An update on the evolving "Session Controller" space

A contribution from Netrake - December 2003

The VoIP industry is now moving from IOC and CLEC deployments to large incumbent carriers. As VoIP deployments grow in size, so does the need for call processing power and scale. IP-to-IP Gateway is the term used by Tier One carriers to define the features and requirements for VoIP Interconnection. Session Controllers are a sub-set of this since they only do pieces of the puzzle and not at high performance rates. An IP-to-IP Gateway is a critical network element, not just a firewall/NAT appliance.

As you know, early session controllers emphasized signaling or software functionality as an extension to a softswitch; with the primary need being firewall, NAT and protocol translation. Capacity requirements from carriers were low and therefore easily met.

Large Tier One carriers, however, need capacity for thousands of simultaneous calls (without latency). The difference between session controllers and IP-to-IP Gateways is quite simple: while the feature set is often similar the environment of the product's use is drastically different. IP-to-IP Gateways have evolved from PSTN-like requirements. The PSTN has a very high expectation on performance, redundancy/reliability, scale, and ease of use. IP-to-IP Gateways were designed to solve these four issues. These products provide similar feature functionality of session controllers - but at PSTN-like performance levels.

What other products could provide this functionality? Media gateways of course. So that puts session controllers in direct competition with media gateways. A few of these media gateway companies are attempting to "graft" an IP-to-IP gateway onto their product. With the high cost of DSPs in those gateways, this is an expensive proposition for a carrier. And the result does not fully satisfy the requirements for IP network control -- such as firewall/NAT, addressing, and QoS. Carriers using Media Gateways for VoIP interconnection would not be able to interconnect with carriers using private address spaces because media gateways lack demarcation and address normalization functionality - a key functionality for Tier 1 carriers. The bottom_line is that carriers using PSTN media gateways for VoIP peering would not be able to sell VoIP services to any private network.

For further information, read this one-page fact sheet that outlines the definition of the new class of products: IP-to-IP Gateways.

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