This
means that there can be instances where the P-CSCF will initiate requests toward an
Application Server (AS) or S-CSCF.
So one should think of the P-CSCF as the gateway into the IMS network itself. It
has the responsibility to ensure that the device accessing the network has been registered
and is allowed access into the IMS, but it does not enforce authentication and
authorization. The P-CSCF also determines how to route the SIP messages received to
the proper networks and network entities, allowing operators to maintain some level
of secrecy regarding their own individual networks, and eliminating the need to create
routing tables at every single node (the mesh network topology).
Interrogating CSCF (I-CSCF) While the P-CSCF is the entry point into the IMS, the
I-CSCF serves as the gateway into each individual IMS network. It is the I-CSCF that
determines whether or not access is granted to other networks forwarding SIP messages
to the operator. For this reason, the I-CSCF can be used to hide network details from
other operators, determining routing within the trusted domain. The I-CSCF helps to
protect the S-CSCF and the HSS from unauthorized access by other networks.
When the S-CSCF is forwarding a request or a response to another network, the message
is forwarded to the I-CSCF, which in turn forwards it to the destination network.
Pages:
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60