| 摘要 |
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. After all the rates are checked, the DSU selects the line rate of the Basic DDS service with the least number of invalid occurrences.
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