| 摘要 |
A selective secondary signalling encoder/decoder for multipoint data communications networks for use on transmission media such as telephone lines provides for selective signalling between a master broadcasting unit and however many slave units are in the network. The network functions by sending a standard (V-29) type modem training sequence and incorporating the address of the particular remote unit with which communication is desired in the data segment of the sequence. Compatibility is maintained with standard slave units that don't have this decoder by appending a sufficient number of marks to the address and message to allow for the standard starting value of a descrambler in the "data mode". When the segment is detected at each remote unit in the system, the address sent is compared to the address of the remote or slave unit. Upon a comparison match, together with a synchronism check and error checks, a valid message flag is set, indicating to the remote unit that it has received a command from the master site and thus the selected remote can be retrained or send a new sequence back to the master. Thus, instead of having to broadcast the same command to all remotes, individual remotes can be singled out to retrain back to the master so the time overhead in the network is significantly reduced since only one unit will be sending back training information to the master.
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