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Introduction to GSM networks

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Faisal ALFARYAN

on 26 February 2014

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Transcript of Introduction to GSM networks

GSM Network Subsystem
1- Network Switching Subsystem:
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
The Authentication Center (AuC)
Equipment identity register (EIR)
Short Messaging Service Center (SMS)
GSM Main Components
History
What is GSM?

Stands for
G
lobal
S
ystem for
M
obile communication.
Standard protocols for mobile phones communications.
GSM (2G) replaced 1G, from analog to digital in the 90s.
First established in Europe then all over the world.
Outline
brief History
GSM network components
GSM architecture
NSS
BSS
Handover
Evolution to GPRS, UMTS and LTE
Introduction to GSM Networks
Faisal ALFARYAN
Zain SA
faisal.alfaryan@sa.zain.com
Mobile Station (MS)
Base Station System (BSS)
Network Subsystem (NSS)
BSS
___
NSS
MS
2-
Base Station System:
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Transcoding and Rate Adaptation Unit (TRAU)
GSM Network Architecture
Mainly responsible for
Switching calls
Subscriber management
Mobility management
NSS
Components
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
The Authentication Center (AuC)
Equipment identity register (EIR)
Short Messaging Service Center (SMS)
MSC
HLR
VLR
AuC
EIR
Main Tasks
Virtual circuit switching.
Subscriber management.
Call control ans SMS.
Authentication.
Location update.
Handover.
Billing.
HLR acts as subscriber database in GSM.
Stores IMSI, same as in SIM.
Stores available services for the subscriber.
Stores home location.
Take a copy from HLR when MS is near.
Update "current" location of MS.
Stores IMSI.
Mobile status.
That saves signaling between MSC and HLR.
Main Tasks
Usually is integrated in HLR.
Grants authentication to subscriber to proceed a request.
Authentication Procedure
Each Subscriber has a key code (Ki) stored in SIM and AuC
MS
MSC
AuC
Initiate request
Send IMSI
(RAND, SERS)
(RAND)
(SERS*)
SERS* = SERS ?

If yes, Authentication granted
It's often integrated with the HLR.
Keeps a list of mobile phones (identified by their IMSI) which are to be banned from the network or monitored.
i.e. Keep track of stolen phones.
SMSC
SMS procedure
MS sends SMS to other party.
MSC get SMS request, which contains phone number of other party.
MSC forward to SMSC.
SMSC check phone number location from HLR.
SMSC forward to MSC concerned.
MSC check other party, if answers, then send SMS.
MSC report to SMSC to delete SMS.
if other party didn't answer (off), then SMSC saves SMS until it answers.
It's also called Radio Network
Connects MS to GSM network through air interface.
Base Station System (BSS)
Main Components
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Transcoding and Rate Adaptation Unit (TRAU)
BTS
Main feature that is replaced wired connection with wireless one to MS.
It contains RF equipments which provide air interface with MS.
It covers a cell up to 35Km radius (Theory)
Practically, the cell coverage is around 3-4Km and for busy areas get down to 100m. i.e. malls and downtown.
BTS
To avoid interference with other cells, each cell operates on a different frequency.
To increase capacity of the cell, it's divided into sectors with different frequency.
BSC
It is responsible for establishment, release and maintenance of connected cells.
Controls one ore more BTSs.
Switches traffic and signaling to\from the BTSs and the MSC.
Controls handovers performed by BTSs within its control.
It "CONTROLS"
TRAU
It converts the data rate of MSC (64Kbit\s) into form specified by GSM specification for transmission over the network.
Usually converts to (16Kbits\s)
Why?
64Kbit\s would use the BW of air interface in an inefficient way.
Handover
When MS is moving away from a cell, then the call is "handovered" to nearest cell fro better coverage.
BTS
BTS can serve multiple subscribers in the same time using two access methods; Time Division Multiple Access (TDMA) and Frequency DMA (FDMA).
Usually in a 3 sector cell, 30 users can be connected in the same time.
However, average use of subscriber is 1min every hour, means 30x60= 1800users.
Air Interface
BTS
When BTS communicates with MS there are two terms called Uplink and Downlink
Frequency Bands
Downlink
Uplink
Operating at 900MHz band
for Uplink 890-915 MHz
for Downlink 935-960MHz
With Bandwidth of 25MHz divided into 125 channels each 200KHz.
BTS
In some areas it became apparent that the number of available channels was not sufficient so the 1800MHZ band was assigned.
Frequency Bands
Downlink
Uplink
Operating at 1800MHz band
for Uplink 1710-1785 MHz
for Downlink 1805-1880MHz
With Bandwidth of 75MHz divided into 375 channels each 200KHz.
Uses
Better coverage.
Free-up capacity.
Avoid interference.
Types of Handover
Intra BTS
Intra BSC
Inter BSC
Inter MSC
Intra BTS
The ME remains attached to the BTS transciever.
Changing just the frequency or the slot used by the ME.
Intra BSC
Different BTS, same BSC.
BSC handles handover by checking reports from BTS regarding signal power.
Inter BSC
Different BSC, same MSC.
Reports show that there is a better coverage at another BTS outside BSC control.
BSC reports MSC.
MSC identify new BTS and inform new BSC.
MSC informs old BSC to tell MS to start handover to new BSC.
MS connected to new BSC through BTS.
Inter MSC
Requires new MSC.
Old BSC informs MSC to initiate handover.
BTS not in coverage, MSC search for nearest MSC.
Old MSC informs new MSC.
New MSC informs new BSC.
New MSC informs old MSC that it's ready.
Old MSC informs old BSC to inform MS.
MS is connected to new BSC through new BTS.
GPRS
Handover Execution
Hard handover
"Break before make".
Usually used in GSM.
Soft handover
"Make before break ".
Usually used in UMTS.
More efficient but expensive.
Mid 90's Internet became important.
GPRS made access to internet.
Used Packet switching technology.
Data sent as a packet.
GPRS
General Packet Radio Service
Why not using Ckt-Switching for internet access?
Ckt-Switching data transmission is ideal for voice but it's not for variable "brusty" BW usage.
Ckt-Switching would use occupy BW inefficiently.
Packet Switching
Uses BW efficiently.
Would charge by data usage.
i.e Web browsing.
Better data rate, up to 177Kbit/s (practical 48Kbit/s)
Packet Switching
Packet Control Unit (PCU)
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
GPRS Network Elements
(added to GSM)
It replaces BSC, since there is no dedicated connection for GPRS subscriber.
PCU
It acts as MSC, connecting RAN to core network for packet switching.
SGSN
It connects GPRS to the external network.
Such as Internet, LAN network.
GGSN
Main tasks
Assign timeslots for subscriber in Up/down link connection.
Flow control of data.
UMTS
LTE
Enhancement
Enhanced Data rate for GSM Evolution (EDGE) was introduced.
Used different type of modulation
Download speed 384Kbit/s (practical 175Kbit/s)
Network elements updated.
UMTS combined the properties of the circuit-switched network with packet-switched network.
UTRAN introduced.
WCDMA introduced.
3G Partnership Project designed UMTS network and had couple of releases over the years.
UMTS gone into many enhancements phases and offers currently so much more than originally designed.
UMTS
BTS is called Node-B
BCS is called RNC
MS is called UE
Main changes in core network is on software level.
UMTS Network Elements
Main Features
RNC supports WCDMA
RNC performs soft handover.
Node-B performs WCDMA
Operating frequency 2100MHz
Download speed started with 348Kbps in the first releases.
Universal Mobile Telecommunications Systems
HSPA
Developed through releases 5 and 7.
MIMO antenna introduced.
New modulation, 16 QAM
Download speed reached 21Mbps.
Long Term Evolution
3GPP designed new network for better performance and reduced cost.
EUTRAN introduced.
OFDM introduced.
Changes on RAN and core levels.
LTE
Main Features
RNC\BSC disappeared.
Flat IP network.
eNode-B performs OFDM.
Operating frequency 1800MHz
Download speed reaches 100Mbps.
Summary
THANK YOU
Full transcript