Jul 14, 2009

Diameter Routing Agent

I want to discuss today a new network function introduced by 3GPP in its Release 8 standards.
The Diameter Routing Agent (DRA), the DRA is a functional element that ensures that all Diameter sessions established over the Gx, S9, Gxx and Rx reference points for a certain IP-CAN session reach the same PCRF when multiple and separately addressable PCRFs have been deployed in a Diameter realm.
What this means in plain English, is that the DRA helps to sort out the Diameter spaghetti in the network.
Routing of Diameter messages from a network element towards the right Diameter realm in a PLMN is based on standard Diameter realm-based routing, as specified in IETF RFC 3588.
The DRA keeps status of the assigned PCRF for a certain UE and IP-CAN session across all reference points (e.g. Gx, Gxx, S9 and Rx interfaces)
The DRA supports the functionality of a proxy agent and a redirect agent as defined in RFC 3588 . The mode in which it operates (i.e. proxy or redirect) shall be based on the operator’s requirements.
Diameter clients of the DRA (i.e. AF, PCEF, BBERF and PCRF) in roaming scenarios shall support all procedures required to properly interoperate with the DRA in both the proxy and redirect modes.

After all this technical flood, I think that the main importance of DRA from Diameter perspective is that it’s the first time that the 3GPP standard body is supporting and backing an “in between” Diameter component.
Those components known as agents are part of Diameter in its IETF base, but were never used and adopted by the telecom standard bodies that adopted Diameter and headed by 3GPP, it was always a client server game. A DRA is really a Diameter Redirect Agent or a Diameter Proxy Agent as defined by the IETF.

In my opinion the adoption and backing of the DRA, is the final stamp of approval to the IETF Diameter work and to the embracement of Diameter as the main signaling protocol for telecommunication networks. I suspect we will see more and more Diameter agents either packaged as DRA or in other names in the coming years with the continuing migration to NGN and the growing amount of signaling.