The Role of Diameter in NGN and IMS Networks

By Michael Khalilian

The NGN Forum/IMS Forum has recently launched a new technical working group focused on strengthening the interoperability of the control and operational interfaces supporting Authentication, Authorization and Accounting (also known as AAA or triple-A) and providing an open interface for third party services.



The “Diameter” Working Group focuses on ensuring that IMS networks and NGN services can rely on a proven vendor infrastructure and solutions. The Diameter protocol plays a crucial role in NGN. It is used as the AAA framework for applications management, mobility, nomadicity, network security, network access security, and services charging. The group’s objectives are the creation and execution of an interoperability event, or Plugfest in the second quarter of 2009. The event, aimed at testing and demonstrating interoperability for all NGN technologies using Diameter interfaces, will include IMS, WiMAX and LTE testing. Some standards used to describe these interfaces include: IETF, 3GPP, 3GPP2, TISPAN, WiMAX, LTE, and Packet Cable.

With the new ‘all-IP’ service-oriented architectures Diameter is widely used in IMS and in the standards developed by the 3rd Generation Partnership Project (3GPP), the international standards group working on the Long Term Evolution (LTE). As examples of the wide usage of Diameter, we don’t have to look further than the IMS control and service planes as also described below:

• The Home Subscriber Server (HSS) is a database containing user identification, user and service control information, user authentication and authorization, location information, and user profiles. As a note, HSS is also used in the LTE architecture.

• The Serving Call Session Control Function (S-CSCF) uses Diameter interfaces to authorize users (by exchanging information with the HSS in response to a SIP registration request) and to retrieve subscriber information.
• Application Servers retrieve subscriber profiles also using Diameter.

• Charging interfaces (Ro and Rf in IMS architecture) are based on the IETF Diameter and on extensions to the protocol resulting from 3GPP.

Diameter also plays a central role in implementing Quality of Service (QoS) in NGN, hence allowing services such as VoIP, video delivery, video conferencing and Enterprise Unified Communications (UC) to be managed in the same converged network.

The Diameter protocol was developed by IETF, as an evolution to the RADIUS (Remote Authentication Dial In User Service). RADIUS is currently the triple-A protocol for most Internet transactions. Diameter, as its name indicates, is ‘twice RADIUS.’ It provides a number of improvements in AAA in response to the evolution of broadband wireless and the necessary flexibility for future extensions. Designed as a Peer-To-Peer protocol it allows each host to act as both a client and a server, Diameter improvements include:

• Security (IPsec or TLS and end-to-end)

• Transport (TCP or SCTP)

• Reliable Proxying (failover recovery)

• Session management

To find out more about the next IMS and NGN interoperability testing event for the control and services planes (Plugfest 7), please visit the NGN Forum/IMS Forum at www.imsforum.org or contact the Chair of Diameter WG, Bruno Deslandes at [email protected].

Michael Khalilian is the Chairman and President of the NGN Forum™ & IMS Forum® (News - Alert) (www.NGNForum.org, [email protected]).

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