Newsgroups: comp.dcom.telecom.tech,alt.dcom.telecom,comp.dcom.cabling,comp.dcom.lans.misc
Subject: Re: 10base-T & POTS in same Cat-5 cable?
References: <[email protected]>  <[email protected]>  <[email protected]>
[email protected] (Floyd L. Davidson) writes:

> >> >
> >> >Yes, it's entirely acceptable.  When twisted pair ethernet was created, it
> >> >was intended to be run on existing cat 3 telephone cables, along side phone
> >> >lines.
> >>
> >> I'm not going to look that up to be certain, but I don't think
> >> it is correct.  T1 was certainly designed for telephone lines,
> >
> >Yes.
> >
> >> but I don't think 10baseT was.  Look at the difference in the
> >> twist on CAT5 compared to lesser grade twisted pair!
> >
> >10BASE-T was designed to operate on early Cat-3 UTP wiring.
> 
> The intent is juxtapositioned.  CAT3 cable was designed for
> 10baseT, and allows VF circuits to ride on the two unused pairs.
>
> >At the time 10Base-T was standardized there was not such
> >thing as CAT5 wiring! At the time the 10Base-T system was
> >started to be deployed on larger scale (somewhere in the
> >beginnignof 1990's) there was no such thign as CAT5
> >(maybe some cable vendors have dreamed on this and worked
> >on standard, but nothign on market). At that time all that
> >was available was CAT3 and CAT4 wiring. In know installations
> >made at that time that used CAT4 for telephone outlets and CAT4
> >for data.
> 
> True, but the typical *telephone* cable was CAT1 quality, not
> CAT3 (and higher) until 10baseT came along.

What the typical telephone cable indide house is depends on the 
country and the year when the building is built. Some countries 
recommended better cabling than CAT1 on 1980's for example to 
be prepared to future technologues (ISDN at that time). 
Some of the cable installed to offices and residential buildings 
from 1980's on has been pretty high quality (CAT3 rating or almost 
like it). I know the situation in Finland best. I wrote one 
paper for one course at Helsinki University of technology on ISDN 
technology (around 1995), and when writing on that I read quite carefully 
one publication from Helsinki telephone company that described 
the suitablility of existing wirings for ISDN use.. gave idea 
what kind of cable was use on buildings in the last decade or two..

In Finland some people are using the old telephone wiring to run 
10Base-T or 100Base-TX Ethernet on them for networking purposes. 
There is information on that at http://www.helsinkiopen.net/
 
At some countries there has been practice to install higher 
quality cable, and some used the cheapest you can get 
(I have see some installations in Russia and i doub that 
if they world even qualify even as CAT1). 

> >> The frequency has little to do with whether it will interfere.
> >> The voltage level is what makes a difference.
> >Frequency has a lot to quite much on the interferences.
> 
> We are discussing systems which encode voltage levels, not
> frequency or phase.  By definition "noise" is a unwanted voltage
> change, and the frequency or phase of the change is
> insignificant.  Only on systems where frequency or phase is used
> for encoding or modulation would that be defined as noise.
> 
> However, frequency relates to the ability to *transport* the
> signal, even though it is the voltage level which actually
> causes interference.
> 
> If the frequency is such that it will not pass through various
> parts of the transmission path, there will likely be
> insufficient voltage at a point (the receiver) where it can
> cause a problem.  But if the voltage is sufficient, it makes no
> difference what frequency it is.

True. 

> See the various discussion articles on Manchester coding and
> frequency spectrum.  The bit rate is indeed fixed at 10 Mbps,
> but that does *not* necessarily translate directly to a 10 MHz
> bandwidth or a 10 MHz fundamental.  In the case of Manchester
> coding only (others are distinctly different) it means a 5 MHz
> bandwidth that ranges from 5 to 10 MHz.  (Other components are
> generated at 15 and 30 MHz, but are not required at the receiver
> for proper operation.)

True. 

> Virtually *all* essential spectral components are at 5 and 10
> MHz.  The transmitter may generate a square wave, 

The transmitted signal on 10Base-T is essentially square wave 
with some pre-distortion added to it and then filtered through 
the low pass filter that revoves all highest frequency components 
(so that system passes the noise limits on above 30 MHz noise). 
So the the signal from 10Base-T transmitter can be viewed as 
slightly distorted swuare wave signal. 

> but the
> receiver only requires a sine wave, therefore none of the other
> components have significance at the receiver (or anywhere else).

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/