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Second Generation

Second Generation. Dr Alison Griffiths Room C203 - Tel: 3292 a.l.griffiths@staffs.ac.uk. Original Credit to J Champion. MCCS – 2nd Gen. Contents Why was this needed GSM Technology. MCCS – 2nd Gen. Why was 2G needed The number of phones & users increased

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Second Generation

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  1. Second Generation Dr Alison Griffiths Room C203 - Tel: 3292 a.l.griffiths@staffs.ac.uk Original Credit to J Champion

  2. MCCS – 2nd Gen • Contents • Why was this needed • GSM • Technology

  3. MCCS – 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

  4. MCCS – 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

  5. MCCS – 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 • Originally called “Groupe Spéciale Mobile” later changed to English

  6. MCCS – 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 • Code division Multiple access (CDMA) (also know as IS-95) was introduced

  7. MCCS – 2nd Generation World • In Japan • Personal Digital Cellular • Introduced by NTT Do Como • Operating in 800 and 1500 MHz band • NTT Do Como introduced i-mode to the world with PDC

  8. MCCS – 2nd Generation World • GSM due to its standards based approach • Now dominates the cellular market • 73% of all mobile phones operate on the GSM standards • Over 1 Billion users • www.gsmworld.com/news/statistics/pdf/gsma_stats_q2_04.pdf • In some countries there are now more phones than people • Users having more than one phone for each of there roles • http://www.inq7.net/inf/2004/jul/09/inf_5-1.htm

  9. MCCS – 2nd Generation World Taken from the report at GSM world for quarter 2, 2004 www.gsmworld.com/news/statistics/pdf/gsma_stats_q2_04.pdf

  10. MCCS – 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

  11. MCCS – 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)

  12. MCCS – 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)

  13. MCCS – GSM • Supplementary Services • User Identification • Call Redirection • Call Hold • Advice of Charge • Call Barring • Call Forwarding • Multiparty calls

  14. MCCS – 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 • Separate frequencies are used for the uplink and downlink • 890-915MHz uplink, 935-960MHz 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 0.577 ms • 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

  15. MCCS – 2nd Gen • TDMA Time Frequency Frequencies 890 MHz - 960 MHz – Europe 1710 – 1880 MHz - Europe 1850 MHz – 1950 MHz - America

  16. MCCS – 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

  17. MCCS – 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

  18. GSM System – Multiple Access 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 Multiframe Frame 1 Frame N …….. Slot 1 Slot 2 Slot i Slot 8 Slot 1 Slot 8 Slot Guard Time Preamble Message Postamble Guard Time

  19. MCCS – 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

  20. MCCS – 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 • Virgin Cola, has a vending machine where you pay via the phone • (news.bbc.co.uk/1/hi/sci/tech/986334.stm, 2000)

  21. MCCS – 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)

  22. MCCS – 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 Theory Reality BS BS Transmission distance

  23. MCCS – 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

  24. BS BS BS BS MCCS – BSS • Base station Controller Base Station Controller

  25. MCCS – 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

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

  27. MCCS – 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

  28. MCCS – 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

  29. MCCS – 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

  30. MCCS – 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 AUC OSS MSC VLR HLR VLR MSC MSC Mobile Switching Center VLR Visitor Location Register HLR Home Location Register

  31. MCCS – GSM Roaming • At the moment what we have discussed is a single company using a single infrastructure • The issue of incompatible systems has been discussed as a problems for 1G • By a large majority of companies using the same technology the availability to communicate across the infrastructures can be achieved • This is a similar concept to how the Internet operates • This is referred to as “GSM Roaming” • A full list of countries that allow roaming with companies and other countries listed • http://www.gsmworld.com/roaming/gsminfo/index.shtml

  32. MCCS – GSM Roaming • In theory you can take your phone and use it abroad • In reality you may need a tri-band phone • This is a phone which can receive and send on all of the frequencies which are used by GSM worldwide • You can not just connect to another GSM network • There has to be a roaming agreement between your operator and the one you wish to connect to

  33. MCCS – GSM Roaming • When you turn on your phone abroad • Your HLR of your operator will be informed where the device is located • The device itself will be attached to the VLR of the operator whom you are connected • Your device will be given • Mobile Station Roaming Number • This is a unique number – a virtual number • Any calls then made to your number will be forwarded to you virtual number

  34. MCCS – GSM Roaming • The operator of the VLR • Will request information from your HLR • Information like • Is the device allowed to roam • Confirmation you are allowed to connect to the network • Subscriber information • Services which the handset can provide

  35. MCCS – GSM Roaming AUC AUC VLR MSC HLR VLR MSC MSC Mobile Switching Center VLR Visitor Location Register HLR Home Location Register

  36. MCCS – GSM Roaming • All calls then to your number will be directed using SS7 • These calls will be direct to the device anywhere on the planet • The HLR of your operator, where the call will go first will have your current location for re-direction • All of this will take place transparently without user intervention

  37. MCCS – 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

  38. MCCS – 2nd Gen • Summary • 2G GSM Communications • Physical Transmissions • GSM Infrastructure • Roaming Agreements

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