----- Original Message -----
Sent: Tuesday, March 14, 2000 10:57
PM
Subject: RE: Unified PMD vs. Unified
PHY
I did not know if this was correct for the reflector, so I
thought I would take this offline.
While the average size of ~380 may be correct, this new
standard is for the future. The current ~380 byte size I believe is due
to the presence of predominately a Wintel architecture throughout the Internet
community. The current installed base of Wintel 95/98 dial-up networking
uses a default IP MTU of 576 for all connections less than ISDN 2B
(128Kbit/sec). That means to me:
Dial-up connections over the next few years are being replaced
with technologies that push the average packet size way up:
* Cable-modems, Satellite and xDSL - 1500 MTU
* E business-business transactions - 1500 MTU
*
VPN tunnels. - default MTU + VPN wrappers
*
Faster speeds mean more graphics-rich traffic as the users continue to crave
higher bandwidth commodities (Video, Audio, Visually Interactive content,
etc...) These tend to fill up the TCP receive window with more full-size
packets versus smaller ones.
* Selective acknowledgements being added to the installed base
now mean the 20-40 byte ack packets that drive the average down low now will
continue to wane.
* Win2K support of RFC-1323 TCP options for very large TCP
receive windows (640Kbytes+) will mean many more (400+) full-size
packets can be "in flight" before the small ack packets are seen.
I believe these will all push the average packet size up quite
a bit, while voice over IP will tend to want to drive it down.
I guess what I am saying is that I think 400 maybe too small
to assume. I am not arguing for or against the Uniphy just sharing some
experience...
As a side note, where I hang my work hat these days, we are
using 9Kbyte Jumbo Frame Ethernet since we cannot afford the CPU overhead of
even single GigE speeds on current systems. The TCP
segmentation/checksum operations are just too great with these small (1500)
MTU packets to utilize the speed of our GigE pipes. As the adapters/OS
interfaces get smarter, some of this will get better I am sure, but much
larger would be better for almost everything except the Internet. Vendor
complain about the compatibility and ASIC troubles, but the users have to live
with things for many years after the ASICs are done and the products are no
longer being sold. Current architectures just do not have the capability
to do all this well. We are only running normal business apps SAP,
Database, WP, Printing, etc... for these things. (no specialty
seismic, simulation, etc...) Besides, even Bob Metcalf said if he could
change one thing, it would be to make the MTU larger.
Thanks for your time, you all have a lot to work out, but I am
sure you will get there.
Good Luck...
-Corey McCormick
CITGO Petroleum
-----Original Message-----
From:
Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
Sent: Tuesday, March 14, 2000 8:34
AM
To: Benjamin J. Brown;
802.3ae
Subject: Re: Unified PMD vs.
Unified PHY
Ben,
The expense in transfer rate is an addtional 3% above the ~4%
of the SONET
framing. This makes the total
bandwidth expense of the Unified PHY close to
7%. This is almost half of the overhead cost of ATM.
With the proposal of IPG compression in the PHY, most of the
~4% overhead of
the SONET framing can be
recovered. The overhead recovery will be more
effective with small frames than with large frames, but I believe that
it
will average out. At present, I have been
told that the average IP datagram
on the Internet is
380 bytes. This is the same as it was two years ago, so
it does not seem to be shifting very much. From this information,
an
average of 400 bytes can be somewhat safely used to
determine the average
overhead recovery that can be
achieved with frame stuffing as proposed by
Nortel and
Lucent. With a reduction of the IPG by 10 bytes, using an
average 400 byte frame (with current IPG, 420bytes), 2.3%
average overhead
recovery can be added to the MAC
transfer rate.
With IPG recovery using frame stuffing, the overhead cost of
the WAN phy
becomes ~1.7%. Compared to the ~7%
overhead of the 64B/66B proposal, that is
a difference
of 6.3%. This makes the cost of the unifed PHY at least
6.3%
greater than the seperate WAN PHY. I think
that the original compromise and
the objectives as
stated are correct, there needs to be seperate LAN and WAN
PHYs.
Thank you,
Roy Bynum
----- Original Message -----
From:
Benjamin J. Brown <bebrown@xxxxxxxxxxxxxxxxxx>
To: 802.3ae <stds-802-3-hssg@xxxxxxxx>
Sent: Monday, March 13, 2000 8:50 AM
Subject:
Re: Unified PMD vs. Unified PHY
>
>
>
Roy,
>
> Let's please
keep this on the reflector so everyone can follow
>
along with the discussion. This way, others with similar concerns
> or questions won't be kept in the dark.
>
> A question has been raised regarding
how tightly coupled the
> XAUI and 64b/66b
encodings are or need to be. Several people,
>
including me, have voiced the opinion that there shouldn't
> be any requirement that 64b/66b uses the encoding of XAUI.
>
> As for the expense in
transfer rate, I'm a little confused. I
> believe
Howard Frazier pointed out that over WAN, the 64b/66b
> encoding scheme is somewhat less efficient (3%?) than a
> scrambled encoding. I agree this is an issue worth
discussing
> but it is a PCS issue, not a PMD
one.
>
> Look at a
serial PHY. From the MAC to the PCS is an XGMII.
>
Some implementations may choose to extend this XGMII using
> XAUI but this interconnect is optional. The PCS should not
> require any features of the XAUI. The PCS encodes the
MAC
> data from the XGMII then this data is
serialized and driven
> onto the fiber. The
encoding scheme within the PCS is the
> factor
which determines the required baud rate on the fiber.
>
> Because we chose to make as an
objective the support of a
> WAN compatible PHY, we
chose a baud rate of 9.95328 G for
> the PMA/PMD.
To share this PMA/PMD with serial LAN solutions
>
(in order to reduce the number of discreet PMA/PMDs in the
> standard), we'd like to choose an encoding scheme for the
> LAN which shares this baud rate (or something close
enough
> that works). We're kind of working this
problem backwards.
>
>
We'd also like to have a common encoding scheme (or as
> common as possible) between the WAN and the LAN. For both
> of these reasons, we're looking at 64b/66b and
scrambling.
> Both of these can support a common
baud rate necessary to
> reduce the number of
PMA/PMDs and a common encoding scheme
> necessary
to support the results of Jonathan's survey.
>
> Ben
>
> Roy Bynum wrote:
> >
> > Ben,
> >
> > Gb-Mtr is an acronym that I
created because I quickly got tired of
> >
repeatedly spelling out "Gigbit MAC transfer rate". The real
question
was
> > not
relative to the baud rate of a LAN PMD vs a WAN PMD, but the
confusion
> > that has been introduced by
the effort to "unify" the PHY. XAUI/64B66B
>
> encoding makes XAUI a requirement, and efforts to reduce the PMD rate
to
a
> > single common
is going to be very expensive in transfer rate. By
abandoning
> > the "Hari" based 8B10B
block encoding, the frame stuffing proposals by
>
> Nortel and Lucent give the ability recover much if not all of the
MAC
> > transfer rate.
> >
> > Johnathan has been using
the object of having common PMDs as the reason
for
> > supporting a PHY that provides a
specific vendor the ability to maintain
the
> > 8B10B to be required at the MAC chip. The
issue is to segregate the
issue
> > of common PMDs from that of a common PHY, so that the
requirement for
8B10B
>
> can be released.
> >
> > Thank you,
> > Roy Bynum
> >
> > ----- Original
Message -----
> > From: Benjamin J. Brown
<bebrown@xxxxxxxxxxxxxxxxxx>
> > To:
802.3ae <stds-802-3-hssg@xxxxxxxx>
> >
Sent: Sunday, March 12, 2000 3:27 PM
> >
Subject: Re: Unified PMD vs. Unified PHY
>
>
> > >
> >
>
> > > Roy,
>
> >
> > > I realize you asked your
question to Jonathan, but if you don't
> > >
mind I'll try an answer to this.
> > >
> > > In support of the WAN, the serial PMDs (and
PMAs) must support
> > > a 9.95328 Gbaud
rate. I think it was fairly clear from early
> >
> on that using an 8b10b encoding for the LAN would require a
> > > 12.5 Gbaud rate and that the PMA/PMD for LAN
& WAN could not
> > > be identical (as
the WAN PMA/PMD doesn't simply scale up in
> >
> baud rate).
> > >
> > > I believe that is the idea behind the 64b/66b and SLP
proposals
> > > as these encodings require
10.3125 and 10.000 Gbaud rates,
> > >
respectively. These baud rates are within the range of current
> > > WAN PMA/PMDs to achieve. This means for the
serial PMA/PMDs,
> > > a single solution can
be generated (or perhaps 2 - longwave
> > >
and shortwave) and dialed with an appropriate oscillator to
> > > support the WAN rate (9.95328 Gbaud) or the LAN rate
(10.3125
> > > or 10.000 Gbaud).
> > >
> > > The
PMA/PMD cares little about the content of the data going
> > > onto or coming off of the fiber. The encoding affects
the baud
> > > rate in order to account for
overhead.
> > >
>
> > BTW: What is a Gb-Mtr?
> > >
> > > Ben
> >
>
> > > Roy Bynum wrote:
> > > >
> > > >
Johnathan,
> > > >
> > > > I was intending to ask you why you did not ask
about unified PMDs
> > > > separate from a
unified PHY as part of your survey but did not get a
> > > > chance. At the 10GEA technical meeting you
were very adamant about
> > > > getting
consensus for a small set of PMDs. I agree that having a
small
> > > > group of
PMDs is preferable. Having a unified PHY in order to have
a
> > > > small set of
PMDs may not be preferable.
> > > >
> > > > The cost of the unified PHY, as
presented, so far has been very high
in
> > > > the form of lost transfer rate. As
it is, the unified PHY, as
> > > >
presented, does not meet the objective to have a 10.000 Gigabit MAC
> > > > data transfer rate (Gb-Mtr).
Separate PHYs, LAN and WAN do meet the
> > >
> objectives. Additionally, one of the scramble encoded WAN
PHY
> > > > presentations was able to
achieve an average 10.000 Gb-Mtr transfer
rate
> > > > by using IPG compression, which can be
inferred to meet the 10.000
> > > > Gb-Mtr
objective in addition to the 9.548 Gb-Mtr objective.
> > > >
> > > > A
unified PMD set can support the block encoded LAN PHY and the
scramble
> > > > encoded WAN PHY,
allowing both to meet the 10.000 Gb-Mtr objective.
> > > > This will allow the PMD people to concentrate on
the technologies of
the
>
> > > PMDs with the consideration of a signaling range to support
both
PHYs.
> > > >
It will also simplify the marketing of 10GbE by reducing the
confusion
> > > > about distances
and fiber types.
> > > >
> > > > As was demonstrated in some of the previous
presentations (SUPI and
OIF
> > > > SERDES), it is possible to have unified PMDs
without having a
unified
>
> > > PHY. If the question had been asked, would it have made
a
difference to
> > >
> separate the issues? If they are separate issues, as a I
believe
they
> > >
> are, then should the survey be redone with that segregation?
Would
this
> > > >
have put less pressure on group to have a unified PHY and changed
the
> > > > scaling of
the responses?
> > > >
> > > > Thank you,
> > >
> Roy Bynum
> > >
> > >
> > > --
> > >
-----------------------------------------
> >
> Benjamin Brown
> > > Router Products
Division
> > > Nortel Networks
> > > 1 Bedford Farms,
>
> > Kilton Road
> > > Bedford, NH
03110
> > > 603-629-3027 - Work
> > > 603-629-3070 - Fax
> > > 603-798-4115 - Home
> >
> bebrown@xxxxxxxxxxxxxxxxxx
> > >
-----------------------------------------
>
>
> --
> -----------------------------------------
> Benjamin Brown
> Router Products
Division
> Nortel Networks
> 1 Bedford Farms,
> Kilton Road
> Bedford, NH 03110
>
603-629-3027 - Work
> 603-629-3070 - Fax
> 603-798-4115 - Home
>
bebrown@xxxxxxxxxxxxxxxxxx
>
-----------------------------------------