FlexE in a Two Act Play
Act One, wherein Ethernet Services (ES) explains Flexible Ethernet to a totally clueless Optical Transport (OT), thus describing what is termed FlexE Unaware Transport.
ES: You haven’t been showing me much love lately.
OT: Whatever do you mean.
ES: You know how deeply I depend on you.
OT: Of course, you rely on me to transport you for any distance beyond a few thousand meters.
ES: And you have always been there for me. Until now. I loved how we grew up in perfect harmony. When I was a 1GE toddler you were there with 1G transport. Then we made our first big jump together to 10GE and 10G transport. And it was perfectly exhilarating when you were there with 100G transport to support me at 100GE.
OT: You didn’t even mention my 40G transport for your 40GE service.
ES: Excuse me, that was your initiative, and I just followed. Besides, hardly anyone uses 40GE today.
OT: So what’s the problem. You know I am pressing ahead with even faster transport rates to support your future needs. 150G, 200G, all the way to 600G today, and even faster in a few years.
ES: A number of issues that have been developing recently, and interestingly, one of them isn’t about going faster. It’s about going slower.
OT: I am all ears. Tell me more. I would like to help if I could.
ES: You say that now. But you have been so focused lately on just going faster, and worrying about how to operate at the edge of the Shannon Limit, that you haven’t been paying attention to what is happening in my world.
OT: I am listening now.
ES: I am sure you’ve heard about me being used to connect data centers, particularly for relatively short distances of 10s of kilometers, for data replication and backup.
OT: Of course, Data Center Interconnect. It’s the fastest growing transport segment.
ES: So here is something you may not know about DCI. A few years ago I introduced a new 25GE service for short distance use within data centers. Now it seems that data center owners want to extend that same 25GE between data centers. You know, create a single distributed data center over a broad geographic area.
OT: I see where you are going with this. You want to know how come I am not there to support you with 25G transport.
ES: Yes, after years of being “joined at the hip,” we have developed different priorities, and are growing apart. Because of that, I am making some changes so that we can continue working together amicably.
OT: Do they impact me?
ES: Hmm, and a minute ago you sounded so concerned. Well, the good news for you is that in the short term there is no impact. You can carry on with your current technology agenda. But once you understand more about what I am doing, I think there are some changes you can make that will make our relationship more intimate again.
OT: Sorry for the negativity. So, what going on?
ES: I am introducing a new technology called Flexible Ethernet, or FlexE for short. In a nutshell, it adds a layer of flexibility between my layer 2 Gigabit Ethernet service rates (MAC layer) and my layer 1 physical interface rates (PHY layer). The only thing that changes is the mapping of my MAC into my PHY, which I do using a FlexE Shim. So my dear friend OT, as you are only concerned about being able to terminate my existing PHY interfaces, and these remain unchanged, you have nothing to worry about.
OT: What you are saying is that FlexE is totally transparent to me. Still, I would like to understand more.
ES: I’ll continue. FlexE is divided into three applications, or use cases. These are: 1) Bonding, 2) Channelization, and 3) Sub-rating. The best way for me to explain them is in terms of problems they solve.
OT: Let’s start with Bonding.
ES: Alright. Let’s say I have routers in two data centers that want to connect using a really high speed 400GE service.
OT: So what’s the problem. I can give you a 400G transport interface today.
ES: Well it is not always available quickly, and the price point may still be too high. But with FlexE I don’t care. I break the 400GE interfaces into four 100GE streams and transport each of these separately. It is very easy to procure 100G transport from you. Once they are transported to the far end, I “bond” them back together again into 400GE.
OT: Okay. I get Bonding. But that deals with going faster. Earlier you mentioned problems with going slower.
ES: Yes, that is where Channelization comes in. This is when I have mix of lower speed GE interfaces I want to transport between points A and B. To make a concrete example, let’s say I have a mix of 6x10GE, 2x25GE, 1x40GE, and 1x50GE. FlexE provides a much more scalable mechanism than other methods available to me today. With FlexE it is a breeze. I just map these multiple GE interfaces into two 100GE streams, which you transport with your eyes closed, and then I unbundle them at the far end.
OT: Okay, I get it. Basically I keep providing you with standards pipes as before, and it seems mostly at 100G.
ES: Yes, meeting my 100GE with your 100G is an excellent match! Let’s go to the last use case, Sub-rating. Say I have a 150GE service to transport, but you can only supply 100G pipes. Using FlexE I can sub-rate my service into two 75GE streams and transport those physically over the 100GE physical interfaces, without resorting to flow control that I need to implement today.
OT: That would mean that on my side I would have 25G unused capacity on each 100G transport connection.
ES: Correct. Now I have no obligation to inform you that you are carrying empty packets. As we already discussed, this whole FlexE stuff can be totally transparent to you. But let’s assume you knew. Then you can re-use that 2x25G capacity for something else.
OT: That is interesting. Come to think of it, if I can instruct you to sub-rate certain services, I can dynamically free up bandwidth capacity in my network, say to deal with emergency conditions, or when I need extra bandwidth for a big event.
ES: Yes I think you are beginning to understand the possibilities. Tell you what. Now that you are “in the loop”, why don’t we pick up this conversation from here next time.
OT: Sounds good to me. We can call it FlexE Aware Transport! I will think about all the possibilities and benefits this can bring.
ES: Great, we’ll cover FlexE Aware Transport in Act Two. I do look forward to working more intimately once again.