SBC (session Border Controller) Functions

Functions

SBCs commonly maintain full session state and offer the following functions:

• Security – protect the network and other devices from:

• Malicious attacks such as a denial-of-service attack (DoS) or distributed DoS
• Toll fraud via rogue media streams
• Topology hiding
• Malformed packet protection
• Encryption of signaling (via TLS and IPSec) and media (SRTP)

• Connectivity – allow different parts of the network to communicate through the use of a variety of techniques such as:

• NAT traversal
• SIP normalization via SIP message and header manipulation
• IPv4 to IPv6 interworking
• VPN connectivity
• Protocol translations between SIP, SIP-I, H.323

• Quality of service – the QoS policy of a network and prioritization of flows is usually implemented by the SBC. It can include such functions as:

• Traffic policing
• Resource allocation
• Rate limiting
• Call admission control
• TOS/DSCP bit setting

• Regulatory – many times the SBC is expected to provide support for regulatory requirements such as:

• emergency calls prioritization and
• lawful interception

• Media services – many of the new generation of SBCs also provide built-in digital signal processors (DSPs) to enable them to offer border-based media control and services such as:

• DTMF relay and interworking
• Media transcoding
• Tones and announcements
• Data and fax interworking
• Support for voice and video calls

• Statistics and billing information – since all sessions that pass through the edge of the network pass through the SBC, it is a natural point to gather statistics and usage based information on these sessions.

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