[vox-tech] Carrying telephone signal over ethernet

[Jeff Newmiller]

On Thu, 18 Mar 2004, Mitch Patenaude wrote:

> I could be wrong, but I believe that Cat5 uses all 4 *pairs* of wires, 
> and not just 4 wires.  Maybe that's only for full duplex....

CAT5 is the wire... it has 8 conductors, which are typically all
terminated in an RJ-45 jack.  CAT5 itself doesn't _use_ any conductors...
it supplies them for your application, with electrical characteristics
suitable for up to 100BaseT operation.

10BaseT and 100BaseT use the same connector pinouts, which leave four
conductors unassigned.  I don't know if any of these standards explicitly
address the compatibility of the unused conductors for telco wiring
(specifically crosstalk between conductors), though I believe that is
exactly what they were intended for.

All 10BaseT and 100BaseT connections are hardware full-duplex... but the
default protocol for their use assumes CDMA (half duplex communication) so
as to be compatible with hubs... if you only have switches, you can set
the NICs to utilize the hardware capability to communicate in both
directions.

Mark's original question is fair... though I think most installations
would install a combined ethernet/phone wall jack and complete the
connections behind the faceplate.

> IIRC, Cat3 (i.e. 10baseT) was designed with phone compatibility in 
> mind.. and leaves the center pair unvired, so that it's compatible with 
> the older rj11 plugs in a very direct way.  You can plug an old rj11 
> plug into a rj45 jack, and I think that the original conception was 
> that every jack would carry both phone and ehternet, and you could plug 
> either computer or phone in as needed.

Again, CAT3 != 10BaseT, though CAT3 can be used to implement 10BaseT.

> 
>    -- Mitch
> 
> 
> On Thursday, Mar 18, 2004, at 13:44 US/Pacific, Mark K. Kim wrote:
> 
> > So my dad's workroom has no phone line, believe it or not.  I do have a
> > phone line in my room, though, and we got a ethernet line between our 
> > two
> > rooms.  Since 10baseT uses only 4 of the 8 lines on the cat5 cable I'd
> > like to use the unused lines to carry the voice signal.  I know cat5 
> > was
> > designed to do this (middle two lines are open), and I've done it 
> > before
> > with custom adapters (messy), but I can't find any splitter online that
> > does this.  Anyone know where I can get a pair?  What's it called?
> >
> > Thanks!
> >
> > -Mark
> >
> >
> > -- 
> > Mark K. Kim
> > AIM: markus kimius
> > Homepage: http://www.cbreak.org/
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> 
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