The ISA Stateful Application Layer Inspection Firewall
There are many things that set the ISA firewall apart from other firewalls in widespread use. But the one thing that stands out is the ISA firewalls unique combination of stateful filtering (stateful packet inspection) and stateful application layer inspection. Combine these features with the ISA firewall’s one of a kind VPN server and Web Proxy/caching capabilities, and you have one powerhouse firewall that causes other firewalls to pale in comparison. Check out this article for details on how the ISA firewall's Firewall client application is a critical components of the ISA firewall's comprehensive defense in depth scheme. Continue at source.