Transcript Document
Second Generation
Dr Alison Griffiths
Room C203 - Tel: 3292
[email protected]
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
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
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
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
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 IS95) was introduced
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
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
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
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
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)
MCCS – GSM
Bearer Services
Bearer
9600 bits per second maximum
Synchronous and asynchronous
Alternate data and speech
Transparent
services are for the transport of data
Fixed delay in data transfer
No guarantees of data integrity
Non transparent
Variable Delay
Guaranteed data integrity via Automatic repeat request (ARQ)
MCCS – GSM
Supplementary Services
User
Identification
Call Redirection
Call Hold
Advice of Charge
Call Barring
Call Forwarding
Multiparty calls
MCCS – 2nd Gen
GSM Operates
Using
This allow the frequency to be broken up into slots
Time Division Multiplex Access (TDMA) & FDMA
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
MCCS – 2nd Gen
TDMA
Time
Frequency
Frequencies
890 MHz - 960 MHz – Europe
1710 – 1880 MHz - Europe
1850 MHz – 1950 MHz - America
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
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
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
Slot 1
Slot 2
Frame N
Slot i
Slot 8
……..
Slot
Guard Time
Preamble
Message
Postamble
Guard Time
Slot 1
Slot 8
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
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)
128 bit encryption key
Basically this is YOUR phone number
PIN to secure the card
SMS messages
Personal data, phone numbers, Phone settings etc
MCCS – 2nd Gen
SIM continued
Each one is unique
e-commerce
Authentication encryption is used called the A3/A8
Purchasing items from your phone, with certainty that your device
bought the item
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 32bit 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)
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)
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
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
MCCS – BSS
Base station Controller
Base Station
Controller
BS
BS
BS
BS
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
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)
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
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
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
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
MSC
AUC
VLR
VLR
MSC Mobile Switching Center
VLR Visitor Location Register
HLR Home Location Register
OSS
HLR
MSC
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
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
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
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
MCCS – GSM Roaming
AUC
VLR
MSC
AUC
HLR
VLR
MSC
MSC Mobile Switching Center
VLR Visitor Location Register
HLR Home Location Register
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 redirection
All of this will take place transparently without user
intervention
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
MCCS – 2nd Gen
Summary
2G
GSM Communications
Physical Transmissions
GSM Infrastructure
Roaming Agreements