Why do we have cross-over cables. - Page 2

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Re: Why do we have cross-over cables.

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They were the ones!



Re: Why do we have cross-over cables.
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Which?

It was always possible to call the operator, or the emergency services,
without any coins, so I don't see how there can have been an interlock.

Sylvia.

Re: Why do we have cross-over cables.

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The 9 and the 0 were OK. It was not possible to get through to anyone else
without pressing button A.  See 'Atkinson's Telephony' for details.



Re: Why do we have cross-over cables.
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Public phone. The trick doesn't work anymore, because they now damp the
hook switch.


--
    W
  . | ,. w ,   "Some people are alive only because
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Re: Why do we have cross-over cables.

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  No luck about it.  Make-and-break dialing STILL works.

Re: Why do we have cross-over cables.
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Not all modems provided electronic control of the "hook switch" (i
forget the correct term) if you were lucky you had one that did.


Re: Why do we have cross-over cables.

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  Most ALL do actually provide such control.  It is referred to as "pulse
dialing" and modems allow selection of pulse or tome dialing.  Pulse
dialing IS make-and-break dialing utilizing "the hook switch" as that is
what pulse dialing is.

Re: Why do we have cross-over cables.

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Is tome dialing where you throw a book at the phone?

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
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Re: Why do we have cross-over cables.
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Sure.  After you've read the fat manual (RTFM), you
throw that at it.  Hence FM modulation.



Re: Why do we have cross-over cables.
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FM modulation - is that like ATM machine?

Re: Why do we have cross-over cables.
On Sun, 15 Mar 2009 12:37:37 -0700, Fred Abse

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  One opens the i ching and picks a tome and speaks it.

Re: Why do we have cross-over cables.
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   My reference states From DTE: pin 2 transmit, pin 4, request to send,
pin 20 data terminal ready (ie output); To DTE: pin 3 received data, pin
5 clear to send, pin 6 data set ready. I left out DCD and secondary /
reverse channel info.
   For a non-cross, one would need to have pin 2 as transmit on one end
and receive on the other, etc.
   Not so nice.

Re: Why do we have cross-over cables.
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That's exactly the situation we do have. Pin 2 is transmit on the DTE
and receive on the DCE.

Sylvia.

Re: Why do we have cross-over cables.
On Thu, 12 Mar 2009 17:29:01 +1100, Sylvia Else

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 EXACTLY!  Which is why, when one needs to hook up a computer that
expects to see a modem to another computer, a reversal is needed on those
two lines so that the two devices *think* they are communicating with a
modem device.  Hence "null modem" cable.

Re: Why do we have cross-over cables.

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Many (most? all?) Intel GB NICs will also crossover automatically.

Re: Why do we have cross-over cables.

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I agree, it does make a great deal of sense to set up the interfaces
in a symmetrical fashion whenever possible.  I've grown fond of the
Yost method of doing serial-port hookup... there's no differentiation
between DTE (e.g. terminal or PC) and DCE (e.g. modem), and you can
hook either to the other.

10BaseT could also have been designed with this sort of symmetry in
mind, I suppose, if we'd started out using the sort of
highly-intelligent auto-adaptive interfaces that we use today on e.g.
100BaseT.

However... these sorts of symmetrical cabling systems don't tend to
arise when there's a big functional asymmetry between the sorts of
devices at either end.  In the case of serial ports, there are some
functions provided by the DCE (e.g. carrier detect, ring indicate, and
master-clock timing in the case of synchronous ports) that the DTE is
physically or philosophically unable to provide... the DTE is a
consumer of these, not a provider.  The Yost serial standard deals
with this issue by simply avoiding it - it doesn't carry those signals
at all and thus they aren't available to the DTE.

In the case of Ethernet, a similar asymmetry existed when the
technology was developed... hubs had functions that clients did not,
and tended to incorporate more-expensive electronics.  It's only more
recently that the "interface intelligence" in a client (e.g. PC) and a
switch have become more comparable and symmetric.

Also (minor issue) it's a trifle easier to extend a straight-through
cable with another... you just use a second straight-through cable and
a one-to-one butt-heads splicer. You can't do this with two crossover
cables, as you'll end up crossing everything over twice and creating
the equivalent of a straight-through cable... your splicer needs to
include a *third* crossover!

--
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
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Re: Why do we have cross-over cables.
On Tue, 10 Mar 2009 23:45:51 -0700, snipped-for-privacy@radagast.org (Dave Platt)

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 The problem is that when these systems of interface were designed, there
was nearly no automated assembly.

 Hand assembly means failures, unless error conditions are reduced to a
minimum.  Wiring both ends identically means that less errors were made
in manufacture of said interface devices and systems.  Making the switch
at the hardware itself was easy, and 100% repeatable.

  Prime pass yield was a huge consideration in labor intensive hand
operation production procedures, and still is.  That is why most
interface cables are pin-for-pin.  Particulalry those that have the same
or very similar connectors on each end.

Re: Why do we have cross-over cables.
On Tue, 10 Mar 2009 23:45:51 -0700, snipped-for-privacy@radagast.org (Dave Platt)

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 Also a very good reason to refrain from the idea.  It can easily be
incorporated into a gender change DONGLE as well.

Yes, folks, that term was in use LONG before software security keys used
it.

Re: Why do we have cross-over cables.
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The reasn this situation persists is that it is written into the
international standards, and a huge installed base of hardware out in
the field conforms to those standards.

I used to know about this when I worked for ITT-Creed in the U.K back
in 1979-1982, in a group that used to send people to the CCIT
standards committee meetings.

The concept dates back to the Telex and Teleprinter networks. The ASR
33 Teletype printer was orginally a data set (IIRR - 1982 is the last
time I was seriously involved) produced in huge numbers of the AT&T
network, and its use as a computer terminal was never more than a
minor spin-off.

http://www.iso.org/iso/livelinkgetfile?llNodeId3D%21523&llVolId3D%-2000

--
Bill Sloman, Nijmegen

Re: Why do we have cross-over cables.

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  Western Electric ALSO hand assembled practically everything back then,
and they knew about error rates in cable assemblies, and they knew how
best to reduce them by making remembering the wiring procedure an easy
thing to do.

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