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Diameter – the main signaling protocol for today’s telecom networks

Once upon a time, network signaling was activated when a phone call began and ended when the two speakers hung up. Today’s mobile network operator growth is fueled by data traffic; voice has become secondary. Almost everything you do with your smartphone depends on data communications. To support the constant increase of need for data traffic, the worldwide adoption of Long Term Evolution (LTE) and IP Multimedia System (IMS) comes as a logic step for network operators. LTE provides speeds that are up to ten times faster than 3G and significantly reduced lag times to increase efficiency, reduce costs, and maximize productivity.

There are currently over 100 commercial LTE networks launched in about 50 countries. Though, LTE is more of an evolution and not a revolution. In practice, new elements are deployed side-by-side with existing legacy network functionalities. This hybrid architecture complicates the network by filling it up with a patchwork of technologies, interfaces, and protocols. This network fragmentation is extremely costly if not handled properly. Minimally, it requires connectivity between the LTE interfaces, protocols, and elements, as well as connectivity between the new and legacy components. Almost all of this connectivity is assured today by the Diameter protocol.

Diameter – the main signaling protocol for telecommunication networks

Just as SIP is THE protocol for session establishment in broadband, the Diameter protocol plays a central role in the management of LTE and IMS networks and 3G charging and policy deployments. In LTE, Diameter is used for signaling across all core network elements. It exists everywhere in the network and is crucial to billing and charging, traffic and subscriber management, subscriber authentication, mobility management, and roaming services. It performs a connecting and routing function among LTE networks, and inside the network between the different network nodes. Diameter is maybe the only signaling protocol that is capable of managing the huge amount of core network signaling in an environment that has become far more complex, with many more network elements compared to how it was few years ago. Though, the protocol was originally envisioned to handle things like charging or simple policy control. As mobile networks have grown and evolved, Diameter has taken on a much broader set of responsibilities, such as mobility management and more. Along with the spreading of LTE adoption, we are witnessing the embracement of Diameter as the main signaling protocol for mobile networks. Even seemingly neutral developments, like the use of TCP as a bearer for Diameter traffic, are increasing the load on mobile networks. Because TCP requires an acknowledgement for every message sent, its use essentially doubles the signaling traffic.

Signaling challenges for LTE operators

Even when a user just turns on their smartphone, a lot of Diameter messages are sent across the network – to user and location databases, to billing platforms, to policy servers, and more. Just as an example, launching the iPhone’s browser, for example, instantly sets off about 15 individual network signaling requests. All of that signaling can flood and take down a network – and indeed in some cases it has. Last year Verizon Wireless suffered an early outage on its high-profile LTE network that was eventually traced back to a signaling problem. Norway’s Telenor also had an 18-hour outage last year that was caused by a “signaling storm.” The traffic between the servers in the mobile network increased far beyond normal levels, to the extent that the servers no longer managed to connect the calls within the network. As 4G networks scale, one of the biggest challenges for operators would be to prevent signaling overload in the control portion of the network. The network fragmentation and the high amount of point-to-point connections cause a major increase of the signaling traffic. Any failures of the signaling system can have disastrous effects for the network operator, such as outages and system latency, resulting in lost revenues and subscriber churn. It is a known fact that 4G networks generate about 30 times more signaling than traditional carrier voice networks!

How a Diameter Router can help

With 3G, LTE and IMS networks having so many Diameter-connected end points, network operators need a Diameter solution to connect the new elements to the old ones, load balancers for scalability – meaning to grow the network easily, and routers that ensure the messages from each subscriber go to the right systems – in short, to support a Diameter architecture that is becoming increasingly complicated. This support can be provided by a new network element, the Diameter router, an “in-between” component which can serve as traffic filterer and load balancer for all the Diameter messages from the network, ensuring that they get routed properly and that they don’t overwhelm any network element, taking down the network with it. Without a core Diameter routing solution, operators would have to rely on all the endpoints to route Diameter messages.  But by putting a Diameter router at the core of the network, they provide a single place to implement network management functions and eliminate the interworking and support issues associated with implementing those functions in edge nodes.
A Diameter router can provide the following functionalities:

  • Simplifies the mesh of connections between the Diameter nodes and organizes the routing of packets within the core network;
  • Performs load balancing to reduce the number of network connections. Can also assure weighted load balancing of Diameter messages to various endpoints;
  • Provides network congestion control;
  • Improves interoperability between multivendor network endpoints, by creating a centralized point for Diameter signaling management;
  • Maintains session state and helps ensure that the same subscriber/session is serviced by the same network element (for example, PCRF, OSC, HSS);
  • Provides protocol translation and customization capabilities.

Considering the growing amount of signaling traffic, it is very likely that a Diameter router system will become a central component in LTE and future telecom networks in the coming years, getting more and more functionalities and responsibility.

Author: Cristian Constantin – System Architect, Computaris