but further development of the ®xed networks as well as convergenceof ®xed and mobile networks could make this possible, too. In that case, a mobile subscri-ber could register at an arbitrary ISDN telephone and would be able to receive calls.In addition, GSM distinguishes between subscriber identity and telephone number. Thisleaves some scope for development of future services when each subscriber may be calledpersonally, independent of reachability or type of connection (mobile or ®xed). B ...