I am looking fwd to get services from a host who claims to have DC as "NAC (Net Access Corporation Data Center)".

I tried googling abt NAC but i would prefer reviews from members here. Anyone here used or using NAC?

How good are they in terms of uptime and connections?

We used NAC for our datacenter, and colo provider at one time, and was nothing but pleased. The connection was great, the support and response times were great, and the server management team was awesome. When we used NAC, the only time we were down was during maintenance.

Explain to me please what such NAC? What advantages it gives?

bandboy explained what such NAC in this post, and I outlined some of the benefits we experienced while with them.