SIP-VoIP SBC-Session Border Controllers – Session Controllers Explained

February 24, 2008
According to our research, "The primary function of the SBC is to serve, basically, as a SIP aware NATing Firewall." SC-Session Controllers or SBC-Session Border Controllers are access devices operate at Layer 5 Session Layer, where as routers operate at Layer 3 Network.   Some of the key SBC/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 - discussed next
- Compatibility with billing - discussed next
- Dialect conversion - discussed next
- Protocol conversion - discussed next
- Codec conversion - discussed next
- Firewall restrictions - discussed next
- Wholesale and Transit peering - discussed next
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.
The previous tutorials explained more details on specific SBC/SC features, CALEA and SIP Wholesale and Transit Peering.
 
SC-Session Controllers or SBC-Session Border Controllers operate at Layer 5 Session Layer, where as routers operate at Layer 3 Network. Some of the key functions are:
Dialect Conversion - SIP-to-H.323 and other translation.
Protocol conversion - inband DTMF to out-of-band - dialed number translations. That is, the SC integrated proxy server forwards SIP invite to the H.323 gateway.
CODEC conversion - COmpression-DECcompression of analog voice packets to various types of ITU standard digital voice compression standards such as G.711 (64 KBPS PCM-Pulse Code Modulation), G.723 (5.3 and 6.3 KBPS), G.726 (16, 24, 32 and 40 KBPS ADPCM-ADaptive PCM), G.728 (16 KBPS CELP-Code Excited Linear Prediction), G.729/a (32 KBPS ADCPM) and others.
Firewall - upon completion of call setup signaling, two-way RTP-Real Time Protocol voice messages are sent and controlled via the SC based on administrative security policies.
The FCC requires that "all domestic communicates be transmitted through U.S. earth stations or routes through a POP-Point of Presence that includes a network switch or router that is located in the U.S. While other countries have adapted CALEA-like regulations, there are many problems to be overcome for international interception. Session Controllers can provide a CALEA interface for mediation (see E-911-CALEA for more on CALEA procedures).
 
1 - Wholesale Peering service - need a “pipe” or circuit connection
- Dedicated connections - generally one circuit or group in each direction - so we know which way to go and for load-balancing
- Reduces router hops for better performance
- Wholesale services available for carrier who wants direct connection to public peer POPs-Points Of Presence
 
2 - Transit Peering services - need a “ride” for your packets
- SPOPs - service points of presence for access to services-servers
- Provides connections to another network and beyond
- May add hops (router connections) for some connections
- For a fee - top secret deals between carriers
 
The complete details on SBC/SC can be found in the SIP Essentials and OCS-Office Communications Server classes. For more go to http://www.techtionary.com.


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