----- 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
>
-----------------------------------------