A Session Border Controller (SBC) is a device employed in a Voice over Internet Protocol (VoIP) system to impose control of a voice (and other signals) over the internet. That control is manifested by a variety of functions, including security, connectivity, quality of service, regulatory matters and gathering of statistics.
An SBS might be oversimplified by comparison with vehicle traffic control via posted traffic laws like speed and road conditions, traffic signal lights, law enforcement officers and the common sense attitude of drivers on the road to self-manage their driving on the road. But the example will serve to demonstrate the basic functions of Session Border Controllers.
With ordinary traffic control and dependence on managing efforts, a driver can expect with relative accuracy to determine that he or she will arrive at their intended destination, that the trip will be non-eventful and productive, that the outbound trip will be accomplished with compliance to all traffic laws and that the inbound return trip will also be accomplished with all of the above considerations.
In a similar fashion, an SBS imposes control over VoIP communications. The control over VoIP is exerted from the beginning of the session, i.e. the initiation of communication over the internet by voice from a sender to a receiver (or multiple receivers), maintenance of the various media streams (voice, data, video) during the session and tearing down the connection at the end of the session.
Security is imposed to protect the session for invisibility of the initiating network (typically the local area network (LAN)) from topology visibility outside the LAN, malicious attack from outside the network, packet integrity and encryption of the signal during the session.
Connectivity allows linkage beyond the LAN firewall to communicate over the VoIP and navigate through the various sub-protocols by which communication traverses the Internet while being protected by the means noted above.
Quality of Service assures that the communications integrity remains sufficiently consistent over the network during a session in all of the available concurrent data streams that can occur during a session.
Regulatory gives priority control of Internet communications to emergency calls and lawful interception of communications so that these essential and potentially life-threatening matters may have uninterrupted service in spite of what other non-essential communications are occurring. This means that, potentially, an otherwise protected, secure quality of VoIP communication may be interrupted by an emergency situation.
Statistical measurement is feasible since all VoIP communications route through SBCs. This allows collection of data concerning usage of the system for statistical analysis. One of the benefits of gathering data is for improvement of the VoIP system.
VoIP’s growing use worldwide is increasing in its abilities and dependence to protect the integrity of all Internet communications. SBCs are contributing to that integrity, however, the system is not without controversy and inconsistencies. Older equipment that may have been functional with the initial efforts with VoIP may not be compatible with modern SBCs, causing failure of connection or interruption of the session. However, as the system matures and more protocols are in place, standardization will assure a smooth operation of VoIP.