What is Session Border Controller (SBC) – A Quick Guide

what is session border controller

VoIP is the most widely used standard in the communication industry due to various reasons such as more flexibility, scalability, less complexity and cost-effectiveness. However, just as with any technology, VoIP has its own set of challenges. Besides quality of communication, security is one of the primary concerns in the IP infrastructures, but thanks to Session Border Controllers that not only improve the quality of the conversations but also act like firewalls to the VoIP networks, i.e. ensure security as well.

What is Session Border Controller?

A Session Border Controller or SBC is a network element (it can be a dedicated hardware or a software) that sits at the perimeter of a VoIP network. SBC is designed to regulate the signals that pass through the VoIP network and in doing so an SBC ensures security and quality of service (QoS) for all the communication streams within the VoIP network.

To understand what is session border controller in an easy way, we shall break the terminology into three simple parts: Session, Border, and Controller. Let’s take a look at each of them one by one:


A session is basically the communication that happens between two parties, which is usually a phone call. It carries the signaling message of the call in its first stream and the second stream carries the audio, video and other information such as call statistics and quality of the exchange.


Just as the term indicates, a border is the boundary that allows flow of data from the internet into the network while validating the security and filtering regulations.


Lastly, the controller does the job of influencing data streams and sessions as they happen over the network.

So, in simple words, a session border controller is a network function that controls and regulates all forms of real-time communication sessions that happens over SIP based VoIP infrastructures.

Types of Session Border Controller

Hardware based SBC

Here the dedicated hardware based SBC device remains onsite i.e. it is installed and managed by the business itself.

Software based SBC

Session Border Controller Software is a software application that runs on the top of a virtualization platform that imitates the function of hardware computing systems/devices.

Cloud Based SBC

Cloud based SBCs are software applications that are hosted in the cloud and can be easily implemented without any need of on-site equipment.

How Do Session Border Controllers Work?

There are several functionalities performed by an SBC for VoIP security, as mentioned below:

Today, SBCs are mainly involved in securing SIP infrastructures, though it also performs the function of a traffic manager and data carrier. Acting both as a User Agent Server (UAS) and User Agent Client (UAC) for each session through termination and re-establishment, an SBC holds a granular level control over the communication sessions. In order to prevent DdoS attacks, SBCs remove malformed packet exploits by making use of Access Control Lists (ACL) and Rate Limiting as it parses each message.

Most of the SBCs enable interoperability across different vendors to efficiently mediate SIP communication known as SIP Normalization which makes sure that signaling instructions and messages are communicated properly. For an easy understanding, an SBC can be considered as a security agent that stands at the gate of a customs station whose job is to inspect everyone going in and out along with the baggage they carry.

Benefits of Session Border Controller

There are several roles played by session border controllers when used in the telecom industry. Let’s have a look:

Better Connectivity

SBCs have brought the concept of connectivity to a whole new level. With SBCs in place, a business need not to depend on traditional separate phone lines as their traffic is routed through internal IPs, saving them a lot of money and time.


Since cyber attackers and hackers are adopting modern-day sophisticated techniques, it becomes essential to back your business’s systems with some extra layer of protection. In case of Session Border Controller, service providers regularly update protocols to ensure systems are not breached. Businesses just need to implement these updates to stay safe from attacks and infections.      

Quality of Service

SBCs ensure efficient and smooth flow of VoIP traffic through intelligent call routing in which optimal route for a call to reach its final destination is selected. Businesses who experience poor call quality and call dropping can significantly benefit from SBC integration.

Business Continuity

Infected systems can remain down for an unknown amount of time, disrupting business operations and loss in terms of time and money. However, with SBCs in place, VoIP systems remain safe from cyber infections leading to more uptime to conduct business.

Final Words

By now, you must have been clear with what is session border controller and why it is used by businesses for VoIP networks. Given the demand for more security and enhanced customer experience along increase in adoption of IP communication platforms, Session Border Controllers are going to make a long lasting presence. At REVE Systems, we understand the need of a robust and reliable SBC for upgradation of your business communication. Give us a call or get in touch to let us help you.

The Author

Kanika Sharma

Kanika is a versatile researcher, blogger, and author, delving into the world of tech blogs covering Telecommunications and Cyber Security. With a solid engineering background, she turns intricate tech jargons into relatable, real-life stories. Her writing isn't just about words; it's a fusion of detail, intrigue, and relevance to the audience, reflecting her passion for writing and design. Beyond her work, Kanika finds joy in painting, and exploring new places while traveling.