I tested this concept on a little network consisting of three PCs running under Windows
2000. It works well. The network adapters are normal Intel and 3Com models, set to 10
Mbps and Half Duplex. The computers are labelled A, B, C, and the UTP cables from the
computers to the hub are 10, 16 and 35 meters long, respectively.
While working half-duplex, each Ethernet adapter is continously monitoring its recieving
pair of conductors (pins 3 and 6) for any traffic and will not start sending its data
as long as anything else is being transferred through the medium. Even when already
transmitting, the Ethernet adapter will fall silent as soon as any other traffic
appears. This event is called ’collision’ and is resolved by both computers waiting
for pseudo-random periods of time before trying again.
So in this mode of operation the hub’s vital task is to enable each adapter to ’hear’
everything others transmit, but at the same time to prevent each adapter from hearing
itself sending data – and falsely detecting collisions.
The letter-number combinations in the schematic refer to connectors (computers) and pin
numbers. For example, A1 means – pin 1 of the connector where the cable from computer A
is connected, or simply – pin 1 of connector A. B6 means – pin 6 of connector B, etc.
Picture of Prototype
The diodes are BA243 or BA244, PIN diodes. There are 24 of them on a tiny piece of PCB inside the little plastic case.
’Passive’ means – not requiring power supply.