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Re: [EFM] Half-duplex deferral for MAC-PHY rate matching a


      my point was actually not about loop aggregation, but on the business case for
more than 100Mb/s aggregate. I agree with Hugh that 100Mb/s duplex will not do much
because the services are mostly asymmetric. If we see >100Mb/s as a business case,
we probably need to consider something as GMII or really define a new "VMII". The
question for me still is, if definiton of the new MII is justified.


christophe.del-toso@xxxxxx wrote:

>      Vladimir, Steven, Arthur and all,
> I think that needs for more than 100 Mbps already exist today (at least in some
> regions of the world) and that generally speaking loop aggregation is a smart an
> appealling concept which can get a lot of momentum.
> Moreover,  deploying fiber to offer 100 Mbps on short loops while in some
> deployment scenario VDSL PHYs can do the job is not a cost effective solution.
> It is proven by theory and confirmed by early field trials (In ST, we did
> several field tests with a VDSL lab-prototype) that on short loops VDSL can
> offer aggregate bit-rates above 100 Mbps.
> I think it would be a pity to limit ourselves at the interfaces with higher
> protocol layers when we have today a PHY that can offer this possibility.
> I think we could regret it in the long run even if I should recognize that this
> business case will not be the most deployed but it will exist.
> I think that the MAC-PHY rate adapation through CRS is a smart solution for our
> problem in the short-terms. It will then allow VDSL PHYs to interface directly
> with conventional and standard ethernet MACs.
> In the other hand, I am wondering myself if, by anticipating long-term
> requirements, the group should also investigate the possibility to extend
> capabilities of MII interfaces by adding few signals.
> On this point I remember a presentation from Michael Beck (Alcatel) (in the
> Austin meeting) presenting the concept of VMII.
> I think that the first objective could be MAC-PHY rate adapation through CRS and
> that second objective could be something of the kind of VMII or something less
> but something that lets maximum freedom.
> Your comments are welcome !
> Regards
> Christophe Del-Toso, ST Micro
> ______________________________ Reply Separator _________________________________
> Subject: Re: [EFM] Half-duplex deferral for MAC-PHY rate matching a
> Author:  oksman (oksman@xxxxxxxxxxxx) at internet
> Date:    12/12/2001 01:23
> Arthur,
>       I would support Steven's idea. For a full duplex 100 Mb/s customer fiber w
> ill probably work better. I would like to notice that the expected aggregate cap
> acity of a VDSL link with loop length zero is close to 100 Mb/s. The first hundr
> eds feet will already reduce it significantly.
>       If we really consider a business case with a distance of 200-300 ft, I wou
> ld look for a fiber solution.
> Vladimir.
> Steven.Haas@xxxxxxxxxxxx wrote:
> > Arthur,
> >
> > Our experience has shown that the half duplex method is the safest way and wor
> ks 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 obj
> ectives.
> >
> > The only drawback is the "limitation" of 100Mbps. This can be overcome with mo
> st 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 ve
> ry 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 c
> ases of rates above 100Mbps.
> >
> > A third option is to create a jump in supported service rates from 100Mbps hal
> f 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 ati
> bility 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@xxxxxxxxxxxxxxx            21885 Bear Creek Way
> > (408) 395-5700                  Los Gatos, CA 95033
> > (408) 395-1966 FAX