Question I know that cables have restrictions on distance, but I really would like to know why

those limits are for each cable. E.g. Why is Cat X cable limited to 100m, and thinnet

185M etc. I have just accepted these values but have been asked why and I do not

know a technical enough answer as I have never been a cabler. I could not find this

on your site and was hoping it might be added or if you could email me back with

why. Thanks. Answer

The length limits are not for the particular cables as such, they are for the type of

data signal that they carry. Let me try and explain! Thinnet (RG58 coax) was used for 10Base2 Ethernet, at 10Mbps on RG58 coax Ethernet can reliably

operate upto a distance of 185m. The native cabling environment of the AS400 is Twinax and the

standard operating speed is only 1Mbps. At this speed it has a maximum distance of 1800m, however, if

Cat 5 forms part or all of the link the distance can drop to between 36m and 364m. So for a proprietary network such as Thinnet, the distance is set at the maximum length that the signal

will work reliably at a given speed over a given type of cable. So far so good! Now, when we talk about Cat 5, 5e, 6 etc. these are cabling 'Standards' which define a method of

connecting all types of networking protocols, over a cabling system that uses a common media, common

connectors and a common topology. So the length limit was arbitrarily set for the worst case scenario.

10BaseT may well work on Cat 5 for 150m but ATM,

AS400, Token Ring etc. may not, and because a

structured cabling system has to work for all

networking methods, a limit had to be set.

I don't think I have explained this very well but I hope

you get idea. Incidentally, I have heard talk of the

length limit being dropped from the standards as it is

the overall Attenuation to Crosstalk Ratio which

determines a cables ability to transmit a signal

successfully, and not the length of the cable. If