01 basic(gsm)
TRANSCRIPT
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Main contents
Related knowledge about GSM
Mobile communication overview
main components in GSM
the interface and protocol between entities
wireless area partition
numbering plan
mobile service management
security management
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Mobile Communication
Overview
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2 The second generation mobile communication
digital cellular mobile communicationFeature:
1)time division multiple access(TDMA)narrow code division multiple access(N-CDMA)
2)digital signal
3)narrow bandMain mode: GSM DAMPS
N-CDMA
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3 The third generation mobile communication
IMT2000 (3G)Feature:
1) code division multiple access(CDMA)
2) digital signal
3) broadband
2000 means: Frequency is 2000MHZ,Maximum service rate is 2000kbit/s.
Main mode: CDMA2000
WCDMA
TD-SCDMA
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Related knowledge about
GSM
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Digital Public Land Mobile communication Network----PLMN
BSC MSC/VLR
HLR/AUC EIR MSC/VLR
OMC
SC
PLMN
PSTN
ISDN
PSPDN
BTS
Um
Abis
A
BTS
No.7 BSSAP
No.7 MAP
No.7 MAP TUP
No.7 TUP
X.25/ No.7
X.25
Signaling Voice
BSS
MSS
MS
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MS:Mobile Station
BSC:Base Station Controller
BTS:Base Transceiver Station
MSC:Mobile Switching Center
HLR:Home Location Register
VLR:Visitor Location Register
AUC:Authentication CenterEIR:Equipment Identity Register
SC:Short Message Center
OMC:Operation and Maintenance Center
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1.Main components of GSM
MS(mobile station)
BSS(base station sub-system)MSS(mobile switching sub-system)
OMC(operation and maintenance center)
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1.1 Mobile Station
Function It is the device of mobile subscriber.
It includes two parts: mobile terminal and SIM card.
Attention:
Physical mobile terminal and mobile subscriber
are different. What is the meaning.
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1.2 Base Station sub-System
FunctionIt provides trunks between wireless part
and fixed part of PLMN network.
---BSC
---BTS
BTS is in charge of wireless transmission.
BSC performs the control and management function.
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FunctionIt performs GSM switching function as well as
manage mobile subscriber data and database for mobile
service. It is interface between GSM network and othernetwork (such as PLMN,PSPDN etc.)
It includes 6 function units:
---MSC ---VLR
---HLR ---AUC
---EIR ---SC
1.3 Mobile Switching sub-System
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1.3.1 Mobile Switching Center(MSC)
Function
It is responsible for setting up,managing and clearing
connections as well as routing the calls to the proper cell.
It provides the interface to the telephone system as well as
provisioning for charging and accounting service.
MSC get data for call handling from 3 databases:
VLR/HLR/AUC GMSC(gateway):It is used to query the mobile subscriber
location information,and connect the route to the VMSC which
the subscriber in at that time.
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1.3.2 Visitor Location Register(VLR)
VLRis a dynamic database,it stores all related information of
mobile subscribers that enter into its coverage area,which enables
MSC to set up incoming and outgoing calls.Subscriber parameters include: subscriber number(MSISDN),
location area identity(LAI),users status , services subscriber can
use, and so on.
When the subscriber leaves this area, it should register in another
VLR,and old VLR will delete all the data about this subscriber.
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1.3.3 Home Location Register(HLR)
HLR: It is a static database. when a user apply for mobile service,
all data about this subscriber will be stored in HLR.
Information:
--- basic service information: including MSISDN, IMSI,the
telecom service, support service,users type, and so on;
--- supplement service information;
---the mobile location information (MSC/VLR address),so as to
realize the call route to the MS and billing.
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1.3.4 Authentication Center(AUC)
It is used to prevent unauthorized subscriber from access GSM
network or from a mobile number being used by unauthorized
person. It operates closely with the HLR.
AUC stores correlativeparametersinformation for subscriber
authentication, encryption to prevent unauthorized access and
guarantee the safety of mobile subscriber communication.
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1.3.5 Equipment identity Register(EIR
It is used to manage the international mobile station equipment
identification number (IMEI) of all mobile station devices and
check whether each mobile station device is a legal equipment.It includes one or more database to store the IMEI.
All IMEI are stored separately in three lists: white name
lists,grey name lists, and blackname lists. Network will
judge whether the IMEI is a legal device and decide to eitheraccept or reject the device.
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1.3.6 Short Message Center(SCIt provides the short message service(SMS). It provides the
delivery and receiving of short message between mobile
subscriber and fixed subscriber or between mobile subscribers.
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1.4 Operation and maintenance center (OMC)
The operation and maintenance center realizes the management
of network. The specific function include: maintain and measure
system, monitor systems status,performance management,traffic
statistics and so on. It can improve the overall system working
efficiency and service quality.
OMC includes two parts:for system(MSS) and forradio(BSS).
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The difference between interface and protocol:
The interface:the connection point between 2 adjacententities.
The protocol: illustrate the rules followed when
information exchanged at the connection point.
2.The interface and protocol between entities
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Main interface:
MS
BTS BSC
MSCBSCBTS
Uminterface Abis interface A interface
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Um interface defines the communication interface between MS and
BTS, also called air interface.Um interface is the most important
interface in all interfaces.
it realizes the compatibility between all kinds of MS and different
network, so that the MS can roam.(it is open interface)
it adopts some anti-jamming technology and measurements to
reduce interferer and improve the frequency spectrum efficiency.
It realizes the physical connection between MS and GSM
network(that is wireless link)at the same time it is also in charge
of transferring of the information about RR, MM and CM.
2.1 Um interface:
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Note:
RR:radio resource management
MM:mobile management
CM:connection management
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2.2 Abis interface:
the intra-interface between the BTS and BSC,used for
remote connection
2Mb/s PCM system
It is an inner interface.
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2.3 A interface and protocol It is an interface between BSC and MSC
It is based on 2.048Mbit/s PCM
CCS signaling (SPC CODE:14 Bits)
Information through this interface include: MS management,
mobility management,BTS management and so on.
It is a open interface.
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2.4 MSS interface and protocol
MSC
VLRB
MSC
VLR
B
E
EIR
HLR/AUC
BSC
BTS
MSS
A
BSS
F
C
D
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2.4.1 B interface:
the interface between MSC and VLR.
MSC transfers the location update information of roaming
subscriber to VLR
MSC queries information of called roaming subscriber
from VLR when setting up the calls
Always associated with VLR, use inner interface.
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The interface between MSC and HLR.
When a MS is called,MSC must query the routing message of
called MS from HLR through this interface to locate called
MS,and HLR will return the routing message(visit MSC/VLR
number) to MSC.
VMSC/VLR send the MSRN assigned to the called subscriber
to HLR.
2.4.2. C interface
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2.4.3. D interface
The interface between VLR and HLR.
This interface is used to transfer location information and
subscriber data information between VLR and HLR.(location
Information,route information, service information and etc.)
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2.4.4. E interface:
the interface between MSC and MSC.
it is used to hand-over channel when MS moves between 2 MSC
offices during the call so that the call will not be disconnected.this interface transfers inter-office signaling which controls voice
connection between MSCs
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2.4.5. F interface :The interface between MSC and EIR.
It is used for MSC to check IMEI of MS
2.4.6. The interface between MSC and PSTN:
The inter-office signaling interface, used for setting up voice
connection between PSTN and PLMN.
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GSM service area
PLMNService area
MSCService area
Cell
Location area
Wireless coverage area structure
3. Wireless area partition
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3.1.Cell
The smallest area that can not be divided.
3.2.Location area:
The area where MS moves without updating location.
It includes some cells.
It only belongs to one MSC.
It includes one or more BSC.
One location area has one LAI to identify each other.
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3.3.MSC service area:The area that all the cell controlled by one MSC covered.
One MSC composes one or more location areas.
3.4 .PLMN service area:It includes one or more MSC service areas.
3.5.GSM service area:
It includes global PLMN networks .
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4.1 ISDN number (MSISDN) of mobile subscribers
A MSISDN number is the number dialed by the caller
subscriber in PLMN.
Composition of a MSISDN number.
Country code +valid national ISDN
International mobile subscriber ISDN number
4.Numbering Plan
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4.2 International mobile subscriber identification number (IMSI)
IMSI is an unique number that can identify a mobile subscriber
in the PLMN network.
MCC MNC MSIN
International
mobile subscriber
identification National mobile
subscriber
identification
Composition of an IMSI number
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MCC mobile country code
MNC mobile network code,
MSIN mobile subscriber identification number, a 10-digit
equi-length number.
IMSI is used in all signaling in a GSM mobile
communication network, stored in HLR, VLR and the SIM
card.
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4.3 International mobile equipment identification number (IMEI)
IMEI is an unique number that can identify a mobile device in
the GSM network.
TAC(Type Approval Code) : 6 digits, assigned by certain department;
FAC(Final Assembly Code) : 2 digits,decide the place of manufacturing or
assembling, coded by manufacturer;
SNR(Serial NumbeR) : 6 digits, assigned by manufacturer in sequence;
Spare bit : 1 digit.
TAC FAC SNR Spare bit
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4.4 .MSC/VLR number
MSC/VLR number is used in the No.7 signaling.
MSC/VLR number structure : CC+NDC+
4.5.HLR number
HLR number is used in the No.7 signaling .
HLR number structure : CC+NDC+
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4.6 Mobile subscriber roaming number (MSRN)MSRN is a number temporarily assigned by VLR to a
called mobilesubscriber which it registers in according to
the request of HLR (of called party) in each call for the
network to re-route.
This number will be released and can be assigned to other
mobile subscriber afterward.
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4.7 Hand-over number (HON)
HON is a number assigned to a mobile subscriber by
the destination MSC/VLR temporarily for routing
during inter-office handover.
This number is part of a MSRN number.
It is used only during inter-office handover of a
mobile subscriber. After the connection, it is released
and used by other subscribers.
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4.8 Temporary mobile subscriber identification number (TMSI)
TMSI is an identification number assigned temporarily to a
visiting mobile subscriber by VLR for the secrecy of IMSI. It isa 4-byte BCD code, used only locally, and assigned by each
MSC/VLR independently.
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4.9 Location area identification number (LAI)LAI is used to identify the location area.
Its number structure is:
MCCMNCLACMCC and MNC : same as the MCC and MNC in IMSI.
LAC is a location area code that uniquely identifies each
location area in digital PLMN. It is a 2-byte hexadecimal
BCD code represented by L1L2L3L4 (with the range of0000FFFF, able to define 65536 different location areas.)
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4.10.Global Cell IdentificationGCI
It is used to identify certain cell in a location area.
Structure:
MCC+MNC+LAC+CI
CI:2 bytes BCD code .
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MS status
Roaming and updating location
Paging
5.Mobile service management
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Mobile subscriber
MS switch onfree
MS switch offMS busy
5.1 MS status
1)MS switch onThe Network should label with attached flag.
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MSC/VLRUpdating locationrequest
HLR
IMSI
Record MSC/VLR number
updating
locate
accept
VLR attachlabel on this
IMSISIM card
record LAI
Case 1:If MS switch on for the first
time(HLR operate)
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Case 2:
Ms switch on again,the LAI it received is the same as
LAI stored in SIM card,VLR only label with attached
flag.
Case 3:
The LAI it received is different from the LAI stored
in SIM card.MS send the message location updating
request to MSC/VLR to update the LAI,VLR will
judge if the data of this MS is in its database.If it has,update the new LAI.
If it hasnt ,repeat the case 1.
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2) Ms switches off
MS get detached from thenetwork
3) MS busy
Assign a service channel to MS for transferring voice and
label with busy for this mobile subscriber.
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5.2 Periodical registration
The GSM system takes the compulsory registration
measure,requiring MS to register periodically. If the GSM
system has not received the periodical registration information
from a certain MS,the VLR of this MS will record it with
hidden detachmentstatus. Only when it receives the correct
periodical registration information again,will it change MS
back into the attached status.
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Location area has been changed, and MS set up location updating.
2 cases:
1)MS location area is changed ,but in the same MSC
2)MS roams from one MSC to another MSC.
5.3 Basic location updating
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BSC
2
1
3 4
BSC
MSC/VLR
M
S
M
S
Location updating in same MSC
Location
area 1
Location
area 2
2
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5
2
3 14
HLR
MSC/VLR1
MSC/VLR2
M
S
M
S
Location updating between MSCs
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PSTN GMSC MSC/VLR
HLR
MS1 6
432
5
1.MSISDN 2. MSISDN 3. IMSI 4. MSRN
5. MSRN 6. MSRN
5.4 Fix subscriber call mobile subscriber
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6
3
4
5
2
9
7
8
10
1
HLR/AUC
MSC1/VLR2 MSC2/VLR2
MS1 MS2
5.5 Mobile subscriber call mobile subscriber
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6. Security management
To guarantees system security ,the following measures are
taken:
1.prevent access of unauthorized subscribers,which is
realized through authentication;
2.protecting subscriber privacy by encrypting;
3.prevent access of invalid mobile device,which is realized
through checking IMEI in EIR;4.preventing subscriber IMSI from being stolen,realized by
TMSI assignment .
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6.1 Authentication service
Authentication is to protect legal subscribers and prevent
intrusion of illegal subscribers. Subscriber authentication
should be performed with the subscriber triad parameters
(RAND , SRES ,Kc)provided by the system.
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MS VLR (MSC, HLR) AUC
A3
A8
Ki RAND
Kc
SRESA3
A8
Ki
Kc
RANDKc
SRES
=?
Step1 obtain
Kc and
SRES by
calculationwith RAND
generated by
Ki obtained
from query
into IMSI
Step2
transfer
3-parameter
RANDKc
SRES
Step3
transfer
RAND
Step5
transfer
SRES
Step4 obtain Kc
and SRES by
calculation
according to Kiand RAND
SteP6compare
SRES
authentication
determination
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Algorithm A3
RAND generatorKi RAND
Ki
Authentication
MSNETWORK
Algorithm A3
SRES SRES