Session Border Controllers (SBCs) were once used primarily as a security device, where they functioned as the Network to Network Interface (NNI) in peering or interconnecting different service providers; and as a border element between the service provider’s core network and their access network connecting to enterprises and residential customers. However, as the industry is transforming and experiencing tremendous growth in IP, SBCs have taken on an expanded role for fostering successful connectivity and providing high quality IP service.

Changing Infrastructure

IP has become the new transport methodology for delivering voice and video services due to the increasingly complex nature of the communications networking environment. As the same time, converged applications are growing quickly and video is expanding at exponential rates. This has led to IP networks being installed and used as core networks, instead of as "adjunct" networks connected to "core" Time Division Mulitplexed (TDM) networks through gateways. HKlett

Yet throughout this transition, the global communications scene has not abandoned the TDM component. Because of this, the all-IP networks that are emerging will still need to interconnect with existing TDM networks. The problem is that they aren’t designed to function together, so service providers will undoubtedly struggle with service delivery challenges in making these disparate networks work well together. And as such, the smart technology solution providers can take advantage. These are the providers that have experience in connecting IP with legacy TDM networks. These providers  know,  understand and appreciate both sides of this mixed communications world, and can develop solutions that can serve the broadest range of networking options while at the same time supporting a wide range of multimedia IP-based services. Solution providers that can do this will be sought after by service providers who want to provide the best service for their customers.

Delivering on Service Providers’ Needs

The smart solution providers are filling this industry need with SBCs. They are being counted upon by service providers as a critical component to interconnect all-IP networks with existing TDM networks.

First, they maintain their traditional role of protecting the network. SBCs inspect the sessions for both multimedia and control traffic as they enter the network, and as such, they are able to play a major role in maintaining high availability by helping to mitigate potential system failures and network overloads that can result when networks are confronted by Denial of Service (DoS) attacks, mass call events or malicious traffic. Second, an SBC enables seamless communication between different service provider networks and end-user networks.  These networks are usually made up of infrastructure from different equipment manufacturers or consist of different generations of technology or use different variations in control and data plane protocols.  SBCs sitting at the border between these networks interconnect and interwork at the application and in some cases at the transport layer to enable the end-to-end delivery of services.  

And there are additional beneficial applications of SBCs emerging that leverage their security and connection capabilities. For example, service providers can deploy SBCs in Value Added Services (VAS) applications, allowing them to greatly accelerate the time to market and improve their top-line revenue. And providers can use these revenue-generating services to remain competitive and differentiate their offerings. Examples of these services are messaging, streaming video, audio conferencing, video collaboration, gaming and other multimedia services. SBCs deployed in VAS applications can be instrumental in helping service providers accelerate the time to market for such services, and in turn can contribute to a service provider’s top-line revenue.  In addition, due to their ability to translate signaling and transcode, transsize and transrate audio and video media, they enable service providers to deploy a service across that can be utilized by customers regardless of the access technology or even device they happen to use.

Service providers can also leverage SBCs to offer Virtual Private Networks (VPN) services, like VoIP calls (and other IP transmission) between customers in different VPNs that are provided by the same service provider. The SBC in the service provider network is configured to be a member of each VPN and thus routable to each.

Finally, features such as access control, interworking, policy enforcement, DoS protection and topology hiding capabilities of SBCs make them well suited for use in the IP Multimedia Subsystem (IMS) architecture. SBCs can provide call session control and border gateway functions at both NNIs (carrier-to-carrier connections) and UNIs (carrier-to-customer connections). While IMS relies on SIP as the primary session control protocol, there are extensions in the applicable architecture standards (for example 3GPP) that SBCs will need to support.

Leveraging SBCs to Improve Your Network

Neither the growing sophistication of our communications networking environment nor consumer demand has any signs of slowing down. Fortunately, there are equally sophisticated technology solution providers that have adapted SBC capabilities to allow service providers to benefit from these industry changes. Providers can and should take advantage of SBCs to improve the functionality and quality of their networks, ultimately improving customer satisfaction and their bottom line.

Harold Klett is vice president and general manager of the service provider infrastructure unit at Dialogic. He can be contacted with questions or comments at