For example the personal identity may use e-mail and instant
messaging, while the work identity only uses e-mail and voice services. The rate plans
can be tailored to a subscriber??™s individual need based on their various identities.
The problem with VoIP implementations has been the lack of being able to validate
identities. There are many ways to obtain services for free through the use of fraudulent
identities. The SIP message itself is not reliable for identifying the true user identity,
96 Chapter 4
which is why the 3GPP added extensions to the SIP protocol for asserting the identity
of a device.
The identities (both public and private) are embedded within the device itself, in a
fashion that cannot be accessed and modified by the user. This is a new requirement
defined by the GSM Association and the 3GPP to thwart fraud in wireless networks.
The identities are part of the SIM card inserted within the device. The SIM application
allows users to purchase various devices and take their identities with them
no matter what device they are using. When subscribers connect the device to the
network, their identities are exchanged with the network as part of the registration
process.
Likewise, they are also challenged by the network during the authentication process,
and therefore authentication and cipher keys are also stored with these identities.
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