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Re: More 100Mbit



>Pardon me for barging in, but did you know that the usual flat cable used
>in 10 MBPS ether with RJ 45 connectors is NOT approved for 100 MBPS ?

The cable for 10BaseT Ethernet is *not* flat. It is made of Twisted
Pairs: each *pair* of leads is twisted within itself. It is the most
important attribute of the cable.

Indeed, the requirements for 100Mb/s are higher than those for 10Mb/s.
The commonly used standard is EIA/TIA-568A, and it categorizes the cables
into 5 categories; only two of them (3 and 5) are actually relevant
when we talk about Ethernet and Fast Ethernet. 10Mb/s can safely run
on cat. 3 cables; 100Mb/s requires cat. 5.

>If you happen to hit a (sub) multiple of lambda with your cable length,
>which is obviously not of the right kind, then you will have problems.
>(lambda is the wavelength of the signal, in theory it should be 100 MHz
>for 100 MBPS, or about 3 meters).

There are many more parameters than the lambda multiples. It's far
more complicated - beyond the scope of this list (we're offtopic
anyway).

>100 MBPS is MUCH heavier on cable quality than 10 MBPS (about TEN TIMES
>more so). If I remember well, they want 120 ohm cables (but I may be
>wrong).

10BaseT and 100BaseTX are specified for 100 ohm cables. Not 120.

>Use anything else and you will have troubles. Incidentally, if
>you'd use coax and the proper coax then there would be no problems (i use
>coax whenever I can, those twisted pairs date back to when coax was
>expensive and people wired large buildings).

You are mixing a few things here. Coax cables may be used (the original
Ethernet was specified for a coax cable), however the signalling is
totally different and you need a different transceiver (either built
in the NIC as in "combo" NICs, or an external one).

>120 ohm 1pair + shield coax
>was used by IBM token ring ? Maybe you can find an old cable and get the
>wire from there.

The IBM Token Ring does not use any coax. Its cable is two-pair, twisted,
each pair separately shielded. You are not supposed to use it for an
Ethernet connection (either 10Mb/s or 100Mb/s).

Doron Shikmoni