GSM transmisyon donanımları gözetim ve denetim arayüzü

Abstract

GSM, genel seyyar anahtarlama şebekesi için tanımlanmış dijital haberleşme sistemi modelidir. Bu sistem iki kısımdan oluşur. Belirli bölgeler içindeki abonelere hizmet veren, temel anahtarlama ve transmisyon donanımlanmn bulunduğu seyyar kısmı (temel istasyon alt sistemi, BSS) ve gerçek anahtarlama işlemelinin yapıldığı, abone bilgilerinin statik ve dinamik olarak tutulduğu, bakım ve işletimin sağlandığı birimlerin bulunduğu sabit kısım (şebeke alt sistemi). GSM modeli, farklı üreticiler tarafından üretilen BSS sistemi İle şebekenin bağlantısını mümkün kılan standart arayüzleri de belirler. BSS sistemi, şebeke alt sistemlerine standart "A" arayüzü üzerinden bağlanır [ 1 ]. BSS sistemi, temel istasyon kontrolcüsü (BSC) ve temel dönüştürücü istasyonundan (BTS) oluşur. Şebeke alt sistemine "A" arayüzü üzerinden bağlanan BSC, BSS transmisyon donanımlarını gözetlemek ve denetlemek üzere bir TSC birimine sahiptir. BSS transmisyon donanımlarının bulunduğu şebeke servis şebekesidir. TSC, servis şebekesi üzerindeki şebeke elemanlarıyla, QMUX protokolü aracılığıyla haberleşir. Gerçekleştirilen projede, TSC, ATSC ismiyle anılmaktadır. Tez kapsamında geliştirilen bu uygulamada, ATSC nin transmisyon donanımlarını sorgulaması QMUX protokolüne uygun olarak gerçeklenmiştir. Üç katmanlı bir protokol olan QMUX protokolünün, uygulama katmam prosesi (SBHNDLR) ve veribağı katmanı prosesleri falıcı ve verici) tasarlanıp gerçeklenmiş ve test edilmiştir. ATSC, bu protokol aracılığıyla transmisyon donanımlarını sorgular, kontrol eder, donanım üzerindeki bazı parametreleri okur, değiştirir, servis şebekesinde meydana gelecek hataları lokalize etmek üzere servis şebekesi elemanlarının sağladığı kolaylıktan yararlanmayı sağlar. Bunun için, servis şebekesi elemanlarının sorgulanması, veritabanı tablolarının güncellenmesı ve OMC ye raporlanmasımn yam sıra, ATSC yerel terminalinden ve BSC den gelen ve bu donanımlar üzerinde gerçeklenmesi istenen birtakım istekler, bu protokol aracılığıyla gerçeklenir. Transmisyon donanımlarından edinilen bilgiler doğrultusunda, tasarımı yapılan veritabanı tabloları veritabanı erişim fonksiyonları aracılığıyla güncellenir. Tasarım SDL dili, yazılım ve test C dili aracılığıyla yapılmıştır. SDL kavramıyla birlikte gelen ADÎ soyut veri yapısı kullanılmıştır ve yazılımı C dili ile yapılmıştır. SDL dili, bu tür haberleşme uygulamaları geliştirmeye yönelik tasarımlarda büyük kolaylıklar getirmektedir.

Use of cellular mobile radio telephones has shown dramatic growth in recent years. This is yet largely uncoordinated growth has resulted in 1 1 types of public radiotelephone network in 20 countries, which are incompatible m their standarts or frequency ranges. Clearly there is a need for standarts to be defined, agreed, and adhered to if a common European system is to be developed and implemented. With this end in mind, the GSM was set up by CEPT m 1982. GSM has steadily drawn up standarts which are now accepted by the majority of European countries. In fact, most European PTTs have already signed an agreement to implement the GSM system, pointing to a future where mobile subscribers will be able to roam across Europe with uninterrupted service. GSM Model : GSM has defined a public land mobile network consisting of two parts: base station subsystem and network subsytem (Figure 2.1.). The GSM model also specifies standard interfaces that will make it possible to interconnect network and base station subsystems supplied by different vendors. The base station subsystem is partitioned into a base station controller and a base transceiver station. The controller is connected to the network subsystem via a standard "A" interface, based on the CCITT No.7 signalling system. The transceiver, which handles radio communication with the mobile stations, can be embedded in a controller or installed remotely. The network subsystem is based on five functional components, as follows. Mobile Services Switching Centre : This is the link between the fixed land network and its mobile subscribers. Mobile network interfaces include a mobile application part for interfacing with network databases and other switching centres via the PSTN, an operations and maintenance application part for interfacing with the network management centre via the data communication network, and a base station subsystem mobile application part for communication with the base station subsystem. Interfaces to the fixed public network include the telephone user part and ISDN user part: all network subsystem interfaces implement CCITT No.7 signalling, except for network management links which are preferably based X.25 protocol Home Location Register : This register is the home database for permanently storing mobile subscriber data. Each subscriber has a directory number in the national plan corresponding to the home location register address. Routing data can be retrieved from the register so that calls can be set up between mobile and fixed public network subscribers. Visitor Location Register : This is the visitors' database which is used to store information about mobile subscribers who are temporarily located within the zone of a mobile switching centre. A single visitor location register can cover a number of zones, the home and visitors location registers are constantly updated by a special dialogue. Authentication Centre : The air interface is the part of the network most vulnerable to intrusion. Measures taken to ensure that communications are secure include ciphering, subscriber authentication, and mobile identity protection. The authentication centre stores subscriber authentication keys from which other security parameters are obtained. Network Management Centre : Operating and maintenance routines for all mobile application equipment are carried out by the network management centre which can be connected to the various system components by links using either X.25 or No 7 signalling interfaces [ 1 ]. BSS SUBSYTEM The Base Station Subsystem (BSS) is the mobile access subsystem to the fixed Network Subsystem (NSS). A BSS is composed of one or more Base Transceiver Stations (BTSs) controlled by one Base Station Controller (BSC). The speech conversion function is done by a separate element called TransCoder (TC). Base Transceiver Station (BTS) : Every cell (the area of the controlled with BTS station) is served by a Base Transceiver Stations (BTSs) that provides the radio link, and is in charge of [ 18 ]; 1. The layer one and the layer two of the radio link. 2. Processing the non-transparent layer three messages. 3. The associated control functions. XI Base Station Controller (BSC) : The BTSs (one or more) of a BSS are controlled by a Base Station Controller (BSC). The BSC has the following tasks [11]; 1. To provide 2 Mbit/s PCM interfaces towards the MSC and BTS. 2. To switch user channels between the MSC interface and BTS interface (A and Abis interface). 3. To terminate and process protocols based on the CCITT No.7 signalling system (MSC interface) and LAPD (BTS interface). 4. Transparent transfer of signalling information between mobile station and MSC. 5. To process and process information (e.g. field strength measurements) required for decisions on handover of calls to other radio interfaces. 6. Operations and maintenance functions. 7. Management of the local database. TRANSMISSION EQUIPMENTS Base Station Interface Equipment (BIE) : BIE is used to provide the Abis-interface. For the BTS and the BSC the BIE is a transparent equipment. It allows multiplexing of four 16 Kbit/s traffic channels onto one 64 Kbit/s channel. According to the operator selection, the BIE interface uses either a 2Mbit link or independent 64 Kbit/s channels. The BIE allows also a 2 Mbit multidrop loop configuration. I.e. the same 2 Mbit link can be used to carry channels from several BTSs, as far as the sum of all the traffic and signalling channels from all the BTSs do not exceed links maximum capacity. The both ends of the link are connected to the BSC, providing thus also a redundant connection. In the combined configurations, the BIE can be omitted. Xll Submultiplexer (SM2M) : The submultiplexer (SM) is an independent equipment which can be used to multiplex subrate channels on the Ater-interface when the TransCoders are located at the MSC site. The basic 2 Mbit SubMultiplexer multiplexes ninety 16 Kbit/s traffic channels of three TC equipment on one 2 Mbit G.703 transmission link. As an option for a 64 Kbit/s service network there is a SubMultiplexer for 64 Kbit/s transmission links (SM64) which multiplexes the thirty 16 Kbit/s traffic channels of one TC equipment mto eight 64 Kbit/s G.703 transmission link. Submultiplexers on the BSC/MSC interface can be used or not, depending on the network configuration. If they are used, they must be used at both ends of the terrestrial transmission link. Transcoder (TRCU) : The conversion of speech between 16 Kbit/s RPE-LTP coding and 64 Kbit/s A-low PCM is done in the TransCoder (TC), that is located in the SYSTEM 900 implementation between the BSC and MSC. The TC can thus be located at the MSCsite and allows to take advantage of the difference in speech codec data rate between PCM A-low and RPE-LTP to perform submultiplexing of speech TCH to save terrestrial PCM link between MSC and BSC on one hand, and between BSC and BTS on the other hand. The interface between the BSC and the TC is called Ater-interface, and between the TC and the MSC the GSM specified A-interface is used [ 18 ]. X1U HANDOVER Figure 1. Handover of a roaming mobile station. As a mobile station moves from one cell to another during a conversation it may travel beyond the reception limits of the base station to which it is linked. To ensure that calls are not interrupted, the system followes the movement of the mobile station (Figure 1.). At the start of an incoming or outgoing call, the mobile station depends on the first base station, and is controlled by MSC(a). The established speech path goes through BSC(l) and uses links 1 and la. Tne mobile station and BSC continually monitor the radio transmission levels. If the measurements made by the mobile station indicate that it would be better to transfer to an adjacent cell, the BSC selects the most likely one. A new link is prepared for this change, and a new traffic channel is selected and communicated to the mobile station. All these tasks are carried out while the mobile station is still controlled by the base station that is leaving. In the present case, the new base station still depends on BSC(l) which set up link lb. XIV When everything is ready for the handover, an order is sent to the mobile station to switch traffic channels. At the same time, the BSC connects link 1 to link lb, and realeses link la. Further movement of the mobile station may take it into a cell that depends on another BSC, such as BSC(2). The procedure is the same, but during preparation for the handover, the MSC reserves a path 2-2a through BSC(2). Handover is carried out by the MSC, which establishes the new link and releases the former one. When a new cell depends upon another MSC (MSC(3) for example) MSCfa} extends the fixed telephone link (which remains unchanged) to the new MSC(3) over the public switched telephone network and act as a transit point. Supervision of the call remains with MSC(a), which delegates activation and deactivation to MSC(3) during handover. When the mobile station enters a cell that depends on another MSC (MSC(4) in this case) a new transit link isprepared by MSC(a) and replaced the previous one which is realesed. This procedure continues until the communication is terminated [ 2 ]. XV BASIC NETWORK SCENARIO HLR GATEWAY MOBILE İERVICE swrrcHiNGj CENTRE 1- 2 3 5 6 9 IAM (Initial Address Message CCITT No 7) INTERROGATION MAC ADDRESS OF SUBCRIBER GET SUBCRIBER DATA PAGING RESPONSE Figure 2. Network scenario for calls terminating at a mobile station. Figure 2 shows the scenario for a call to a mobile station. Calls from the ISDN or public switching telephone network (1) are routed to the gateway MSC (an MSC with a connection to the fixed network) which interrogates the HLR (2, 3) to obtain the address of the MSC within the area where the subscriber is currently located. The gateway MSC sets up the call (4) to this MSC, which then consults the VLR to obtain the necessary subsciber data (5, 6). The mobile station is then paged through all base stations (6, 7) that are served by the MSC, as the exact location of me mobile station is unknown. This is accepted as it reduces the frequency with which the location register for a roaming mobile station needs to be updated. On receiving a response (8, 9) authentication and ciphering take place. Finally, the call is directed to the mobile station [ 11 ]. XVI TSC TSC is required to monitor transmission equipments in the BSS network via QMUX protocol. Service terminal has the same protocol called as QMUX protocol. TSC communicates with BSC via the LAPD link. II Ibis 1 »Ml Abis INTERFACE 2 M highway |2M highway redundant BIU2M ?kT OMC I X.25 l( I \ l( I \ " BSC LAID IfeC QMIL\ A INTERFACE Wt rm»rjw»mM>}» M^< TRCU CZ) VT100 Figure 3. TSC context. TSC main features: 1. Monitor status of transmission equipment (fault detection). 2. Do fault localization. 3. Report re-configuration requirements. 4. Report fault information. 5. Give access to fault-localisation features of the equipments (e.g. loop test, monitor). 6. Provide details of hardware configuration. 7. The TSC has no affect on traffic. xvu TSC software: 1. Polls equipment looking for a change in status. 2. Updates changes in if s database. 3. Convert raw board level faults into SBL/RIT format. 4. Maintains a database SBL/RIT format. 5. Reports faults and recovery actions to the BSC. 6. Maintains a local interface to display, configure and monitor the transmission system. TSC functionality: 1. Fault management. Autonomous reporting of alarms. Summry current alarms. Autonomous reporting of recovery actions to the BSC. Summary of current recoveries. Performing transcoder loop tests on request. Disabling and initialisation of equipments. Local display of alarms. Service terminal emulation Read and report state of an SBL on request 2. Configuration management. Report hardware configuration to BSC/OMC. Perform a restart on request. erform a reset (reboot) on request. Configuration of equipment from the local terminal. Configuration of TSC database from local terminal QMUX bus: 1. Physical layer - CCITT Vll. Wire (2 incoming, 2 outgoing data). Connects to local equipment directly and to remote equipment via usage of spare bits on time slot (TS) 0. 2. Layer 2 - Nokia proprietry interface 3. Layer 3. Master - slave relationship between TSC and AUs (Network elements). There are number of commands defined which are performed on the xviii AU and FEs (Functional Entities). Commands are always initiated by the TSC in order that bus activity may be regulated safely. In this project, QMUX protocol is realized. BSS subsystem 1 Mobile stations 1 sy BTS \ / BIÜ2M/BIÜMD BSC Nf S/ \ / SM2M I TRCU MSC Bus system for transmission management (QMUX PROTOCOL) Transmission equipment Figure 4. GSM transmission network. QMUX protocol consists of three layers; application, datalink and physical layer. First two layers are designed and tested. The application layer is as the SB HNDLR process, the datalink layer is as DATALINK RECEIVE and DATALINK TRANSMIT processes. The RECEIVE process of the datalink layer is in charge of reception, the TRANSMIT process of the datalink layer is in charge of transmission. They works independantly. Primitives used between the QMUX protocol layers, communication between the SB HNDLR process and the other processes which run on the ATSC and database relations used by the SB^HNDLR are also designed. Database relations are used via the database functions. Database semaphores are used by all the processes themselfs. XIX The QMUX integration test is finished. The ATSC integration test has been continuing. The processes of these protocol layers are designed with SDL language. Abstract data type with which the SDL concept brings is also used and ADTs are realized with C language. A process consists of the process C code and ADTs C codes which are used in this process. The processes which are designed with SDL are converted to the C code. Protocol layers' processes and its ADTs are compiled and linked together, then tested. Then, these processes and the others which run on the TSC are integrated and then tested. From now on, ATSC software is ready for testing with the other BSS subsystem components. CCITT specification language SDL is used to designe the project. Because, SDL provides early error detection, reducing maintenance cost and easier communication between customer and producer. And also, SDL is now an international standard, both powerful and user - friendly and it is supported by powerful computer based tools. The used operating system is the MTOS-UX. This is a convenient OS for real time system.