What is NATS?
'NATS' is 'Network Address Translation with Sub-Address' in short. It is enhanced NAT which is widely used in the Internet. On residential network, especially, NAT is used for sharing many network terminals such as PCs using only one IP address.
The big advantage of NATS protocol is that most terminals which is placed in residential network as using private addresses can work NATS protocol with no-support NATS.
Concept of specification
Recently, people feel evil accessing to the Internet when they use NAT/NAPT in many cases. The reason of this situation might increases many interactive communication softwares using high bandwidth and permanent connection such as xDSL. Especially, some internet telephone softwares and some internet games connect from their server or a person on the other end of telephone call to residential terminals which is placed behind NAT/NAPT directly. In this case, NAT/NAPT boxes can not decide to forward their connection to residential terminal. That is when people uses those software they saliently feel evil of NAT/NAPT.