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