RE: 850 nm solutions
Infiniband will be using something very similar to the HARI interface over
short copper links though the distance goal is, I think, 6 m. To travel over
short copper cables, it may make sense to use a 4 wide signal from HARI
rather than 10 Gbit/s serial.
From: Rick Walker [mailto:walker@xxxxxxxxxxxxxxxxx]
Sent: Wednesday, April 19, 2000 4:58 PM
Subject: Re: 850 nm solutions
> Jim Tatum writes:
> But why does it matter? Why limit the users? Why not put in the table. It
> costs nothing. Just put in what the model and data tell us to. It is
> my opinion that a large percentage of 10GB style links are going to be
> very short, less than 10m. If you look at the way many fiber ports
> are being used today, many are in the 10m range. Also, since copper
> cables are going to be EXTREMELY challanged to go that distance at
> 10GB, why not let the market choose the lowest cost solution using
> 850nm VCSELs and 62.5um fiber?
FWIW, I agree that 10G across CAT-6 or other twisted pair would be very
difficult. However 10G across coaxial cable is fairly easy. It can be
done with 0.1" diameter coaxial cable using simple NRZ data encoding. A
simple FIR pre-equalizer can double this distance. Without a doubt
copper would be the cheapest solution for links under 10M. I would
estimate a mature chipset price of about $50 per end and $15 for the
This performance was demonstrated in 1998 using a 25GHz bipolar chipset.
See: Walker, R. C., K. Hsieh, T. A. Knotts and C. Yen, "A 10Gb/s
Si-Bipolar TX/RX Chipset for Computer Data Transmission" , ISSCC Digest
of Technical Papers 41(February 1998), 302,303,450.
A Copper PHY was voted down by the committee because it was thought that
there was no market for this type of low-cost short distance link.