How Does a Session Border Controller (SBC) Work?

A Session Border Controller (SBC) is a powerful back-to-back user agent device that sits at a point of demarcation for SMB and Enterprise businesses to provide services such as call control, security, interoperability and voice optimization. Let’s take a closer look at how a Session Border Controller works to optimize your VoIP performance!

Generally, the main duties of an SBC can be separated into four sections: Topology Hiding, IP Addresses Translation, Encryption and Transcoding, and Classification.

Topology Hiding

An SBC locates in the middle of the call path between a service provider and an IP-PBX. When a call is generated and arrives at an SBC from the PBX, the SBC filters out any sensitive information, so no outside intruders can exploit this information for hacking the enterprise VoIP network. This is called Topology Hiding.

IP Addresses Translation

An SBC also translates local IP addresses of the callers to the WAN IP address of the SBC and performs protocol normalization, a process that an SBC manipulates the call message to adhere to the service provider’s protocol implementation including possible number manipulation.

Encryption and Transcoding

Some SBCs also encrypt calls and perform transcoding when necessary. If an enterprise is connected to multiple branches and service providers, an SBC will decide where to route the calls to. It makes routing decisions based on multiple criteria: reachability, call cost optimization and path with the best quality.


So far, we have only talked about the outgoing calls. What about the incoming calls? It basically follows the same steps as for outgoing calls but with one extra layer of examination which is called classification, a process of careful inspection on the incoming calls to identify intruders and hackers.

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