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]> 
Robert Redelmeier  writes:

> In comp.dcom.cabling Floyd L. Davidson  wrote:
> > It doesn't have to be.  Frequency is *not* what determines
> > whether it will interfere or not.
> 
> Then what does?  Voltage?  Far enough apart, frequencies
> don't interfere.  Do you have trouble understanding speech
> on an elevator ride?  Both are changes in air pressure,
> but at ~100,000x different frequency.
> 
> >>You could place that ringing current directly on the ethernet
> >>pair and it wouldn't have much effect.
> 
> > Please cite the specs for a form of ethernet where the
> > receiver can handle +/- 300 volt burst of random noise hits.
> 
> Ethernet transceivers are designed for 500V isolation.

10Base-T Ethernet transceivers and Ethernet cards are typically 
designed with around 1500V isolation. 

That 500V isolation level was used on Ethernet that used 
coaxial cable. 

> AFAIK, ringing voltage is 90V max P-P (still above LV specs!).
> Capacitive effects cause very little crosstalk.  Most is from
> induction.  Current matters, not voltage.
> 
> Ethernet is differential signalling which further isolates
> noise.  I haven't tested, but a phone ring to a modern set may
> not even spoil a single ethernet packet inside a shared sheath.
> Easy enough to test with a flood ping.

I have not found any ring signal relared problems for Ethernet 
at tests where I have had 10Base-T and PSTN line signal 
on a shared sheath. I have not made any wide tests on this though.. 

I have even tested application where you put normal telephone 
signals and Ethernet signals on the same wire pair. 
Just two small capacitors for block DC + attenuate low frequencies 
for Ethernet input/output. And then a suitable low pass 
filter for telephone line signals input/output. 
Worked at least on laboratory setup without problems 
for 10Base-T Ethernet. No packet loss because of 
ring current... On hook/off hook situation and 
pulse dialling were more challenging signals for 
this setup, but di dnot cause great problems either.

The setup was like this (idea from Petri Krohn):


                              Computer Ethernet(Tx)
                                /----||---------
                               / /---||---------
 CO   ________                / /  ________
 ----|LPfilter|----/----~~~--/-/--|LPfilter|----
 ----|________|---/-/---~~~---/---|________|----
                 / /                   Telephone equipment
 ----------||---/ /
 ----------||----/
 Ethernet switch (Rx)


 Ethernet switch (Tx)       Computer Ethernet(Rx)
 _______________________________________________
 _______________________________________________


  

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