I agree completely with Bill,
the distinction between LAN and WAN
is artificial , there is no technical barrier
to provide city wide "LAN". More and more fiber
is available and bandwidth is a commodity.
( look at news of Enron's new market, symbol ENE ).
The distinction is true today.
mostly because the telecos developed a connection based
synchronous network. It all change if you use
a connection-less packet based "Ethernet" like network.
Selection of Jitter ad BER performance implies a decision
on distance, 10GBE could be the standard for
metropolitan Wide networks, you do not need
the complexity of Sonet for a packet switched, asynchronous,
So we can start from the Sonet spec and scale it
down but still be able to send data across a city
or we can use the Fibre Channel spec and limit the scope of
a 10BGE network to a building.
From the PHY point of view, the selection of the PHY/ASIC interface
( single ended or diff ) have an impact on jitter performance
to get good jitter performance ( closer to Sonet spec )
one needs a diff interface.
At 08:51 AM 5/28/99 -0400, Bill St. Arnaud wrote:
>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
>Bill St Arnaud
>Director Network Projects
>> -----Original Message-----
>> From: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx
>> [mailto:owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx]On Behalf Of
>> 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
>> 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
>> 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
>> 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.
>> 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
>> > >========================
PH 408-343-0192 cell 408-892-1838 fax 408-873-2642