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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