Global System for Mobile Communications - Essay Example

Global System for Mobile Communications (GSM) Global system for mobile communications (GSM) is one of the widely used digital mobile telephony technology used for relaying mobile data and voice data. The system has become the most common cellular service in the European countries since its adoption as a standard in 1982. Apart from Europe, the GSM technology is also applicable in many countries, in the world. It is arguably one of the systems that have revolutionized the world over the last few years making communication easier than before. Global System for Mobile Communications (GSM) Introduction The Global System for Mobile Communications (GSM) is one of the widely used digital mobile telephony technology used for relaying mobile data and voice data (Rhee 2009, p.1). The system has become the most common cellular service in the European countries since its adoption as a standard in 1982. Apart from Europe, the GSM technology is also applicable in many countries, in the world (Friedhelm 2001, p.6). The use of the technology continues to grow in different parts of the world including the developing countries in the world. Background The systems are said to have been developed during a research conducted by the Conference of European Posts and Telegraphs (CEPT) in 1982, with the aim of determining the advantages of coming up with a mobile communication standard for European countries. The GSM system makes use of a variation of time division multiple accesses (TDMA) during voice and data transmission. When transmitting data, the GSM first digitalizes and compresses data, which is then transmitted using double streams of data at a frequency of either 900MHz or 1800MHz (Rhee 2009, p.1). Despite its invention in 1982, the application of the system began a decade later in 1991, when the first mobile service based on the technology was launched in Finland. It is estimated that over 6901 mobile networks spread globally nowadays provide GSM services. A survey indicates that the technology has been adopted by more than 213 countries and that the GSM system accounts for over 82.4 percent of all international mobile connections. A survey conducted by GSM World found out that there are over 2 billion people using GSM mobile. Presently, China leads in terms of GSM market, having more than 370 million GSM mobile users, Russia follows a distant second with about 145 million users, then India and the U.S.A with 83 million and 78 million FSM mobile users respectively (Talukdar 2010, p.116-117). GSM World reveals that because there is a rooming consent allowed among foreign operators with regard to GSM networks, the users of the system are able to continue enjoying the services regardless of the countries they travel into. GSW World reveal that once in a foreign country, the subscriber is able to configure the network to the local network of the country directly without having to incur a lot of roaming costs. The GSM technology has indeed revolutionized the mobile telephone by moving away from the analogue system, which used to less effective to a digital system that is more convenient in terms of speed and usability (Talukdar 2010, p.116-117). GSM Architecture The GSM system consists of three major components: Switching system (SS), Base station system (BSS) and the mobile station (MS). 1. The Switching system (SS). The switching is one of the major parts of the GSM system, which is responsible for processing of calls and subscriber functions. In order for the SS to function effectively, it has functional units within it that does different functions related to call processing and other user-related functions (Rhee 2009, p.3).. This includes: Home location registers (HLR) The HLR is one of the main functional unit of the SS that acts as a database for management and storage of subscriptions. The subscriber information stored by the HLR includes status of activity, subscriber’s location and his profile. The good thing with the HLR is that once data pertaining to the subscriber have been received it stores it permanently for future references in case of need. For instance, when an individual subscribe to the service using one of the PCS operators, the information is usually entered in the HLR of the operator in question (Talukdar 2010, p.118-119). Authentic Centre (AUC) AUC is a functional unit of the SS used for encryption and authentication of the parameters used for verification of the subscriber’s identity to ensure that confidentially of the call is maintained. Today world is full of fraud and hacking of data which sometimes affect the confidentially of a users call. This is because some fraudsters are nowadays able to use technology to intercept communication between people. Therefore, to ensure that people are protected from such fraudsters, the GSM is fitted with the AUC to ensure that confidentially is maintained all the time. The AUC makes it hard for the data fraudsters to hack calls (Rhee 2009, p.3). Mobile service switching Centre (MSC) This is another important component of the SS used for switching the telephone system. GSM World reveals the MSC is also the unit that controls voice data during communication between subscribers. Other important functions of the MSC include signalling of channels, interfacing of networks and toll ticketing (Talukdar 2010, p.118-119). Equipment identity registers (EIR). This is a functional unit of the SS component of the GSM system that acts as a database for storing information related to the identity of the mobile. In doing so, it helps in preventing calls from being hacked by fraudsters or defective mobile station. They usually work in unison with AUS in preventing fraudsters from stealing calls, thereby giving an assurance of the confidentiality of the voice calls and data (Talukdar 2010, p.118-119). Visitor location register (VLR) This is another important functional unit of the SS component used for storing temporary information relating to the user that may be required by the MSC to aid in assisting a subscriber with a query regarding his information. As a result, the functional units, VRL and MSC are usually integrated together for ease of obtaining user’s information in case of need (Talukdar 2010, p.118-119). 2. Base Station System (BSS) This acts as the engine of the GSM system since it performs all radio related functions. It consists of two major parts namely the base transmitter station (BTSs) and base station controller (BSCs) (Talukdar 2010, p.118). Base transmitter station (BTS)-This is the component that contains radio antennas and transceivers used for defining cell and controls the radio signal to the mobile station. The number of BTS required for use usually depends on the population of the number of users defined by the population density. For instance, an urban city with a high number of users will require several BTSs to be deployed (Talukdar 2010, p.118-119). The base station controller (BSC)-this is a BSS component that controls and links the BTS and MSC. The general functions of the BSC include frequency hopping, set up of radio frequency, and data configuration in the cell (Quek 2010, p.5) 3. Mobile Station (MS) The mobile station (MS) is another part of the GSM architecture made up of two components namely the smart card (SIM card) and mobile equipment (terminal). The SIM card is a garget slotted into the GSM terminal in order to be able to receive make calls to other users or receive calls made by other subscribers. Initially most phones had only a single GSM terminal slot for a SIM card. This implies that a subscriber can only slot in one SIM card at a time. Nevertheless, as technology advances, some mobile phones nowadays have two GSM terminals for SIM cards (Rhee 2009, p.6). The mobile equipment is defined by International Mobile Equipment Identity (IMEI). The IMEI is also used for identifying authentic phones. Currently there have been rising cases of fake mobile phones being introduced in the market. However, the authenticity of the type of phone is identified using the IMEI number (Talukdar 2010, p.120). Every SIM card has an International Mobile Subscriber Identity (IMSI) used for recognizing users to a given system. It also acts as a secrete key for authentication as well as obtaining other pertinent information regarding the subscriber. In addition, the SIM cards are usually controlled using the personal identity number of password to prevent unauthorized use of the phone (Talukdar 2010, p.120). GSM Radio Interface The radio interface is the boundary between the fixed infrastructure and the mobile station. It performs an important function in the GSM system. This is because it aids mobility and wireless access into the system. Roaming is a major purpose of GSM system, which can only be obtained by ensuring that the radio interface is well defined. This is because it ensured that there is the mobile station, and networks of different operators are compatible with one another (Pesch 2002, p.2-5). Setting up a call A number of activities usually take place when making a call using a cell phone. For instance, when one makes a call when the other subscriber being called is also in the process of making a call, the MS is usually said to be in a busy mode. This happens when the MS is using a TCH or SDCCH. Usually, there are two types of call set-up namely Mobile Terminal (MT) and Mobile Originated (MO). The MT set up is that involving calls directed to the MS (Quek 2010, p.2) However, before any call can be connected between subscribers, a thorough security check is usually conducted, which involves ciphering and authentication. The security check is conducted within the dedicated signalling channel. Once the security check has been done, the system assign traffic channel before the call can be connected (Quek 2010, p.2). Call to MS (MT) As earlier stated, an MT call is set up when the subscriber making the call (A-subscriber) makes a call by dialling a given telephone number (MSISDN) to a user B-subscriber (MS) (Quek 2010, p.3). The set up is as described hereunder: When A-subscriber dials the MSISDN number, the call is first directed to a GSM gateway, GMSC. A new routing information then initiates the call to the right VLR/MSC. The GMSC then uses the MSISDN to address the HLR where the registration of MS takes place. The GMSC then makes a request to the HLR asking to be supplied with new routing information containing the MSISDN. As this happens, the HLR translates the MISIDN into IMSI in order to find the right database. The HLR also monitors the subscription and other services attached. In this regard, HLR finds out that the incoming call is invalid then the GMSC automatically rejects the request made by GMSC. In addition, if call forwarding is active, then a C-number is relayed back to the GMSC. The C-number in this case could be in the form of a mailbox number or any chosen by the subscriber. (Quek 2010, p.3) However, in case the request is accepted, then the HLR studies the address to the VLR/MSC where the registration of MS takes place. It then makes another request to the VLR/MSC requesting to be supplied with a Mobile Station Roaming Number (MSRN), informing it to relay routing information such as the IMSI to the GMSC. The VLR/MSC then identifies an MSRN, which it then transmits through HLR to the GMSC. The VLR/MSC stores the IMSI and MSRN temporarily. The GMSC then directs the call to the VLR/MSC, which makes use of the correlation between IMSI and MSRN to locate the right file in the database. The MS is then checked by the VLR/MSC in case it is attached or busy. In case it is found busy, then the call will be forwarded (Quek 2010, p.4). However, is the MS is free, the VLR/MSC will trace for the position of MS and route a paging information to the BSCs. The function of BSC is to transmit the information to BTSs, which then passes it on to PCH. What is noted is that the paging information usually has the MS identity, that is IMSI or TMSI. All the necessary signals needed to make a call set up is then transmitted to the SDCCH via the VLR/MSC. A security check is then performed, which includes ciphering, authentication and identification of equipment. Finally, the VLR/MSC will then send a message to the BSC charged with the responsibility of allocating TCH necessary for service acceptance, which is then transformed to a BTS servicing. The channel then allocates the MS, which then relocate to the time slot and indicated carrier. The call then gets connected and communication takes place (Quek 2010, p.5). GSM handover GSM handover is the process of changing a radio connection from one BS and is aimed at maintaining seamless radio connection during mobile station movement. The process is administered using the Mobile Assisted Handover (MAHO), as well as backward handover. The process is usually implemented in BSS, MS and MSC. The GSM handover processes usually follows the following steps: measurement, handover request, handover decision and handover execution (Pesch 2000, p.2). GSM Localization of a user Localization of users can be done using three GSM localization methods. Firstly, it can be done using the subscribers cell ID. Here, the user’s cell ID is used to locate the position of the subscriber by mapping the area using the broadcasting towers. Therefore, when a subscriber makes a call, then the operator can easily locate where the caller is using the broadcasting tower that the subscriber uses. Secondly, a user can be localized using the signal transmit time. This is done using need net-assistance and triangulation. Thirdly, localization can be conducted using angles. Here, the operators can localize the user by calculating the angle of the incoming signal. Finally, localization can be done using the pattern matching technique. This involves the application of network topology technique. Conclusion GSM system is one of the technologies that have revolutionized the world in over the last two decades it has been in existence. This is because it has made communication easier because it involves the use of digital signal. References Friedhelm H. 2001, GSM and UMTS, The Creation of Global Mobile Communications, John Wiley & Sons, New York. Pesch, D. 2000, GSM Concepts. Telecommunications MSc in Software Development, viewed 6 Novermber, 2012 www.aws.cit.ie/personnel/dpesch/notes/msc_sw/gsm_concepts.pdf Pesch, D. 2002, The GSM Radio Interface. CIT Pesch, D. 2002, The GSM Radio Interface. CIT viewed 6 November, 2012 Quek, M. 2010, Call Set-up, viewed 6 November, 2012 www.hexazona.com/nexwave/docs/.../GSM%20Overview%2010.pdf Rhee, M. 2009, Mobile Communication Systems and Security, John Wiley & Sons, Hoboken, NJ. Talukdar, A. 2010, Mobile Computing, 2E, Tata McGraw-Hill Education, New York. Read More