"The National Traffic System plan is a means for systematizing amateur traffic handling facilities by making a structure available for an integrated traffic facility designed to achieve the utmost in two principal objectives: rapid movement of traffic from origin to destination, and training amateur operators to handle written traffic and participate in directed nets. These two objectives, which sometimes conflict with each other, are the underlying foundations of the National Traffic System. 

NTS operates daily, even continuously with the advent of the advanced digital links of today."

source ... http://www.arrl.org/FandES/field/pscm/sec2-ch1.html