Global System for Mobile communication GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity. GSM networks operate in four different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated. The rarer 400 and 450 MHz frequency bands are assigned in some countries, notably Scandinavia, where these frequencies were previously used for first-generation systems.  Course Name: Networking Level(UG/PG): UG  Author(s) : Phani Swathi Chitta  Mentor: Aruna Adil *The contents in this ppt are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 2.5 India license

Learning Objectives After interacting with this Learning Object, the learner will be able to: Explain the GSM architecture and its functionality

Definitions of the components/Keywords: Global System for Mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is a digital cellular phone system using FDMA and TDMA. A GSM digitizes and compresses data, then sends it down through a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band. GSM is a fully digitized technology for better speech quality. The key elements of GSM technology are:  MS – Mobile Station  BTS – Base Transceiver Station  BSC – Base Station Controller  MSC – Mobile Switching Center  HLR – Home Location register  VLR – Visitor Location Register  The elements shown in this LO are BTS, BSC and MSC

Definitions of the components/Keywords: The general architecture of a full GSM network:

Definitions of the components/Keywords: MS – Mobile Station consists of two units  Mobile Hand set is one of the most complicated GSM device. It provides user the access to the Network. Each handset has unique identity no. called IMEI.  SIM is a removable module goes into the mobile handset. Each SIM has unique number called International Mobile Subscriber Identity (IMSI).It has built in Micro- computer & memory into it. It contains the ROM of 6 to 16KB,RAM of 128 to256 bytes and EEPROM of 3 to 8KB. BTS - Base Transceiver Station  Cellular networks are based on the use of a central transmitter-receiver in each cell, called a “base station” or Base Transceiver Station, BTS.  Cell is the basic unit of GSM system. It has one or several frequencies depending on the traffic load.  MS (Mobile Station) or mobile phone connects to mobile network through BTS; it handles communication using radio transmission with mobile station. As name suggests, Base transceiver Station is the radio equipment which receive and transmit voice data at the same time.  The BTS corresponds to the transceivers and antennas used in each cell of the network.  BTS functions also include encoding, encrypting, multiplexing, modulating, feeding the RF signals to the antenna, decoding, decrypting, and equalizing received signals

Definitions of the components/Keywords: BSC – Base Station Controller  The BSC provides all the control functions and physical links between the MSC and BTS.  It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations.  A number of BSCs are served by an MSC. MSC – Mobile Switching Center  It handles technical end of telephony.  The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems.  It is connected to HLR & VLR for subscriber identification & routing incoming calls.  Its capacity is in terms of no of subscribers.  It is connected to BSC at one end and Fixed Line network on other end

Definitions of the components/Keywords: HLR – Home Location Register  All Subscribers data is stored in HLR.  It has permanent data base of all the registered subscribers.  HLR has series of numbers for all subscribers. VLR - Visitor Location Register  It is a database containing information of users other than the local subscribers.  VLR retrieves the data of a new subscriber from the HLR of the subscriber’s zone. The data is maintained as long as the subscriber is in the new MSC zone and is deleted when the user leaves or after a long period of inactivity

Definitions of the components/Keywords: How it works: MS connects to mobile network through BTS BTS is responsible for carrying out the radio communication between MS and the network This radio signal is sent to BSC

Definitions of the components/Keywords: How it works (contd..): BSC controls multiple BTSs It handles power and signal measurements from the MS and handovers from one BTS to another (if both BTSs are controlled by same BSC) Thereby it reduces number of connections to the MSC and allows for higher capacity connections to the MSC

Definitions of the components/Keywords: How it works (contd..) : MSC is the heart of GSM network It handles call routing, call setup and basic switching functions It handles inter BSC handoffs as well as coordinates with other MScs for inter MSC handoffs

Definitions of the components/Keywords: How it works (contd..) : HLR, VLR and EIR are connected to MSC HLR and VLR are the databases that stores data about subscribers and this data is used by MSC during call setup HLR: It is a large database that permanently stores data about subscribers. It maintains subscriber-specific information. VLR: It contains information similar to HLR but for subscribers currently in its location area

Definitions of the components/Keywords: How it works (contd..) : EIR: It is a database that keeps track of handsets on the network It is composed of three lists The black list: The handsets that are to be denied service reasons like stolen or cloned or if the handset is malfunctioning or doesn’t have the technical capabilities to operate on the network The gray list: The handsets that are to be monitored for suspicious activity The white list: The handsets not on the black list or on the gray list AUC: This is responsible for generating the necessary crypto variables for authentication and encryption on the network It is generally placed together with HLR

Master Layout Give START, RESET, CLEAR buttons Give a HELP button and the text to be displayed when HELP button is pressed is shown in next slide Give a slider to control the speed of animation Greet Acknowledgement Delink Roaming No Fig. A Update VLR

HELP button: Instructions for usage... I1. You have to select the position for the receiver only after choosing the position for sender I2. The sender is fixed I3. For selecting the position of the sender, You have to left-click at the position you wish to place the sender I4. The receiver can move I5. For selecting the initial & final positions of the receiver, you have to left-click at the positions you wish to place the receiver I6. Blue colored filled circles indicate the present position of the node(sender/receiver) while the unfilled circle indicate the destination point for the receiver I7. Important messages like control messages shall be shown on the violet colored text area at the side of the simulation area I8. If u want to know the HLR,VLR details in MSC area, just a right-click on that specific MSC will do Assumptions made... A1. Home Location of the sender is MSC2 A2. Home Location of the receiver is MSC1

Step 1: I nstruction for the animator T ext to be displayed in the working area (DT) Initially show the figure in the master layout The text in DT should appear in parallel to the figure Click the initial position of SENDER Mobile Click the initial position of ROAMING Mobile Click the destination position of ROAMING Mobile

Step 2: I nstruction for the animator T ext to be displayed in the working area (DT) When the user selects START, show the above figure The text in DT should appear in parallel to the figure

Step 3: I nstruction for the animator T ext to be displayed in the working area (DT) Blue round has to be moved to nearest blue square The text in DT should appear in parallel to the figure Mobile has moved to new BTS

Step 4: I nstruction for the animator T ext to be displayed in the working area (DT) A red line should be drawn between blue round and green square The text in DT should appear in parallel to the figure Data coming from sender BTS ->*: Mobile received Broadcast Message Signal strength is different from old one Data coming from sender M: Sends greet (IMSI) to the new BTS

Step 5: I nstruction for the animator T ext to be displayed in the working area (DT) A green line is drawn between green square and blue round The text in DT should appear in parallel to the figure Data coming from sender BTS(new): Sends greet ACK to the Mobile Data coming from sender New BTS -> BSC: Sends handoff signal to Data coming from sender BSC -> old BTS: Send signal to delink Mobile

Step 6: I nstruction for the animator T ext to be displayed in the working area (DT) Blue round has to be moved to new blue square The text in DT should appear in parallel to the figure Mobile has moved to new BTS

Step 7: I nstruction for the animator T ext to be displayed in the working area (DT) An yellow line should be drawn between blue round and green square The text in DT should appear in parallel to the figure BTS(new): Sends greet ACK to the Mobile

Step 8: I nstruction for the animator T ext to be displayed in the working area (DT) show circles around all green squares The text in DT should appear in parallel to the figure BSC-> Old BTS: Send signal to delink Mobile

Step 9: I nstruction for the animator T ext to be displayed in the working area (DT) Move blue round to new brown square as shown in figure The text in DT should appear in parallel to the figure Mobile has moved to new MSC

Step 10: I nstruction for the animator T ext to be displayed in the working area (DT) show circles around all green squares The text in DT should appear in parallel to the figure Old BSC-> old BTS: Send signal to delink mobile

Step 11: I nstruction for the animator T ext to be displayed in the working area (DT) show circles around all green squares The text in DT should appear in parallel to the figure Old BSC-> old BTS: Send signal to delink mobile

Step 12: I nstruction for the animator T ext to be displayed in the working area (DT) Move blue round to new brown square as shown in figure The text in DT should appear in parallel to the figure Mobile has moved to new MSC

Step 13: I nstruction for the animator T ext to be displayed in the working area (DT) Show a red line between brown square and blue round The text in DT should appear in parallel to the figure M-> new VLR: IMSI thru new MSC

Step 14: I nstruction for the animator T ext to be displayed in the working area (DT) Show the figure as shown above The text in DT should appear in parallel to the figure M-> old VLR: cancellation

Step 15: I nstruction for the animator T ext to be displayed in the working area (DT) show circles around all green squares The text in DT should appear in parallel to the figure Old BSC-> old BTS: Send signal to delink mobile

Step 16: I nstruction for the animator T ext to be displayed in the working area (DT) show circles around all green squares The text in DT should appear in parallel to the figure Old BSC-> old BTS: Send signal to delink mobile

Step 17: I nstruction for the animator T ext to be displayed in the working area (DT) Show red lines between blue round and green square and green square and blue square The text in DT should appear in parallel to the figure M: Sends greet (IMSI…) to the new BTS/BSC

Step 18: I nstruction for the animator T ext to be displayed in the working area (DT) Show figure as shown above The text in DT should appear in parallel to the figure New BSC -> old BSC : Sends handoff signal

Step 19: I nstruction for the animator T ext to be displayed in the working area (DT) show figure as shown above The text in DT should appear in parallel to the figure Old BSC-> old BTS: Send signal to delink mobile Press RESET button to re-run the simulation

Introduction Credits 34 Definitions Test your understanding (questionnaire) ‏ Lets Sum up (summary) ‏ Want to know more… (Further Reading) ‏ Try it yourself Interactivity: Analogy Slide 1 Slide 3 Slide Slide 40 Electrical Engineering The demo itself is interactivity in this LO

Questionnaire 1.GSM is a digital cellular phone system using Answers: a)FDMA b) CDMA c) TDMA d) TDMA and FDMA

Questionnaire 2. The handset is under observation from the network for the possible problems. Under which list will this belong in EIR? Answers: a) White List b) Grey List c) Black List d) None of the above

Questionnaire 3. GSM includes HLR and VLR databases. Their uses may be described as: Answers: a) a VLR copies all relevant information for a user from the HLR every time a user moves from one cell to another. b) every time a user moves into a location area of a different MSC, all relevant user information is copied from the VLR to the HLR associated with the new MSC. c) the contents of HLR's and VLR's is always the same. d) every time a user moves into the location area of a different MSC, all relevant user information is copied from the HLR to the VLR associated with the new MSC

Questionnaire 4. The process of channel coding, Encryption, Multiplexing and modulation for Trans direction and reverse for reception are to be carried out by Answers: a) BTS b) BSC c) MSC d) MS

Questionnaire 5. Which of these statements are correct? I.Mobile Switching Centre(MSC) would process the call made by one mobile phone user to another mobile phone user. II.Public Switched Telephone Network(PSTN) would be involved in processing a call when the call is made by a mobile phone user to a land phone. III.Both MSC and PSTN processes a call made from a mobile phone to a land phone. Answers: a)III only b)I and III c)I and II d)II and III

Links for further reading Reference websites: Books: