| 摘要 |
A universal digital communication system is described which can be built up on the existing analog communication system in compatible steps. It is based on the 64-kbit/s channel. Measures are described which make it possible to switch the digital data streams on two wires through the local exchanges and on four wires through the trunk exchanges. The analogue exchanges can remain for the time being. The uniformly established pulse signalling system also remains for the time being. The subscriber terminals have two operating modes: firstly analogue, secondly digital. In the digital mode, several operating modes are provided for the data traffic. No second B channel and no D channel is required. The digital network is synchronized by a central clock.
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