Re: Wide Area Networking for the Rest of US - the debate on BER and other issues

[Roy Bynum <rabynum@airmail.net>]

Bill,

We are supposed to be working on 10 Gigabit 802.3, not IP protocols. 
Why are the functionalities, problems, and futures of IP protocols an
issue here.  IP was invented before Ethernet.  It has been trying to
solve Wide Area Networking issues that are connected with transport over
Time Domain Multiplexing channelized services for many years.  IP was
not desiged to run over Ethernet or 802.3. Special modifications were
made to allow IP to run over Ethernet or 802.3 LANs.  

I think that you are not properly thinking though what you are doing
with the long haul implementation of GbE that you refered to in another
memo.  I think that you need to reconsider the functionality and
operation of IP over a LAN.  IP will operate almost the same way over a
VLAN on a bridged, semi-mesh, GbE transport system.  The rules for the
nodal failure may not have changed, but the rules for the transport sure
have/will.  If implemented, tightly coupled resilency at the PHY level
in 10GbE will make a very big improvement to transport reliability.   

					Thank you,
					Roy Bynum
Bill St. Arnaud wrote:
> 
> >
> > It is this very mechanism of using dropped TCP packets as a mechanism to
> > signal flow control that is at issue.  This mechanism was designed into
> > TCP because of the use of unreliable transmission media.  It was
> > designed over twenty years ago, long before optical data networking came
> > into existance.  It was designed at a time when a BER of 10^-8 was
> > considered the best that could ever be achieved.  It was designed before
> > there was any congestion control at the lower layers.  It was designed
> > before Ethernet or 802.3 came into existance.
> 
> Roy:
> 
> I don't disagree that the TCP flow control mechanism is ugly.  But it works.
> And it works with millions and millions of computers across the net.  So it
> is unlikely to change anytime in the near future.
> 
> As you know there are newer flow control mechanisms being developed for real
> time video and voice - RTP,RTSP, etc.  How well they succeed is anybody's
> guess.
> 
> In the advanced reserach networks like Internet 2 and CA*net 3 a number of
> us are coming to the conclusion that VOI and IVC and other real time
> applications will not be the compelling applications that drive bandwidth.
> Admittedly we are a small sample and our conclusions may not relate to the
> larger commercial world.  What is the killer app?  E-mail and FTP. Our
> reserachers have the most sophisticated networks on the planet and the
> biggest use is to transmit humongous data files.  Internet 2 for example had
> one file transfer so huge that it took over a month to transmit at OC-12
> rates!!!!
> 
> >
> > Today, the transmission media is much more reliable.  The congestion can
> > be controled at the physical access point on the originating system.
> 
> Which gives us countless grief.  That is why we can't wait to get rid of
> ATM.  It is nothing to do with the cell tax, but with all the strange
> interactions that happen between ATM flow control and TCP flow control.  As
> much as practically possible all levers and knobs should be visible at the
> IP layer.  That is the message I am tryin to get across about BER, flow
> control ect.  Hiding functionality from upper layers only makes our life
> more difficult and complex it also makes it very difficult to optimize and
> simplify our network.  You also end up duplicating many of the same
> functions e.g retransmissions, flow control, QoS, etc etc
> 
> > This change started when the original Ethernet started using collision
> > detection to control congestion.  (A loss of a frame due to collision is
> > at the MAC layer,2, not at the Transmission layer,4.) A congested
> > Ethernet shared media LAN was measured by collisions.  Even today, on
> > switched 802.3 LANs congestion is measured by looking at "runts".  On
> > full duplex 100BaseT LANs flow control prevents even this level of
> > congestion.  If you loose packets on a LAN today, it is generally in the
> > receiving system, not the transmission system.  Today, on a 802.3 GbE or
> > 100Mb LAN, TCP flow control is a refection of the performance of the end
> > systems, not the transmission media.
> 
> Agree 100%.  And it is the end systems that are now causing most of the
> problems related to BER and retransmission on the network
> 
> > At present, GbE ( 1000BaseLX ) is already moving into the WAN
> > environment. You have made the statement that it is being used in the
> > Internet.  This means that the "rules" are changing for the Internet as
> > well as for private intranets.  This is a very "Darwinian" reality.
> > What, and whomever, is unable to adapt, will not survive.
> >
> > In order for the Internet, and such things as E-Commerce to continue to
> > grow, the issue of stability and reliability must be addressed.
> 
> Agree 100%.  But in excellent study done by C Huitema at Bellcore he showed
> that most of the reliability and congestion problems on the Internet are not
> due to the network.  In fact less than 42% of the congestion and reliability
> is due to network issues!  So where should you spend your money on making
> the internet more reliable?
> 
>  The
> > promise of Internet based abstracted services, such as VOI and IVC
> > (Internet Video Conferencing), can only be realized on a stable and
> > reliable Internet.  Bandwidth is increasing to residential systems as
> > well as other access facilities.  Cable modem systems are a shared media
> > access facility, not too much unlike the old shared media LANs.  The
> > stability and reliability of the transmission media is being addressed
> > in the access systems.  It must also be addressed in the core
> > transmission media as well.
> 
> You may want to look at our engineering paper on optical Internets for
> further debate on this issue.
> 
> >
> > The way that the TCP flow control process works over the Internet today,
> > applies to today.  Why should it apply to they way the Internet works in
> > the future?  Should that also restrict the way that private intranets
> > work?  The implementation of 1000BaseLX in the WAN environment says that
> > the way the processes will be applied in the future is different.  This
> > door has been opened and can not be closed.  Can you help me and others
> > figure out what and how those processes will be changing, and how to go
> > forward and improve them?
> 
> Yes please see "Architectural and Engineering Issues of Building Optical
> Internet"  www.canet3.net
> 
> Bill
> 
> >
> >                                       Thank you,
> >                                       Roy Bynum
> >
> >
> >
> > Bill St. Arnaud wrote:
> > >
> > > Larry:
> > >
> > > What you say may be true for other types of networks.  But
> > dropped packets
> > > and re-transmissions are an essential feature of Internet networks.  The
> > > TCP/IP congestion control mechanisms uses dropped packets as a
> > mechanism to
> > > signal the source to throttle back the data flow.
> > >
> > > In fact many ISPs use a utility called RED ( Random Early
> > Discard ) or WRED
> > > ( Weighted Early Random Discard) to deliberately drop packets
> > as a mechanism
> > > to throttle traffic on congested links.   Yes this does cause a
> > > re-transmission, but TCP automatically drops down to a lower
> > speed when this
> > > happens.  As a result on most Internet links about 1-3% of the
> > traffic is
> > > dropped packet and re=transmissions.  However, most of these
> > dropped packets
> > > are not due to RED but to buffer overflow at the destination receiver.
> > > SIGCOMM'98 has some excellent papers documenting this behaviour on the
> > > Internet.
> > >
> > > If I have to do packet discard in any event I might as well do
> > it a layer 1
> > > just as well as at layer 3.  More importantly if I am already dropping
> > > packets for other reasons, then as long as the number of dropped packets
> > > from BER is less than the number of dropped packets from TCP congestion
> > > control then the actual BER (whether it is 10^-15 or 10^-8) is
> > irrelevant to
> > > me.
> > >
> > > I am assuming that if 10XGbE is used in the long haul the primary
> > > application will be to carry Internet traffic.  That is why it
> > would be nice
> > > to have an option for those of use who are running Internet
> > networks to have
> > > a BER Knob.  With a BER knob I may be able to extend my
> > repeater distance,
> > > use lower cost lasers, etc etc.  However, as I said before this
> > may still
> > > may not be practical because of other issues particularly with
> > respect to
> > > the non-linear factors that affect BER.  But it still might be worth a
> > > cursory investigation.
> > >
> > > Bill
> > >
> > > -------------------------------------------
> > > Bill St Arnaud
> > > Director Network Projects
> > > CANARIE
> > > bill.st.arnaud@canarie.ca
> > > http://tweetie.canarie.ca/~bstarn
> > >
> > >
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: owner-stds-802-3-hssg@majordomo.ieee.org
> > > > [mailto:owner-stds-802-3-hssg@majordomo.ieee.org]On Behalf Of Larry
> > > > Miller
> > > > Sent: Wednesday, June 02, 1999 11:38 AM
> > > > To: stds-802-3-hssg@ieee.org
> > > > Subject: Re: Wide Area Networking for the Rest of US - the
> > debate on BER
> > > > and other issues
> > > >
> > > >
> > > >
> > > > I think the bit is that when you report bad frames upward to
> > higher layers
> > > > they have to do some work to re-request those frames and that
> > takes much
> > > > longer than the time actually burned by the dropped frames.
> > Hence, if you
> > > > get too low of a raw BER you spend all (or maybe more than all)
> > > > of your time
> > > > with higher layer thrashing and never get through with the (say) file
> > > > transfer.
> > > >
> > > > This, I think, is the fallacy in Mr St. Arnaud's notion.
> > > >
> > > > Larry Miller
> > > > Nortel Networks
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: Mike Dudek <mdudek@cieloinc.com>
> > > > To: Chang, Edward S <Edward.Chang@unisys.com>
> > > > Cc: bin.guo@amd.com <bin.guo@amd.com>; bill.st.arnaud@canarie.ca
> > > > <bill.st.arnaud@canarie.ca>; rtaborek@transcendata.com
> > > > <rtaborek@transcendata.com>; dwmartin@nortelnetworks.com
> > > > <dwmartin@nortelnetworks.com>; stds-802-3-hssg@ieee.org
> > > > <stds-802-3-hssg@ieee.org>; sachs@watson.ibm.com
> > <sachs@watson.ibm.com>
> > > > Date: Tuesday, June 01, 1999 5:42 PM
> > > > Subject: Re: Wide Area Networking for the Rest of US - the debate
> > > > on BER and
> > > > other issues
> > > >
> > > >
> > > > >
> > > > >Agreed, but the percentage of good frames stays the same.  ie the
> > > > percentage
> > > > >bandwidth used for retransmissions is the same.
> > > > >
> > > > >"Chang, Edward S" wrote:
> > > > >
> > > > >> Mike:
> > > > >>
> > > > >> If the BER is maintained the same for both GbE and 10xGbE
> > and assume
> > > > >> everything is equal, the frequency of getting error from
> > 10GbE is 10
> > > > times
> > > > >> than GbE from PHY.  Of course, the whole system has other
> > factors to be
> > > > >> included to find the final throughput.  In another word,
> > the occurrence
> > > > of
> > > > >> frame error will be much more for 10GbE than GbE.
> > > > >>
> > > > >> I may present mathematical analysis in July, if my time is allowed.
> > > > >>
> > > > >> Ed Chang
> > > > >> Unisys Corporation
> > > > >>
> > > > >> -----Original Message-----
> > > > >> From: Mike Dudek [mailto:mdudek@cieloinc.com]
> > > > >> Sent: Tuesday, June 01, 1999 10:07 AM
> > > > >> To: Chang, Edward S
> > > > >> Cc: bin.guo@amd.com; bill.st.arnaud@canarie.ca;
> > > > >> rtaborek@transcendata.com; dwmartin@nortelnetworks.com;
> > > > >> stds-802-3-hssg@ieee.org; sachs@watson.ibm.com
> > > > >> Subject: Re: Wide Area Networking for the Rest of US - the
> > > > debate on BER
> > > > >> and other issues
> > > > >>
> > > > >> I do not agree that the BER must be improved with data
> > rate increase in
> > > > >> order to
> > > > >> obtain the higher throughput.  At least for packet based
> > transmission
> > > > with
> > > > >> retransmission of errored packets, the throughput increases in
> > > > proportion
> > > > to
> > > > >> the
> > > > >> data rate for the same BER, assuming that the packet
> > length (in bytes)
> > > > >> remains
> > > > >> fixed.  I do not think that anyone has proposed changing the packet
> > > > length,
> > > > >> but
> > > > >> if they did then the BER might have to be improved.  The
> > > > throughput is of
> > > > >> course
> > > > >> the number of good packets in any interval of time.
> > > > >>
> > > > >> "Chang, Edward S" wrote:
> > > > >>
> > > > >> > Bin:
> > > > >> >
> > > > >> > Yes, I agree.  The BER should be improved with data rate
> > increase, if
> > > > the
> > > > >> > through put gained from higher data rate is to be maintained.  In
> > > > addition
> > > > >> > to the retry times wasted, the external sources of noise
> > remain the
> > > > same,
> > > > >> > which further requires the lower BER.  These are the
> > correct design
> > > > goals
> > > > >> we
> > > > >> > should work on.  Although, we also should keep the
> > cost-effectiveness
> > > > in
> > > > >> > mind to maintain optimum balance between performance and cost.
> > > > >> >
> > > > >> > Ed Chang
> > > > >> > Unisys Corporation
> > > > >> >
> > > > >> > -----Original Message-----
> > > > >> > From: bin.guo@amd.com [mailto:bin.guo@amd.com]
> > > > >> > Sent: Friday, May 28, 1999 4:57 PM
> > > > >> > To: Edward.Chang@unisys.com; bill.st.arnaud@canarie.ca;
> > > > >> > rtaborek@transcendata.com; dwmartin@nortelnetworks.com
> > > > >> > Cc: stds-802-3-hssg@ieee.org; sachs@watson.ibm.com;
> > > > "widmer@us.ibm.com
> > > > >> > widmer@us.ibm.com widmer"@us.ibm.com
> > > > >> > Subject: RE: Wide Area Networking for the Rest of US -
> > the debate on
> > > > BER
> > > > >> > a nd other issues
> > > > >> >
> > > > >> > Ed,
> > > > >> >
> > > > >> > If the specified BER for 1000BASE-X is 10^ -12, then to have
> > > > the equal
> > > > >> > error-free period the specified BER for 10G should be at
> > > > least 10^ -13.
> > > > >> > Based on Rich T and Rich S's BER number:
> > > > >> >
> > > > >> > A system BER of 10 E - 8 @  10 Mbps = a bit error every
> > 10 seconds.
> > > > >> > (10BASE-T)
> > > > >> > A system BER of 10 E-12 @ 100 Mbps = a bit error every 166
> > > > minutes, 40
> > > > >> > seconds.        (100BASE-X)
> > > > >> > A system BER of 10 E-10 @     1 Gbps = a bit error every 1
> > > > minutes, 40
> > > > >> > seconds.                (1000BASE-T)
> > > > >> > A system BER of 10 E-12 @     1 Gbps = a bit error every 16
> > > > minutes, 40
> > > > >> > seconds.        (1000BASE-X)
> > > > >> > A system BER of 10 E-12 @   10 Gbps = a bit error every
> > 1 minutes, 40
> > > > >> > seconds.
> > > > >> > A system BER of 10 E-13 @   10 Gbps = a bit error every 16
> > > > minutes, 40
> > > > >> > seconds.
> > > > >> >
> > > > >> > If the TCP/IP is the only protocol 10G PHY needs to
> > support, then the
> > > > >> above
> > > > >> > specified BER may be more than enough.  Moving from 1G to
> > > > 10G, the bit
> > > > >> > period is scaled 10X smaller while jitter and noise from
> > some sources
> > > > are
> > > > >> > not scaled the same way -- much tight control should be
> > applied to
> > > > achieve
> > > > >> > even the same BER.
> > > > >> >
> > > > >> > Bin
> > > > >> >
> > > > >> > ADL,AMD
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> > > -----Original Message-----
> > > > >> > > From: Chang, Edward S [SMTP:Edward.Chang@unisys.com]
> > > > >> > > Sent: Friday, May 28, 1999 12:44 PM
> > > > >> > > To:   bill.st.arnaud@canarie.ca; Guo, Bin;
> > > > rtaborek@transcendata.com;
> > > > >> > > dwmartin@nortelnetworks.com
> > > > >> > > Cc:   stds-802-3-hssg@ieee.org; sachs@watson.ibm.com;
> > > > "widmer@us.ibm.com
> > > > >> > > widmer@us.ibm.com          widmer"@us.ibm.com
> > > > >> > > Subject:      RE: Wide Area Networking for the Rest of US - the
> > > > debate
> > > > >> on
> > > > >> > > BER a nd other issues
> > > > >> > >
> > > > >> > > Bill:
> > > > >> > >
> > > > >> > > I like your idea of implementing native 10xGBE for
> > > > intermediate long
> > > > >> haul
> > > > >> > > and WAN, which is a good move.  The advantage you are
> > > > mentioning will
> > > > >> > > greatly reduce the cost to users.
> > > > >> > >
> > > > >> > > It is true, in a TCP/IP links, the TCP flow control causes more
> > > > >> > > retransmission than BER. Therefore, the extremely low
> > BER, 10^-15,
> > > > does
> > > > >> > > not
> > > > >> > > necessarily gain any more advantage than the specified BER
> > > > of 10^-12.
> > > > >> > >
> > > > >> > >
> > > > >> > > Ed Chang
> > > > >> > >
> > > > >> > > -----Original Message-----
> > > > >> > > From: Bill St. Arnaud [mailto:bill.st.arnaud@canarie.ca]
> > > > >> > > Sent: Friday, May 28, 1999 8:52 AM
> > > > >> > > To: bin.guo@amd.com; rtaborek@transcendata.com;
> > > > >> > > dwmartin@nortelnetworks.com
> > > > >> > > Cc: stds-802-3-hssg@ieee.org; sachs@watson.ibm.com;
> > > > "widmer@us.ibm.com
> > > > >> > > widmer@us.ibm.com widmer"@us.ibm.com
> > > > >> > > Subject: Wide Area Networking for the Rest of US - the
> > > > debate on BER
> > > > and
> > > > >> > > other issues
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > > All:
> > > > >> > > I have been following the interesting debate about BER.
> > > > Let me bring
> > > > >> some
> > > > >> > > further issues into the debate.
> > > > >> > >
> > > > >> > > I am assuming that on WAN and long haul GbE the upper
> > > > layer protocol
> > > > >> will
> > > > >> > > only be IP.
> > > > >> > >
> > > > >> > > On most IP links, even ones with BERs of 10^-15 there
> > is about 1-3%
> > > > >> packet
> > > > >> > > loss and retransmission.  This is due to a number of
> > > > factors but most
> > > > >> > > typically it relates to TCP flow control mechanism from
> > > > server bound
> > > > >> > > congestion (not network congestion) and the use of
> > WRED in routers.
> > > > >> > >
> > > > >> > > So, on most IP links the packet loss due to BER is
> > > > significantly less
> > > > >> than
> > > > >> > > that due to normal TCP congestion.  As long as that ratio is
> > > > maintained
> > > > >> it
> > > > >> > > is largely irrelevant what the absolute BER value is.
> > > > There will be
> > > > >> many
> > > > >> > > more retransmissions from the IP layer than there will
> > be at the
> > > > >> physical
> > > > >> > > layer due to BER.
> > > > >> > >
> > > > >> > > Other protocols like Frame Relay and SNA are a lot more
> > > > sensitive to
> > > > >> high
> > > > >> > > BERs.  IP ( in particular TCP/IP) is significantly
> > more robust and
> > > > can
> > > > >> > > work
> > > > >> > > quite effectively in high BER environments e.g. TCP/IP
> > over barbed
> > > > wire.
> > > > >> > >
> > > > >> > > I would like to suggest that the 802.3 HSSG group consider an 2
> > > > >> solutions
> > > > >> > > for 10xGbE WAN:
> > > > >> > > (1) native 10xGbE using 8b/10b; and
> > > > >> > > (2)10xGbE mapped to a SONET STS OC-192 frame
> > > > >> > >
> > > > >> > > For extreme long haul solutions SONET makes a lot of sense as a
> > > > >> transport
> > > > >> > > technology.  However for intermediate long haul (up to
> > 1000 km) and
> > > > WAN
> > > > >> > > native 10xGbE is more attractive. Native GbE can be either
> > > > transported
> > > > >> on
> > > > >> > > a
> > > > >> > > transparent optical network or carried directly on a CWDM
> > > > system with
> > > > >> > > transceivers. In medium range networks coding
> > efficiency is not as
> > > > >> > > important
> > > > >> > > as it is in long haul networks. If coding efficiency
> > is important
> > > > then
> > > > >> in
> > > > >> > > my
> > > > >> > > opinion, it does not make sense to invent a new coding
> > scheme for
> > > > 10xGbE
> > > > >> > > when it would be just as easy to map it to a SONET frame.
> > > > >> > >
> > > > >> > > The attraction of native 10xGbE for the WAN is that it
> > is a "wide
> > > > area
> > > > >> > > networking solution for the rest of us".  You don't
> > need to hire
> > > > >> > > specialized
> > > > >> > > SONET engineers to run and manage your networks.  The 18
> > > > year old kid
> > > > >> who
> > > > >> > > is
> > > > >> > > running your LAN can now easily learn to operate and
> > manage a WAN.
> > > > >> > >
> > > > >> > > In Canada and the US, there are several vendors who
> > are willing to
> > > > sell
> > > > >> > > dark
> > > > >> > > fiber at a very reasonable cost.  Right now the cost
> > of building a
> > > > WAN
> > > > >> > > with
> > > > >> > > 10xGbE and CWDM is substantially less (for comparable
> > data rates)
> > > > than
> > > > >> > > using
> > > > >> > > SONET equipment.
> > > > >> > >
> > > > >> > > Bill
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > > -------------------------------------------
> > > > >> > > Bill St Arnaud
> > > > >> > > Director Network Projects
> > > > >> > > CANARIE
> > > > >> > > bill.st.arnaud@canarie.ca
> > > > >> > > http://tweetie.canarie.ca/~bstarn
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > >
> > > > >> > > > -----Original Message-----
> > > > >> > > > From: owner-stds-802-3-hssg@majordomo.ieee.org
> > > > >> > > > [mailto:owner-stds-802-3-hssg@majordomo.ieee.org]On Behalf Of
> > > > >> > > > bin.guo@amd.com
> > > > >> > > > Sent: Thursday, May 27, 1999 7:28 PM
> > > > >> > > > To: rtaborek@transcendata.com; dwmartin@nortelnetworks.com
> > > > >> > > > Cc: stds-802-3-hssg@ieee.org; sachs@watson.ibm.com;
> > > > "widmer@us.ibm.com
> > > > >> > > > widmer@us.ibm.com widmer"@us.ibm.com
> > > > >> > > > Subject: RE: 1000BASE-T PCS question
> > > > >> > > >
> > > > >> > > >
> > > > >> > > >
> > > > >> > > > Rich,
> > > > >> > > >
> > > > >> > > > The DC balance can be directly translated into jitter
> > > > (when timing
> > > > is
> > > > >> > > > concerned) and offset (when threshold slicing is
> > concerned).  You
> > > > >> > > > only need
> > > > >> > > > to deal with the former if the signal is 2-level
> > NRZI, while you
> > > > need
> > > > >> to
> > > > >> > > > deal with both if multi-level signal modulation is used.
> > > > >> > > >
> > > > >> > > > For long term DC imbalance, it translates into low
> > > > frequency jitter
> > > > >> and
> > > > >> > > if
> > > > >> > > > it's low enough(<1 KHz ?), it's called baseline wonder.  For
> > > > >> > > > short term, it
> > > > >> > > > relates to Data Dependent Jitter, which is more difficult for
> > > > timing
> > > > >> > > > recovery to handle since it's not from system or channel
> > > > imparity,
> > > > and
> > > > >> > > > therefore it's harder to compensate.
> > > > >> > > >
> > > > >> > > > When you have a lot of jitter margin, for example in
> > lower speed
> > > > >> > > clocking,
> > > > >> > > > the amount of jitter, translated from DC drift
> > resulted from data
> > > > >> > > > imbalance
> > > > >> > > > coupled by AC circuit, percentage wise is a small
> > portion of the
> > > > clock
> > > > >> > > > period and therefore does not contribute to much of the eye
> > > > >> > > > closing.  On the
> > > > >> > > > other hand, for high speed clocking at 10G (100
> > ps?), the jitter
> > > > >> > > > translated
> > > > >> > > > from the same amount of DC drift can be a
> > significant portion of
> > > > the
> > > > >> > > clock
> > > > >> > > > period, so contributes to much large percentage wise
> > jitter which
> > > > >> > > > results in
> > > > >> > > > reduced eye opening -- higher BER.
> > > > >> > > >
> > > > >> > > > Dave said in his mail that "The limiting factor is enough RX
> > > > optical
> > > > >> > > power
> > > > >> > > > to provide a sufficiently open eye." but you still
> > have to deal
> > > > with
> > > > >> the
> > > > >> > > > data dependent jitter due to DC imbalance generated
> > > > after O/E, that
> > > > >> can
> > > > >> > > > close the eye further again.
> > > > >> > > >
> > > > >> > > > Bin
> > > > >> > > >
> > > > >> > > > ADL, AMD
> > > > >> > > >
> > > > >> > > > > -----Original Message-----
> > > > >> > > > > From:     Rich Taborek [SMTP:rtaborek@transcendata.com]
> > > > >> > > > > Sent:     Thursday, May 27, 1999 3:23 PM
> > > > >> > > > > To:       David Martin
> > > > >> > > > > Cc:       HSSG_reflector; Sachs,Marty; Widmer,Albert_X
> > > > >> > > > > Subject:  Re: 1000BASE-T PCS question
> > > > >> > > > >
> > > > >> > > > >
> > > > >> > > > > Dave,
> > > > >> > > > >
> > > > >> > > > > Do you know of any research or other proofs in this
> > > > area? You say
> > > > >> that
> > > > >> > > > > lower speed SONET links regularly achieves BERs of
> > < 10 E-15. I
> > > > have
> > > > >> > > > > substantial experience with mainframe serial links such as
> > > > ESCON(tm)
> > > > >> > > > > where the effective system BERs are in the same
> > ballpark. SONET
> > > > uses
> > > > >> > > > > scrambling with long term DC balance and ESCON
> > uses 8B/10B with
> > > > >> short
> > > > >> > > > > term DC balance. The following questions come to mind:
> > > > >> > > > >
> > > > >> > > > > - How important is DC balance?
> > > > >> > > > > - How does this importance scale in going to 10 Gbps?
> > > > >> > > > >
> > > > >> > > > > I'll see if I can get some 8B/10B experts to chime in
> > > > here if you
> > > > >> can
> > > > >> > > > > get scrambling experts to bear down on the same problem.
> > > > >> > > > >
> > > > >> > > > > --
> > > > >> > > > >
> > > > >> > > > > >(text deleted)
> > > > >> > > > > >
> > > > >> > > > > >The point here is that the SONET scrambler is not
> > the limiting
> > > > >> issue
> > > > >> > > in
> > > > >> > > > > >achieving low error rates. The issue is having enough
> > > > photons/bit,
> > > > >> or
> > > > >> > > > > >optical SNR (eye-Q) to accurately recover the data.
> > > > >> > > > > >
> > > > >> > > > > >...Dave
> > > > >> > > > > >
> > > > >> > > > > >David W. Martin
> > > > >> > > > > >Nortel Networks
> > > > >> > > > > >+1 613 765-2901
> > > > >> > > > > >+1 613 763-2388 (fax)
> > > > >> > > > > >dwmartin@nortelnetworks.com
> > > > >> > > > > >========================
> > > > >> > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> >