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