These are also
exchanged during the registration process after the first registration is challenged. The
authentication and cipher keys allow the device to calculate proper credentials that
should match with those stored on the HSS and the S-CSCF.
Following are the headers and parameters used in the REGISTER message:
?– REQUEST-URI populated with the subscriber??™s public user identity and domain
name of the home network
?– FROM header populated with the public user identity being registered
?– TO header containing the public user identity being registered
?– AUTHORIZATION header populated with the private user identity being registered
?– CONTACT header populated with the subscriber??™s IP address for direct routing of
messages
?– VIA header populated with the IP address or domain name of the device initiating
the registration
?– EXPIRES header set to 600,000 seconds
?– SECURITY-CLIENT header identifying the security methods supported, the IPsec
algorithm, and security association parameters
The domain name will be used to identify the Interrogating??”Call Session Control
Function (I-CSCF) for the subscriber??™s home network. The P-CSCF must resolve the
domain name through a DNS query to obtain the actual IP address of the I-CSCF.
The P-CSCF will add several headers and parameters to the REGISTER prior to
forwarding it to the I-CSCF:
?– PATH header populated with the P-CSCF address
?– REQUIRE header populated with the option tag PATH
?– P-CHARGING-VECTOR header populated with the IMS CHARGING IDENTITY
(ICID)
?– AUTHORIZATION header populated with the INTEGRITY PROTECTED=YES if
the registration was received through secure procedures and NO if not
?– Remove the SECURITY-CLIENT header and store it if the registration was received
without integrity protection
?– P-VISITED-NETWORK-ID header populated with the visited network domain
name
112 Chapter 5
The I-CSCF serves as the access point into the subscriber??™s home network.
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