Abstract: Disclosed is a Digital Service Unit (DSU) which, in response to a digital signal from a Digital Data System (DDS) network, uses different techniques for different possible DDS services (include DDS-SC, CC64, and basic DDS services) to determine the type of DDS service providing the digital signal services and the line rates for such services. With respect to DDS-SC service, the DSU utilizes the fact that this DDS-SC service provides network defined frames of data to which the DSU tries establish frame synchronization at different line rates. The DSU also resolves the fact the DDS-SC service and CC64 service have the same 72 KBPS line rate by detecting the presence or absence of a control bit. For Basic DDS service, the DSU monitors the received signal for a plurality of possible invalid conditions. For each line rate, an error counter for that line rate is incremented each time an invalid condition is detected.

Abstract: In a Digital Data System (DDS) a method and apparatus for providing multipoint multiport service. Differences in time delays through the network are compensated by an alignment training wherein the delays from each remote station are measured at a Central station. The Central station determines how much delay to insert at each remote station and then instructs the remote stations to insert the delays. This allows all inbound data to be aligned in time so that when the data are combined within the network by the Multipoint Junction Units (MJU) data errors are not produced. Aligned frames are combined in the MJU operating in data mode in a logical AND operation so that marks transmitted by inactive ports are combined with data from active ports to produce a composite signal which is passed to the Central DSU.