01225 800 800
01225 800 888

What is a Session Border Controller?

Session Border Control

A Session Border Controller or SBC is a device that is deployed in SIP-based VoIP networks to protect and regulate communication sessions. In the early days of SBC, it was focused on the borders between service provider networks and controlling VoIP systems. Its role has expanded to regulating all forms of real-time communications, like video, text and other media. 

Whether you’re a big corporation or a small business, an SBC is a vital element that’s recommended when using VoIP and SIP systems, to ensure network security and efficiency.  

What does Session Border Controller mean? 

To understand what an SBC is and does, it’s best to break the terminology down into simple terms.  

A ‘session’ refers to communication between two parties, typically a phone call. Each call is made up of two streams. The first stream consists of one or more signaling message exchanges that controls the call. The other is made up of one or more call media streams that carries the audio, video and data within the call, along with other information, statistics and quality of the exchange. Together, these streams make up a ‘session’. The SBC controls and supports the data flows of each call session. 

A ‘border’ is the boundary between one part of a network and the other. The border allows information, calls and other media to flow from the internet into a network, while upholding security and filtering regulations. The SBC’s job is to assist with managing the flow of data across these borders. 

Finally, a ‘controller’ is the part of the SBC that controls and influences data streams and sessions as they travel across borders and from one part of a network to another.  

In simple terms, the SBC controls and regulates any form of communication that comes from the internet or an outside connection into your personal network. 

What are the benefits of an SBC for businesses? 


The main reason Session Border Controllers are used within businesses is for security. SBC protects against hacking, cyber-attacks and any bad influence from outside the network. The SBC is essentially a more efficient and secure firewall. Where a firewall is in place for most general systems and networks, an SBC is specifically designed to protect your personal network. The SBC also encrypts data, signaling and media, preventing outside influences from monitoring your information and activity.  

SIP communications 

SBCs allow different parts of a network to communicate and share data with each other. An example of how SBCs do this is through SIP normalisation. A key role of an SBC is to mediate SIP communication between different devices, systems or gateways that use or ‘speak’ SIP differently. The SBC modifies (or normalises) and translates SIP signaling and messaging so everything is properly communicated. 

Quality of service 

The SBC implements the Quality of Service or QoS policy, that measures the performance of a service or network. The SBC regulates and prioritises rate limiting, traffic policing, call admission control and data flows that come into or go out of the network.  

Media services 

The newer version of the SBC regulates real-time communications, particularly media services. This includes supporting voice and video calls, data and fax interworking and media transcoding. Media transcoding is where the SBC translates between different codecs. Essentially, codecs convert voice and video signals for digital transmission. The SBC can translate these through transcoding, resulting in better sound quality and reducing network bandwidths. This in turn results in a better call experience for your colleagues and clients. 

Direct routing 

One increasingly common use for SBCs is in Direct Routing. which connects Microsoft Teams to the PTSN, or the Public Service Telephone Network. Not sure what Microsoft Teams is? It’s an internal communications tool from Microsoft which provides you with instant messenger, app integrations and document management.  

Direct Routing uses a combination of SIP Trunking and SBC to connect the Teams system so it can be used as an official business phone system. This allows you to take advantage of cheaper call rates, better support and full flexibility to choose your own telephony provider. 

microsoft teams direct routing

Your SBC questions answered

Who or what is an SBC for?

Ultimately, SBCs are for anyone who uses IP technology, especially if you’re using SIP. We recommend any business, however big or small, that is installing phone systems to get an SBC. 

How do SBCs limit call traffic?

As SBCs control the flow of data that comes in and out of networks, they can also limit the amount of data that is exchanged at one time, if you’re experiencing high call traffic. SBCs have speed limiting capabilities if too many calls are coming in or going out at the same time. For example, if there has been a recent power outage and your system is just coming back online, you may be bombarded with calls because of the time you’ve been offline. 

The SBC handles congestion, where it slows your responses and incoming call flow, by forming your calls in a queue. It also decides a maximum number of inbound and outbound calls, to limit the amount of traffic at one time. 

What’s the difference between an SBC and a firewall? 

A firewall is a network security device that prevents unauthorised access to or from a private network and monitors incoming and outgoing traffic, based on security rules. Where a firewall differs from an SBC is how much it covers. 

A firewall is focused on monitoring and controlling data from networks to networks, whereas an SBC can do this on a wider scale and through telephony systems, like SIP and VoIP. Firewalls have limited awareness to SIP signalling and programs, however an SBC is more sensitive to telephony systems and can translate and scan them. Simply put, a firewall is for more general network use and protection and an SBC is more developed and tailored to VoIP systems. 

Do I need an SBC if I have a firewall? 

Yes and no. For added protection and better integration with VoIP systems, it’s best to have both a firewall and an SBC. Depending on how big your organisation is and if you use VoIP and SIP systems on a regular basis, SBC is essential and will provide extra protection alongside a firewall. However, if VoIP and SIP aren’t part of your everyday, you can get by with only using a firewall. 

How do I install an SBC?

SBCs are used in select VoIP networks so if you have a VoIP system, chances are you already have an SBC. SBCs are often installed at a point between one part of a network and another and will be installed by your VoIP provider. 

Find out more

Whether you’re looking at turning your organisation’s Microsoft Teams system into a PBX or just researching your various options, why not chat to our team to see if we can help?

Related Blog Posts

Direct Routing & Disruption in Telecoms Partner Event

On Thursday 12th March, the Gradwell team headed to Eight Members Club in Moorgate, London, for our first partner event of the year. Our event was focused on Direct Routing &…

What we’re doing in response to Coronavirus

Like many of our customers, we’re following the news surrounding the Coronavirus outbreak very closely.   As a supplier of critical communications infrastructure to many businesses, we wanted to keep our…

Updates to the Gradwell Control Panel

At Gradwell, we’re constantly building new products and improving our systems. We've been working hard to update your user control panel, and you’ll be able to see these changes on…

Product Update: Why we're turning off the Gradwell Phone App

On 27th March, we’re switching off an old version of our Gradwell softphone app. This feature was intended as a useful tool for our original Multi User VoIP product, but we feel…

Introducing: The Partner Portal

We’ve recently revealed our latest product, Wave, a new hosted VoIP phone system designed for SMEs. In conjunction with the launch of Wave, our dedicated team of experts have been working on…

An easier way to log in to your Gradwell account

Starting from next week, we’re changing the way you log in to your Gradwell account. This simple but important change makes logging in easier and quicker. It will also unify…

Are we running out of 020 numbers?

In late 2019, Ofcom introduced a new 020 range of landline phone numbers for London, to keep the city connected. The demand for numbers has been on the rise, especially in London,…

What is a hunt group and how should you use them?

Having a phone system for your business is a great way to strengthen your communications with your colleagues and clients. While a phone system is vital for making and receiving…

How to choose a phone system for your startup

Starting a business is hard. You have to develop a product or service, find your target market, create your proposition and sort your commercials. When you start a business, it’s…

Partner update: January 2020

This year is shaping up to be pretty transformative; it's already seen us working on new products and improving some of our existing services. A new Wave (and a special…

What are the Ofcom end-of-contract notifications?

On the 15th February 2020, broadband, pay TV and mobile and home phone providers must notify their customers when their minimum contract period is coming to an end. This is a new…

What is a Session Border Controller?

A Session Border Controller or SBC is a device that is deployed in SIP-based VoIP networks to protect and regulate communication sessions. In the early days of SBC, it was focused on the…

Connecting Crisis at Christmas

We are delighted to announce that we'll be supporting the homelessness charity Crisis, this Christmas. With the festive period quickly approaching and temperatures plummeting, we are proud to be able to…

What does Labour’s “free broadband” promise really mean?

As part of their election manifesto, Labour have pledged that they will nationalise Openreach, who maintain most of the UK’s communications infrastructure, and provide full-fibre broadband to every UK home and business, for free. The project will…

Introducing Wave

We're delighted to announce a new product: Wave, a new hosted phone system designed for UK SMEs. Wave is the result of over 15 years of developing and providing cutting…

Get in touch with an expert today.