From the Greek plesio, meaning near, and chronos, meaning time, plesiochronous communications involves devices running at nominally the same rate. Plesiochronous networks comprise subnetworks and devices that are free-running, although at approximately the same rate and within defined parameters of tolerance for variation. Much as clocks and watches run at approximately the same rate, devices in a digital network are free-running, with some running at a slightly faster or slower pace.