A session border controller is a device that can provide signaling and media streams in voice over IP networks. It’s usually involved in setting up, conducting, and tearing down sessions (or telephone calls) as well as other interactive media communications.
In this case border is typically a demarcation between one network or another. Just as a firewall demarcs the end of the campus network the SBC provide security and manage session flow data across borders.
So this black box is typically viewed as a security box for VoIP communications. It’s use is on the rise and I’m sure we will think of other methods of implementation in the future.
One implementation is between Office Communications Server (OCS) IBM Lotus Sametime.
The job of an SBC, then, is to sit in amongst the streams of SIP, and facilitate voice, video, IM and presence, which could mean protection against denial-of-service (DoS) attack at the SIP interface, but could equally mean just simply overcoming connectivity difficulties such as getting past NAT or firewall devices.
Today we typically see SBC’s in use with Service providers but new devices are bringing this to the masses. Convergence and BorderWare are using typical server specs to bring SBC Software to the masses. So SBCs can and probably will be used by customers on-premise to connect to external services.
Today Microsoft is using SBCs with Service providers to provide SIP Trunking for OCS R2. This trunking provides ability of OCS to connect to the IP Telephony Service Provider for PSTN connectivity. We currently have Sprint and Global Crossing qualified for SIP trunking.