On 30/08/18 05:50, Harold Hallikainen wrote:
> I have a hub here that I use all the time with Wire Shark. Sometimes I
> need to help someone debug something in the field, and they don't have a
> hub, and they are getting hard to come by.
>
> Since 10/100 Ethernet uses two pair, one for transmit, and one for
> receive, it SEEMS like it should be possible to make a resistive hub wher=
e
> each transmit pair drives the receive pairs of the other two ports (total
> of 3 ports).
There are a few problems.

1. Modern Ethernet hardware usually has auto-negotation and auto-mdix, thes=
e are very likely to get confused by any such contraption.
2. IIRC 100 megabit Ethernet continuously transmits a carrier even when not=
 sending data. So afaict this a passive hub can only ever work for 10M.
3. If signal gets reflected back to the receive pair of the sender then the=
 sender will detect false collisons. This is a problem because a resistive/=
combiner splitter will reflect power back out of it's other input. So signa=
l can go from e.g. TX1 to RX2 to TX3 to RX1.

I belive point 3 is why the original design used diodes, to ensure any refl=
ected back signals were sufficiently weakened that they would not cause fal=
se collisions.
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.