The present invention relates to a data channel access unit and, more particularly, to a drop/insert multiplexer of the type capable of receiving PCM signals from two directions and connecting a channel from either direction with own channel or connecting some channels of PCM signals from one direction with certain channels of PCM signals for the other direction.
A fundamental drop/insert MUX (multiplexer) is functionally shown in FIG. 1, wherein RPCM 1 and SPCM 1 denote a receive PCM signal and a send PCM signal in one direction (direction 1), similarly, SPCM 2 and RPCM 2 denote a send PCM signal and a receive PCM signal in the other direction (direction 2) and MULDEM 1, 2 denote a respective multiplexer/de-multiplexer for each direction. Numeral 10 denotes a through switch unit and is brought into a "through" condition by turning switches S1 and S2 to "a" side for connecting the RPCM 1 to the SPCM 2 and the RPCM 2 to the SPCM 1 reciprocally, thereby permitting a communication between stations (not shown) installed in the direction 1 and in the direction 2 whilst brought into a "drop/insert" condition by turning the switches S1 and S2 to "b" side for dropping the RPCM 1, 2 into the channel section 12 and inserting the SPCM 1, 2 therefrom, thereby permitting a communication between stations installed at the channel section 12 side and in either direction 1 or 2. It is, therefore, a desirable feature for this type of multiplexer to accommodate any channel in the channel section 12 to operate in the direction 1 or the direction 2 with no restrictions. Block 14 is provided by the present invention to solve these and other problems.
In FIG. 3, there is shown a block diagram of the prior art drop/insert multiplexer, wherein four data lines of R (receive) data 1, R data 2, S (send) data 1, and S data 2 have associated exclusively with four sets of channel pulse [9] for R side in the direction 1, channel pulse [1Q] for R side in the direction 2, channel pulse [11] for S side in the direction 1 and channel pulse [12] for S side in the direction 2.
As seen in the foregoing, in accordance with the prior art, wirings between the MULDEM side and the channel (CH) side are increased in number and there have been caused such problems as lack of flexibility in wiring and, in some occasions, surplus of channel slots due to channel installation spaces provided exclusively for each direction 1 and 2 as it is shown in FIG. 2(a).
In the PCM-30 system, for example, in case of setting 1 CH for the direction 1, 10 CH for the direction 2 and 19 CH for through channels between the direction 1 and 2, there may cause many unused surplus channel slots for the direction 1. More specifically, if full channel slots are provided for the both directions by assigning one slot for one channel, as it is seen in FIG. 2a, there need 30 by 2 slots and 29 slots for the direction 1 will be left unused (20 slots will be left unused for the direction 2). In practice, for making use of the space efficiently, it is common to adopt such an arrangement that one slot is assigned for one sheet and several channels are provided thereon, a number of slots is limited to small instead, of providing full slots, or the like. However, if slots for the directions 1 and 2 are the same in number, for example, and there needed are 29 CH for the direction 1 and 1 CH for the through operation, it will also be of necessity to provide 29 CH for the direction 2 and resulting in a problem of flexibility.
It is, therefore, a principle object of the invention to solve the aforesaid problems and to eliminate the difficulties to be encountered in the installation for providing a drop/insert multiplexer for channel access units having flexibility in the installation of channel slots.
It is another object of the invention to provide a drop/insert multiplexer for channel access units having simple wiring by employing a multiplex channel pulse transmission system.