Why do we have cross-over cables. - Page 4

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Re: Why do we have cross-over cables.
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situation.
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Yep. All you have to do is establish communication first, so that you
can decide whose turn it is.

Sylvia.

Re: Why do we have cross-over cables.
On Thu, 12 Mar 2009 20:36:48 +1100, Sylvia Else

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situation.
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Even when "communication"fails, as in no handshake acknowledged, the
exchange will eventually match, with 'eventually' being a fairly quick
process.  In dumb systems handshake simply fails.

 In a smart system, it senses the presence of the comm cable, but the
failed handshake sets off the pair swap retry.

Re: Why do we have cross-over cables.
On Thu, 12 Mar 2009 20:36:48 +1100, Sylvia Else

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situation.
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It's pretty much like calling someone on the phone.

You're familiar with that procedure, aren't you?

JF  

Re: Why do we have cross-over cables.

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situation.
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logical
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need
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She probably is. And with a small group of callers making a lot of
calls to each other it is likely that none of them will ever get
through. Everyone will get the engaged signal because the called party
is dialing someone else.
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Re: Why do we have cross-over cables.

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situation.
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That is how Token Ring works but not Ethernet. Ethernet uses a
"cocktail party" protocol where you wait for a pause in the
conversation before speaking and, if after you start, someone else is
speaking you back off until there is another pause. It's usually
efficient but if the group is too large and a few speakers are too
verbose there will be no communication. Token Ring works by passing
the microphone around the group so that everyone who has something to
say gets a chance to say it. It can't catastrophically fail but, for
normal conversation, it can be extremely slow.

Re: Why do we have cross-over cables.

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situation.
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So you're supporting Sylvia's position?

JF  

Re: Why do we have cross-over cables.

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situation.
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logical
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need
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Obviously, I think she is right in this sub-thread. I also tend to
agree with her original post although others have explained why,
historically, a crossover cable was not standard and why there was a
distinction between terminal and communication equipment.

The only point I might disagree with her on is the assumption that
"this situation persists". Modern interfaces, like USB, use a single
pair of wires for communication which avoids the problem.

Re: Why do we have cross-over cables.

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 A cross-over cable most certainly WAS and IS the standard for attaching
two like terminals through this interface (serial)

  When will you grasp the concept, dolt?

Re: Why do we have cross-over cables.

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You seem to have missed the point of the OP's question. You are
excused because you are of an age when an RS232 or Centronics
interface was normal.

As other posters have pointed out it was cheaper to manufacture
straight through cables and in those days there was a clear
distinction the devices at each end of a cable. Pin n of one device
could reasonably be defined as a receiver and Pin n of the "other"
device could be defined as a transmitter. In the last thirty years
that has changed and today it is preferable to treat all devices as
peers.

The OP wanted to know why the distinction between devices existed
rather than _always_ connecting them with a crossover cable. It was a
perfectly reasonable question and she has been provided with sensible
answers by those who managed to understand it.

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Re: Why do we have cross-over cables.

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 It is an entirely different schema altogether.  Wake up.

Re: Why do we have cross-over cables.
On Fri, 13 Mar 2009 09:57:23 -0500, John Fields

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  Remember TCNS?  I think it was token ring.  It had hubs all over the
place.

  Thomas Conrad Network Systems.

  I remember Tandy's 'Arcnet' at 150kb/s  (small 'b').  :-)

Re: Why do we have cross-over cables.
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It's not really relevant anyway. Neither a token ring, now Ethernet's
backoff approach, can work before it's been established which wires are
which.

There may be a standard that describes the process of identifying the
wires. Whether there is is what I asked.

Sylvia.

Re: Why do we have cross-over cables.
On Sat, 14 Mar 2009 11:55:24 +1100, Sylvia Else

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It never was.
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Re: Why do we have cross-over cables.

Typo. Should have been obvious.

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Sometimes. Sometimes not.

If you know of a standard, then why not provide a reference?

Sylvia.

Re: Why do we have cross-over cables.
On Sat, 14 Mar 2009 22:32:51 +1100, Sylvia Else

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As should have been the reason why we have crossover cables.
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Re: Why do we have cross-over cables.
On Sat, 14 Mar 2009 22:32:51 +1100, Sylvia Else

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  If you know how to use Google, why be a lazy ditz?

Re: Why do we have cross-over cables.
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Here you go: <http://en.wikipedia.org/wiki/Ethernet_crossover_cable
And: <http://en.wikipedia.org/wiki/Auto-MDIX for the auto detection
standard.


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


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I don't think it requires a "standard" to identify the wires. A NIC
must be able to identify a valid packet so swapping two wires until it
does so is not a demanding task now that a microprocessor is
incorporated on every device.

Re: Why do we have cross-over cables.
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I was thinking that a standard would be required that specified the
delays, or the means of calculation of the delays, to be used between
trying different combinations, so as to avoid the situation where two
NICs undermine each other's attempts to find a working combination.

Sylvia.

Re: Why do we have cross-over cables.

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I think you will find what you are looking for in "IEEE 802.3 LAN/MAN
CSMA/CD Access Method"
<http://standards.ieee.org/getieee802/802.3.html> but I have not read
it.

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