What is an SBC?

The SBC, or often E-SBC for Enterprise Session Border Controller, is one of the most important elements of UC implementation. Understanding the role of an SBC is essential for a successful and complete Lync deployment.

Firstly, a “session” refers to a telephone call, an IM conversation, a Video call, etc. The session consists of one or more call signaling message exchanges that control the call, and one or more call media streams which carry the call’s audio, video, or other data along with information of call statistics and quality. Together, these streams make up a session. It is therefore the job of a session border controller to control, manage and secure the signaling and media flow of sessions.  The SBC sits as the border of a network, hence the name is explained.  Although security is only one of the functions of an SBC, the device is analogous to a firewall and could be summarised in a simple way:

A session border controller behaves like a firewall for voice, blocking anomalous code and preventing calls from being hijacked 

An SBC in position

what is an sbc?

What else can the SBC do

The control part of Session Border Controller refers to role which ‘controls, manages and secures’ the sessions. To expand on what that mean, there are four different categories which can describe the roles of an SBC:


All UC real time voice and applications traffic is transmitted and received using the Session Initiation Protocol, or SIP. It is essential that all this traffic is protected against threats and vulnerabilities to the infrastructure, especially as traffic is traversing public networks. Encrypting the signalling and media protects user details and telephone numbers from attacks such as toll fraud and content such as IM discussions, voice or video calls from being read or played back, to be used by fraudsters. By preventing theft of sensitive data, the SBC ensured that all telephony services deliver maximum uptime to the enterprise.


UC deployments are often using disparate technologies with products and solutions from different manufacturers. An SBC can enable such setups to communicate seamlessly, therefore protecting investment and reducing Capex. For example, a PBX from manufacturer ‘A’ and a messaging platform of manufacturer ‘B’ both use SIP that is slightly customised to their specific solutions. Deploying an SBC normalises these differences of the SIP protocol, providing transparent communications between the two manufacturers


As technology moves away from fixed line PSTN trunks to ‘soft’ SIP trunks, an SBC can deliver Quality of Service (QoS) to ensure that voice calls are prioritised over other traffic streams, are of consistent high quality and are managed dynamically based upon bandwidth and call quality metrics received. The SBC can be set up with redundancy, so that traffic in the event that a service becomes unavailable on one SBC, traffic is directed through the secondary SBC to maintain voice access.


In sectors where sensitive data is discussed such as banking, stock trading, healthcare, etc, then enterprises are expected to meet compliance standards such as PCI (Payment Card Initiative), FCC (Federal Communications Commission) and HIPPA (Health Insurance Portability and Accountability Act).  It is essential that all calls are monitored, secured and in relevant cases recorded. SBCs are able to securely manage the sensitive communications that take place irrespective of the specific market sector or type of media.  This is achieved through encryption and or mirroring of calls and traffic to specific call recording and storage platforms.


In summary, the SBC is a very versatile device that performs a number of UC specific tasks. Sitting on the border of a network, it makes sure sessions (calls, IMs, video, etc) are controlled, managed and secured to maintain compliance with data protection laws and also maximise telephony uptime. For a session based solution such as Microsoft Lync, the SBC is a critical part of the deployment and should always be included to make sure the best of the solution is being delivered.  Remember – Westcon are experts in SBCs, so don’t hesitate to contact us!

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