Swimming in 100GbE’s alphabet soup - Lightwave

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Swimming in 100GbE’s alphabet soup

By Jim Theodoras <br>ADVA Optical Networking

Recently, there has been a lot of confusion around the area of next-generation 100-Gigabit Ethernet (100GbE) development and who is doing what. Given the alphabet soup of acronyms one has to wade through when dealing with standards bodies and multisource agreements (MSA), such confusion perhaps is not surprising. For example, I have recently seen multiple reputable news sources report that IEEE 802.3bj is going to be working on 400GbE! Given the fact that “100GbE” and “four-lane” were bandied about, one could perhaps understand the faux pas. Since this is by no means the only example of confusion out there, let’s do a quick rundown of some recent 100GbE announcements and what they really mean.

Let’s start with the aforementioned IEEE 802.3bj. According to the effort’s chair, John D’Ambrosia, chief Ethernet evangelist within the CTO Office at Dell, “The IEEE 802.3bj is currently in task force status, with a mission to define next-generation 100GE copper interfaces for backplanes and client ports.” Notice he said copper. As optical client ports have leaped to 40- and 100GbE capacities, it seems the bottleneck has moved once again to the backplanes that interconnect them. Moreover, denser 40/100GbE client ports are on the horizon, and backplanes must scale to leverage the new capacity.

That is not to say backplanes are the only focus. It turns out backplane technologies work great for very short reach copper cable client connections in applications where even the cost of an optical alignment ferrule would be prohibitive. The end goal appears to be 1 m on a backplane and 5 m in a cable, with both using four parallel lanes of 25 Gbps in place of today’s 10 lanes of 10 Gbps.

Wait, did I just say four lanes of 25G? Does that mean the end of the 10X10 MSA? Of course not -- the two efforts are totally unrelated. IEEE 802.3bj is working on backplane interconnect and client ports, not the electrical interface to optical modules, though admittedly it could be re-tasked for such in a pinch. In fact, the CFP MSA recently amended the electrical connector pin-out definition for their CFP2 module to increase the number of pins so that a 10-wide bus could be accommodated, though a 4:10 reverse multiplexer appears to be the preferred approach at the moment.

According to the 10x10 MSA, “The 10X10 MSA set of solutions has set a new price point for 100 Gigabit Ethernet and thousands of ports have shipped because of their low cost. When the industry goes to 4x25Gbps electrical signaling in the CFP2, a reverse gearbox can be used to break out the lanes into 10 lanes of 10G to support the low cost 10G lasers and receivers.”

And speaking of CFPs, the CFP package was the first generation of 100GbE pluggable optical modules. The CFP was developed by the CFP MSA, and has been a great success for 100GbE as a whole as it allowed the industry to focus all of its investments on a single form factor. However, like all first-generation optical modules, it was rather large, with four being about the most you could fit onto the faceplate of a line card. Not one to rest on their laurels, “The CFP MSA is now working on two next generation form factors, CFP2 and CFP4, to double and quadruple the front panel density, respectively,“ explains Chris Cole, CFP MSA spokesperson.

Similarly, the IEEE has formed a Study Group with an eye on higher-density 100GbE. According to Dan Dove, senior director of technology at AppliedMicro and chair of the IEEE 802.3 Next Generation Optical Study Group, “We are currently in the Study Group phase, investigating next generation 100G optical PMD alternatives with a goal to reduce the cost, power, and size required for 100G links.”

So, what of the aforementioned 400GbE? It turns out, before moving to the next speed step, the thought leaders in Ethernet have been striving to better understand the bandwidth needs of end users, as well as bandwidth consumption models and trends. Sometimes you don’t just climb a mountain because it is there. John D’Ambrosia also leads the IEEE 802.3 Industry Connections Ethernet Bandwidth Assessment Ad Hoc which has been meeting regularly to discuss these topics, as well as listen to invited speakers from some of the largest bandwidth providers/consumers today.

The need to better understand all aspects of bandwidth is universal and an important prerequisite to the move to even higher data speeds. To help foster discussion, the Ethernet Alliance will be centering its next Technology Exploration Forum (TEF) on this very topic, “The End User Speaks!”

So, hopefully, this clears things up. And before being hasty and jumping to the next speed plateau of Ethernet, it appears there is plenty of work still to be done with 100GbE.

Jim Theodoras is senior director of technical marketing at ADVA Optical Networking and a past president of the Ethernet Alliance.

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