GLOBAL SYSTEM FOR MOBILE
COMMUNICATION (GSM)
IDENTIFIERS
ECE 2515 – WIRELESS COMMUNICATION
Monday, 14 October 2019
GSM IDENTIFIERS
GSM uses the following identifiers
1. Mobile system International Subscriber Dialling Number (MSISDN)
2. Mobile Station Roaming Number (MSRN) - The routing address to
route the call to the MS through the visited MSC.
3. International Mobile Subscriber Identity (IMSI)
4. Temporary Mobile Subscriber Identity (TMSI)
5. International Mobile station Equipment Identity (IMEI)
6. Location Area Identity (LAI)
7. Cell Global Identity (CAI)
INTERNATIONAL MOBILE SUBSCRIBER IDENTITY
• Each mobile unit is identified uniquely with an International Subsriber Identity
(IMSI.
• IMSI includes the country, mobile network Code, mobile subscriber Number.
639
02
722770567
MCC & MNCs FOR KENYA
MOBILE SYSTEM ISDN (MSISDN)
• MSISDN uses the same format as the ISDN address (based on ITU-T
Recommendation E.164).
• HLR uses MSISDN to provide routing instructions to other
components in order to reach the subscriber
Country Code
(CC)
+254
National Destination Code
(NDC)
733
Subscriber Number
(SN)
770567
TEMPORARY MOBILE SUBSCRIBER IDENTITY
• Temporary Subsriber Identity (TMSI) is sent over the air interface in place
of the IMSI to ensure security.
LOCATION AREA IDENTITY (LAI)
• Location Area Identity (LAI) identifies a location area (LA).
• When an MS roams into a new location area, the HLR is updated
according
• LAI consists of a total up to 15 digits
639
2 (Safaricom)
xxxxxxx
USE OF LOCATION AREA IDENTITY (LAI)
• The LAI is broadcast regularly through a broadcast control channel (BCCH).
• A mobile station recognizes a new LAI it updates the contents of the SIM
memory.
• If the mobile station is moving and notices a change of LAI, it will issue a
location update request, thereby informing the MSC of its new LAI.
• This allows the MSC to locate the mobile station in case of an incoming
voice call or SMS.
CELL GLOBAL IDENTITY (CGI)
• CGI = LAI + CI
= MCC + MNC + LAC + CI
Where CI is the Cell Identity
IDENTITIFIERS & COMPONENTS
LOCATION UPDATE PROCEDURE
Registration: the location update procedure initiated by the MS
• Step 1: BS periodically broadcasts the LA address.
• Step 2: When an MS finds the LA of BS different from the one stored
in it SIM, it sends a registration message to the MSC.
• Step 3.The new LAI is updated in the SIM and HLR.
INTERNATIONAL MOBILE EQUIPMENT IDENTITY (IMEI)
• International Mobile Equipment Identity (IMEI) uniquely identifies the
Mobile Equipment.
• IMEI is used to prevent a misplaced or stolen phone from initiating
calls.
• The current format for the IMEI is composed of three parts:
1. Type Allocation Code (TAC) - 8 digits
2. Serial Number (SNR) - 6 digits
3. Check Digit (SP) - 1 digit