Intro to GSM - GSM Security Overview GSM(Part 1(Part...

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Unformatted text preview: GSM Security Overview GSM (Part 1) (Part Wireless telephone history Yuri Sherman Yuri It all started like this It First telephone (photophone) – Alexander First Bell, 1880 Bell, The first car mounted radio The telephone – 1921 telephone Going further Going 1946 – First commercial mobile radiotelephone service by Bell and AT&T in telephone Saint Louis, USA. Half duplex(PTT) Saint 1973 – First handheld cellular phone – 1973 Motorola. Motorola. First cellular net First Bahrein 1978 Bahrein But what’s cellular? But MSC BS PSTN HLR, VLR, AC, EIR Cellular principles Cellular Frequency reuse – same frequency in many cell sites many Cellular expansion – easy to add new cells Cellular Handover – moving between cells Handover Roaming between networks Generation Gap Generation Generation #1 – Analog [routines for Generation sending voice] All systems are incompatible All No international roaming Little capacity – cannot accommodate Little masses of subscribers masses Generation Gap(2) Generation Generation #2 – digital [voice encoding] Increased capacity More security Compatibility Can use TDMA or CDMA for increasing capacity capacity TDMA TDMA Time Division Multiple Access Each channel is divided into timeslots, Each each conversation uses one timeslot. each Many conversations are multiplexed into a Many single channel. Used in GSM Used CDMA CDMA Code Division Multiple Access All users share the same frequency all the All time! time! To pick out the signal of specific user, this To signal is modulated with a unique code sequence. sequence. Back to Generations Back Generation #2.5 – packet-switching Connection to the internet is paid by Connection packets and not by connection time. packets Connection to internet is cheaper and Connection faster [up to 56KBps] faster The service name is GPRS – General The Packet Radio Services Packet The future is now The Generation #3 Generation Permanent web connection at 2Mbps Internet, phone and media: 3 in 1 Internet, The standard based on GSM is called The UMTS. Not yet implemented. UMTS. The EDGE standard is the development of The GSM towards 3G. GSM GSM More than 800 million end users in 190 countries and representing over 70% of today's digital wireless market. source: GSM Association Israel Orange uses GSM Pelephone and Cellcom are about to use GSM GSM Overview GSM Into the architecture Into Mobile phone is identified by SIM card. Key feature of the GSM Has the “secret” for authentication Into the architecture(2) Into BTS – houses the radiotransceivers of the BTS cell and handles the radio-link protocols with the mobile with BSC – manages radio resources (channel BSC setup, handover) for one or more BTSs setup, Into the architecture(3) Into MSC – Mobile Switching Center The central component of the network Like a telephony switch plus everything for Like a mobile subscriber: registration, authentication, handovers, call routing, connection to fixed networks. connection Each switch handles dozens of cells Into the architecture(4) Into HLR – database of all users + current HLR location. One per network location. VLR – database of users + roamers in VLR some geographic area. Caches the HLR some EIR – database of valid equipment AuC – Database of users’ secret keys More GSM More GSM comes in three flavors(frequency GSM bands): 900, 1800, 1900 MHz. 900 is the Orange flavour in Israel. Orange Voice is digitized using Full-Rate coding. 20 ms sample => 260 bits . 13 Kbps 20 bitrate bitrate Sharing Sharing GSM uses TDMA and FDMA to let GSM everybody talk. everybody FDMA: 25MHz freq. is divided into 124 FDMA: carrier frequencies. Each base station gets few of those. few TDMA: Each carrier frequency is divided TDMA: into bursts [0.577 ms]. 8 bursts are a frame. Channels Channels The physical channel in GSM is the The timeslot. The logical channel is the information which goes through the physical ch. which Both user data and signaling are logical Both channels. Channels(2) Channels(2) User data is carried on the traffic channel User (TCH) , which is defined as 26 TDMA frames. There are lots of control channels for signaling, base station to mobile, mobile to base station (“aloha” to request network access) SS7 SS7 Signaling protocol for networks Packet – switching [like IP] GSM uses SS7 for communication GSM between HLR and VLR (allowing roaming) and other advanced capabilities. and GSM’s protocol which sits on top of SS7 is GSM’s MAP – mobile application part MAP ...
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