GSM switching services and protocols P4

Các dịch vụ được cung cấp tại ± người dùng giao diện mạng (UNI) của GSM thường là màu sau khi dịch vụ được cung cấp bởi các dịch vụ kỹ thuật số tích hợp Network (ISDN) [7] cho ® xed thiết bị đầu cuối gắn với các dòng máy điện thoại. dịch vụ GSM do đó chia giống như dịch vụ ISDN thành ba loại: dịch vụ không ghi tên, teleservices, và các dịch vụ bổ sung. Một dịch vụ không ghi tên cung cấp các khả năng kỹ thuật cơ bản cho việc truyền tải dữ liệu nhị...
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GSM switching services and protocols P4 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 4 ServicesThe services offered at the User±Network Interface (UNI) of GSM are patterned after theservices offered by the Integrated Services Digital Network (ISDN) [7] for ®xed terminalstied to telephone lines. GSM services are therefore divided just like ISDN services intothree categories: bearer services, teleservices, and supplementary services. A bearerservice offers the basic technical capability for the transmission of binary data; i.e. it offersthe data transfer between end terminals at reference points R or S of the Reference Model(Figures 4.1 and 9.1). Such bearer services are made use of by the teleservices for thetransfer of data with higher-level protocols. Figure 4.1: Bearer and teleservicesNotice that bearer and teleservices both require special measures not only at the air inter-face, but also inside the PLMN, which must offer a matching ®xed-net infrastructure andspecial Interworking Functions (IWFs). Especially at the level of bearer services, the IWFmust provide a mapping of GSM PLMN services within their respective service charac-teristics onto corresponding bearer services and characteristics of the other networks, suchas PSTN and ISDN. Teleservices are end-to-end services, for which there is usually notranslation in the IWF. But they do use bearer services, which again need IWF functions.Bearer and teleservices are carried under the umbrella term telecommunication services.The simultaneous use of two telecommunication services is precluded, except for the caseof Short Message Services (SMS), which can at least be received during the use of anothertelecommunication service. Supplementary services are complementing the control andmodi®cation of extended services and are only usable in connection with a telecommuni-cation service.48 4 ServicesFor telecommunication services, the GSM standard includes agreements of target times fortheir market introduction. This fact is especially important, since GSM is an internationalstandard which aims at worldwide compatibility of mobile stations and networks. Accord-ingly, only a minimum of services has been de®ned, which must be offered by the opera-tors at various time phases. For this purpose, the services are divided into the categoriesessential (E) and additional (A). Group E must be implemented at the given date by allnetwork operators, whereas the decision about the time of introduction of Group Aservices is left to the operators. Table 4.1 gives a rough overview over the implementationand introduction phases. The most important services to be implemented and introducedwith their respective introduction dates are described brie¯y in the following. Table 4.1: Phases of implementation and introductionClass Introduction ServicesE1 1991 Basic operation consisting of telephone services and some appropriate supplementary servicesE2 1994 Extended operation with telephone services, ®rst non- speech services (e.g. BS26) and an extended range of supplementary servicesE3 1996 Enhanced service range with even more telecommunication and supplementary services4.1 Bearer ServicesThe basic services of a GSM network are the foundation for data transmission, i.e. a basicservice provides the fundamental technical facilities at the end terminal interface (refer-ence point R) to transport user payloads. The basic services are called transport services [7]or bearer services in ISDN ± and therefore in GSM, too. The GSM bearer services offerasynchronous or synchronous data transport capabilities with circuit-switched or packet-switched data rates of 300±9600 bit/s, with a 13 kbit/s bearer service for voice.Bearer services carry only the coding- and application-independent information transportbetween the user±network interfaces (Figure 4.1); they represent the services of Layers 1,2, and 3 of the OSI ...