[Gllug] Ethernet crossover wiring

[Chris Bell]

On Mon 27 Feb, Russell Howe wrote:
> 
> On Fri, Feb 24, 2006 at 07:04:22PM +0000, Matthew King wrote:
> > 
> > Well I guess this answers the question I never got around to asking of
> > whether I should use one cable for both phone and ethernet connections.
> > 
> > I'm quite glad now that it was an option I never seriously entertained.
> 
> FYI, we do this at work with no problems at all. The telephones are
> digital though, so I don't know if the wiring is different to your
> 'standard' telephone wiring...
> 
   "Standard" analogue phones require connections to the line pair, while
the ringer connects between the A leg and a capacitor connected to the B
leg. Using a shared capacitor avoided "bell tinkle" while dialling. The
normal phone wiring uses

A leg  White/blue    BT connector pin 5
B leg  Blue/white    BT connector pin 2
Ringer Orange/white  BT connector pin 3

   The relationship between the ringer wire and the B leg is important. BT
retains the same polarity of the A and B legs, but I understand that (most?)
phones do not care. Recent mains powered phones may not use the ringer
circuit, or may only use the ringer circuit when local mains fails; BT
approved phones should fall back to using line volts when the local power
fails in case of emergencies.
   Internal PABX (non BT standard) digital phones use BT connector pins 1
and 6. They may also work with either polarity, but are again normally
connected the same way round.
   Cat5 adapters are available for using a spare Cat5 cable for telephone.
   Cat5 splitters are available which separate the normally used and
not-used pairs (10/100 only) for either two ethernet connections or one
ethernet plus telephone.
   Cat5 10/100 ethernet crossover connections only need to cross the
normally used pairs, more expensive recent 10/100 and (all?) 1000base
equipment auto sense the connections and do not require cross-over cables.
   Cat5 cables can be joined using off-the-shelf double female connectors
which are available either 1-1 or crossover.
   Many of these items, together with RJ45 plugs specifically designed for
both stranded and solid Cat5 are available from NetShop in Slough, close to
the bus and train stations, and not too far from Heathrow.

http://www.NetShop.co.uk


-- 
Chris Bell

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