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Using Session Border Controllers in VoIP networks

Updated on September 5, 2013

A Session Border Controller or (SBC) is a physical device or software application on a server in a VoIP network that controls the signaling, call admission and data streams of a telephone call. It may be located on the border between a private network such as a company intranet and the public internet or between different parts of the same network.

They can perform the following functions:

Session Border Controllers and VoIP
Session Border Controllers and VoIP


SBCs keep the network secure from external threats such as Denial of Service attacks and can reject calls to prevent sudden spikes in congestion. They can perform topology hiding to prevent customers or outsiders from learning the configuration of the VoIP network. They are also used to encrypt both the message signals and media content of data streams. Any connection with an outside network carries a risk and an SBC can act as a firewall at the boundary, allowing VoIP calls access to protected enterprise networks

Quality of Service

Network administrators can control traffic flows and implement QoS policy through SBCs. VoIP streams can be prioritized over other data to ensure audio quality. They can reserve bandwidth for calls that are being setup and also ensure adequate resources are always available to let authorized calls through, even at peak usage.


An SBC can allow various parts of the network to connect with each other. It is capable of handling codec conversions and translating between protocols such as SIP and H.323. It can also allow IPv4 and IPv6 networks to work together. In some cases, it may also perform SIP normalization which resolves incompatible SIP devices inside the network.

Regulatory and statistics

SBCs can be configured to support regulatory functions such as giving priority to emergency calls and allow law enforcement agencies to intercept communication data for evidence. Since SBCs sit at the border of networks, all calls to the outside must pass through them. So they are often used to generate usage reports for statistical analysis or billing purposes. Business VoIP routers often integrate their services to provide more advanced functionality

As you can see, SBCs provide a host of functions that serve many purposes. Network operators and enterprises use them in various ways to achieve different goals. The same SBC can perform different functions depending on the use case. Of course SBCs also have to be maintained which introduces additional costs for the system, but their advantages far outweighs the expense. Depending on the connectivity and network solutions being used, most organizations will need them to implement security and quality control policies.


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