RE: [EFM] Half-duplex deferral for MAC-PHY rate matching and comp atibility with existing silicon
At 7:17 AM -0800 12/10/01, Behrooz Rezvani wrote:
>Arthur,
>
>As I mentioned in our conference call we need to support data rate greater
>than 100 Mbps in total. As I have been listening to you, Rich and Shimon, I
>gather that there is a way to operate the MAC such that we can exceed the
>half duplex rate.
Operating at data rates in excess of 50 Mb/s (full duplex) would be
problematic with the system being proposed so far. Since it is
predicated on a single, 100 Mb/s MAC operating in half-duplex mode,
the combined transmit+receive rate cannot exceed 100 Mb/s; this is
the equivalent of a 50 Mb/s symmetrical full-duplex PHY.
In order to operate at greater data rates, one would need to use a
Gigabit MAC operating in half-duplex mode. Such MACs are relatively
rare; indeed, even if they exist, the use of half-duplex GbE is more
theoretical than practical--there are no GbE repeaters in commercial
use. It is not even clear that such MACs work properly in half-duplex
mode.
In addition, it is not possible to aggregate multiple 100 Mb/s MACs
when operating in half-duplex mode. The current Link Aggregation
standard restricts aggregation to full-duplex links only.
>Note that VDSL PHY is full duplex system, and it can transmit and receive
>independently.
>
I suspect that EFM will want to operate over a variety of PHY types
and speeds. Rather than trying to cobble all of these systems to some
pre-existing MAC chips (which I agree may provide some short-term
benefit), perhaps it would be wiser in the long run to define a
full-duplex MAC with a variable (quasi-static) data rate.
--
--
Rich Seifert Networks and Communications Consulting
rich@richseifert.com 21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 395-1966 FAX