1. Dr Alison Griffiths Room C203 - Tel: 3292 a.l.griffiths@staffs.ac.uk
Second Generation
Dr Alison Griffiths
Room C203 - Tel: 3292
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
In some countries there are now more phones than people
Users having more than one phone for each of there roles

9. MCCS – 2nd Generation World
Taken from the report at GSM world for quarter 2, 2004

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 Emergency Calls Voice Mail Fax Mail
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
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 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 Frequencies 890 MHz - 960 MHz – Europe
Time
Frequency
Frequencies
890 MHz 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/ 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. MCCS – BSS
Base station Controller
Base Station
Controller BS BS BS BS

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

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 MSC MSC VLR HLR VLR
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