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A Primer on the Diameter Signaling Protocol – and Why It’s Solely a Carrier Concern

Posted by Paul Desmond

Mar 19, 2015


We’ve written about the session initiation protocol (SIP) many times on this site, and with good reason: it’s crucial to establishing sessions in various unified communications applications. In the reporting of these stories, we are increasingly hearing about another, related protocol: Diameter. Figuring our readers were likewise hearing Diameter chatter, we thought we’d dedicate a post to explaining what the protocol is all about and just how important it is. 

As it turns out, Diameter is indeed important, but really only to carriers.  It’s part of the plumbing that enables effective communications for smart phones, tablets and the like in a wireless 4G/LTE network. But thankfully for enterprises, it’s not something they need to worry about.

Diameter: An Upgrade from RADIUS

Diameter is essentially a replacement for RADIUS, the protocol that companies have used for ages to support authentication, authorization and accounting management (AAA) in their networks. Its formal name – Remote Authentication Dial In User Service – shows just how dated RADIUS is. Anyone out there dialing in to much of anything these days? If so, I feel for you.

OK, that’s not quite fair because RADIUS still gets plenty of use, but the point is it was time for a refresher. And the emergence of 4G/LTE cellular services presented the impetus for that refresher.

While SIP is used for real-time applications such as VoIP and videoconferencing, Diameter provides data signaling and AAA services for mobile devices such as smart phones and tablets communicating over 4G/LTE networks, says Bill Welch, senior product manager for signaling at Sonus Networks.

“You can think of RADIUS as a 1.0 version protocol. Diameter is the next-generation, 2.0 version with more capabilities,” Welch says.

For one, RADIUS uses UDP as its transport, which is an unreliable, best-effort protocol. That means you need intelligent clients and servers to manage the back and forth communications and ensure all packets reach their destination. Diameter, on the other hand, works with SIP, providing authentication functions to ensure subscribers are who they say they are and determining which network services they’re authorized to use.

Diameter at Work in Carrier Networks

For carriers, Diameter enables a number of services and capabilities. Roaming is one example, as Diameter handles the hand-off of calls from one carrier’s network to another’s, supporting authentication and the all-important billing services.

Another case where Diameter would come into play for carriers is enabling sharing plans, such as where a family can share a pool of, say, 10G of data each month. Various policy and charging systems in the carrier network keep track of usage but it’s Diameter that enables communication and authorization between them.

All this Diameter traffic flying around the network has led to the emergence of a new product to handle it all: the Diameter Signaling Controller (DSC). A DSC provides functions similar to what a session border controller (SBC) does for SIP. Those functions include efficiently routing messages, preventing network overloads, and interworking different variations of Diameter signaling between devices.

Diameter is Poised for Rapid Growth

As service providers deploy more 4G/LTE networks, the use of Diameter is expected to grow exponentially. Each smartphone, for example, causes the LTE network to generate Diameter messages when it accesses applications, downloads data, when roaming or even when just turning on or off. That will drive the need for more and more DSCs in carrier networks.

What’s more, while 4G/LTE networks have been rolling out in the U.S. and Europe for several years, they are just now coming online in India and China, Welch says. “If even half of the consumers in those big marketplaces get a 4G phone, it becomes a much bigger tipping point of Diameter usage,” he says.

Diameter may also come into play as carriers try to come up with more business-class services for corporate customers, such as hosted UC services. “A lot of the back-end capabilities in and around that would be using Diameter,” Welch says. The good news? Even then,  corporate customers would not need to install and manage their own DSC – you can leave that to the carriers.

Topics: video, networking, Mobility, Wireless