RE: [EFM] Half-duplex - definition of a repeater
Bob,
I had an e-mail discussion about this with Geoff Thompson several months
ago. His comment that there was nothing in the current standard that
defined a full duplex "repeater". He did say that for 100Mb, a FDDI
repeater could be used because of the encoding scheme that was used for
100BaseX. As he is the co-author of much of the "repeater" clauses in the
standard, he would be best qualified to answer that question.
Thank you,
Roy Bynum
At 10:52 AM 12/11/2001 +0000, Bob Barrett wrote:
>General question:
>
>Is the 802.3 definition of a repeater explicitly limited to half duplex
>only?
>
>I am only asking this here for the sake of expediency. I could go through
>the CDROM but that would take me a day and I still wouldn't be sure of the
>negative answer.
>
>I guess there is a supplementary question that members of this group may
>ask, which is 'why would anybody want a full duplex repeater?'. The answer
>being 'as a full duplex media converter, with management'. If there isn't a
>definition for this within 802.3 then would anybody be interested in
>supporting a proposal to create a standard definition for one?
>
>Please respond to this directly rather than busy the reflector.
>
>Thanks
>
>Bob
>
> > -----Original Message-----
> > From: owner-stds-802-3-efm@majordomo.ieee.org
> > [mailto:owner-stds-802-3-efm@majordomo.ieee.org]On Behalf Of Rich
> > Seifert
> > Sent: 10 December 2001 17:25
> > To: Behrooz Rezvani; 'Arthur Marris'; 'Shimon Muller';
> > stds-802-3-efm@ieee.org
> > 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 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