GSM Dr. Risanuri Hidayat Pendahuluan Global System for Mobile Communications. Sjktk Sejak teknologi selular l ini idigunakan pertama kali pada tahun 1991, penggunaan GSM telah berkembang dengan pesat. Saat ini GSM paling banyak diterapkan di dunia. pelanggan GSM mencapai 1 000 000 000 pada bulan Februari Fb i2004, dan kini i lebih 3 milyar pelanggan. Dan jumlah ini masih akan terus meningkat. 1
Pendahuluan GSM adalah teknologi telepon seluler generasi kd kedua (2G) telepon tl seluler. l Kapasitasnya jauh lebih besar dari pada sistem analog generasi sebelumnya pertama. GSM menggunakan kombinasi access antara FDMA dan TDMA. Bandingkan dengan seluler 1G yang hanya FDMA. Services (Layanan) Fungsi utama GSM adalah untuk layanan (komunikasi) suara. Suara ini disandikan secara digital. GSM juga memberikan layanan data. Berbagai layanan data tersedia dengan kecepatan hingga 9.6 kbps. Layanan data meliputi facsimile, videotext dan teletex. Salah satu layanan yang menjadi sangat populer di lingkungan GSM adalah dlhlayanan short message service, yang dikembangkan sebagai bagian spesifikasi GSM. Layanan ini menjadi sangat populer dan penting karena sederhana, mudah, dan murah. 2
Kemampuan GSM Teknologi GSM dirancang untuk memenuhi tujuan sebagai berikut: Mempunyai mutu suara yang cukup bagus Pesawat telepon murah / harga mampu dijangkau masyarakat Pesawat telepon dapat dipegang / dibawa ke mana mana Sistem mampu melakukan roaming secara internasional Mempunyai spektrum frekuensi yang effisien Sistem mempunyai kompatibilitas dengan ISDN Dari rancangan kemampuan teknologi GSM seperti di atas, permasalahan sistem GSM tidak hanya masalah RF saja, tetapi juga masalah jaringan dan infrastrukturnya. Sebagaimana kemampuan roaming internasional menuntut elemen elemen jaringan yang dibuat oleh berbagai industri harus mampu berkomunikasi dan compatible satu sama lain. GSM Architecture 3
GSM Architecture GSM Architecture MS Mobile Station, telephone genggam anda BTS Base Tranceiver Station, station radio basis (menara), yang berkomunikasi secara langsung melalui RF dengan MS anda. BTS contains transmitter and receiver equipment, such as antennas and amplifiers, as well as a few components for signal and protocol processing. BSC Base Station Controller, berisi fungsi fungsi protocol for radio channel allocation, channel setup and management of handovers. Typically, several BTSs are controlled by one BSC. In practice, the BTS and BSC are connected by fixed lines or point to point radio links. 4
MSC Mobile Switching Center, performs all of the switching functions of a switching node in a fixed telephone network. This includes path search, data forwarding and service feature processing. HLR Home Location Register VLR Visited Location Register store the current location of a mobile user. This is needed since the network must know the current cell of a user to establish a call to the correct base station. these registers store the profiles of users for charging and billing and other administrative issues. AUC Authentication Center, stores security related data (keys used for authentication and encryption) EIR Equipment Identity Register, registers equipment data (rather than subscriber data) OMC Operation and Maintenance Center, network management organized from a central place the administration of subscribers, terminals, charging data, network configuration, operation, performance monitoring and Network maintenance. 5
Subscriber Identity Module (SIM) a card that must be plugged into a piece of mobile equipment. only SIM of a subscriber turns a piece of mobile equipment into a complete mobile station with network usage privileges, which can be used to make calls or receive calls. This concept distinguish between equipment mobility and subscriber mobility SIM can store short messages and charging information, telephone book function and short list of call numbers, and so on security functions: all of the cryptographic algorithms 6
Berbagai Identitas di GSM GSM distinguishes explicitly between a user and their equipment. There are specific address types for users and specific address types for MSs. The user identities are stored on the SIM; the equipment identities on the mobile equipment. In addition, GSM distinguishes between user identity and their telephone number. International mobile station equipment identity (IMEI) uniquely identifies a mobile station internationally ti and gives clues about tits manufacturer and the date of manufacturing. It is a kind of serial number of product. The IMEI is allocated by the equipment manufacturer and registeredby the network operator, who stores it in the EIR. 7
stolen or nonfunctional equipment and can deny service if required IMEI is assigned to one or more of the following three categories within the EIR. The white list is a register of all equipment. Theblack list contains all suspended equipment. This list is periodically exchanged among network operators. The IMEI is requested by the network at registration, or can be requested repeatedly. It is a hierarchical address, containing the following parts: Type Approval Code (TAC), six digits, centrally assigned; Final Assembly Code (FAC), six digits, assigned by the manufacturer; Serial Number, six digits, assigned by the manufacturer; Spare, one digit. 8
International Mobile Subscriber Identity (IMSI) When registering for service with a mobile network operator, each subscriber receives a unique identifier, the International Mobile Subscriber Identity (IMSI). IMSI is stored in the SIM. IMSI need not be made public. A mobile station can only be operated if a SIM with a valid IMSI is inserted into equipment with a valid IMEI The IMSI uses a maximum of 15 decimal digits and consists of three parts: Mobile Country Code (MCC), three digits, internationally standardized; Mobile Network Code (MNC), two digits, for unique identification of mobile networks within a country; Mobile Subscriber Identification Number (MSIN), maximum of 10 digits, identification number of the subscriber in their mobile home network. A three digit MCC has been assigned to each of the GSMcountries, and two digit MNCs have been assigned within countries (e.g., 262 as MCC for Germany; and MNC 01, 02 and 07 for the networks of T Mobile, Vodafone, and O2, respectively). Whereas the MCC is defined internationally, the National Mobile Subscriber Identity (NMSI = MNC + MSIN) is assigned by the operator of the home network. 9
the Mobile Subscriber ISDN Number (MSISDN) GSM was the first mobile system to distinguish between subscriber identity and the number to call. This is the real telephone number of a mobile user called the Mobile Subscriber ISDN Number (MSISDN). It is assigned to the subscriber (their SIM), such that a mobile station can have several MSISDNs depending on the SIM. The separation of call number (MSISDN) and subscriber identity (IMSI) primarily serves to protect the confidentiality of the IMSI. MSISDN is public. With this separation, one cannotderive the subscriber identity from the MSISDN, unless the association of IMSI and MSISDN as stored in the HLR has been made public. Mobile station roaming number The Mobile Station Roaming Number (MSRN) is a temporary location dependent ISDN number. It is assigned by the locally responsible VLR to each MS in its area. Calls are routed to the MS by using the MSRN. The MSRN has the same structure as the MSISDN: CC of the visited network; NDC of the visited network; SN in the current mobile network. 10
Location area identity Each LA of a cellular network has its own identifier. The Location Area Identifier (LAI) is structured hierarchically and internationally unique, with LAI again consisting of an internationally standardized part and an operator dependent part: CC, three digits; MNC, two digits; Location Area Code (LAC), a maximum of five digits or a maximum of 2 8 bits, coded in hexadecimal. Registers and subscriber data GSM standard defines two database types for the management of user data and location: the HLR and the VLR. HLR has a record for all subscribers registered with a network operator. user s telephone number, service subscriptions, permissions and authentication data. it also contains temporary data, current location of a subscriber. The full list of subscriber data stored in the HLR is given in Table. 11
HLR VLR VLR is responsible for a group of location areas and stores the data of all users that are currently located in this area. The data includes part of the permanent user data, which h iscopied id from the HLR to the VLR for fast access. In addition, the VLR may also assign and store local data, such as temporary identifiers. A user may either be registered with a VLR of their home network or a foreign network. Upon a location update, the MSC forwards the user s identity and current location to the VLR, which subsequently updates its database. If the user has not been registered with this VLR before, the HLR is informed about the current VLR of the user. This process enables incoming calls to be routed to this MS. Typically, there is one central HLR per network and one VLR for each MSC. 12
VLR AUC and EIR System security of GSM networks is based primarily on the verification of equipment and subscriber identity; therefore, the databases serve for subscriber identification and authentication and for equipment registration. Confidential data and keys are stored or generated in the AUC. The keys serve for user authentication and authorize the respective service access. The EIR stores the serial numbers (supplied by the manufacturer) of the terminals (IMEI) 13
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ARSITEKTUR JARINGAN GSM Jaringan GSM dapat dibagi ke dalam tiga bagian utama yaitu : Mobile Station (MS), Base Station Subsystem (BSS), dan Network Subsystem (NSS). MS dibawa oleh pelanggan yang bergerak. BSS mengendalikan jalur radio dengan MS. Sedangkan NSS melakukan switching panggilan antar pelanggan bergerak, dan antara pelanggan bergerak dengan pelanggan tidak bergerak. MS dan BSS berkomunikasi melalui antarmuka Um yang juga dikenal sebagai antarmuka udara. BSS berkomunikasi dengan NSS melalui antarmuka A. 16
GSM dasar Teknologi GSM menggunakan accsss FDMA dengan masing masing kanal RF adalah 200 khz. Menggunakan access TDMA yang mampu mengangkut 8 saluran per frekuensi pembawa. Inilah kombinasi TDMA dan FDMA. BTS (base transceiver stations) adalah menara stasion RF, yang dikendalikan oleh BSC (base station controller). BSC dapat mengendalikan beberapa BTS, dan lokasinya berada di salah satu BTS. BTS + BSC disebut BSS (base station subsystem). GSM dasar Di atasnya adalah MSC (mobile switching centre). Di dalamnya terdapat HLR (home location register) dan VLR (visitor location register) Di MSC pula terdapat AuC (Authentication Centre ) dan EIR (Equipment Identify Register) untuk autentikasi pada saat pesawat mobile memasuki jaringan dan untuk keperluan billing (tagihan pembayaran) Yang terpenting adalah pesawat telepon mobile nya itu sendiri. Pesawat mobile ini sering disebut dengan ME (mobile equipment). Di dalamnya terdapat kartu Subscriber Identity Module (SIM card). Kartu ini berisi identitas pengguna dan informasi2 lainnya. 17
GSM system overview Specification Summary for GSM Cellular System Multiple access technology FDMA / TDMA Duplex technique Uplink frequency band (base transmit) Downlink frequency band (mobile transmit) Channel spacing FDD 933 960 MHz (basic 900 MHz band only) 890 915 MHz (basic 900 MHz band only) 200 khz Modulation GMSK Speech coding Various original was RPE LTP/13 Speech channels per RF channel 8 Channel data rate 270.833 kbps Frame duration 4.615 ms MS Transmission Band : 890 915 MHZ GSM Architecture BS Transmission Band : 935 960 MHZ 45 MHz Year Introduced 1990 F1 F2 F1' F2' Frequency 1 2 3 4 5 6 7 8 Access method Channel Bandwidth Number of duplex channels TDMA 200 khz 125 Users per channel 8 Speech coding bit rate 13 kbps Data coding bit rate 12 kbps Frame size 4.6 ms 18
GSM system overview http://www.pacificwave wireless.com/pw_product/theory white_paper_and_tehnical_notes/ theory_and_%20reference_table/indonesia%20cellular%20freq%20in%202008.pdf 19