{HEAD ~ A communications apparatus} comprising a plurality of communication devices each having a plurality of ports and a data bus interconnecting the plurality of units, wherein each device is provided with means enabling the device to detect automatically {TAIL ~ its position} on the data bus 
{ HEAD ~ A communications apparatus } comprising a plurality of communication devices each having a plurality of ports and a data bus interconnecting the plurality of units , wherein each device is provided with means enabling the device to detect automatically { TAIL ~ its position } on the data bus
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