Technical data

92 Theoretical and general applications www.westermo.com
A packet switching network is a network where the traffic
is divided up into small packages which are sent over the
network. This means that others can utilise the network at
the same time. If you compare a circuit switching network
with a telephone call, you can compare a packet switching
network with a haulage contractor or the post office.
Several persons can send a lot of packages at the same
time. The post office or haulage contractor ensures that all
packages arrive at the recipient. The packages share the
trucks and facilities on the roads.
In February 2004 there were 172 operators in numerous countries that offered the
option of GPRS. The number of mobile telephones with GPRS is expected to grow
from 10 million in 2001 to 280 million in 2005.
Network security
GSM
The most important security mechanisms on the GSM network are:
… Strong authentication of users (the network authenticates the SIM card,
the SIM card authenticates the user with the PIN code).
… Protection against tapping data on the radio interface.
… Protection against tapping signalling on the radio interface.
… Check of the unit’s identity, can be blocked if stolen.
Encryption of data over the radio connection, i.e. between the unit and the base
station. Each user’s secret encryption key is stored on the SIM card, the home
operator’s authentication central.
GPRS
Uses essentially the same security mechanisms as GSM. Authentication is done in the
same way, the same authentication technology and SIM card can be used. However,
the cryptographic key generated is always different for GSM and GPRS. Special crypto-
graphic algorithms are used for GPRS, these use 64 bit keys.
Information packet 1
Information packet 2
B A C K