1 / 38

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

bracha
Télécharger la présentation

Second Generation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related