The animated TECHTip Tutorial is available here.

According to one provider, “The primary function of the SBC is to serve, basically, as an SIP-aware NATing Firewall.” SCs [Session Controllers] or SBCs [Session Border Controllers] are access devices operate at session layer 5, whereas routers operate at layer 3 network. Some of the key SC functions are:

• Secure network peering - private and public to enhance performance
• Topology hiding - using various types of inter-AS [Autonomous System] features as well as separating media (voice) and hide signaling (IP addresses) data streams (traffic)
• Border call routing - routing at AS level rather than with interior protocols
• Interoperability - access/restrict to reduce voice spam
• QoS & Call Admission Control - load/jitter correction
• Billing systems interoperability - reduce billing errors
• NAT [Network Address Translation] - routing for maximum performance
• CALEA [Communications Assistance for Law Enforcement Act]
• Compatibility with billing
• Dialect conversion
• Protocol conversion
• Codec conversion
• Firewall restrictions

Various types of stateful (interconnect different networks such as H.323, MGCP [Media Gateway Control Protocol], and SIP [Session Initiation Protocol]) and stateless (same networks) session controllers exist depending on the VoIP network features required.

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[tags]TECHtionary, VoIP, session controller, session border controller, sc, sbc[/tags]