Circuitry behind an Ethernet tap ?

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

Hi

I am trying to figure out what it would take to turn a homemade passive
ethernet tap into one that has activity and collision LEDs ? I take it
a PHY chip would be necessary but I don't understand how these come
into it because these taps are transparent on the network and I have
always thought of PHY chips as negotiators of speed and duplex (if that
makes sense). Does anyone know what ICs higher end taps use and how
they operate ?

Many Thanks

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

noplacelike127001@hotmail.com wrote:

> Hi
>
> I am trying to figure out what it would take to turn a homemade passive
> ethernet tap into one that has activity and collision LEDs ? I take it
> a PHY chip would be necessary but I don't understand how these come
> into it because these taps are transparent on the network and I have
> always thought of PHY chips as negotiators of speed and duplex (if that
> makes sense). Does anyone know what ICs higher end taps use and how
> they operate ?

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).

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

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

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

noplacelike127001@hotmail.com writes:

> Hi
>
> I am trying to figure out what it would take to turn a homemade passive
> ethernet tap into one that has activity and collision LEDs ? I take it
> a PHY chip would be necessary but I don't understand how these come
> into it because these taps are transparent on the network and I have
> always thought of PHY chips as negotiators of speed and duplex (if that
> makes sense). Does anyone know what ICs higher end taps use and how
> they operate ?

There one plan for simple Ethernet tap at
http://www.snort.org/docs/tap/

The higher end taps somethign like ones at
http://www.comcraftfr.com/ethertap100tx.htm
have 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.


--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

noplacelike127001@hotmail.com wrote:

> 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.

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

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

James Knott wrote:

> noplacelike127001@hotmail.com wrote:
>
>> Hi
>>
>> I am trying to figure out what it would take to turn a homemade passive
>> ethernet tap into one that has activity and collision LEDs ? I take it
>> a PHY chip would be necessary but I don't understand how these come
>> into it because these taps are transparent on the network and I have
>> always thought of PHY chips as negotiators of speed and duplex (if that
>> makes sense). Does anyone know what ICs higher end taps use and how
>> they operate ?
>
> 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).

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.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

 

[Guest]

Archived from groups: comp.dcom.lans.ethernet (More info?)

J. Clarke wrote:

(snip)

> 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.

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