[vortex] Sorry to trouble you, I wonder if you could help me.

BIWU.XIE biwu.xie@mic.com.tw
Wed Apr 17 23:34:02 2002

Dear Boqdan,

       Thank you for your help and kindness. Now I know more about MAC
loopback and PHY loopback. :-)

	Exactly how to do remote loopback control is an issue. somebody is
trying to decide.  In general, a signal is sent to the other end of the
link.  That signal may be carried within the preamble bits or within an
Ethernet control frame.  The signal is intepreted by the far end as an
indication to go into loopback mode, where either bits or frames are
received and then echoed out the interface.  
	I want to know what your idear about that?

	You know that the MAC loopback test occurs before the transceiver,
while the PHY loopback occurs after the transceiver.

So I have another detail questions:
How to decide the  MAC loopback test and the PHY loopback test success or

Best regards.

-----Original Message-----
From: Bogdan Costescu [mailto:bogdan.costescu@iwr.uni-heidelberg.de] 
Sent: 2002?4?18? 1:57
To: biwu.xie [???]
Cc: 'vortex@scyld.com'
Subject: Re: [vortex] Sorry to trouble you, I wonder if you could help me.

On Wed, 17 Apr 2002, [big5] biwu.xie [¥Z] wrote:

> 1) what are MAC loopback and PHY loopback?

AFAIK, a loopback means that the Tx path is wired to the Rx path, so that 
whatever is sent comes back immediately. The fact that you have them 
integrated on the card makes easy to test both paths without the need for 
an external device.

> 2) I know that remote loopback can check PHY/MAC level loop back for each
> layer health. But how to do remote loopback?

Uh, what is a "remote loopback" ?

>    Wish you can give me some experience and documents about them.

You can always register for free as a developer on the 3Com site and have 
access to the documentation in PDF format. That's all I have, anyway.

Bogdan Costescu

IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen
Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY
Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868
E-mail: Bogdan.Costescu@IWR.Uni-Heidelberg.De