Load Balancer

The massive growth in the Diameter signaling traffic is forcing reconsideration of solutions used for network service elements such as Home Subscriber Servers (HSS) and Online and Offline Charging Servers (OCS and OFCS).

Load balancing, active congestion management, and the ability to dynamically expand capacity are important considerations for both network operators and telecom equipment manufacturers.

When deployed as an integrated load balancer the DSC can front-end a cluster of service nodes enabling an IT style server-farm deployment. The Mitel DSC Load Balancer feature enables very high service availability and performance.  Security is enhanced through topology hiding, and scripting can be employed to compensate for variants in the network.  Use of a load balancer also simplifies the service application, reducing opportunities for application failure and enabling functions such as seamless online upgrade of software and equipment.


As the volume of Diameter traffic increases and the number of Diameter server elements increases, MNOs are faced with a daunting challenge of how to operate and maintain key services, such as converged charging (OCS), policy control (PCRF) and subscriber data management (HSS) in a scalable, resilient and cost effective manner.

Limitations in early standards have also created opportunities for improvement in Diameter signaling deployments.

Service Scalability – Diameter service elements like OCS and HSS are typically deployed on multiple servers to handle traffic volume requirements. When traffic increases and a new server is needed, many of the other Diameter network elements (PDN Gateway, MME, SGSN, etc.) need to be updated with Diameter connections to this new server. Instead of being an isolated action to increase service capacity it involves updating the entire network.

Service Resiliency –  A key element in deploying a network service is its ability to survive in case of a failure. With all servers interconnected to the network, a single server failure and the resulting recovery not only depends on the failed server coming back online, but also re-establishing the connections to the other elements.

DSC Solution

The solution to these challenges is to deploy the Diameter Signaling Controller (DSC) as an advanced load balancer.

The above figure shows the DSC in front of an Online Charging System. In this configuration, the DSC “front-ends” a set of service nodes. These service nodes may be at the same location or may be geographically dispersed.

The DSC enables an IT style server-farm deployment model allowing high service availability, topology hiding, and seamless back-end capacity upgrades. The Diameter network elements only need be concerned with connections to the DSC. Changes to the back-end servers are transparent to the network.

The DSC manages and routes traffic flow between the available back-end servers. If traffic volume increases new servers can be added without any impact to the Diameter network. This allows for a “start small” service deployment and subsequently adds capacity in the form of new servers as traffic volume increases.

The DSC maintains service availability during loss of any server without involving the Diameter network, by load sharing all traffic between the other available servers.

The DSC also provides a minimum constituency function, which prevents instabilities as pools of servers are started, restarted, or fail.

Load balancing also supports multiple traffic distribution algorithms, allowing optimal load management for a particular service’s characteristics or equipment configuration.  These algorithms enable optimal distribution when the server pool is built with identical servers, is built with non-homogeneous servers, or when the characteristics of a server pool change during operation due to reconfiguration or virtual platform management.