IT Baseline Protection Manual - The Information Warfare Site

Other IT Components Mobile Telephones
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The information stored on the SIM card includes the subscriber-specific call number (MSISDN). The
cryptographic algorithms for authentication and encryption of user data are also implemented on the
SIM card. In addition, short text messages, call charge information and a personal telephone directory
can also be stored on the card.
SIM Toolkit
Since 1999, mobile phones and SIM cards with extended menu functionality have been available on
the market. This new standard "SIM Toolkit" defines new functions between SIM card and mobile
transceiver. As such, it is now possible to download new data and programs provided by the network
provider on a regular basis. In this way SIM Toolkit allows some completely new services to be
implemented. For example, it provides the card provider with the means to tailor the menu structure of
the mobile phone to individual customers’ requirements. Thus, if the customer would like to make a
hotel reservation or make the travel arrangements for a business trip using his mobile phone, the menu
structure of the mobile phone is appropriately modified by the service provider. However, this does
require that both the card and also the mobile terminal support the SIM Toolkit standard.
Base station
Every network provider maintains a large number of transmitting stations also called Base Transceiver
System (BTS). Each of these stations can cover an area having a radius of between 250m and 35km,
depending on the transmitter power and terrain conditions. The coverage area of a transmitting station
is referred to as a radio cell. Several radio cells are controlled from one control station or Base Station
Controller (BSC). The combination of transmitting stations and control station in turn is referred to as
Base Station Subsystem (BSS) or base station for short.
The base station thus constitutes the interface between the network and the mobile phone. It is here
that channels for signalling data and user data are made available. The base station is controlled via the
Mobile Switching Centre (MSC). This switching node assumes all the technical functions of a landline
network switching node, for example, path search, signal path switching and processing of
supplementary services. If there is a requirement for a connection to a subscriber in the landline
network, this is forwarded by the MSC to the landline network over a switching path (the Gateway
Mobile Switching Centre, GMSC).
The encryption of the data on the radio interface, i.e. between mobile phone and base station, can be
viewed as a special feature of the GSM network as opposed to the landline network. This should
protect the subscriber against unauthorised passive monitoring.
Registers
In order that the network provider is in a position to provide all the services for which demand exists,
it must store various items of data. For example, it must know which subscribers are using its network
and which services they wish to use. This data, such as the name of the subscriber, his customer
number and the services he requires, are stored in the Home Location Register (HLR). If a connection
is to be established, for example from a landline network terminal to a mobile phone, the network
provider needs to know where the subscriber is and whether his mobile phone is switched on. This
information is held in the Visitor Location Register (VLR) and the HLR. To check whether the
subscriber is entitled to use the mobile communication network (i.e. he has taken out a card contract),
the network provider maintains an identification register at the Authentication Centre (AUC). This
holds the security code of the SIM card as well as the PINs determined by the subscriber.
The network provider can also maintain an equipment register, the Equipment Identification Register
(EIR), which holds details of all the mobile transceivers permitted on the network broken down into
three groups known as the white, grey and black lists. The white list is a register of all the mobile
phones which are functioning reliably, the grey list contains all the phones which may possibly be
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IT-Baseline Protection Manual: Otober 2000