Session Border Controllers and Routers are deployed on the border of company’s private network and VOIP service provider’s public network. While sitting on the border of public and private network, a Session Border Controller can perform the following functions:

1. The SBC can protect the private network and other devices from Malicious attacks such as a denial-of-service attack (DoS) or distributed DoS, toll fraud via rogue media streams, Malformed packet protection, and performs encryption of signaling and media due to privacy reasons.

2. The SBC can allow different parts of the network to communicate through the use of a variety of techniques such as NAT traversal, SIP message and header manipulation, IPv4 to IPv6 interworking, VPN connectivity, Protocol translations between SIP, SIP-I, H.323.

3. An SBC can help in implementing a QoS policy for a network. It can include functions like traffic policing, resource allocation, call admission control, etc.

4. An SBC can provide support for regulatory requirements such as emergency calls prioritization and lawful interception.

5. Some newer SBCs also have built-in digital signal processors (DSPs), through which it can have greater control over media/voice and can provide services such as DTMF relay and interworking, media transcoding, tones and announcements, data and fax interworking, etc.

6. Since all outside communication occurs through the SBC, it is a natural point to gather statistics and usage based information on these sessions.