straight-through / cross-over RJ45: interchangeable: why?

straight-through / cross-over RJ45: interchangeable: why?
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Subject Author Date
straight-through / cross-over RJ45: interchangeable: why? Bicycle6228 07-01-2007
Posted by Bicycle6228 on July 1, 2007, 3:08 pm
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: quoted-printable

Everywhere I read about this, straight-through and cross-over RJ45 =
ethernet cables are _not_ interchangeable:

http://www.microsoft.com/windowsxp/using/networking/expert/russel_hni.msp=
x
" ... straight-through and cross-over cables ... the two are not =
interchangeable ..."

=3D>however<=3D
1) Two PC's connected via crossover cable: connectivity OK
2) Add a 3rd PC and hub*, using the _same_ crossover cable from the =
server now to the hub.=20
3) Connect Client1 to the hub using another crossover cable.
4) Connect Client2 to the hub using a third crossover cable.
This couldn't possibly work I thought, but the above described 3-station =
Win98 network using specified IP addresses, appears to be working fine =
at a local business I assisted this week, and there's doesn't appear to =
be the slightest difference in performance of the network and their =
application.

Why does this work?
*Is this success of this dependant upon the use of a hub vs. router vs. =
switch?=20
I didn't take a good luck at the 5-port hub, router or switch they have.
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<DIV><FONT face=3DArial size=3D2>Everywhere I read about this,=20
straight-through&nbsp;and cross-over RJ45 ethernet cables are _not_=20
interchangeable:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><A=20
href=3D"http://www.microsoft.com/windowsxp/using/networking/expert/russel=
_hni.mspx">http://www.microsoft.com/windowsxp/using/networking/expert/rus=
sel_hni.mspx</A></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>" ... straight-through and cross-over =
cables ...=20
the two are not interchangeable ..."</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>=3D&gt;however&lt;=3D</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>1)&nbsp;Two PC's connected via =
crossover cable:=20
connectivity OK</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>2) Add a 3rd PC and hub*, using the =
_same_=20
crossover cable from the server now to the hub. </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>3) Connect Client1 to the hub using =
another=20
crossover cable.</FONT></DIV>
<DIV>
<DIV><FONT face=3DArial size=3D2>4) Connect Client2 to the hub using a=20
third&nbsp;crossover cable.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>This couldn't possibly work&nbsp;I =
thought, but the=20
above described 3-station Win98 network using specified IP addresses, =
appears to=20
be working fine at a local business I assisted this week, and there's =
doesn't=20
appear to be the slightest difference in performance of the network and =
their=20
application.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Why does this work?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>*Is this&nbsp;success of =
this&nbsp;dependant upon=20
the use of a hub vs. router vs. switch? </FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I didn't take a good luck at the 5-port =
hub, router=20
or switch they have.</FONT></DIV></DIV></BODY></HTML>

------=
NMFall 20%
Posted by glen herrmannsfeldt on July 1, 2007, 4:02 pm
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Bicycle6228 wrote:

>
> Everywhere I read about this, straight-through and cross-over RJ45
> ethernet cables are _not_ interchangeable:

(snip)

> 1) Two PC's connected via crossover cable: connectivity OK
> 2) Add a 3rd PC and hub*, using the _same_ crossover cable from the
> server now to the hub.
> 3) Connect Client1 to the hub using another crossover cable.
> 4) Connect Client2 to the hub using a third crossover cable.
> This couldn't possibly work I thought, but the above described 3-station

More and more hubs (in the generic sense) have auto MDI-X, that is,
auto crossover detection. This is especially true for gigabit
which requires drivers on all four pairs.

Otherwise, it is usual to have one port switchable between
MDI and MDI-X so you would be able to use one crossover cable.

-- glen


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