Second Generation Justin Champion Room C203 - Tel: 3292

FMC – 2nd Gen Contents  Why was this needed  GSM  Technology

FMC – 2nd Gen Why was 2G needed  The number of phones & users increased The user base which was originally mostly business related started to change to include other groups  This increased the number of users which were on the networks  Became a supply and demand problem  If current providers could not provide for the demand users would move away from the technology.  As the user base increased in size users in peak areas would find that they could not connect to the network

FMC – 2nd Gen Second Generation (2G) Technology  Mobile phones became popular and requirements changed Users wanted more from the phones  The frequency for the phones to use was limited and better use of this frequency was required  Guarantee that a call was possible when needed  Privacy was needed as the phones may be used for business or personal conversations.  The phones needed to be smaller for ease of carrying  Improved battery life

FMC – 2nd Gen Global System for Mobile Communications (GSM)  1982 the European Commission requested that 900 MHz be reserved for the use of GSM Before the use of TACS and NMT !!!!  1989 ETSI defined the standard which was GSM  European Telecommunication Standards Institute (ETSI) Originally called “Groupe Spéciale Mobile” later changed to English

FMC – 2nd Generation World There was a recognition of the problems with 1G and compatibility issues  To deal with this 2 approaches were taken Force adoption of a standard  European Commission decided that all member countries should use one system GSM Market forces dictating  United States of America adopted this approach  In the US the 2G system had to use the same spectrum as 1G  AMPS – became DAMPS – Digital AMPS - TDMA  Code division Multiple access (CDMA) (also know as IS- 95) was introduced

FMC – 2nd Generation World GSM due to its standards based approach  Now dominates the cellular market  80.79% of all mobile phones operate on the GSM standards Just under 3 Billion users   Although a slow down is now being seen in the number of phones being sold  mobile mobile-2011  This is most likely due to saturation of the market  In some countries there are now more phones than people  Users having more than one phone for each of there roles   More phones than people in the UK and Italy

FMC – 2nd Generation World Subscriber statistics end Q  World 3,665,389,343  cdmaOne 7,919, %  CDMA2000 1X 292,479, %  CDMA2000 1xEV ‐ DO 101,171, %  CDMA2000 1xEV ‐ DO Rev. A 2,349, %  GSM 2,961,292, %  WCDMA 216,434, %  WCDMA HSPA 43,416, %  TDMA 3,042, %  PDC 9,150, %  iDEN 27,610, %  Analog 522, %

FMC – 2nd Gen GSM Services  Intended primarily as a voice service Although now we can see the benefit of data, the increasing use of voice calls was the issue addressed by this standard GSM does support some limited data services  Three services are offered by GSM Teleservices Bearer Services Supplementary Service

FMC – GSM Teleservices  Telephony Codecs for voice and data Encryption of voice data  Emergency Calls These calls must have the highest priority Directing you to the nearest connection point  Voice Mail  Fax Mail  Facsimile Group 3  Short Messaging Service (SMS) Including the SMS – Cell Broadcast (SMS-CB)

FMC – GSM Bearer Services  Bearer services are for the transport of data 9600 bits per second maximum  Synchronous and asynchronous  Alternate data and speech Transparent  Fixed delay in data transfer  No guarantees of data integrity Non transparent  Variable Delay  Guaranteed data integrity via Automatic repeat request (ARQ)

FMC – GSM Supplementary Services  User Identification  Call Redirection  Call Hold  Advice of Charge  Call Barring  Call Forwarding  Multiparty calls

FMC – 2nd Gen GSM Operates  Using Time Division Multiplex Access (TDMA) & FDMA This allow the frequency to be broken up into slots  The frequencies used are GSM 900, GSM 1800 and GSM 1900  Possible selling off though of the 900 Mhz range   Separate frequencies are used for the uplink and downlink  MHz uplink, MHz downlink for example  Uplink and Downlink are 45 MHz apart  200KHz spacing on the frequency  124 pairs of channels  These channels are then divided into 8 time slices  For GSM each slice is 577 ns ( seconds)  Total channels available is 8 * 124 = 992 (in a theoretical context) This means that there is eight times the capacity as before in one part of the frequency  Assuming the same rate is used

FMC – 2nd Gen TDMA & FDMA Frequency Time Frequencies 890 MHz MHz – Europe 1710 – 1880 MHz - Europe 1850 MHz – 1950 MHz - America

FMC – 2nd Gen TDMA & FDMA  Same diagram in a different view  Four devices all communicating at an exact time All of the devices will act as though they are the only device transmitting/receiving Frequency – Uplink Time

FMC – 2nd Gen GSM Operates  One of the features which allowed the increase in the number of users is digitisation of voice The voice is sampled using a (analogue to Digital Converter) ADC  8KHz / second, with an 8 bit result The voice information is then transferred using one of these methods  Enhanced Full Rate  Best quality speech  Uses a full slot  Marginal increase in processor overhead  Full Rate  Improved speech quality  Takes a full slot to transfer  Half Rate  This mode allows for a doubling of capacity to a base station  Loss in speech quality, but not significant  Half a slot to transfer

FMC – 2nd Gen Analogue to Digital Convertor (ADC)  Regular samples are taken from the analogue signal and converted into a digital value The more samples you take with a higher level of precision the more accurate the representation of the original signal  8Khz with a 8 bit result  8000 samples taken per second with a value of 0 to Time

FMC – 2nd Gen Digitisation  Of voice allows for a number of features Takes less bandwidth to transfer the voice The data once digital  Can be encrypted  Can be recovered even with the attenuation effects  Additional bits can be added to allow for errors within transport  Without the need for retransmission – Forward Error Checking (FEC)  The digital voice data can then be place inside of a packet for transport

Time Division Multiple Access (TDMA)  Guard Time: Interval between bursts used to avoid overlapping  Preamble: First part of the burst  Message: Part of burst that includes user data  Postamble: Last part of burst – used to initialise following burst Slot 1Slot 2Slot 8 Slot 1 Frame 1Frame 26 Multiframe Guard TimePreambleMessagePostambleGuard Time Slot Slot i …….. GSM System – Multiple Access

FMC – 2nd Gen - SIM Subscriber Identity Module (SIM) Card  Essential for the GSM network  The SIM is located within the Mobile station (MS) Basically the phone handset you use  Contains Subscriber Authentication key  128 bit encryption key International Mobile Subscriber Identity (IMSI)  A unique international none dialable number which is attached to your device Temporary Mobile Subscriber Identity Mobile Station Integrated Service Digital Network (MSISDN)  Basically this is YOUR phone number PIN to secure the card SMS messages Personal data, phone numbers, Phone settings etc

FMC – 2nd Gen SIM continued  Each one is unique e-commerce  Purchasing items from your phone, with certainty that your device bought the item Authentication encryption is used called the A3/A8  This is used to authenticate your device using challenge/response  A random number is sent  The A3/A8 algorithm then works on the number and returns a 32- bit response.  If this matches the one which the network has calculated the device is authenticated A5 Encryption is used for the voice calls  Using your mobile as an electronic wallet  ticle ece ticle ece

FMC – Location GSM consists of three major systems: Base-Station System (BSS) Network Switiching Sub-System (NSS) Operation and Support System (OSS)  The Switching System performs call processing and subscriber related functions  The system contains the following functional units Home Location Register (HLR) Mobile Switching Center (MSC) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)

FMC – BSS Base Station System (BSS)  This is the part of the network which connects the MS to the network via the radio interface Base Station (BS)  Know as (Base Transceiver Station (BTS) ) in official GSM documentation  This is the radio transceiver the area of transmission is referred to as the cell BS Theory BS Reality Transmission distance

FMC – 2nd Gen Base station controller  This node takes overall control of a number of base stations a point of control for the BS Other functionality  Traffic concentration  Switching operations  Data based and voice  Network management to all BS attached  Radio channel management for all BS attached  Conversion of air interface rates to network applicable rates  13 Kbps to 64 Kbps  Handover control  This is for base stations which it has control of

FMC – BSS Base station Controller BS Base Station Controller

FMC – GSM - NSS Network Switching Sub-System (NSS)  Responsible for the transfer of information from the handsets to the correct part of the infrastructure  Functions Handovers between BSC’s Allow communication between mobile and PSTN networks Allows for roaming between networks A number of nodes are a part of the NSS

FMC – GSM - NSS NSS nodes consist of  Mobile Switching Centre (MSC)  Home Location Register (HLR)  Visitor Location Register (VLR)  Authentication Centre (AuC)  Equipment Identity Register (EIR)

FMC – GSM - NSS HLR is the most important database  Storage and management of subscriptions  Permanent data includes: Subscriber's service profile Subscriber's location information Subscriber‘s activity status  Subscribing to a particular provider‘s service registers you in the HLR of that provider The MSC performs the telephony switching functions of the network  Controls call to and from other telephone and data systems Also performs functions such as  Toll ticketing  Network interfacing  Common Channel signalling

FMC – GSM - NSS VLR contains data on visiting (roaming) subscribers  Integrated with the MSC  When a roamer enters the service area the VLR queries the appropriate HLR  If a roamer makes a call the VLR will already have the information it needs for call setup The AUC verifies the identity of the user and ensures and ensures the confidentiality of each call  By provide authenticity and encryption parameters for every call  Protects network operators from fraud  Assures a certain level of security for the content of each call The EIR is a database that includes info solely about the identity mobile equipment  Prevents calls from stolen, unauthorised or defective mobile devices Since 2002 all UK based operators have shared the contents of the EIR database This is also true for countries which have roaming agreements with UK operators If a phone is stolen anywhere in the world, it can now be registered as stolen and traced within 24 hours

FMC – GSM - OSS Operation and Support System  This part of the network allows monitoring of the network  Ensures the smooth running and involves management tasks Accounting and Billing Status Reports Traffic monitoring In addition if a BSC can not carry out all of its tasks the OSS will take control of the BSC’s tasks  The OSS is logically connected to all equipment in the infrastructure

FMC – 2nd Gen GSM Infrastructure  The specifications created by ETSI do not require any of the following infrastructure but recommends it ! All mobile operators have it VLR MSC VLR MSC HLR MSC Mobile Switching Center VLR Visitor Location Register HLR Home Location Register OSS AUC

FMC – GSM The infrastructure which has been discussed  Is ever expanding  As new functionality is required this is built into the infrastructure This gives GSM the ability to remain future proof without large investment in new infrastructure when new technology becomes available This will be seen more in the future lectures when we can see that new technology uses GSM as a basis and essential part  Even for 3G/4G communications

FMC – 2nd Gen Summary  2G GSM Communications Physical Transmissions GSM Infrastructure