Re: [tlug] test of ethernet cable length

[Edward Middleton <emiddleton@example.com>]

Lars Kotthoff wrote:
>> recently I have seen a computer with a bios, that could test the length of an
>> ethernet cable connected to it's NIC.
>>     
>
> That was most likely using a special cable/NIC/...
> The speed of signals through a network cable is near the speed of light, i.e.
> even if your clock had a resolution of a microsecond it would only be able to
> measure the length of the cable in multiples of 100m -- assuming that you're
> able to pinpoint exactly how long it takes the signal to go through the cable.
> Even when the firmware of the other NIC replies directly to your ping packet or
> whatever you're sending it's rather unlikely that you'll be able to say exactly
> how much time it spent processing it (unless you're using specialised
> hardware).
>   
Some CISCO switches seem to have build-in TDR[1] which could do this and
more but I can't find any NIC's with built-in support.  What sort of
card is this?

Edward

1. http://en.wikipedia.org/wiki/Time_Domain_Reflectometer