Re: Wide Area Networking for the Rest of US - the debate on BER a nd other issues
- To: Iain Verigin <Iain_Verigin@xxxxxxxxxxxxxx>
- Subject: Re: Wide Area Networking for the Rest of US - the debate on BER a nd other issues
- From: Roy Bynum <rabynum@xxxxxxxxxxx>
- Date: Fri, 28 May 1999 20:49:27 -0500
- CC: "'bill.st.arnaud@xxxxxxxxxx'" <bill.st.arnaud@xxxxxxxxxx>, bin.guo@xxxxxxx, rtaborek@xxxxxxxxxxxxxxxx, dwmartin@xxxxxxxxxxxxxxxxxx, stds-802-3-hssg@xxxxxxxx, sachs@xxxxxxxxxxxxxx, widmer@xxxxxxxxxx
- Organization: .
- References: <F723EB5DB6EAD111BC460060B067AD5F03E8E179@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Reply-To: rabynum@xxxxxxxxxxx
- Sender: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx
There are several issues that need to be addressed before
IP/Ethernet/SONET is directly addopted. In a native 802.3 network, the
link mangager over a WAN is by means of MAC Bridging, creating virtual
segment extension. While I think that this will lend itself very
readily to the WAN systems; IP routing and restoration protocols, as
written, may act differently than they do over "circuits".
The question returns to the need for active fault restoration at the
Ethernet/SONET level. I believe that the current IP protocols will work
even better over reliable virtual segments than the currently do over
unreliable "circuits". I am currently attempting to put together a lab
setup to test this and return some hard data.
I welcome others to consider the changes to the architecture of IP
intranets and the Internet that reliable IP/Ethernet/SONET would make.
The first of course is that a partial mesh WAN which uses MAC bridging
over reliable services can now be treated as a single virtual segment.
The latencies within the virtual segment are directly realated to
distance and L2 switch transit latency. The virtual segment can now be
a single broadcast domain within any one WAN mesh domain. IP routing
protocols will now only need to send a single update or LSA for the
entire segment. This may have the effect of reducing the size of
various routing tables. This could have the effect of improving the
scalability of the Internet. It also means that such protocols as
Cisco's HSRP might be used over the WAN to resolve router/switch
failures. The number of changes and the way that things will change are
not yet fully understood.
The next question is how much this reliability will cost. It should not
cost any more than current WAN services do. It should cost less. There
is work going on to model the economics of this.
Iain Verigin wrote:
> As I know it, there could be three IP stacks at 10G. Two exist today at
> lower rates, they are:
> 1. IP/Ethernet - General use is intra-CO (LAN) interconnect.
> 2. IP/Packet-over-Sonet (POS) RFC 1619 - General use is inter-CO (WAN)
> (Note IETF RFC 1619 has been revised to include OC-192c.)
> I agree with Bill that we should investigate a third stack that would be
> consistent with today's WAN infrastructure.
> 3. IP/Ethernet/SONET.
> * there are many reasons for this. I believe one of the strongest is that it
> removes the need for Layer 3 processing that POS imposes. A negative is
> that it adds more bytes, an Ethernet tax, which may not be desirable on long
> haul links.
> * the IEEE could work on this because no other standards body is.
> Iain Verigin
> -----Original Message-----
> From: Bill St. Arnaud [mailto:bill.st.arnaud@xxxxxxxxxx]
> Sent: May 28, 1999 5:52 AM
> To: bin.guo@xxxxxxx; rtaborek@xxxxxxxxxxxxxxxx;
> 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
> 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 St Arnaud
> Director Network Projects
> > -----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
> > > >========================