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

Use of only low data rate for VDSL has not been our experience. We in fact
have seen a demand for 100 Mbits inside medium size buildings for reaches of
1000+ ft (over 2-4 pairs of copper) where fiber has been brought in to the
basement . For example this topic was covered in Stanford Conference by
YIPES. Aside from 50+ stories, class A buildings, which are small in
percentages (they use fiber) everybody else likes copper, saves them money.
There is an excellent report by Robertson Stephens, Inc. in Comm. IC section
regarding the aspect of pulling fiber and the cost and the time associated
with that.

I think we should not limit our capability by allowing only half-duplex
operation mounting to 100 Mbps in total. As I mentioned before we can adopt
this method as one of the options but not the only possible method because
it is not enough for all applications.


-----Original Message-----
From: Vladimir Oksman [mailto:oksman@xxxxxxxxxxxx]
Sent: Tuesday, December 11, 2001 4:24 PM
To: Steven.Haas@xxxxxxxxxxxx
Subject: Re: [EFM] Half-duplex deferral for MAC-PHY rate matching
andcomp atibility with existing silicon


      I would support Steven's idea. For a full duplex 100 Mb/s customer
fiber will probably work better. I would like to notice that the expected
aggregate capacity of a VDSL link with loop length zero is close to 100
Mb/s. The first hundreds feet will already reduce it significantly.
      If we really consider a business case with a distance of 200-300 ft, I
would look for a fiber solution.


Steven.Haas@xxxxxxxxxxxx wrote:

> Arthur,
> Our experience has shown that the half duplex method is the safest way and
works with most MACs. The CRS can always be used to control the flow of
frames from the MAC to the PHY, even at all the different rates proposed for
EFM copper objectives.
> The only drawback is the "limitation" of 100Mbps. This can be overcome
with most MACs using a flow control message (802.3x). This method is not
watertight and not all MACs process this in a timely fashion so buffers are
needed in the PHY. The case of an EFM PHY working above 100Mbps will most
likely only happen in very short range loop aggregation scenarios when there
are multiple lines going to a business customer. I expect fiber to be used
in these cases so creating a new MAC seems unnecessary.
> I propose the following engineering tradeoff:
> 1. Use of the half duplex method for most modes of operation. This covers
all rates up to 100Mbps aggregate.
> 2. Usage of flow control, combined with the appropriate buffers, in the
rare cases of rates above 100Mbps.
> A third option is to create a jump in supported service rates from 100Mbps
half duplex to 100Mbps full duplex.
> Steven
> -----Original Message-----
> From: Rich Seifert [mailto:rich@xxxxxxxxxxxxxxx]
> Sent: Monday, December 10, 2001 7:25 PM
> 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:
> >Arthur,
> >
> >As I mentioned in our conference call we need to support data rate
> >than 100 Mbps in total. As I have been listening to you, Rich and Shimon,
> >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
> (408) 395-1966 FAX