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1000Base-T, Crossover?

masterk

Hello all

I understand that 1000Base-T uses all four pairs to send AND receive data (each pair is bi-directional). So if Auto MDIX was switched off, and there was no auto sensing........why would you need a crossover cable to connect a switch to a switch if all pairs send and receive?

Any help appreciated!!

Thanks

Jamie

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Comments

Priston

giga-bit crossover cables have a different pinout.

Gigabit Ethernet crossover cord pin layout

If you used a straight-through, your sends pins on switch 1 would connect to your send pins on switch 2 and your receive pins on switch 1 would connect to your receieve pins on switch 2. Which won't work.

When you use the crossover your send pins on switch 1 connect to the receive pins on switch 2 and your send pins on switch 2 connect to the receive pins on switch 1.

SteveThing

What he said... beat me to it.

masterk

Thanks guys but i think you might have missed the question slightly. I know how a crossover cable works, but 1000Base-T sends and receives on all pairs, not just sending on some and receiving on others, so if there are no particular pairs that send or receive and they do both, why is there still a need for a crossover cable?

tha_dub

Maybe I've just been lucky but doesn't all the the gig ethernet support auto mdi mdi-x ?

I checked Wikipedia and it said although it's an optional part of the standard it is always implemented...

I guess here we have an exception. What kind of crap branded Ethernet card did you buy?

;)

masterk

Its pure theory!!

I just wanted to know why there is still the concept of a crossover cable in gig ethernet, if there are no specific twisted pairs that just send or receive data.

alan2308

tha_dub wrote: »

it is always implemented...

That's the kind of assumption that will cause no end of frustration one day.

Priston

[FONT=Arial,Bold]Did some research.[/FONT]
[FONT=Arial,Bold][FONT=Arial,Bold][FONT=Arial,Bold][FONT=Arial,Bold]read "40.1.3 Operation of 1000BASE-T" in section3, page 151[/FONT][/FONT][/FONT][/FONT]
[FONT=Arial,Bold][FONT=Arial,Bold]"40.8.2 Crossover function" in section3, page 229[/FONT]
[/FONT]
[FONT=Arial,Bold][FONT=Arial,Bold][FONT=Arial,Bold]http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf[/FONT]
[FONT=Arial,Bold]http://standards.ieee.org/getieee802/download/802.3-2008_section2.pdf[/FONT]
[FONT=Arial,Bold]http://standards.ieee.org/getieee802/download/802.3-2008_section3.pdf[/FONT]

[FONT=Arial,Bold]Not sure if this helps or makes you more confused [/FONT]
[/FONT][/FONT]