On Feb 8, 5:12pm, "CCIE TB" wrote:
}
} In TP cables we have eight wires. Only four are used. Why we need the other
} four. The same thing applies to DB-25 and other types of cables. We don't
} use all of the wires. Why?
Because the standard actually comes from the telephony industry,
where it has other uses such as ISDN. In the data industry, 100BaseT4
runs over Cat 3 using all four pairs; 100BaseVG, something that was
proposed by HP but never caught on, uses all four pairs; and 1000BaseT
runs over Cat 5 using all four pairs. So, if you want your cable to be
usable in the future, or for other things, then you'd better wire it
according to the standards. Cabling is by far the single most
expensive part of installing a network. Recabling after a building is
finished, as opposed to prewiring when the building is only framed, is
even more expensive. This is why it is best to overwire. The marginal
cost of pulling extra cable or hooking up extra pairs is very cheap as
opposed to having to recable.
The RS-232 standard, which I assume is what you mean by DB-25,
actually defines all 25 pins; but, in reality, most are rarely used.
}-- End of excerpt from "CCIE TB"
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