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Why need to re-plug the LAN cable to restore the link ?

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Junior Member level 2
Oct 19, 2012
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What's the difference if replug LAN cable at board side or at switch side

I met with an issue when design with Intel I210. Connect my board and a switch with LAN cable, then power on the board, sometimes the link fails, and can be restored by re-plugging the LAN cable.
The issue happens when board connect to several models of switch and PC, while others never happen.

When duplicate the issue, I found an interesting phenomenon that sometimes I replug at the board side for many times, it will not restore, then replug at the switch side for just one time, the link restored.

My question is, what the difference if I replug at the board side or at switch side ?

I met with a problem when design with the ethernet controller I210(Intel chip). When LAN port connect with several brand of switch, the link failed after power on, and could be restored by replug the LAN cable. When the LAN port connect with other switch, the problem won't happen.

I have no idea with this issue. Anyone could help me ?

"Link failed" is a bit vague, particularly if said by somebody designing a network interface.

Are you talking about physical link failure, or some problem on the network layers? What do you see at the management interface? Do the negotiated interface parameters change? What's signalled by the switch (e.g. speed)?

My first guess would be inconsistent PHY parameters, respectively parameters not supported by your actual interface, possibly some default PHY settings after power-on.

It could be also a signal integrety problem of your board, resulting in unrealiable 1 GBit links.

Physical layer link issue. I judge the issue from LED status. When link up, LED on RJ45 connector is on, while it's off when link is down. When issue happened, ping I210 fails either.

It should not be SI problem, because once replug the cable the link would restore, and issue never happens again before power off. And I have tested the signals without any problem.

I'm wondering the parameters also, and tried to disable EEE function(=low power mode). But it didn't work.

I tested the signal at RJ45 pins when the issue happened, found there was sleep--pulse--sleep--pulse cycle. It seems related to sleep--refresh--sleep--refresh mechanism at below picture shows:

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