Subject: Re: How does 10baseT/FDX work?
To: None <>
From: Jason Thorpe <>
List: tech-net
Date: 09/25/1999 19:19:10
On Sat, 25 Sep 1999 13:25:36 -0700 
 "Justin C. Walker" <> wrote:

 >   - external loopback is normally a diagnostic mode, so I don't know  
 > if the device would work differently than in "normal mode (does it  
 > require a loopback connector?); and

Agreed... in order for it to work, the chip has to be physically
wired to the board in such a way as it won't provide the loopback

 >   - this definitely won't get you N-way (autonegotiation) support,  
 > but most (some?) switches are configurable for this feature (finding  
 > out about it is another trick).  However, hubs and switches won't  
 > default to FDX, so for general use, you're looking at some trouble.   
 > If you're using this in a limited, controlled environment, it may  
 > work.

Right, but this is the same problem you have if you have one of
the original DEC Tulip chips (a 21040).  They could do full-duplex,
but Nway didn't appear in that line until the 21041 (which had a very
limited Nway block specifically for negotiating FDX with switches).

        -- Jason R. Thorpe <>