Multipoint digital data services networks are frequently employed to link a plurality of (digital data-sourcing) sites to a remotely located (information processing) site. A typical application of a relatively large multipoint network is a lottery system, where thousands of data terminals that source lottery numbers input by individual players are distributed over a large (statewide) geographical area. A reduced complexity example of a typical multipoint network is diagrammatically illustrated in FIG. 1, as comprising a first (information processing) data terminal equipment `master` site 11 located at a west end (as viewed in the Figure) of the network, and a plurality of second through fifth (data-sourcing) data terminal equipment `slave` sites 21, 22, 23 and 24 dispersed at east ends of the network.
Each of the data-sourcing sites 21, 22, 23 and 24 is linked to master site 11 by way of a multipoint junction unit 31, which is coupled to each of a plurality of respective (four wire) local loop channels or branches 41, 42, 43, 44 that serve sites 21, 22, 23 and 24, respectively, and to a `control` channel 51 that forwards data transmitted from any of the sourcing sites to master site 11. Coupled in respective ones of local loop channels 41-44 are office channel units (OCUs) 61-64 and communication services units (data service/channel service units (DSU/CSU)) 71-74 that interface to each data terminal equipment site 21-24 by way of a standard digital transmission link (such as RS-232, V.35). Similarly, master channel 51 contains an office channel unit 81 coupled to multipoint junction unit 31 and a (DSU/CSU) 91 coupled to data terminal equipment site 11.
In the course of normal operation, multipoint junction unit 31 is operative to combine respective digital data bytes as they are sourced (on a normally non-continuous basis) from sites 21-24 on channels 41-44 and outputs the data over master channel 51 to data terminal site 11. An anomaly on one of the local loop channels 41-44, for example between a DSU and a office channel unit, may cause that local loop channel to become continuously active, which ties up the entire network, so that no other channel can transmit data upstream to the master site, and therefore effectively prevents all data transmission for the entire network in the upstream direction.
Reasons for a channel going continuously active, or `streaming` data, include bad cable splices, one or more broken wires, the DSU not being connected or powered, and an excessive noise condition. Because the entire network is disabled whenever a single channel becomes continuously active, the location of which channel is faulty is relatively hard to detect.