Wednesday 1 August 2018

Ethernet bugs

I can remember when Ethernet was young, and it was battling it out with the Cambridge Ring as a system for connecting computers.   The Ethernet protocol was called CSMACD (carrier sense multiple access / collision detect) which probably explains why a different name was chosen for commercialising it.  The advantage of the Cambridge Ring, a token-based protocol, is that performance degraded gracefully as the system became more heavily loaded.  Its disadvantage was that the cable had to be in one big loop connecting everything; it had to go out to, and back from, wherever it was going.   Ethernet on the other hand, would suddenly hit a performance wall as the load increased, but had the advantage of only needing the wire to go out to the computers it was connecting. (Well 8 wires actually but there is no need for a closed loop)  A closed loop is also much more vulnerable to the man with a spade cutting your cable, and Ethernet is more resilient to this kind of problem.   As we know, it was Ethernet that won, and as it happens, in 40 years of using it, I don't think I have come across a performance bottleneck.

Our telephone line comes to our house supported on long poles that are, at a certain point, the highest things on a nearby hill.  Lightning loves it, and we get zapped more often than we would like.  Most recently, it fried Anita's PC, via, of all things, the Ethernet connection to which the spark had jumped.  Not only did it fry the PC, but the cable that passes through the wall to connect it to the router no longer works either.  I have spent the best part of an afternoon trying to work out where the problem is.

The difficulty in this kind of diagnosis is that you can't leave anything to chance.  You have to know that the test kit is working, know that a certain cable is good.  Negative results must be confirmed by careful re-checking.  Anything unknown is going to come back and bite your bum.  The result of careful testing is that I believe I need a new wall-mounted RJ45 socket.  I will get one this afternoon, but I might wait until tomorrow to connect it.  Had enough of this crap, basically.


P.S.  I fitted the new socket this morning and it works.




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