These could be used to identify the number of hops to the
S-CSCF, as well as other ???proprietary??? network information that the operator may not
want to share with another network.
If a hacker were able to capture all of the SIP messages using a protocol analyzer (or
other method of sniffing on the network), the hacker could also use this information to
determine round trip time in the network and calculate other parameters that could
Architecture of the IMS 15
then be used in a denial of service attack. Security measures are described in more
detail in Chapter 5.
The I-CSCF could be considered as your firewall into your IMS network, routing
between other networks, and preventing other networks from accessing your network.
The I-CSCF function therefore plays an important role in security for IMS.
Serving CSCF (S-CSCF) The S-CSCF serves as the core to the IMS. It controls all aspects
of a subscriber??™s service, maintaining status on every session he or she initiates.
Remember that a session is anything that the device wishes to do, including e-mail,
instant messaging, sending pictures to a mailing list, and voice. The S-CSCF controls
messaging and delivery of content. It provides the status of a subscriber??™s registration
to other applications (application servers) and maintains control over these services as
long as the device is registered.
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