IT Baseline Protection Manual - The Information Warfare Site

Other IT Components Mobile Telephones
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8.6 Mobile Telephones
Description
Over the last few years mobile telephones have become an
indispensable element of the communications infrastructure.
This raises the issue of how they can be used securely.
This chapter considers digital mobile telephone systems
based on the GSM standard (D and E networks). To ensure
that they can be used securely, a number of components and
their interaction need to be considered (see diagram):
- Mobile telephone
- Base station
- Landline network
Register
SIM
The mobile phone
has two primary
components, the
SIM card and the
phone itself.
BTS
BTS
BTS
BTS
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IT-Baseline Protection Manual: Otober 2000
BSC
BSC
Base station with its components, the
transmitting station and control unit
EIR HLR
AUC VLR
MSC GMSC
MSC
Interface to the
landline
network
Switching node with
registers
Mobile telephone
A mobile phone consists of two components, the mobile transceiver itself and the identification
module, the Subscriber Identity Module (SIM) card. This enables the GSM network to distinguish
between user and mobile terminal.
The mobile transceiver is characterised by its internationally unique serial number or International
Mobile Equipment Identity (IMEI). The user is identified by his customer number (International
Mobile Subscriber Identity or IMSI), which is stored on the SIM card and is assigned to the subscriber
by the network provider at the time that the subscriber enters into a contract with the network provider.
This must be distinguished from the telephone number that is assigned to the subscriber (the Mobile
Station ISDN Number or MSISDN). This distinction enables a subscriber to use different mobile
transceivers with the same SIM card.