Circuitry behind an Ethernet tap ?

All you need is a hub, not a switch, to monitor ethernet. However, using the hub will force half duplex and 10 Mb (unless a dual speed hub).

Thanks Tomi

I must say that I do not want to use the tap in the conventional sense. I want to use a tap to monitor traffic load and collision rates and to display that info on an LED. I was going to purchase a NICholas card from edtp.com and output the stats to an LED.

I may use the LED pins on the edtp to show collisions.

Since the information I require is not detailed, do you think I could use only one port (instead of two) to get the information ?

Regards

There one plan for simple Ethernet tap at

The higher end taps somethign like ones at

some more electronics to operate. Basically such tap for 10/100Base-T systems can be built by passing the two data pairs through the device, and having two high impedance differential amplifiers that "listen to" at the signals on those data pairs, and send an amplified copy of the signal on those to the corresponding TAP output connectors. Signal from each pair gets to one TAP output. No matter which direction data on those pairs go, it gets picked up by the receiver in the middle of the pair.

I once looked inside one such TAP unit and found there several high speed differential amplifier ICs and some Ethernet line transformers. I do not have a circuit diagram of this kind of device.

I once thought about building such a device for coaxial ethernet, measuring the average voltage on the cable as a traffic indicator.

I believe a simple system like that would still work for 10baseT, but it gets much more complicated for 100baseTX.

Transceivers that indicate collisions with an LED need to keep it on somewhat longer than the actual time needed to resolve a collision. That time will affect how it looks relative to the collision frequency.

-- glen

Well, actually there were at one time single-speed 100 Mb/sec hubs available. There are a couple of them on the shelf in front of me as I type this.

(snip)

I gave all of my 3C250's away. They probably make good door stops, as they are pretty solid. They didn't cost me very much, other than the shipping.

-- glen