what it is, and why GE selected Sophos as their NAC toolset 

"Most organizations today have a set of comprehensive information security policies, but very few are able to confidently say they enforce these policies consistently across the organization."
Khalid Mark, Forrester

Early in June 2007 Sophos announced an agreement with GE which allows GE to deploy centrally managed network access control (NAC), anti-virus and firewall protection for up to 350,000 endpoints (laptops, desktops and servers) throughout the world and within every division of the company. 

So why did GE - a diversified technology, media and financial services company and one of the world's most recognised brands – choose to partner with Sophos?   And why Sophos NAC when it seems like Cisco and Microsoft are the ones making all the noise?

Let’s start by taking a bit more of a peek at what’s behind “network access control””.

NAC is currently one of the most discussed - and confusing - areas of network security.   And understandably so, once you realise that it’s actually an overview of a centrally managed host of discrete policies, technologies and actions.  These combine to define which resources (human or otherwise) are able to access the network, and under what conditions. 
This article shows an unashamed leaning towards the Sophos NAC solution, given CoreSight’s ongoing relationship with Sophos.  However many of the basic principles apply regardless of the specific solution.

In Sophos’ words about their NAC Advanced product, “(it) quickly enables you to control who and what is allowed onto your network; blocking rogue users, controlling guest access, and ensuring compliance with your company's security policy for employees.   By implementing NAC you reduce the risk of rogue, guest, non-compliant, or infected systems compromising your network. A NAC solution gives you a framework to ensure that only correctly secured computers gain network access. “

“Fixed, mobile, wired or wireless computers connecting to the network can be detected and managed suitably with NAC in place. If operating systems are unpatched, personal firewalls are turned off, or unauthorized applications are being used, access to your network can be denied.”