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

["Larry Miller" <l_d_miller@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxx>
To: Chang, Edward S <Edward.Chang@xxxxxxxxxx>
Cc: bin.guo@xxxxxxx <bin.guo@xxxxxxx>; bill.st.arnaud@xxxxxxxxxx
<bill.st.arnaud@xxxxxxxxxx>; rtaborek@xxxxxxxxxxxxxxxx
<rtaborek@xxxxxxxxxxxxxxxx>; dwmartin@xxxxxxxxxxxxxxxxxx
<dwmartin@xxxxxxxxxxxxxxxxxx>; stds-802-3-hssg@xxxxxxxx
<stds-802-3-hssg@xxxxxxxx>; sachs@xxxxxxxxxxxxxx <sachs@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxx]
>> Sent: Tuesday, June 01, 1999 10:07 AM
>> To: Chang, Edward S
>> Cc: bin.guo@xxxxxxx; bill.st.arnaud@xxxxxxxxxx;
>> rtaborek@xxxxxxxxxxxxxxxx; dwmartin@xxxxxxxxxxxxxxxxxx;
>> stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx
>> 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@xxxxxxx [mailto:bin.guo@xxxxxxx]
>> > Sent: Friday, May 28, 1999 4:57 PM
>> > To: Edward.Chang@xxxxxxxxxx; bill.st.arnaud@xxxxxxxxxx;
>> > rtaborek@xxxxxxxxxxxxxxxx; dwmartin@xxxxxxxxxxxxxxxxxx
>> > Cc: stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx; "widmer@xxxxxxxxxx
>> > widmer@xxxxxxxxxx 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@xxxxxxxxxx]
>> > > Sent: Friday, May 28, 1999 12:44 PM
>> > > To:   bill.st.arnaud@xxxxxxxxxx; Guo, Bin; rtaborek@xxxxxxxxxxxxxxxx;
>> > > dwmartin@xxxxxxxxxxxxxxxxxx
>> > > Cc:   stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx;
"widmer@xxxxxxxxxx
>> > > widmer@xxxxxxxxxx          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@xxxxxxxxxx]
>> > > Sent: Friday, May 28, 1999 8:52 AM
>> > > To: bin.guo@xxxxxxx; rtaborek@xxxxxxxxxxxxxxxx;
>> > > dwmartin@xxxxxxxxxxxxxxxxxx
>> > > Cc: stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx;
"widmer@xxxxxxxxxx
>> > > widmer@xxxxxxxxxx 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@xxxxxxxxxx
>> > > http://tweetie.canarie.ca/~bstarn
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > > -----Original Message-----
>> > > > From: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx
>> > > > [mailto:owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx]On Behalf Of
>> > > > bin.guo@xxxxxxx
>> > > > Sent: Thursday, May 27, 1999 7:28 PM
>> > > > To: rtaborek@xxxxxxxxxxxxxxxx; dwmartin@xxxxxxxxxxxxxxxxxx
>> > > > Cc: stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx;
"widmer@xxxxxxxxxx
>> > > > widmer@xxxxxxxxxx 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@xxxxxxxxxxxxxxxx]
>> > > > > 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@xxxxxxxxxxxxxxxxxx
>> > > > > >========================
>> > > >
>
>