Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

RE: [EFM] Half-duplex deferral for MAC-PHY rate matching and comp atibility with existing silicon


I don't think GMAC is good idea for this applications. We need a system that
can deliver 100+ mbps (total=Tx+Rx >100) or 100 full duplex. It can be on a
single pair or multipair.

I think we can support an option to operate the EFM-MAC in half-duplex mode
as well which is enough for most single pair applications

I think you are correct that we should seriously consider to look into other
options for EFM-MAC.  This copper channel is very different as compared to
other Ethernet PHY channels


-----Original Message-----
From: Rich Seifert [mailto:rich@xxxxxxxxxxxxxxx]
Sent: Monday, December 10, 2001 9:25 AM
To: Behrooz Rezvani; 'Arthur Marris'; 'Shimon Muller';
Subject: 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:
>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 

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

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@xxxxxxxxxxxxxxx            21885 Bear Creek Way
(408) 395-5700                  Los Gatos, CA 95033
(408) 395-1966 FAX