The Role of DIAMETER in IMS?

Question

Probably I know the part of the answer, still want to understand and debate the full role on Diameter Protocol in IMS. Diameter is used in all interfaces where AAA service is required in LTE may be more then 50+ interfaces are there where diameter is required. Now the question is - can we say similar thing about the IMS too or still Radius rules in IMS.

Answer 1

Diameter is the dominant and most popular protocol in the 3GPP world when it comes to non-call related signalling.
Not sure whether you are looking at the advantages of Diameter. It has several(atleast compared to RADIUS). viz., flexibility in terms of large space for creating custom AVPs(even custom messages), SCTP support for multihoming, Keepalive framework etc.
Therefore Diameter is the protocol used in IMS as it is a 3GPP standard. Non-3GPP standards use RADIUS.
IMS diameter interfaces :
Cx/Dx are used between the I/S-CSCF to query the HSS regarding the subscribers home-S-CSCF/Authentication data/Authorization data/Location info/Services that he is subscribed to.
Sh is used between the IMS-AS and the HSS to get the Application server specific subscriber data such as 'Presence status' in case of a Presence application. This is also used for Subscribing for notifications from AS to HSS and Pushing notifications from HSS towards AS.
Then of course there is a policy dip and charging the P-CSCF interfaces with PCRF using Rx.
In addition to these there could be application/implementation specific interfaces for eg. GSM-SCF to AS.
Hope this satisfies.

Answer 2

Actually, IMS was the first thing in 3GPP to pick up Diameter in Rel-5. I-WLAN followed in Rel-6 and then in Rel-8 rest of the places where things like SS7 was used earlier.

You can still find RADIUS in 3GPP specs (as of Rel-12) in (S)Gi interface between the GGSN/PGW and the external network AAA server (like corporate RADIUS server).

Answer 3

IMS also uses Diameter (not RADIUS).
In mobile networks Diameter is used all over the place.

Answer 4

Early on, the 3GPP standards body adopted DIAMETER as the primary signaling protocol for AAA and mobility management in IMS. The Home Subscriber Server (HSS), or User Profile Server Function (UPSF), is essentially a more advanced IMS version of a GSM Home Location Register (HLR) and Authentication Center (AUC). Thus, the HSS is the master user database supporting the IMS network entities that handle calls. It contains subscription-related information (user profile data) and control information for user authentication and authorization. It also performs authentication and authorization of the user, and can provide information about the user’s physical location. If multiple HSSs must be called upon then a Subscriber Location Function (SLF) is used to map user addresses. Both the HSS and the SLF communicate via DIAMETER.

The Call Session Control Function (CSCF) performs SIP session management for any user or SIP client requesting access to IMS services. SIP signaling is used to register with the Serving CSCF in the user’s home network. The S-CSCF uses the DIAMETER “Cx” interface both to request authorization information from the HSS in response to a SIP registration request and to retrieve subscriber information. The CSCF uses another DIAMETER interface, the “Dx” to locate the particular HSS serving the subscriber using a Service Location Feature.

Yet another DIAMETER interface, “Sh” is used by the Application Servers or an OSA/Parlay Gateway to retrieve and update subscriber profiles and shared database information such as call directories, screening lists, or presence information made accessible for authorized application platforms.

Finally, IMS charging is performed via the DIAMETER “Ro” and “Rf” interfaces, which support both on-line charging and off-line collection and forwarding of Call Detail Records (CDRs) using a DIAMETER protocol interface. The Ro interface is a 3GPP extension to the Diameter Credit-Control specification.