Re: [EFM] Half-duplex deferral for MAC-PHY rate matching and compatibility with existing silicon
What is the case for <100 Mb/s
Jack Andresen
Rich Seifert wrote:
>
> 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@xxxxxxxxxxxxxxx 21885 Bear Creek Way
> (408) 395-5700 Los Gatos, CA 95033
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