Data Center Optics - TIA Data Center Workshop and 7x24 Exchange Delaware Valley Chapter Meeting

I just finished a quick trip to Arlington, VA and Philadelphia, PA to participate in two events:  TIA Data Center Workshop and 7x24 Exchange Delaware Valley Chapter Meeting. Both had excellent discussions about the role of optics in the data center.

The panel I moderated at the TIA Workshop had representatives from Microsoft, Google, Dell and Sumitomo. The discussion brought home to me the fact that there is a large gap between the needs of the small, medium and even large enterprise data center and the needs of Internet Data Centers. The chart below, that was provided by Dell, tries to summarize the point.

Here in 2014, we still have many enterprise data centers that run 1G servers with uplinks of 10G. At the same time, Microsoft is moving from a combination of 10G and 40G servers with uplinks of 40G and 100G, to pushing for 25G servers to connect to one 100G top-of-rack (ToR) switch-port (a breakout cable). And, Microsoft is also currently working on 400G and above for the rest of its data center network. Clearly a vast difference in Ethernet application.

The diversity of data center needs will continue to broaden over the next five to ten years so the IEEE is trying to address this in its Ethernet standards development. Data rates like 2.5G, 5G, 25G and 400G are now being considered in order to address both ends of the market "spectrum." Pun intended.

At the 7x24 Exchange Delaware Valley meeting, I discussed this trend and more from our recent study on data center optics. Here is a link to a copy of the presentation.

More to come later on trends in data center optics.

Next Generation 100G Ethernet (with corrections)

Ever since the 40/100G Ethernet standard was completed in 2010, the IEEE standards group has been working on ways to improve it. In my opinion, there were two very serious holes in the original standard. The 40G long-reach variant did not match the existing telecom standard for 40G so some type of conversion equipment would be needed. This was fixed when the IEEE 802.3bg 40GBASE-FR single mode fiber standard was released in 2010. The second concern, which still exists, is the 100GBASE variants. Four standardized and one MSA currently exist and are shown in the following table.

Ethernet Variant	Data rate (Gbps)	Min. Reach (meters)	Form Factors	Media Wavelength	Standard IEEE 802.3
100GBASE-
CR10	10x10	7	CXP Direct Attach Copper	Twinax Copper	ba
SR10		100/150	CXP, CFP	LOMF 850nm
LR4	4x25	10,000	QSFP+, CFP	SMF 1310nm
ER4		40,000	CFP	SMF 1310nm
LR10	10x10	2,000	CFP	SMF 1550nm	Not supported

40/100G, the IEEE did not want to make the mistake of too many variants and form factors again (like they did for 10G) so consciously limited them. But, in our opinion, may have restricted them too much. By reducing the laser-optimized multi-mode fiber (LOMF) optical reach to 100m over OM3 and 150m for OM4, the IEEE left a huge gap in distance covered for data center applications – in fact, a two orders of magnitude gap – from 100m to 10km. This results in an enormous difference in cost as well. For example, a 100GBASE-SR10 CXP module average selling price is about $200, while the 100GBASE-LR4 average price is more than $20,000. So it is currently cost-prohibitive to design a data center with connections longer than 100m. This is not realistic. In order to address this shortcoming, the top transceiver manufacturers are working on SR4 products that have the potential to reach to 300m. Recently, the IEEE has recognized this issue and is looking to address it in its next generation study group. It is called the Next Generation 100Gb/s Optical Ethernet Study Group and its charter is to investigate 25G-per-lane standards and to explore lower-cost solutions to cover reaches perhaps up to a kilometer.

Any 100G variant using 25G signaling is still under development. While the optical devices are almost ready to go, there are long-term projects to ascertain how 25G is going to run on a printed-circuit board (PCBs) or on twinax cable. The group that was studying this has just officially been named a task force in the IEEE – the P802.3bj 100 Gb/s Backplane and Copper Cable Task Force. There are chip sets available to run 25G signals over PCBs that will be available in the coming months. Texas Instruments was demonstrating this at SC11 and Altera, Amphenol, Semtech/Gennum, IBM, Inphi, TE Connectivity and Xilinx showed 25G products in the OIF booth at OFC/NFOEC 2012.

Notice in the table above that there are different signaling schemes and form factors between 100GBASE-CR10, SR10 and 100GBASE-LR4. The CXP that was chosen for short-reach copper and LOMF is not suitable for longer-reach SMF operation. Even though most of them were involved in the IEEE process, equipment manufacturers are not happy about this because that means their products must support two different form factors at the same time. It may also doom CXP to only the initial products until another, better form factor can be developed that will cover both cost effectively – maybe a CFP2 or CFP4? Or the 25G signaling matures and the SR4 and CR4 variants are created in the QSFP28 (now being worked on in the SFF committee) is used.

The LR10 variant is not standardized, but is backed by a consortium of vendors and end users – including Google and Facebook. Whether this will take hold in the industry at large remains to be seen, but some of the industry leaders are boasting that it is actually selling very well currently at more than 2,500 units already.

So, while we talk about Terabit Ethernet being on the horizon and there have been multi-vendor demonstrations of 25G signaling for 100G operation, plenty of work remains to bring 100G to fruition prior to the next speed bump.

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.