Re: Unified PMD vs. Unified PHY
Walter,
I was not advocating viloating the structure of the MAC frames by
concatenating smaller ones into larger ones. I was just trying to be
realistic about some potential real world results of some of the proposals.
Thank you,
Roy Bynum
----- Original Message -----
From: Walter Thirion <wthirion@jatotech.com>
To: <stds-802-3-hssg@ieee.org>
Sent: Thursday, March 16, 2000 9:06 PM
Subject: RE: Unified PMD vs. Unified PHY
>
> Mike,
>
> I guess my use of the word "application" was a little sloppy. I should
have
> been more precise and said the network transport layer (i.e. IP, IPX,
etc.)
> sets the packet size (obviously based on how the upper layer applications
> are using the network).
>
> What I was trying to highlight is that in normal LAN traffic, packets are
> not coalesced into larger packets, but kept individually with an IPG
between
> each one. So, though a mixture of large and small frames may "average" to
> 400 bytes or so, the physical layer actually sees bimodal peaks of small
and
> large frames. What I was asking Roy was whether he was advocating some
kind
> of coalescing function to combine small frames into larger ones.
>
> Clearer?
>
> Walter Thirion
> wthirion@jatotech.com
>
>
>
> > -----Original Message-----
> > From: Van Scherrenburg, Mike
> > [mailto:Mike.Van.Scherrenburg@SynergySemi.Com]
> > Sent: Thursday, March 16, 2000 2:22 PM
> > To: 'stds-802-3-hssg@ieee.org'
> > Subject: Re: Unified PMD vs. Unified PHY
> >
> >
> >
> > Walter,
> >
> > Are you suggesting that what the application thinks is a
> > packet size
> > should be what the network physically uses as a packet size?
> > I suspect that
> > setting the physical (as in on a medium) packet size should
> > be a network
> > responsibility, involving issues of medium efficiency, and
> > error performance
> > (which an application should not have to worry about), and
> > issues of mixing
> > traffic types.(an application should not have to know what
> > else is going
> > over a channel, IMHO).
> >
> > For example, PPP limits MTU so that the response time of a remote
> > terminal application will not be significantly degraded, by
> > the network,
> > should another data rate hungry application (say an ftp) also
> > share the line
> > (in the case of PPP, typically an analog modem link). The
> > MTU limit would
> > be drastically different if the "line" were at 1Mbit instead
> > of 50Kbit. I
> > don't see how we can fashion the ftp application, in this example, to
> > dynamically change it's "logical" MTU (if it were determining
> > the physical
> > packet size), based on whether a remote terminal application
> > also happens to
> > be sharing the line, and simultaneously keep a sane world here.
> >
> >
> >
> > ----------
> > From: Walter Thirion[SMTP:wthirion@jatotech.com]
> > Sent: Wednesday, March 15, 2000 7:02 PM
> > To: stds-802-3-hssg@ieee.org
> > Subject: RE: Unified PMD vs. Unified PHY
> >
> > Roy,
> >
> > What does the speed of the transmission system have to do
> > with changing the
> > packet size? Applications determine the packet size unless
> > the transport is
> > doing some kind of packet packing/blocking, etc.
> >
> > Walt
> >
> > -----Original Message-----
> > From: Roy Bynum [mailto:rabynum@mindspring.com]
> > Sent: Wednesday, March 15, 2000 8:53 PM
> > To: Walter Thirion; stds-802-3-hssg@ieee.org
> > Subject: Re: Unified PMD vs. Unified PHY
> >
> >
> > Walter,
> >
> > I agree with the bimodal nature of the data packet size
> > spectrum.
> > In very high bandwidth transmission systems these bimodel
> > aspects tend to
> > disapear. True, any one SONET/SDH frame will directly see these
> > differences, which is why there still needs to be rate
> > adaption between the
> > MAC and the WAN PHY. However, over a period of time the
> > transfer rate will
> > average out. With at the average of 400 byte frames, frame
> > stuffing and IPG
> > compression will recover only a certain amount of bandwidth.
> > The reason
> > that I made this analysis is to be able to make some
> > realistic comparisons
> > between the various PCS/PMA options.
> >
> > Thank you,
> > Roy Bynum
> >
> > ----- Original Message -----
> > From: Walter Thirion
> > To: 'stds-802-3-hssg@ieee.org'
> > Sent: Wednesday, March 15, 2000 7:23 AM
> > Subject: RE: Unified PMD vs. Unified PHY
> >
> > Roy,
> >
> > I don't know how it affects your view of
> > overhead, but the
> > fact that the average packet is 400 bytes doesn't really mean
> > anything. In
> > most traffic studies I've seen, the traffic is somewhat
> > bi-modal. There is a
> > peak in the 64-100 byte range and another peak either just
> > above 1k or at
> > the max packet size, depending on where the traffic is
> > measured. Though
> > these two peaks may average to 400, there is, in fact, very
> > little traffic
> > in the middle range.
> >
> > Walt
> >
> >
> >
> > -----Original Message-----
> > From: Roy Bynum [mailto:rabynum@mindspring.com]
> > Sent: Tuesday, March 14, 2000 11:35 PM
> > To: McCormick, Corey
> > Cc: 802.3ae
> > Subject: Re: Unified PMD vs. Unified PHY
> >
> >
> > Corey,
> >
> > Actually, the reflector is probably a very good
> > place to discuss this. I think that you have an interesting
> > question that
> > should be addressed. It goes directly to the efficiency of
> > improving MAC
> > transfer rate by IPG compression.
> >
> > The average datagram size that I refereed to was
> > originally from Internet MCI and then again from vBNS and
> > UUNet. These are
> > diverse sources, in both time and typical access. Internet MCI was
> > functional before the massive numbers of high speed dial up
> > ISPs came into
> > being. The vBNS network is primarily universities with direct circuit
> > access. UUNet is a NSP that supports dial ISPs and
> > commercial services with
> > direct circuit access. That the average datagram size has not changed
> > speaks more to the applications on the desk tops and in the
> > homes than to
> > the access method. As more and more voice, which uses a very small
> > datagram, and video, which uses a large datagram, become even more
> > prevalent, the weighting at the extremes of frame sizes will
> > increase, but I
> > don't think that will change the overall average Ethernet
> > frame size at the
> > higher bandwidths such as 10 Gigabit.
> >
> > While the P802.3ae TF has stated that
> > it will not
> > take on the issue of increasing the MTU size, I have been
> > told that almost
> > all of the GbE vendors support jumbo frames. One of the
> > problems of having
> > larger MTU size years ago was that the technology and cost required to
> > support any larger frames was a paradigm based probem. It
> > goes back to
> > issue why the original microprocessors chips only supported a
> > limited amount
> > of memory, or why the original PC only supported 640K of
> > application memory.
> > Hindsight is allways 20/20. Those of us that have been
> > around long enough
> > and worked in enough diverse environments, to understand how
> > and why things
> > got where they are, have the oportunity to perhaps avoid some
> > of the same
> > types of mistakes.
> >
> > Thank you,
> > Roy Bynum
> >
> >
> > ----- Original Message -----
> > From: McCormick, Corey
> > To: Roy Bynum
> > 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@mindspring.com]
> > 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@nortelnetworks.com>
> > To: 802.3ae <stds-802-3-hssg@ieee.org>
> > 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@nortelnetworks.com>
> > > > To: 802.3ae
> > <stds-802-3-hssg@ieee.org>
> > > > 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@nortelnetworks.com
> > > > >
> > -----------------------------------------
> > >
> > >
> > > --
> > >
> > -----------------------------------------
> > > 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@nortelnetworks.com
> > >
> > -----------------------------------------
> >
> >