RE: Short haul PMDs
So, does anyone have data on what percentage of Gigabit Ethernet links
ship with 1000BASE-CX?
From: Geoff Thompson [mailto:gthompso@xxxxxxxxxxxxxxxxxx]
Sent: Wednesday, August 02, 2000 4:45 PM
To: Hakimi, Sharam (Sharam)
Subject: RE: Short haul PMDs
I think 15 years is a slight exaggeration. 10BASE-T started as a Study
Group in August of 1987. It was the first group to have a 100 meter
Before 10BASE-T there was the following:
10BASE5 + AUI The AUI cable was 50 meters max
10BASE2 The coax was daisy-chained w/ an overall max of 185m
1BASE5 (StarLAN) The hub to DTE distance was 250 m
10BROAD36 Broadband diameter of 2800 meters
FOIRL 1000 meter links
The point here is that topology has evolved as well as speed.
We have in the recent past had a distance objective for short cables in
802.3z (ref: 1000BASE-CX).
The 100 meter distance history is rooted in facilities cabling and is based
on the (literally) cast-in-concrete distance of 90 m max from the cabling
closet to the telecommunications outlet.
If the prime market for an Ethernet project is not oriented to
"in-the-wall" cabling then the 100 meter distance is not sacrosanct. The
objective for 100 meters as approved in York was for "installed" cabling
from ISO/IEC 11801. That means that we were talking about generic
facilities cabling at the time, not application specific cabling.
If we do go to application specific cabling then we have to do the
specification in our own standard instead of referencing an outside cabling
standard such as ISO/IEC 11801.
At 11:16 AM 8/2/00 -0400, Hakimi, Sharam (Sharam) wrote:
>During the past 15 years and through all of 802.3 distance Objectives, 100
>meters has been the minimum and essentially the trademark of IEEE 802.3.
>There has always been discussions that if the distance is reduced we can
>provide less expensive PHYs, but the cost difference never justified
>development of these PHYs . Providing 100 meter solutions does not prevent
>anyone from using a 10, 20, 30 or other length cables as their needs
>require. However, if time has come that the cost difference between a 100
>meter solution and something less will justify such development then we
>could look at it later, but changing the objectives at this time is a BAD
>idea in my opinion.