1. In a network testing and control system for use with a digital communications network which provides digital communication between a plurality of sites, one of said sites being designated a central site and the other sites being designated remote sites and said digital communications between said central site and said remote sites being over a plurality of analog communications links, each remote site having means for generating a unique site address identifying said site, and wherein said remote sites can dynamically connect to and disconnect from said network, an improvement for reporting on the operational status of remote sites connected to said communication network communications links, said improvement comprising, at the central site means for polling the remote sites connected to said communications links with an address inquiry signal to determine their addresses; means for storing at the central site a record of the addresses determined by remote site responses to such polling, to provide a site location table containing the addresses of the remote sites; means for updating said site location table as remote sites connect to and disconnect from said communications links; means for transmitting, over said communications links in a shared and selectively concurrent arrangement with said digital communications network, a status request signal to each remote site address contained in the site location table, in response to a command, to evoke a status signal from each remote site indicative of the status of at least one selected variable associated with that remote site, said variable comprising a status condition, signal or operating parameter at the remote site; and means for receiving remote site status signals transmitted from remote sites over said communication links in a shared and selectively concurrent arrangement with said digital communications network.