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




     In that case I think I can subscribe ;-)
     Cheers
     CDT


______________________________ Reply Separator _________________________________
Subject: Re: [EFM] Half-duplex deferral for MAC-PHY rate matching a
Author:  hbarrass (hbarrass@xxxxxxxxx) at internet
Date:    12/12/2001 16:54


Christophe,
     
As I said in my e-mail
     
2. We have an augmentation that will work for most existing and all future MACs 
which allows 100Mbps full duplex data transfer. That is as fast as you will get 
with an MII interface. It's perfect - you cannot do any better.
     
I will say it again:
     
YOU CANNOT DO ANY BETTER!
     
The maximum possible data rate that an MII interface will go is 200Mbps aggregat
e (100Mbps in each
direction). I you want any more go to GMII.
     
Hugh.
     
christophe.del-toso@xxxxxx wrote:
     
>
> Hugh,
>
> I don't want you to misunderstand my concern.
> Arthur's proposal is a smart solution and I like it.
> Moreover, it limits buffering in the PHY which is a good point.
> However my concern is that I want to be sure that we don't miss applications 
> which could require rates above 100Mbps.
>
> If we can be sure that all existing MACs configured in half-duplex mode can
> continue to receive packets while transmitting thus making a workaround to the
> 100Mbps bottleneck then I will definetly support this concept.
> This solution is for sure plug and play and off-the-shelf ;-) 
>
> The point I was raising is that this solution even accepted may not preclude t
o
> envision future MAC evolutions with support of a VMII or similar concept while
> keeping backward compatibility with today's MACs.
> >From what I understood the VMII concept was not to fundamentaly change the MA
C
> specs.
> Now, if we can impose in future MAC designs that even when working in
> half-duplex mode a MAC shall continue to receive packets thus solving our issu
e
> it simplifies all the problems
>
> VBR
> Christophe
>
> ______________________________ Reply Separator _______________________________
__
> Subject: Re: [EFM] Half-duplex deferral for MAC-PHY rate matching a 
> Author:  hbarrass (hbarrass@xxxxxxxxx) at internet
> Date:    12/12/2001 15:29
>
> Christophe,
>
> Arthur has already proposed a scheme using deferral which will work with all c
ur
> rent
> MACs. As has been pointed out the limitation of Arthur's scheme is that it is 
> genuinely half-duplex and so may only support an aggregate data rate of 100Mbp
s.
> However, Shimon Muller pointed out that any MAC which is designed according to
 t
> he
> specification will work with deferral (as Arthur suggests) but may also receiv
e
> while transmitting in half-duplex mode. Some of us think there is some risk in
> assuming that all existing MACs will work like this and so we would like to ma
ke
> this operation optional in the PHY. However, we can make it obligatory that fu
tu
> re
> MAC designs work in this manner by making the MAC specification more explicit.
>
> Let me summarize:
>
> 1. We have a proposal that we know will work for every existing MAC. 
>
> 2. We have an augmentation that will work for most existing and all future MAC
s
> which allows 100Mbps full duplex data transfer. That is as fast as you will ge
t
> with
> an MII interface. It's perfect - you cannot do any better. 
>
> Remind me again, why do you want to invent more schemes? 
>
> Hugh.
>
> 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 s
om
> e
> > regions of the world) and that generally speaking loop aggregation is a smar
t
> 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 solutio
n.
> > 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 t
hi
> s
> > 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 
ou
> r
> > problem in the short-terms. It will then allow VDSL PHYs to interface direct
ly
> > 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
 a
> nd
> > that second objective could be something of the kind of VMII or something le
ss
> > 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 fib
er
>  w
> > ill probably work better. I would like to notice that the expected aggregate
 c
> ap
> > acity of a VDSL link with loop length zero is close to 100 Mb/s. The first h
un
> dr
> > eds feet will already reduce it significantly.
> >       If we really consider a business case with a distance of 200-300 ft, I
 w
> ou
> > 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
 w
> or
> > ks with most MACs. The CRS can always be used to control the flow of frames 
fr
> om
> >  the MAC to the PHY, even at all the different rates proposed for EFM copper
 o
> bj
> > ectives.
> > >
> > > The only drawback is the "limitation" of 100Mbps. This can be overcome wit
h
> mo
> > st MACs using a flow control message (802.3x). This method is not watertight
 a
> nd
> >  not all MACs process this in a timely fashion so buffers are needed in the 
PH
> Y.
> >  The case of an EFM PHY working above 100Mbps will most likely only happen i
n
> ve
> > ry short range loop aggregation scenarios when there are multiple lines goin
g
> to
> >  a business customer. I expect fiber to be used in these cases so creating a
 n
> ew
> >  MAC seems unnecessary.
> > >
> > > I propose the following engineering tradeoff:
> > > 1. Use of the half duplex method for most modes of operation. This covers 
al
> l
> > rates up to 100Mbps aggregate.
> > > 2. Usage of flow control, combined with the appropriate buffers, in the ra
re
>  c
> > ases of rates above 100Mbps.
> > >
> > > A third option is to create a jump in supported service rates from 100Mbps
 h
> al
> > 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'; stds-802-3-efm@ieee
.o
> rg
> > > Subject: RE: [EFM] Half-duplex deferral for MAC-PHY rate matching and comp
 a
> ti
> > 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 greate
r
> > > >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
> >
> >
>