Evolution Of Gsm

Evolution of GSM

Birth of GSM Rules-CEPT • •

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Find the Background??? The need came when there were different mobile phone systems in European countries. They were incompatible.Each region used different mobile system working on different technology.Hence they were incompatible. Communication between the different regions was Eg:AMPS,PCS(personal communication systems), analog systems etc(find the earlier commn systems) Eurpoean countries formed a committee. So A group called European Conference of Postal and Telecommunications Administrations –june 26 1959 created ETSI in (1988)European Telecommunications Standard Institute ) formed by European countries CEPT made experiments , freezed the frequency band 900MHZ. They formed a common mobile system called GSM. GSM came into existence in -1992-Finland-launching of Network.

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SPECIFICATIONS:

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PSTN should not be altered. Several Operators in the country-which would lead to rapid expansion of GSM and hence lead to reduction in cost/call. Should be an open system-defined interfaces between the network elements leading to co-existing of equipment manufacturers. System should be PAN European, good quality, security issues,ISDN Compatible( what is ISDN), compatible with other Data communication systems.

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Organisations : 3GPP 3GPP2 ETSI,www.etsi.org CEPT

GSM Architecture

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The network is divided into 3 parts: BSS(Base Station Subsystem) NSS(Network Switching Subsystem) NMS(Network Management Subsystem) BSS:-responsible for establishing calls. Establishing a radio path. NSS:-responsible for call control functions. NMS: maintains the whole GSM network. (O&M)

GSM System Architecture-1 •

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Mobile Station (MS) Mobile Equipment (ME) Subscriber Identity Module (SIM) Base Station Subsystem (BSS) Base Transceiver Station (BTS) TRAU Base Station Controller (BSC) Network Switching Subsystem(NSS) Mobile Switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)

Ideas /Points

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MS-Mobile Station: SIM card: card Overview of GSM system(eg:PLMN ) Ask to name GSM operators in INDIA

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PLMN:PLMN mostly refers to the whole system of hardware and software which enables wireless communication, irrespective of the service area or service provider . Sometimes separate PLMN is defined for each country or for each service provider A public land mobile network may be defined as a number of mobile services switching centre areas within a common numbering plan and a common routing plan.

• HPLMN:denotes the Home PLMN (the PLMN the customer belongs to). • VPLMN: denotes the Visitor PLMN (the PLMN the customer is roaming in). • It interfaces with other networks through Gateway MSC • India has Multiple PLMN’s E.g.:

PLMN

GSM Network Areas

GSM Network Areas •

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CELL (area covered by BTS) :The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. LA: The location area is a group of cells . Each LA is served by one or more base station controllers, yet only by a single MSC . Each LA is assigned a location area identity (LAI) number.

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An MSC/VLR service area represents the part of the GSM network that is covered by one MSC.

GSM Specifications • • • • • • • • • •

GSM Specifications Before looking at the GSM specifications, it is important to understand the following basic terms: bandwidth—the range of a channel's limits; the broader the bandwidth, the faster data can be sent bits per second (bps)—a single on-off pulse of data; eight bits are equivalent to one byte frequency—the number of cycles per unit of time; frequency is measured in hertz (Hz) kilo (k)—kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits per second megahertz (MHz)—1,000,000 hertz (cycles per second) milliseconds (ms)—one-thousandth of a second watt (W)—a measure of power of a transmitter

GSM Specifications

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Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM. frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station). duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart. channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz. modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps. access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot. speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps.

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During the 1st week at Motorola, I need to hv some basic study again which related to this field. When I come across this topic “type of communication” just recall back on my academic study on “Communication Network“, almost the same, just that here, I can get know more detail which does not include in my study. Radio systems use any of three types of communication: simplex, semi-duplex, and fullduplex. The communication type used depends on the number of users and the type of equipment available. This section provides a description of the three types of communication. Simplex Communication The most basic type of radio communication is simplex. Simplex communication consists of radio units operating on a single frequency. Because everyone transmits and receives on the same frequency, users cannot talk and listen at the same time. Simplex means transmission in one direction at a time.

Eg. Walkie Talkie, which only able to transmit 1 way, while another end can transmit after the other end stop.

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A simplex radio system works well when there are only a few users who are closely located. When additional users are added to the system, the competition for the one available frequency can make it difficult to get a message across. In addition, great distances and natural obstacles such as high hills and tall buildings can interfere with the single frequency. Do you know: Television Channel and Radio Channel (FM or AM) are using simplex communication type? Which mean we can receive at our television and radio only, while we cannot make respond. Semi-Duplex Communication Semi-duplex communication uses two frequencies: one for receive and one for transmit. A radio operating in semi-duplex mode can only transmit or receive at any particular time.

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Duplex Communication Duplex communication uses different frequencies simultaneously, one to transmit and the second to receive. The transmitter output is isolated and separated in frequency to prevent blocking the input of its companion receiver. Also called full-duplex, this type of operation is used to indicate that the equipment can receive and transmit at the same time. Normally, fixed equipment (a base station) operates in full-duplex mode while mobile equipment typically operates in half-duplex mode. Eg. Cell Phone and Mobile Phone that able to communicate in both way at the same time.

GSM Elements & Their Functions •

MS-Mobile Station: It is a combination of • Mobile Equipment:IMEI can be viewed on your phone screen using (*#06#) into the keypad ). to identify valid devices and therefore can be used to stop a stolen phone from accessing the network . allocated by equipment manufacturer If the local operator possesses an Equipment Identity Register (EIR), it then will put the device IMEI into it.15 Digit. Conversely, one can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. . • For the example IMEI 49015420323751?, • IMEI49015420323751 ?Double every other4180258203431452 ?Sum digits4 + (1 + 8) + 0 + 2 + 5 + 8 + 2 + 0 + 3 + 4 + 3 + (1 + 4) + 5 + 2 + ? = 52 + ?To make the sum divisible by 10, we set ? = 8, so the IMEI is 490154203237518.

• Subscriber’s data (SIM): A SIM Card contains • -International unique number of the mobile user (IMSI) • -Security authentication and ciphering information • -Temporary information related to the local network (also temporary local id that has been issued to the user) • -List of the services the user has access to and two passwords (regular PIN and unblocking PUK). • • • •

Frequensies(latch BCCH) alloted by an operator Authentication key/number Forbidden PLMN’s (doubt) Roaming PLMN’s

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IMSI : International Mobile Subscriber Identity International unique number of the mobile user (IMSI): Stored in the SIM (Subscriber Identity Module) It is sent by the phone to the network for identification as a subscriber. E.g.: In order to avoid the subscriber being identified and tracked by eavesdroppers on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated TMSI (Temporary Mobile Subscriber Identity) is sent instead. IMSI:15 digits long. The first 3 digits are the Mobile Country Code (MCC), and is followed by the Mobile Network Code (MNC), either 2 digits (European standard) or 3 digits ( North American standard . The remaining digits are the mobile station identification number (MSIN) within the network's customer base. Examples IMSI:429019989552070 MCC429NepalMNC01Nepal TelecomMSIN1234567890IMSI: 310150123456789 MCC310USAMNC150AT&TMSIN123456789 MCC for INDIA:404,405 MNC: identifies an operator It is used to identify to which network the subscriber belongs to and whether he is able to use the network.

The Base Station Subsystem (BSS)

NSS-Network Switching Subsystem Functions-what it does and responsibilities? • It is the component of a GSM system where it carries out switching functions and manages the communications between mobile phones and the Public Switched Telephone Network (PSTN) • It is also referred to as the GSM core network. • Main function and responsibility of MSC is Call connections and database management. • Call connections functions are done using Encryption, Authentication and Roaming. To process and setup a call following elements are needed: • MSC-mobile switching center • VLR-Visitor location register • HLR/ AUC-home location register/Authentication centre • EIR-Equipment identity register

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How are these connected

MSC: • responsible for handling voice calls and SMS as well as other services (such as conference calls, FAX • Connecting outgoing calls to other mobile subscribers or the PSTN. • sets up and releases the end-to-end connection • handles mobility • Registration • Location Updating • hand-over requirements during the call ,inter BSC’s • Carrying out handovers from this MSC to another. • takes care of charging and real time pre-paid account monitoring. Billing and accounting) • There are various different names for MSCs depending on doing different things at different times • The gateway MSC (G-MSC) is the MSC that determines which visited MSC the subscriber who is being called is currently located

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GMSCMobile to Mobile calls PSTN to Mobile calls are routed through a G-MSC Inter Network Operator Calls are also routed through G-MSC Any MSC may provide both the gateway function and the Visited MSC function But some manufacturers design dedicated high capacity MSCs which do not have any BSC’s connected to them .Then these MSC’s will be termed as G-MSC for the calls. The visited MSC (V-MSC) is the MSC where a customer is currently located. The VLR associated with this MSC will have the subscriber's data in it. The anchor MSC is the MSC from which a handover has been initiated. The target MSC is the MSC toward which a Handover should take place.

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The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units. HLR: is a database of user (subscriber) information. What it stores:???? A HLR contains user information such as account information- prepaid/postpaid, account statusactive or inacive, user preferences, supplementary services-features subscribed to by the user, user’s current location, IMSI,MSISDN(Phone number), roaming restrictions Functions: call-routing and roaming capabilities VLR: A VLR is a database, similar to a HLR, which is used by the mobile network to temporarily hold profiles of roaming users (users outside their home area). The VLR is integrated to a (telephone exchange) switching equipment called MSC. This VLR data is based on the user information retrieved from a HLR.When the subscriber moves to another VLR area,its data is erased from the old VLR and stored in the new VLR. All manufacturers of switching equipment to date implement the VLR together with the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, thus simplifying the signaling required. Note that the MSC contains no information about particular mobile stations --- this information is stored in the location registers. MSCs use a VLR to handle roaming users

• What it stores??? - Database contains IMSI,TMSI,MSISDN,MSRN,Location Area,authentication key

How are the HLR and VLR used? • • • • • • • • • •

Each mobile network has its own HLRs and VLRs. When a MSC detects a mobile user’s presence in the area covered by its network, it first checks a database to determine if the user is in his/her home area or is roaming, i.e., the user is a visitor. o User in Home Area: HLR has the necessary information for initiating, terminating, or receiving a call. o User is Roaming: VLR contacts the user’s HLR to get the necessary information to set up a temporary user profile. The user’s location is recorded in the HLR, and in case the user roaming, it is also recorded in the VLR. Suppose that the user wants to make a call: o User in Home Area: MSC contacts the HLR prior to setting up the call. o User is Roaming: MSC contacts the VLR prior to setting up the call. Suppose that there is a call for the user (call goes to the home MSC): o User in Home Area: Home MSC delivers the call immediately. o User is Roaming: Home MSC contacts the VLR to determine the appropriate switch in the roaming area to handle the arriving call and then transfers the call to the roaming area MSC.

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MSC-the mobile service switching centre (MSC) is the core switching entity in the network. It is the central component of the Network Subsystem. all calls to and from the user are controlled by the MSC. The MSC is connected to the radio access network (RAN); the RAN is formed by the BSCs and BTSs within the Public Land Mobile Network (PLMN) one or more MSCs, geographically distributed. Where is the subscriber,who and what he wants

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HLR:Stores basic data of the subscriber on a permanent basis. The only variable data is VLR address. VLR:Temporar

What happens when you first switch on the mobile???? • • •

Registration and Database: Authentication Updations in HLR and VLR about the current location in the

The GSM System Hierarchy

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STEPS INVOLVED WHEN MOBILE IS SWITCHED ON When is a is mobile switch on following procedure is followed step1: It Scan all the available RF channels and measure signal strength Step2: Tune to the RF channel with the highest received average signal strength step3: Determine if it is a correct BCCH carrier by searching for frequency correction bursts. step4: If it is correct a BCCH carrier then the Mobile shall attempt to synchronize to This carrier and read BCCH info. STEP5: check for if it is the wanted PLMN? step6: check if the cell is barred for access if not #latch on to the cell. IF THE ONE OF THIS STAGES NOT ACCOMPLISHED THE MOBILE WILL TUNE AGAIN AT ANOTHER STRONGE FREQUENCY

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Uplink (UL) Formula (MHz)FUL(n) = 890 + 0.2*n Downlink (DL) Formula (MHz)FDL(n) = FUL(n)+45