Gsm architecture


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Gsm architecture

  1. 1. GSM Architecture
  2. 3. Component groups of a GSM network <ul><li>The principle component groups of a GSM network are: </li></ul><ul><li>The Mobile Station (MS) </li></ul><ul><li>The MS consists of two parts, the Mobile Equipment (ME) and an electronic ‘smart </li></ul><ul><li>card’ called a Subscriber Identity module (SIM). </li></ul><ul><li>The ME is the hardware used by the subscriber to access the network. The hardware </li></ul><ul><li>has an identity number associated with it, which is unique for that particular device and </li></ul><ul><li>permanently stored in it. This identity number is called the International Mobile </li></ul><ul><li>Equipment Identity (IMEI) and enables the network operator to identify mobile equipment </li></ul><ul><li>which may be causing problems on the system. </li></ul><ul><li>The SIM is a card which plugs into the ME. This card identifies the MS subscriber and </li></ul><ul><li>also provides other information regarding the service that subscriber should receive. The </li></ul><ul><li>subscriber is identified by an identity number called the International Mobile Subscriber </li></ul><ul><li>Identity (IMSI). </li></ul><ul><li>The Base Station System (BSS) </li></ul><ul><li>This is the part of the network which provides the radio interconnection from the MS to the </li></ul><ul><li>land-based switching equipment. </li></ul>
  3. 4. Mobile Station <ul><li>MOBILE STATION (MS) :- </li></ul><ul><li>The mobile station </li></ul><ul><li>(MS) represents the terminal equipment </li></ul><ul><li>used by the wireless subscriber supported </li></ul><ul><li>by the GSM Wireless system. </li></ul><ul><li>The SIM may be a removable module, while the equipment identity is not linked to a particular subscriber. </li></ul><ul><li>Functions of a Mobile Station :- </li></ul><ul><li>Radio transmission termination. </li></ul><ul><li>Radio Channel Management. </li></ul><ul><li>Speech Encoding/Decoding </li></ul><ul><li>Radio Link error Protection. </li></ul><ul><li>Flow control of data. </li></ul><ul><li>Mobility Management. </li></ul>
  4. 5. SIM <ul><li>The SIM contains several pieces of information: </li></ul><ul><li>International Mobile Subscriber Identity (IMSI) </li></ul><ul><li>This number identifies the MS subscriber. It is only transmitted over the air during </li></ul><ul><li>initialization. The IMSI identifies the subscriber within the GSM network while the MS </li></ul><ul><li>ISDN is the actual telephone number a caller (possibly in another network) </li></ul><ul><li>uses to reach that person. </li></ul><ul><li>Security is provided by the use of an authentication key (explained later in </li></ul><ul><li>this section) and by the transmission of a temporary subscriber identity </li></ul><ul><li>(TMSI) across the radio interface where possible to avoid using the permanent </li></ul><ul><li>IMSI identity. </li></ul><ul><li>Temporary Mobile Subscriber Identity (TMSI) </li></ul><ul><li>This number identifies the subscriber, it is periodically changed by the system </li></ul><ul><li>management to protect the subscriber from being identified by someone </li></ul><ul><li>attempting to monitor the radio interface. </li></ul><ul><li>Location Area Identity (LAI) </li></ul><ul><li>Identifies the current location of the subscriber. </li></ul><ul><li>Subscriber Authentication Key (Ki) </li></ul><ul><li>This is used to authenticate the SIM card. </li></ul><ul><li>Mobile Station International Services Digital Network (MSISDN) </li></ul><ul><li>This is the telephone number of the mobile subscriber. It is comprised of a country </li></ul><ul><li>code, a network code and a subscriber number. </li></ul>
  5. 6. BASE STATION SYSTEM (BSS) :- (BSC+BTS) <ul><li>The BSS consists of three major hardware components: </li></ul><ul><li>1) The Base Transceiver Station – BTS </li></ul><ul><li>The BTS contains the RF components that provide the air interface for a particular </li></ul><ul><li>cell .This is the part of the GSM network which communicates with the MS. The </li></ul><ul><li>antenna is included as part of the BTS. </li></ul><ul><li>The Base Station Controller – BSC </li></ul><ul><li>The BSC as its name implies provides the control for the BSS. The BSC communicates </li></ul><ul><li>directly with the MSC. The BSC may control single or multiple BTS. The BSC switching </li></ul><ul><li>matrix also allows the BSC to perform “handovers” between radio channels on BTSs, under </li></ul><ul><li>its control, without involving the MSC. </li></ul><ul><li>The Transcoder – XCDR </li></ul><ul><li>The Transcoder (XCDR) is required to convert the speech or data output from the MSC </li></ul><ul><li>(64 kbit/s PCM), into the form specified by GSM specifications for transmission over the </li></ul><ul><li>air interface, that is, between the BSS and MS (64 kbit/s to 16 kbit/s and vice versa) </li></ul>
  6. 7. <ul><li>Characteristics of the Base Station System (BSS) are : </li></ul><ul><li>The BSS is responsible for communicating with mobile stations in cell areas. </li></ul><ul><li>One BSC controls one or more BTS’s and can perform inter-BTS and intra-BTS </li></ul><ul><li>handover. As we have mentioned, a BSC may control several BTSs, the maximum number of </li></ul><ul><li>BTSs which may be controlled by one BSC is not specified by GSM . </li></ul><ul><li>- Each PLMN Should have at least one HLR </li></ul><ul><li>- One VLR is connected to several MSC ,but one MSC has one VLR </li></ul><ul><li>Characteristics of the Base Station System (BSS) are : </li></ul><ul><li>The BSS is responsible for communicating with mobile stations in cell areas. </li></ul><ul><li>One BSC controls one or more BTS’s and can perform inter-BTS and intra-BTS handover. </li></ul><ul><li>The Transcoder – XCDR </li></ul><ul><li>The Transcoder is used to compact the signals from the MS so that they are </li></ul><ul><li>more efficiently sent over the terrestrial interfaces. </li></ul>
  7. 8. <ul><li>MOBILE SWITCHING CENTER (MSC) :- </li></ul><ul><li>Mobile services switching center </li></ul><ul><li>(MSC) performs the switching functions for all mobile stations located in the </li></ul><ul><li>geographical area covered by its assigned BSSs. </li></ul><ul><li>Each MSC provides service to MSs located within a defined geographic coverage </li></ul><ul><li>area,the network typically contains more than one MSC. One MSC is capable of </li></ul><ul><li>supporting a regional capital with approximately one million inhabitants. An MSC </li></ul><ul><li>of this size will be contained in about half a dozen racks. </li></ul><ul><li>The functions carried out by the MSC are listed below: </li></ul><ul><li>Call Processing </li></ul><ul><li>Includes control of data/voice call setup, inter-BSS and inter-MSC handovers and </li></ul><ul><li>control of mobility management (subscriber validation and location). </li></ul><ul><li>Operations and Maintenance Support </li></ul><ul><li>Includes database management, traffic metering and measurement, and a </li></ul><ul><li>man–machine interface. </li></ul><ul><li>Internetwork Interworking </li></ul><ul><li>Manages the interface between the GSM network and the PSTN. </li></ul><ul><li>Billing </li></ul><ul><li>Collects call billing data. </li></ul>
  8. 9. HLR <ul><li>HOME LOCATION REGISTER (HLR) :- </li></ul><ul><li>The Home Location Register (HLR) </li></ul><ul><li>Contains the identities of mobile subscribers, their service </li></ul><ul><li>parameters, and their location information.HLR deals with tasks that </li></ul><ul><li>are independent of Subscriber location. </li></ul><ul><li>Function of the HLR include:- </li></ul><ul><li>Identity of mobile subscriber </li></ul><ul><li>Location information for call routing. </li></ul><ul><li>HLR stores Ki parameter (for each subscriber) which is also stored in SIM. </li></ul><ul><li>HLR contains IMSI,MSISDN,VLR add.,Subscriber data. </li></ul>
  9. 10. <ul><li>VISITOR LOCATION REGISTER (VLR) :- </li></ul><ul><li>The Visitor Location Register (VLR) contains the subscriber parameters and location information </li></ul><ul><li>for all mobile subscribers currently located in the geographical area controlled by that VLR. </li></ul><ul><li>Functions of the VLR include :- </li></ul><ul><li>Identity of mobile subscriber. </li></ul><ul><li>Any temporary mobile subscriber identity (TMSI) allocation. </li></ul><ul><li>Location area where the mobile station is registered </li></ul><ul><li>Copy of the subscriber data from the HLR. </li></ul><ul><li>- Each PLMN Should have at least one HLR </li></ul><ul><li>- One VLR is connected to several MSC ,but one MSC has one VLR </li></ul>
  10. 11. Authentication Centre (AUC) HLR MSC <ul><li>Authentication is a process to verify the subscriber SIM. </li></ul><ul><li>Secret data & verification algorithm are stored in to the </li></ul><ul><li>AUC. </li></ul><ul><li>AUC & HLR combined to authenticate the subscribers. </li></ul><ul><li>Subscriber authentication can be done on every call, if required. </li></ul>AUC
  11. 12. EIR <ul><li>EQUIPMENT IDENTITY REGISTER </li></ul><ul><li>(EIR) : </li></ul><ul><li>The Equipment Identity Register (EIR) is </li></ul><ul><li>accessed during the equipment validation </li></ul><ul><li>procedure when a mobile station accesses the </li></ul><ul><li>system .It contains the identity of mobile station </li></ul><ul><li>equipment which may be valid, suspect, or </li></ul><ul><li>known to be fraudulent. </li></ul><ul><li>This contains : </li></ul><ul><li>White or Valid list – list of valid MS equipment identities. </li></ul><ul><li>Grey or Monitored list – list of suspected mobiles under observation. </li></ul><ul><li>Black or prohibited list – list of mobiles for which service is barred </li></ul>
  12. 13. <ul><li>OPERATION AND MAINTENANCE CENTER </li></ul><ul><li>(OMC) :- </li></ul><ul><li>The Operation and maintenance Center (OMC) is the </li></ul><ul><li>centralized maintenance and diagnostic heart of the base </li></ul><ul><li>station system (BSS). It allows the network provider to </li></ul><ul><li>operate, administer , and monitor the functioning of the BSS. </li></ul><ul><li>This enables the network provider to configure and </li></ul><ul><li>maintain the network from a central location. </li></ul><ul><li>Includes database management, traffic metering and measurement, </li></ul><ul><li>man–machine interface. </li></ul>
  13. 15. Mobility Management
  15. 17. <ul><li>Other optional network elements that the MSC can interface include: </li></ul><ul><li>Internetwork Interworking </li></ul><ul><li>The IWF provides the function to enable the GSM system to interface with the various </li></ul><ul><li>forms of public and private data networks currently available. </li></ul><ul><li>Echo Cancellor </li></ul><ul><li>An EC is used on the PSTN side of the MSC for all voice circuits. Echo control is </li></ul><ul><li>required at the switch because the inherent GSM system delay can cause an </li></ul><ul><li>unacceptable echo condition, even on short distance PSTN circuit connections. </li></ul><ul><li>During a normal PSTN land to land call, no echo is apparent because the delay is too </li></ul><ul><li>short and the user is unable to distinguish between the echo and the normal telephone </li></ul><ul><li>“ side tone”. However, without the EC and with the GSM round trip delay added, the effect </li></ul><ul><li>would be very irritating to the MS subscriber, disrupting speech and concentration. </li></ul><ul><li>Gateway MSC </li></ul><ul><li>The GMSC routes calls out of the network and is the point of access for calls entering the </li></ul><ul><li>network from outside. </li></ul><ul><li>GMSC--------PSTN+ISDN (other N/W). </li></ul>
  16. 18. Network Management Centre
  17. 19. NMC