An Overview of Session Border Controller | SBC Software

Session Border Controller

In today’s unified communication environment, session border controller (SBC) plays a major role for security, interoperability and transcoding. An SBC is highly capable to automate the entire process and do the call translations with the help of built-in interoperability features. Advanced transcoding capabilities of an SBC allows it to execute the audio translation process seamlessly.

 Session border controller vendors nowadays continuously try to add new features to make this solution more robust and effective. So,  lets discuss in detail, what is a session border controller and how this solution works for communication providers as well as for enterprises.

What is a Session Border Controller?

A Session Border Controller is a dedicated network element used to control real-time communication calls/sessions over SIP (Session Initiation Protocol) based VoIP (Voice over Internet Protocol) infrastructures. It protects & governs the IP communication flows, or in simplified terms, governs the manner in which calls are initiated, conducted & terminated over the VoIP network. Furthermore, Session Border Controllers secures enterprises and service provider’s RTC infrastructure.

By the word “session” it means a communication that take place between the caller and the receiver. There are call media streams in the calls which works to carry the audio and video elements of the call along with other data. Session border controller works to manage the data flows of the sessions.

The term ‘border’ indicates a point of separation between each part of the network. In organizations, Session Border Controller works to manage the flow data across these borders.

Finally by the terminology ‘controller’, it means the control of SBC on the data streams that have sessions within it. A dedicated SBC also works to execute data conversion facilities and measurement, access control for all controlled calls.

Types of Session Border Controller

An SBC can be of any type, depending upon your requirements. It comes as a:

Hardware: dedicated physical equipment installed on your business’s premises.
Software: a virtual SBC software running on your server.
Cloud: a cloud-based SBC VoIP solutions for your business.

How a Session Border Controller works?

An SBC literally is a wall or a point of demarcation between your enterprise network & the service providers network (the internet). It secures and controls an SIP network by admitting (or not admitting) & directing communications between the internal & external world, such as a VoIP call between two phones or a video collaboration between multiple devices.

SBCs deployed at the network perimeter (or border as the name suggests). So that they can control and secure real-time communication sessions for both enterprises and service providers.

Early models of Session Border Controllers were used to protect & control the networks of VoIP service providers, but today it’s used to regulate all kinds of real-time communications in modern businesses. That includes phone calls, instant messaging, video & audio collaboration, & also desktop sharing. Today enterprise Session Border Controllers are also quite popular to provide a robust secured environment.

How does Session Border Controller works

Functions an SBC Performs

SBC software are used by telecom carriers for signal translation and security. In VoIP network, SBC implies control over media streams and signalling.  Let us look into some of the core functions:

1. Securing RTC Network

A Session Border Controller protects real-time communications from threats such as toll fraud, DoS attacks (Denial of Service) & spoofing by acting as a Back-to-Back User Agent (B2BUA) & hiding network topology. SBC software also enables encryption of signaling & media to prevent communication tampering. Further, call admission control & dynamic blacklisting of rogue endpoints avoids toll fraud & telephony DoS.

2. Enabling SIP Trunking

As mentioned above, SBC is a demarcation or termination point of the SIP trunk connection in your communications network. It’s more like a SIP firewall that also includes an array of value‐added services like signaling and media inter-working, intelligent routing control, resiliency, and high quality of service between different network devices.

3. Interconnecting Networks & Protocols

SBC smoothly performs the inter-working & interconnecting tasks, such as dealing with SIP variants & translating protocols, between different networks & the protocols running over them. SIP has a lot of variants; an SBC software can translate these variants between devices so that the calls get through with all their features intact.

4. Session Admission Control

SBC performs session admission control which basically means it inspects & sees who should be allowed to access the network & who shouldn’t. To perform this task, it creates three lists: whitelists, blacklists & greylists. With this task, it maintains the QoS (Quality of Service) on the network.

5. Intelligent Policy & Routing Controls

A policy has a set of rules that defines how the SBC treats different kinds of VoIP events. It allows control of the VoIP signaling and media that passes through the SBC at an application level. We can set multiple policies on a single SBC.

So now, you know what a session border controller is, what are its types & what it does. These are some very basic functions but pertaining to the application of SBC, it might vary for each organization.

Difference between an SBC and a Firewall

Most business owners, who are not much into the concept wonder if an SBC is similar to a firewall as they are not must sure about their exact requirements. Once, you have set up your company, it is important for you to apply all types of security protocols.  So what type of solution do you need? Is it a Firewall or an SBC.  Lets discuss each in detail.


A computer network is divided into seven layers. These layers are separated by the Open System Interconnection (OSI). From the frame to the network segment, Firewall works to control up to layer 3 and 4. In a typical VoIP network, Signalling and Media are two types of streams. To execute signalling, a firewall has to open only a couple of ports but opening of thousands of ports are needed for media exchange. Organizations thereby adds firewalls into the DMZ but that does not prove much effective.

Session Border Controller

On the other hand a Session Border Controller is capable of working in the 7th layer. Based on Signalling, an SBC controls port access. In many situations, private IP addresses are rewrite by SIP headers, which plays effective in case of internal to external routing migration.

Now that you have understood the difference between an SBC and a Firewall, you need to make the right choice for your business. No doubt SBC is most advanced form of solution based in today unsecured environment.

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REVE Systems

Reve Systems editorial team aims to keep readers informed about the latest ongoings in the telecom technology.
REVE Systems