The document provides an overview of GSM system components and protocols. It discusses key aspects of GSM including that it uses TDMA and FDD, describes the development of GSM standards over time, and outlines the main network components like the BTS, BSC, MSC, HLR, VLR, and interfaces between them. It also discusses protocols like IMSI, TMSI, IMEI, LAI and their roles in the GSM network.

1. DIT
Dar es Salaam institute of Technology (DIT)
ETU 07420
Switching Systems
Ally, J
jumannea@gmail.com

2. DIT
Mobile Core Network Overview

3. DIT
GSM system overview
 The GSM system is a frequency- and time-division
cellular system, each physical channel is characterized
by a carrier frequency and a time slot number
 Cellular systems are designed to operate with groups of
low-power radios spread out over the geographical
service area. Each group of radios serve MSs presently
located near them. The area served by each group of
radios is called a CELL
 Uplink and downlink signals for one user are assigned
different frequencies, this kind of technique is called
Frequency Division Duplex (FDD)
 Data for different users is conveyed in time intervals
called slots , several slots make up a frame. This kind of
technique is called Time Division Multiple Access
(TDMA)

4. DIT
GSM Development
Standard Protocol for GSM take effect
System was named as Global System for
Mobile Communication
GSM system began to provide service in Europe(2G)
Provide services for the whole world
Micro Cell Technique is used in GSM system
1989
1991
1992
1994
1996

5. DIT
GSM-GPRS Network Component
GSM /GPRS BSS
BTS
BSC
BTS
BSC
PCU
SS7
SMS system
PSTN
ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
GPRS Backbone
Other PLMN
MS
MS
OMC

6. DIT
Mobile Station—MS
International Mobile Equipment Identity (IMEI)
– Mobile Equipment
MS=ME+SIM
International Mobile Subscriber Identity (IMSI)
– Subscriber Identity Module

7. DIT
Subscriber Identity Module – SIM
 International Mobile Subscriber
Identity (IMSI)
 Temporary Mobile Subscriber Identity
(TMSI)
 Location Area Identity (LAI)
 Subscriber Authentication Key (Ki)
SIM

8. DIT
BTSBTS
BSCBSC
TC/SMTC/SM
BSS
MSC
Base Station Subsystem – BSS
 The Base Station
Controller – BSC
 The Base Transceiver
Station – BTS
 The Trans-coder – TC
and Sub multiplexer
(SM)

9. DIT
BTSBTS
BSCBSC
TC/SMTC/SM
BSS
MSC
Packet Control Unit-----PCU
 Packet data
switching
 Bridge between
SGSN and BSC
 Provide Pb and Gb
interface
GPRS
Backbone
PCUPCU SGSNSGSN

10. DIT
Mobile-service Switching Center – MSC
Home Location Register – HLR
Visitor Location Register – VLR
Equipment Identity Register – EIR
Authentication Center – AUC
Echo Cancellor – EC
AUCAUC
HLRHLR
MSC/VLRMSC/VLR
PSTN
NSS
EIREIROMC
BSS
ECEC
The Network Switching System

11. DIT
Mobile-Service Switching Center – MSC
 Call Processing
 Operations and Maintenance Support
 Interface management
 Inter-network & Inter-working
Inter-network: communication between GSM network
and other network
Inter-working : communication between different
entities inside the GSM network
 Billing

12. DIT
Home Location Register – HLR
 Subscriber ID (IMSI and MSISDN)
 Current subscriber VLR (current location)
 Supplementary service information
 Subscriber status (registered/deregistered)
 Authentication key and AuC functionality

13. DIT
Visitor Location Register – VLR
 Mobile Status (IMSI attached / detached /
busy / idle etc.)
 Location Area Identity (LAI)
 Temporary Mobile Subscriber Identity (TMSI)
 Allocating the Roaming Number

14. DIT
IMEI is Checked In White List
IMEI is Checked in Black/Grey List
If NOT found
EIR focus on the
equipment , not the
subscriber!!
Equipment Identity Register – EIR
 White List
 Black List
 Grey List

15. DIT
OMC Functional Architecture
OS
MMI
DB
Event/Alarm
Management
Security
Management
Configuration
Management
Performance
Management
Fault
Management

16. DIT
Service Area
PLMN service area
......
Service Area
MSC service area...
Location area...
cell
PLMN service area PLMN service area
MSC service area...
Location area...
cell

17. DIT
LAI
Location Area Identification
The LAI is the international code for a location area.
MCC: Mobile Country Code ， It consists of 3 digits .
For example: The MCC of Tanzania is “640"
MNC: Mobile Network Code ， It consists of 2 digits .
For example: The MNC of Vodacom is "03"
LAC: Location Area Code ， It is a two bytes hex code.
The value 0000 and FFFF is invalid.
For example: 640-03-0011
MCC MNC LAC

18. DIT
CGI
The CGI is a unique international identification for a cell
The format is LAI+CI
LAI: Location Area Identification
CI: Cell Identity. This code uses two bytes hex code to
identify the cells within an LAI.
For example : 640-03-0011-0001
CGI: Cell Global Identification

19. DIT
BSIC
NCC: PLMN network color code. It comprises 3 bit. It
allows various neighboring PLMNs to be
distinguished.
BCC: BTS color code. It comprises 3 bit, used to
distinguish different cells assigned the same
frequency!
NCC BCC
BSIC
BSIC （ Base Station Identification Color Code)

20. DIT
CC: Country Code. For example: The CC of Tanzania is “255".
NDC: National Destination Code. For example: The NDC of
vodacomis 75 and 76.
SN: Subscriber Number. Format:H0 H1 H2 H3 ABCD
Example: 255-75-0666234
MSISDN
CC NDC SN
National (significant)
Mobile number
Mobile station international
ISDN number

21. DIT
MCC: Mobile Country Code ， It consists of 3 digits .
For example: The MCC of Tanzania is "640" 。
MNC: Mobile Network Code ， It consists of 2 digits .
For example: The MNC of Vodacom is "03" 。
MSIN: Mobile Subscriber Identification Number. H1H2H3 S ABCDEF
For example: 75-0666234
NMSI: National Mobile Subscriber Identification ， MNC and MSIN
form it together.
For Example of IMSI : 640-03-75-0777001
Not more than 15 digits
3 digits 2 digits
IMSI
MCC MNC MSIN
NMSI
IMSI

22. DIT
TMSI
 The TMSI is assigned only after successful
subscriber authentication.
 The VLR controls the allocation of new TMSI
numbers and notifies them to the HLR.
 TMSI is used to ensure that the identity of
the mobile subscriber on the air interface is
kept secret.
 The TMSI consists of 4 bytes( 8 HEX
numbers) and determined by the operator.
TMSI: Temporary Mobile Subscriber Identification)

23. DIT
IMEI
TAC FAC SNR SP
IMEI
IMEI: International Mobile Station Equipment Identification
TAC: Type Approval Code, 6 bit, determined by the type approval
center
FAC: Final Assembly Code, 2 bit, It is determined by the
manufacturer.
SNR: Serial number, 6 bits, It is issued by the manufacturer of the
MS. SP: 1 bit , Not used.
Check the IMEI in your MS : *#06#
TAC: Type Approval Code, 6 bit, determined by the type approval
center
FAC: Final Assembly Code, 2 bit, It is determined by the
manufacturer.
SNR: Serial number, 6 bits, It is issued by the manufacturer of the
MS. SP: 1 bit , Not used.
Check the IMEI in your MS : *#06#

24. DIT
UMTS R99 Network Architecture
GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UMTS
UTRAN
SS7
SCP
SMS
SCE
Other PLMN
PSTN,ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
GPRS
backbone
Other PLMN’s
GPRS network

25. DIT
R99 CN Feature
 Core Network is split into CS domain and PS domain.
 CS domain is in charge of call control and mobility
management of circuit service.
 Call control: ISUP/TUP
 Mobility management: enhanced MAP
 Physical node:MSC,GMSC,VLR
 PS domain is in charge of session management and mobility
management of Packet service.
 There are some change from GPRS: interfaces, flows, some
functions
 Physical node: SGSN,GGSN,CG
 Transcoders is placed in CN side
 TFO: Tandem Free Operation
 Supporting inter-system handover (UMTS/GSM)

26. DIT
UMTS R4 Network Architecture
GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UMTS
UTRAN
SS7
SCP
SMS
SCE
Internet,
Intranet
HLR/AUC
SGSN
CG BG
GGSN
MGWMGW MGWMGW
VMSC Server GMSC Server
IP/ATM Backbone
Other PLMN
PSTN,ISDN
Other PLMN’s
GPRS network
GPRS
backbone

27. DIT
R4 CN Feature
 CS domain
 Control is separated from bearer,MSC is split
into MSC server and MGW
 Traffic bearer can be IP , ATM or TDM
 Signaling bearer can be IP or TDM
 TrFO: Transcoder Free Operation

28. DIT
MSC
SCP HLR
MSC
RAN RAN RAN
TDM
MSC Server
SCP HLR
RAN RAN RAN
TDM/ATM/IP
CS-MGW CS-MGW
MSC ServerTUP/ISUP/BICC
TUP/ISUP
Notes: PS domain structure remain unchanged
R99 R4
H.248 H.248
MAP Over TDM MAP Over TDM/IPCAP Over TDM CAP Over TDM/IP
CS domain evolution
Difference Between R99 and R4

29. DIT
Interfaces in R99 network
GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UMTS
UTRAN
SS7
SCP
SMS
SCE
PSTN
ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
Other PLMN
A
Gb
Iu-CS
Iu-PS
Gi
Gp
C/D/Gs
Gr/Gs/Gd/Ge Gc
GPRS
backbone
Ga

30. DIT
MSC/VLR GMSC
Node B
RNC
HLR/AuC
GGSNSGSN
PSTN
GPRS
backbone
CGF BG
SS7 SCP
Inter-PLMN
Iub
Iu-PS
Iu-CS
L1 （ PHY ）
ATM
AAL5
SSCOP
SSCF-NNI
MTP3B
SCCP
RANAP
AAL2
IuUP
Control PlaneControl Plane User PlaneUser Plane
Iu-CS Interface Protocol Stack

31. DIT
SS7 Interface Protocol Stack
MSC/VLR GMSC
Node B
RNC
HLR/AuC
GGSNSGSN
GPRS
backbone
CGF BG
SS7
SCP
Inter-PLMN
Iub
M
A
P
C
A
P
I
S
U
P
T
U
PTCAP
SCCP
MTP3
MTP2
MTP1
B
S
S
A
P+
PSTN

32. DIT
PS Domain Interface Protocol Stack
MSC/VLR GMSC
Node B
RNC
HLR/AuC
GGSNSGSN
CGF BG
SS7
SCP
Inter-PLMN
Iub
L1 （ PHY ）
ATM
AAL5
SSCOP
SSCF-NNI
MTP3B
SCCP
RANAP
AAL5
GTP-U
Control PlaneControl Plane User PlaneUser Plane
IP
UDP
Iu-PS
GTP(GTP')
UDP
IP
L2(MAC)
L1(PHY)
Gn/Gp/Ga
GPRS
backbone
PSTN

33. DIT
New Interfaces in R4
GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UMTS
UTRAN
SS7
SCP
SMS
SCE
PSTN
ISDN
Internet,
Intranet
HLR/AUC
SGSN
CG BG
GGSN
GPRS
backbone
Other PLMN
MGWMGW MGWMGW
VMSC Server GMSC Server
IP/ATM Backbone
Nc
Mc
Nb

34. DIT
Interfaces in R4 CS Domain
MGW
Mc Mc
Nb
Nc
MSC
Server
MGW
GMSC
Server
BICC/ISUP/TUP
MTP3 MTP3B M3UA
MTP2 SSCF/SSCOP SCTP
MTP1 AAL5/ATM IP
H.248
SCTP UDP MTP3B
IP SSCF/SSCOP/AAL5
RTP AAL2 Voice
UDP/IP ATM PCM

35. DIT
Wireless Intelligent Network (WIN)

36. DIT
Concept of Wireless Intelligent Network
 Wireless Intelligent Network (WIN) is a network in which the
functional entities of the Intelligent Network (IN) are introduced to
the mobile network to realize the intelligent control to mobile calls.
 It is the combination of the current mobile network and the
intelligent network.
 The introduction of the mobile service switching point into the
mobile network has enabled the connection of the mobile network
at the lower layer with the intelligent network at the higher layer,
thus forming the wireless intelligent network.
 As a high layer service network of the mobile network, WIN can
create and realize all kinds of new mobile services rapidly,
conveniently, flexibly, economically and efficiently, facilitating the
customers to get the required information.
 The major characteristic of WIN is that it separates the switching
function from the control function of the network.
 It processes the intelligent call with the support of Signaling
System No.7 (SS7) network and large centralized database, while
the original exchange only performs the basic connection
functions.

37. DIT
Features of Wireless Intelligent Network
 Extensively using information processing technology
 Effectively using network resources
 Modularizing the network functions that can be used
repeatedly
 Using the reusable modular network function to generate and
implement a new service
 Network functions being flexibly distributed in physical entities
 Portable network functions in a physical entity
 Providing standard communications between network
functions through the service-independent interfaces
 Service subscribers being able to control the service
properties defined by themselves
 Service users being able to control the service properties
defined by themselves
 Standardized management of service logic

38. DIT
Target of Wireless Intelligent Network
 WIN is aimed at providing the existing mobile network with
some additional abilities that facilitates the carriers to
provide new services.
 It is required that the newly-provided service should be
independent from the network, i.e., the service is irrelevant
to the equipment running in the mobile network and does
not care about who provides the equipment.
 The independent implementation of a service enables a
service provider to define his own service without relying
on the specific service products of the equipment vendor.
 The independent implementation of the network enables a
network operator to allocate the functions and resources
within his network and manage his network effectively
without relying on the specific network implementation
mode of an equipment vendor.

39. DIT
Intelligent Network Layer

40. DIT
Evolution and Development of Wireless
Intelligent Network
 The study on WIN was started as early as 1995.
 At first, there was no concrete standard protocol, and
different companies laid down their own standards and
have carried out a good deal of studies on such basis.
 In January, 1998, European Telecommunications
Standards Institute (ETSI) introduced Customised
Application for Mobile network Enhanced Logic (CAMEL) in
GSM Phase 2+. The version at that time is Phase 1.
 With the accomplishment of CAMEL Phase 1 in GSM
Phase 2+, the development of WIN has entered a new
phase.
 Thanks to the open interface provided by CAMEL Phase 1,
the equipment from different manufacturers can
interconnect with each other.

41. DIT
Architecture of Wireless Intelligent Network
WIN is composed of
 Service Switching Point (SSP)
 Service Control Point (SCP)
 Intelligent Peripheral (IP)
 Service Management System (SMS)
 Service Creation Environment (SCE)

42. DIT
Service Switching Point (SSP)
 SSP connects the mobile network to IN, providing IN access
function (IN call detection).
 SSP contains the capability to detect requests for IN services
and communicate with SCP. It responds to the requirements
from SCP and enables SCP to affect the call flow with the
service logic.
 SSP contains Call Control Function (CCF) and Service Switching
Function (SSF). If there is no independent IP established, SSP
should also has part of Specialized Resource Function (SRF).
 CCF is responsible for basic connection functions such as
receiving user calls, performing call setup and call holding etc.
SSF can receive and identify the intelligent service call and
report to SCP, meanwhile it will accept the instruction from SCP
as well.
 SSP is generally based on Mobile Switching Center (MSC) and
provided with the necessary software and hardware, as well as
signaling No.7 network interface.

43. DIT
Service Control Point (SCP)
 SCP is the core component of the intelligent network, SCP
stores user data and service logic.
 SCP is responsible for receiving the querying information
from SSP, querying the database, and encoding the
information in various ways.
 SCP initiates different service logic according to call events
reported from SSP, and sends call control instructions to
the corresponding SSP according to service logic, that is
the implementation of various IN calls.
 All the service control functions provided by WIN are
concentrated in SCP.
 The communication between SCP and SSP is carried out
based on the standard interface protocols of WIN.
 SCP, which must be highly reliable, comprises
minicomputers and large real-time high-speed databases.

44. DIT
Intelligent Peripherals
 IP is the special resource to consist the intelligent
service.
 Usually it contains various voice manipulation functions,
like combining voice, playing recorded announcements,
receiving numbers sent in DTMF (Dual Tone Multi-
Frequency), performing voice identification, and so on.
 As the standalone equipment or part of SSP, IP can
receive the control of SCP and perform the operation
specified by SCP service logic.
 If IP is set individually in the network, it can be shared by
other switches, which is a cost cutting solution.
 Meanwhile it is convenient for the uniform management
of voice resource and helpful for the deployment of
services whose voices are changed frequently.

45. DIT
Service Management System (SMS)
 SMS is the manager of WIN.
 It has the following functions: service logic
management, service data management,
user data management, system data
management and the management of daily
operation and maintenance.
 A new service logic created in SCE is
transferred to SMS, then loaded to SCP by
SMS to run the new service over the mobile
network.

46. DIT
Service Creation Environment (SCE)
 SCE has the function of creating new service logic
according to the requirement from users.
 SCE provides the service designer with the friendly
graphical editing interface.
 Customer use the various standard graphical
elements to design the new service logic and define
the relevant data.
 After the designing, the service should first pass the
strict verification and simulation, which is to ensure
that the new service will not bring any negative
influence to the existing services.
 After that, SCE will transfer the service logic to SMS
which will load it to SCP for running.

47. DIT
Creating and Loading a New Service
The procedures are described as follows:
 Design a new service.
 Transfer the designed service to SMS.
 Load the logic program of the new service to SCP according to
the instruction of system administrator.
 The customer begins to use the new service.

48. DIT
Thanks!
Technology changes but communication lasts.