These may be SIP phones, PDAs with network access cards, or similar types of
data devices.
Network Domain Security
To understand security measures for the IMS, you must first understand the concept
of a ???trusted domain.??? This is quite simply a network domain where the ???owners??? trust
one another, or there is only one ???owner.??? For example, in telecommunications networks,
your service provider owns their own network. This network will interconnect with
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many other networks to offer global service. However, those other networks belong to
other companies, or ???owners.???
Through special agreements and arrangements, the various network operators build a
trust among each other. This trust allows for the exchange of certain data and information
about the subscribers, routing information, and addresses for resources within each network.
The IMS is no different and uses the same ???trusted domain??? model.
Securing the network boundaries through the use of gateways is a critical part to
any network security and is no different in the IMS. The P-CSCF acts as the first point
of contact for any user of the network and provides some important security functions.
Forcing routing based on route lists established during registration (strict routing) is
one form of security that the P-CSCF can provide to the network.
The I-CSCF acts as the gateway between two IMS networks.
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