About GSM Network

1. Telecommunication Basics
(GSM Network)
Software Engineering Lab - 김영기 책임

2. Remember Again !!!
1G 2G 3G 3.5G 4G
WiMAX track 802.15e Wave1 802.15e Wave2 802.16e 802.16n
(Mobile WiMAX) (Mobile WiMAX) WiMAX R1.5 WiMAX R2.0
CDMA-1X CDMA-1X CDMA-1X
CDMA track
EV-DO r0 EV-DO rA EV-DO rB UMB
AMPS IS-95 A IS-95 B CDMA-1X
EV-DV
GSM track EDGE
LTE LTE Advanced
NMT GSM GPRS W-CDMA W-CDMA W-CDMA W-CDMA
W-CDMA
R5 R6 R7 HSPA+
R3
(HSCPA) (HSUPA) (HSPA+) Phase2
음성 통화 통화, 문자, 이메일 통화, 문자, 멀티미디어, 무선인터넷 초고속 인터넷 초고속 무선 인터넷
유,무선간 연동

3. GSM Characteristics
MS Transmission BS Transmission
Year Introduced 1990
Band : 890 – 915 Band : 935 – 960
MHZ MHZ
Access method TDMA
45 MHz
Channel
200 kHz
Bandwidth
Number of duplex
1 125
channels
2
3 Users per channel 8
4
5 Speech coding bit
13 kbps
6 rate
7 Data coding bit
12 kbps
F1 F2 F1' F2' 8 rate
Frequency
Frame size 4.6 ms

4. GSM Nework Architecture
Base Station Subsystem Network Subsystem
MS
Abis A
SIM
HLR VLR
ME BSC
PSTN
ISDN, PSPDN
Mobile CSPDN
BTS
Station
MSC
UM
BSC
BTS
EIR AuC
O&M
Database Network Planning
Data Sever
System
Communication Network Measurement
System
Network
Network Management Subsystem
SIM : Subscriber Identity Module BSC : Base Station Controller MSC : Mobile Service Switching Station
ME : Mobile Equipment HLR : Home Location Register AuC : Authentication Center
MS : Mobile Station VLR : Visitor Location Register UM : Radio Link
BTS : Base Transceiver Station EIR : Equipment Identify Register NMS : Network Management System

5. GSM Interface (1/2)
Interface Description
 The "air" or radio interface standard that is used for exchanges between a mobile (ME) and a
Um Interface base station (BTS / BSC). For signaling, a modified version of the ISDN LAPD, known as
LAPDm is used
 This is a BSS internal interface linking the BSC and a BTS, and it has not been totally
Abis Interface standardized. The Abis interface allows control of the radio equipment and radio frequency
allocation in the BTS
 The A interface is used to provide communication between the BSS and the MSC. The
interface carries information to enable the channels, timeslots and the like to be allocated to
A Interface the mobile equipment being serviced by the BSSs. The messaging required within the network
to enable handover etc to be undertaken is carried over the interface
 The B interface exists between the MSC and the VLR . It uses a protocol known as the MAP/B
protocol. As most VLRs are collocated with an MSC, this makes the interface purely an
B Interface "internal" interface. The interface is used whenever the MSC needs access to data regarding a
MS located in its area
 The C interface is located between the HLR and a GMSC or a SMS-G. When a call originates
from outside the network, i.e. from the PSTN or another mobile network it ahs to pass
through the gateway so that routing information required to complete the call may be gained.
C Interface The protocol used for communication is MAP/C, the letter "C" indicating that the protocol is
used for the "C" interface. In addition to this, the MSC may optionally forward billing
information to the HLR after the call is completed and cleared down
 The D interface is situated between the VLR and HLR. It uses the MAP/D protocol to
D Interface exchange the data related to the location of the ME and to the management of the
subscriber
 The E interface provides communication between two MSCs. The E interface exchanges data
E Interface related to handover between the anchor and relay MSCs using the MAP/E protocol

6. GSM Interface (1/2)
Interface Description
 The F interface is used between an MSC and EIR. It uses the MAP/F protocol. The
F Interface communications along this interface are used to confirm the status of the IMEI of the ME
gaining access to the network
 The G interface interconnects two VLRs of different MSCs and uses the MAP/G protocol to
G Interface transfer subscriber information, during e.g. a location update procedure
 The H interface exists between the MSC the SMS-G. It transfers short messages and uses the
H Interface MAP/H protocol
 The I interface can be found between the MSC and the ME. Messages exchanged over the I
I Interface interface are relayed transparently through the BSS
CM CM
MM MM
DTAP
RR BSSMAP BSSMAP/DTAP
RR SCCP SCCP
RR BTSM BTSM
MTP 3 MTP 3
LAPDm LAPDm LAPD LAPD MTP 2 MTP 2
GSM RF GSM RF Layer 1 Layer 1 MTP 1 MTP 1
UM Abis A
The layered model of the GSM architecture integrates and links the peer-to-peer communications between two
different systems

7. Mobile Station
 GSM MSs consist of
MS
Mobile Equipment
SIM
SIM (Subscriber Identity Module)
 Functions of Mobile Station ME
Voice and data transmission & receipt
Mobile
Can receive, store, send SMS up to 160 charactors Station
Frequency and time synchronization
Monitoring of power and signal quality of the surrounding cells
Power levels of 20W, 8W, 5W, 2W and .8W
Provision of location updates even during inactive state
MS identified by unique IMEI shown on pressing “*#06#”

8. SIM (Subscriber Identity Module) (1/2)
 SIM has microprocessor and memory
Fixed data stored for the subscription
IMSI
Authentication Key , Ki
Security Algorithms : Kc, A3, A8
PIN & PUK
 Network Identities
IMEI (International Mobile Equipment Identity)
Unique Code and is checked in the EIR White list : IMEI, assigned to valid ME.
Black list : IMEI reported stolen
White List, Grey List, Black List Gray list : IMEI having problems like faulty
software, wrong make of equipment etc.
MSISDN (Mobile Station ISDN Number)
Is register in the telephone directory and used by the calling party for dialing
Shall not exceed 15 digits
1 to 3 digits Variable Variable
NDC : National Destination Code
CC NDC SN SN : Subscriber Number

9. SIM (Subscriber Identity Module) (2/2)
 Network Identities (cont.)
IMSI (International Mobile Subscriber Identity)
An unique identity which is used internationally and
used within the network to identify the mobile subscribers
Stored in the SIM, the HLR, VLR database
TMSI (Temporary Mobile Subscriber Identity)
Is a temporary IMSI No. made known to an MS at registration
The VLR assigns a TMSI to each mobile subscribers entering the VLR area
Assigned only after successful authentication
MSRN (Mobile Station Roaming Number)
Used in the GMSC to setup a connection to the visited MSC/VLR
Is a temporary identity which is assigned during the establishment of a call to a roaming
subs

10. NSS (Network Subsystem)
 Network Subsystem contains
MSC, VLR, HLR, AC and EIR
 Main Functions
Call control
Identifies the subscriber, establish a call, and clear connection
Charging
Collect the charging information about a call and transferers it to the Billing Center
Mobility management
Maintain information about subscriber’s location
Signaling
Interface with the BSS and PSTN
Subscriber data handling
Permanent data  HLR
Temporary data  VLR

11. NSS Entities
Entity Functionality
 Call control (Switching and call routing)
 Initiation of paging
MSC
 Charging data collection
(Mobile service Switching Center)
 Service provisioning
 Communication with other NEs (HLR, VLR, MSCs, BSCs)
 Temporary data (data valid when subscriber is within its service area)
 Identification numbers of the subscribers
VLR  Security information for authentication of the SIM card and for ciphering
(Visitor Location Register)  Services that the subscriber can use
 Data in VLR : IMSI & TMSI, MSISDN, MSRN, Location Area,
Supplementary service parameters, MS category, Authentication Key
 Permanent data
HLR
 Keeps track of the current location of its customers
(Home Location Register)
 Same functionality the VLR
AC  Provides security information to the network (for verify the SIM cards)
(Authentication Center) - TRIPLET : RAND, SRES, Kc
EIR  Responsible for IMSI checking (for verify the mobile equipment)
(Equipment Identity Register)  Only one EIR per PLMN

12. BSS (Base Station Subsystem)
 Base Satation Subsystem contains
BSC, BTS and TC (Transcoder)
 Main Functions
Radio path control
Taking care of radio resources (channel allocation and quality of the radio connection)
Synchronisation
It is a critical issue in the GSM network due to the nature of the information transferred
Air-and A-interface signalling
Connection establishment between the MS and the NSS
May be either Signalling connection or a traffic(speech, data) connection
Mobile management and speech transcoding
Handover and transcoding

13. BSS Entities
Entity Functionality
 Connection establishment between the MS and the NSS
 Mobility management (Handling of MS connections)
BSC
 Statistical raw data collection (Internal BSC O&M)
(Base Station Controller)
 Air-and A-interface signaling support (Radio Resource Management)
 BTS and TC control
 Air interface signaling (Radio resource, Signaling link management)
BTS
 Ciphering (Synchronization)
(Base Transceiver Station)
 Speech processing (Signal processing)
TC(SM)  To enable an efficient transmission, the digital speech signal is
(Transcoder (SubMultiplexer)) compressed
A ter Interface A ter’ Interface A Interface
TC
TC
TC
SM2M
TC
BSC TCSM
(Transcoder and Submultiplexer) MSC
TC is a device that takes 13 KBPS speech data and multiplexes four of them into standard 64 Kbps data

14. NMS (Network Management Subsystem)
 Network Management Subsystem contains
Workstation, Servers, and router, etc
 Main Functions
Fault management
Ensure the smooth operation of the network
Rapid correction of any kind of problems that are detected
Configuration management
Maintain up-to-date information about operation and configuration status of NE
Including management of the radio network, S/W and H/W , time synchronization,
security operation
Performance management
Collects measurement data from individual network elements and stores it in a database
Network operator is able to compare the actual performance of the network with the
planned performance

15. OMC (Operations and Maintenance Centre)
 Dynamic monitoring & Controlling of the network
The centralized operation of the various units in the system and
functions needed to maintain the subsystems
Functions
O&M data function
Configuration management
Fault report and alarm handling
Performance supervision/management
Storage of system software and data

16. GSM Frame Structure
Hyperframe = 2048 Superframes
0 1 2 3 4 5 6 7 0
Base station transmit
Slot
Superframe = 51 Traffic Multiframe numbers Corresponding
Or 26 Control Multififrame receive frame
5 6 7 0 1 2 3 4 5
Base station receive
Traffic Multifame Control Multiframes
= 26 Frames = 51 Frames Time
120ms 235.4ms
Traffic multiframe: The Traffic Channel frames are organised into multiframes
consisting of 26 bursts and taking 120 ms. In a traffic multiframe, 24 bursts are
used for traffic. These are numbered 0 to 11 and 13 to 24. One of the remaining
Frame = 8 Slots bursts is then used to accommodate the SACCH, the remaining frame remaining
free. The actual position used alternates between position 12 and 25.
Control multiframe: the Control Channel multiframe that comprises 51 bursts
and occupies 235.4 ms. This always occurs on the beacon frequency in time slot
zero and it may also occur within slots 2, 4 and 6 of the beacon frequency as
Slot = 577µs
well. This multiframe is subdivided into logical channels which are time-
scheduled
- Frequency correction burst, Synchronization burst
- Broadcast channel (BCH), Paging and Access Grant Channel (PACCH),
Stand Alone Dedicated Control Channel (SDCCH)

17. GSM Channels
GSM Channels
Traffic Channels Signaling Channels
Broadcast Channels Common Control Channels Dedicate Control Channels
Full-rate Half-rate downlink uplink slow fast
TCH/F TCH/H BCCH FCCH SCH PCH AGCH RACH TCH/H TCH/H TCH/H
 The forward common channels are used for paging to inform a mobile of an incoming call, responding to
channel requests, and broadcasting bulletin board information.
Common Channel  The return common channel is a random access channel used by the mobile to request channel resources
before timing information is conveyed by the BSS
 The signaling channels are used for maintenance of the call and for enabling call set up, providing
Dedicate Channel facilities such as handover when the call is in progress, and finally terminating the call.
 The traffic channels handle the actual payload
TCHf : Full rate traffic channel. RACHMS : access requests, response to call announcement,
TCH h : Half rate traffic channel. location update, etc.
BCCH : Broadcast Network information, FACCHt : For time critical signalling over the TCH
SCH : Synchronisation of the MSs. (e.g. for handover signalling)
FCHMS : frequency correction. SACCHt : TCH in-band signalling, (e.g. for link monitoring)
AGCH : Acknowledge channel requests from MS and allocate SDCCH : For signalling exchanges,
a SDCCH. (e.g. during call setup, registration / location updates)
PCHMS : terminating call announcement. FACCHs : FACCH for the SDCCH.
SACCHs : SDCCH in-band signalling (e.g. for link monitoring)

18. GSM Call Scenario 1
 Location update
Previous
BSS MSC/VLR HLR/AuC MSC/VLR
Channel Request
Immediate Assignment
Location Update Request
Complete L3 Info
(location updating request)
Send Authentication Info
Send Authentication Info RR
Authentication Request
Authentication Response
Update Location
Cancel Location
Cancel Location RR
Insert Subscriber Data
Insert Subscriber Data RR
Update Location RR
Location Updating Accept
Clear Command
Clear Complete
Channel Release

19. GSM Call Scenario 2
 Mobile to Network
Cell Site MSC PSTN
CM Service Request
(Service type = mobile originated call) Complete Layer3 Info
(CM Service Request)
Authentication Request
Authentication Response
Cipher Mode Command
Cipher Mode Command
Cipher Mode Complete
Cipher Mode Complete
Setup
Calling Proceeding
Assignment Request
Assignment Command
Assignment Complete
Assignment Complete
IAM
ACM
Alerting
ANM
Connect
Connect Acknowledge

20. GSM Call Scenario 3
 Network to Mobile
BSS MSC/VLR HLR GMSC PSTN
IAM
SRI (MSISDN)
PRN (IMSI)
PRN RR (MSRN)
PRI RR (MSRN)
IAM (MSRN)
Paging
Paging Request
Channel Request
Immediate Assignment
Paging Response
Complete Layer 3 info (Paging Response)
Cipher Mode Command
Ciphering Mode Command
Ciphering Mode Complete
Ciphering Mode Complete
Setup
Call Confirmed
Assignment Request
Assignment Command
Assignment Complete
Assignment Complete
Alerting
ACM ACM
Connect
ANM ANM
Connect Acknowledge

21. GSM Handover Scenario
 Handover between BSCs
Serving BSS MSC/VLR Target BSS
Measurement Report
Measurement Report
Handover Required
Handover Request
Handover Request Ack
Handover Command
Handover Command
MS tunes to
New channel
Handover Access
Handover Detect
Handover Complete
Handover Complete
Clear Command
Measurement Report
Clear Complete
Measurement Report
Measurement Report

22. Appendix : Mobility Management
 In-session mobility management
Move during an active call
Hand-off management
 Out-of-session mobility management
Move in standby mode
Location management : Update (Registration) and Paging
LA-1
LA-2

23. Appendix : Hand-off
 Hand-off = Handover
Transfer of a MS from one cell to another
Each BS constantly monitors the received power from each MS
When power drops below given threshold
BS asks neighbor station (with stronger received power) to pic up the MS, on a
new channel
 Hand-off Types
Intra-Cell Inter-Cell
Soft Hand-off Hard Hand-off
x

24. Appendix : Hand-off Problem
 Hand-off is
the process of switching from one frequency channel to another by the user in
midst of a communication
Normally induced by …
Received Signal Strength (RSS)
Signal-to-Noise Ration (SNR)
Bit Error Rate (BER)
Triggered either by the BS or the mobile station
In GSM, MAHO (Mobile-Assisted HandOver)
Ratio of power Handover Threshold
Received
From current BS Receiver Threshold
To next BS
time
t0 t1
Base Station 1 Base Station 2