Wednesday, December 15, 2010

The 10X10 MSA: Niche, Distraction or the Right Answer? (Continued)

While Vipul has a point that this new MSA is probably a distraction, it is difficult to deny that there is a market for cost-effective devices with optical reaches between 100m and 10km. In fact, 100m to 300m is the market that multi-mode fiber has served so well for the last 20 years. And, 300m to 2km has been a niche for lower-cost 1310nm single mode products like 1000BASE-LX. So I have a slightly different opinion about this 10x10 MSA and whether it’s a niche, distraction or the right answer.

In a recent article written on Optical Reflection, Pauline Rigby quotes Google’s senior network architect, Bikash Koley. About 100GBASE-SR10, he says 100m isn’t long enough for Google – that it won’t even cover room-to-room connections and that “ribbon fibres are hard to deploy, hard to manage, hard to terminate and hard to connect. We don’t like them.” There is an answer for this ribbon-fiber problem – don’t use it. There are many optical fiber manufacturers that now provide round multi-fiber cables that are only “ribbonized” at the ends for use with the 12-position MPO connector and are much easier to install – Berk-Tek, A Nexans Company, AFL and even Corning have released products that address this concern. But, the 100m optical reach is another matter.

I have to agree with Google about one other thing – 4x25G QSFP+ solutions are at least four years away from reality (and I would say probably even longer). This solution will eventually have the low-cost, low-power and high-density Google requires, but not quick enough. I think something needs to be done to address Google’s and others requirements between 300m and 2km in the short term, but I also believe that it needs to be standardized. There is no IEEE variant that would currently cover a 10x10G single mode device. However, there is an effort currently going on in the IEEE for 40G over SMF up to 2km. Perhaps the members of the MSA should look to work with this group to expand its work or start a new related project to cover 100G for 2km as well? I know this was thrown out of the IEEE before, but so were 1000BASE-T and 10GBASE-T initially.

So what I'm saying is that the market is more than a niche - hundreds of millions of dollars of LOMF sales at 1G and 10G would attest to that. And it's more than a distraction because there is a need. But I don't think it's entirely the right answer without an IEEE variant to back it up.

Let us know what you think.

Monday, December 13, 2010

The 10X10 MSA: Niche, Distraction or the Right Answer?

{For today’s blog, our guest author is Vipul Bhatt. I have known Vipul for several years, since when he was the Director of High Speed Optical Subsystems at Finisar. He has served as the Chair of Optical PMD Subgroup of IEEE 802.3ah Ethernet in the First Mile (EFM), and the Chair of Equalization Ad Hoc of IEEE 802.3ae 10G Ethernet. He can be reached at}

Last week, Google, JDSU, Brocade and Santur Corp announced the 10X10 Multi-Source Agreement (MSA) to establish sources of 100G transceivers. It will have 10 optical lanes of 10G each. Their focus is on using single mode fiber to achieve a link length of up to 2 km. The key idea is that a transceiver based on 10 lanes of 10G will have lower power consumption and cost because it doesn’t need the 10:4 gearbox and 25G components. But is this a good idea? What is the tradeoff? Based on my conversations with colleagues in the industry, it seems there are three different opinions emerging about how this will play out. I will label them as niche, distraction, or the right answer. Here is a paraphrasing of those three opinions.

It’s a niche: It’s a solution optimized for giant data centers – we’re talking about a minority of data centers (a) that are [already] rich in single mode fiber, (b) where the 100-meter reach of multi-mode 100GBASE-SR10 is inadequate, and (c) where the need for enormous bandwidth is so urgent that the density of 10G ports is not enough, and 100G ports can be consumed in respectable quantities in 2011.

It’s a distraction: Why create another MSA that is less comprehensive in scope than CFP, when the CFP has sufficient support and momentum already? Ethernet addresses various needs – large campuses, metro links, etc. – with specifications like the LR4 that need to support link lengths of well beyond 2 km over one pair of fiber. We [do] need an MSA that implements LR4, and the SR10 meets the needs of a vast majority of data centers, so why not go with CFP that can implement both LR4 and SR10? As for reducing power consumption and cost, the CFP folks are already working on it. And it’s not like we don’t have time – the 10G volume curve hasn’t peaked yet, and may not even peak in 2011. Question: What is the surest way to slow down the decisions of Ethernet switch vendors? Answer: Have one MSA too many.

It’s the right answer: What is the point of having a standard if we can’t implement it for two years? The CFP just isn’t at the right price-performance point today. The 10X10 MSA can be the “here and now” solution because it will be built with 10G components that have already traversed the experience curve. It can be built with power, density and cost figures that will excite the switch vendors, which may accelerate the adoption of 100G Ethernet, not distract it. As for 1-pair vs. 10-pairs of fiber, the first swelling of 100G demand will be in data centers where it’s easier to lay more fiber, if there isn’t plenty installed already. The 2-km length is sufficient to serve small campuses and large urban buildings as well.

Okay, so what do I think? I think the distraction argument is the most persuasive. An implementation that is neither SR10-compliant nor LR4-compliant is going to have a tough time winning the commitment of Ethernet switch vendors, even if it’s cheaper and cooler than the CFP in the short term.

Thursday, December 9, 2010

SFP+ - The New Optical RJ45?

For those of you that have been in the industry for what seems to be 100 years, but is really about 25 years, you know that the one “connector” that hasn’t changed much is the RJ45. While there have been improvements by adding compensation for the error that was made way back when AT&T developed the wiring pattern (splitting the pair causing major crosstalk issues), the connector itself has remained intact. Contrastingly, optical connectors for datacom applications have changed several times – ST to SC to MT-RJ to LC. They have finally seemed to settle on the LC and perhaps on a transceiver form factor – the SFP+. The SFP was originally introduced at 1G, was used for 2G and 4G and with slight improvements has become the SFP+ and the dominant form factor now used for 10G. Well, it is in the process of getting some slight improvements again and promises to make it all the way to 32G. That’s six generations of data rates – pretty impressive. But how?

The INCITS T11.2 Committee's Fibre Channel Physical Layer – 5 (FC-PI-5) standard was ratified in September. It specifies 16G Fibre Channel. Meanwhile, the top transceiver manufacturers have been demonstrating pre-standard 16G SFP+ SW devices. But, wait a minute – short-wavelength VCSELs were supposed to be very unstable when trying to modulate them at data rates above 10G right? Well, it seems that at least Avago and Finisar have figured this out. New microcontrollers and adding at least one clock and data recovery (CDR) device in the module to help clean up the signals have proven to be keys. Both vendors believe it is possible to do this and not add too much cost to the modules. In fact, both also think that possibly by adding electronic dispersion compensation (EDC) they can push the SFP+ to 32G as well - which is the next step for Fibre Channel - hoping to stop at 20G and 25G to cover developments in Ethernet and InfiniBand.

And what about long wavelength devices? It has always been a challenge fitting the components needed to drive long distances into such a small package mainly because the lasers need to be cooled. But not anymore – Opnext has figured it out. In fact, it was showing its 10km 16G FC SFP+ devices long before any of the SW ones were out (March 2010). Of course, this isn't surprising considering Opnext has already figured out 100G long haul as well.

These developments are important to datacom optical networking for a few of reasons:  
  1. They show that Fibre Channel is not dead.
  2. The optical connector and form factor "wars" have seemed to subsided so transceiver manufacturers and optical components vendors can focus on cooperation instead of positioning.
  3. They will impact the path other networking technologies are taking – Ethernet and InfiniBand are using parallel optics for speeds above 10G – will they switch back to serial?
Stay tuned for more on these points later.