GSM Security And Encryption

[seminar class]

Presented by:
Vikas Yadav

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What is GSM ?
Global System for Mobile (GSM) is second generation cellular standard developed to cater voice services and data delivery using Digital modulation.
GSM in India
Tele-Services
 Telecommunication services that enable voice communication via mobile phones.
 Offered services
- Mobile telephony
 Bearer Services
 Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at the rate from 300 to 9600 bps.
 Short message services
- up to 160 character alphanumeric data transmission to/from the mobile terminal.
 Unified Messaging Services (UMS).
Supplementary Services
 Call related services-
 Call Waiting- Notification of an incoming call while on the handset.
 Call Hold- Put a caller on hold to take another call.
 Call Barring- All calls, outgoing calls, incoming calls.
 Call forwarding- Call can be send to various numbers defined by user.
 Multi Party Call Conferencing- Link multiple calls together.
 CLIP- Caller line identification presentation.
 CLIR- Caller line identification restriction.
GSM System Architecture-1
Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Switching Subsystem (NSS)
Mobile switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
System Architecture Mobile Station
 The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
Therefore, ME+SIM=MS
Mobile Station
Mobile Equipment (ME)
 Uniquely identified by an IMEI (International Mobile Equipment Identity)
 Voice & data transmission
 Monitoring power & signal quality of surrounding cells for optimum handover
 Power level: 0.8W-20W
Mobile Station
Subscriber Identity Module (SIM)
 Smart card contains the International Mobile Subscriber Identity (IMSI).
 Allows user to send & receive calls and receive other subscribed services.
 Protected by a password or PIN.
System Architecture Base Station Subsystem (BSS)
 BSS is composed of two parts.
1.Base Transceiver Station (BTS)
2.Base Station Controller (BSC)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
 Consist of Transceivers (TRX) units.
 Encodes, multiplexes, modulates & feed the RF signal to the antenna.
 Communicates with Mobile Station & BSC.
Base Station Controller (BSC)
 Manages resources for BTS.
 Handles call set up.
 Radio power control.
 It communicates with MSC & BTS.
System Architecture Network Switching System (NSS)
Mobile Switching center (MSC)
 Heart of the network.
 Manages communication between GSM & other networks.
 Call setup function & basic switching.
 Call routing.
 Billing information & collection.
Network Switching System (NSS)
Home Location Register (HLR)
-It is a Static database, when a user applied for mobile services, all data about this subscriber will be store in HLR.
-Database contains IMSI ,MSISDN, prepaid/postpaid,roaming restrictions, supplementary services.
Visitor Location register (VLR)
-VLR is Dynamic database used by MSC for information index, it stores all related information of mobile subscriber that enter into the coverage area.
-Reduces the no. of queries to HLR.
-VLR can built together with MSC or set separately.
Network Switching System (NSS)
Authentication Center (AUC)
-Element to prevent illegal subscriber from accessing
GSM network.
-It can generate the parameters to confirm subscriber’s identity.
-Generally associated with HLR.
Equipment Identity Register (EIR)
-Database that is used to track handsets using IMEI.
-Made up of three sub class; White list, Black list &
Gary list.
Operation & Maintenance Subsystem (OSS)
 Used for network planning to enhance the overall working efficiency and service quality of the system.
Parts of OSS
 It contains two parts;
1.OMC-S: Responsible for the operation &
maintenance related to MSS.
2.OMC-R: Responsible for the operation &
maintenance related to BSS.
Call Routing Outgoing Call
1. MS sends dialled number to BSS
2. BSS sends dialled number to MSC
3,4 MSC checks VLR if MS is allowed the requested service.If so MSC asks BSS to allocate resources for call.
5 MSC routes the call to GMSC
6 GMSC routes the call to local exchange of called user
7, 8,
9,10 Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS