Kevin Deierling has served as Mellanox's vice president of marketing since March 2013. Previously, he was chief architect at Silver Spring Networks from 2007 to 2012. From 2005 to 2007, he was vice president of marketing and business development at Spans Logic. From 1999 to 2005, Mr. Deierling was vice president of product marketing at Mellanox Technologies. Kevin has contributed to multiple technology standards through organization including the InfiniBand Trade Association and PCI Industrial Manufacturing Group. He has over 20 patents and was a contributing author of a text on BiCmos design. Kevin holds a BA in Solid State Physics from UC Berkeley. Follow Kevin on Twitter: @TechseerKD
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So in two previous posts, I discussed the innovations required at the transport, network, and link layer of the communications protocol stack to take advantage of 100Gb/s networks . Let’s now talk about the physical layer. A 100Gb/sec signaling rate implies a 10ps symbol period.
Frankly, this is just not possible on a commercial basis with current technology. Neither is it possible on copper nor on optical interfaces. At this rate the electrical and optical pules just can’t travel any useful distance without smearing into each other and getting corrupted.
So there are two possible solutions. The first is to use 4 parallel connections each running @25Gb/sec. The second is to use a single channel with a 25Gb/sec symbol rate but to send four bits per symbol. This can be done either through techniques like Pulse Amplitude Modulation (PAM4) or optically by sending four different colors of light on a single fiber using Wavelength Division Multiplexing (WDM) techniques. Continue reading →
Network and Link Layer Innovation: Lossless Networks
In a previous post, I discussed that innovations are required to take advantage of 100Gb/s at every layer of the communications protocol stack networks – starting off with the need for RDMA at the transport layer. So now let’s look at the requirements at the next two layers of the protocol stack. It turns out that RDMA transport requires innovation at the Network and Link layers in order to provide a lossless infrastructure.
‘Lossless’ in this context does not mean that the network can never lose a packet, as some level of noise and data corruption is unavoidable. Rather by ‘lossless’ we mean a network that is designed such that it avoids intentional, systematic packet loss as a means of signaling congestion. That is packet loss is the exception rather than the rule.
Lossless networks can be achieved by using priority flow control at the link layer which allows packets to be forwarded only if there is buffer space available in the receiving device. In this way buffer overflow and packet loss is avoided and the network becomes lossless.
In the Ethernet world, this is standardized as 802.1 QBB Priority Flow Control (PFC) and is equivalent to putting stop lights at each intersection. A packet on a given priority class can only be forwarded when the light is green.
During my undergraduate days at UC Berkeley in the 1980’s, I remember climbing through the attic of Cory Hall running 10Mbit/sec coaxial cables to professors’ offices. Man, that 10base2 coax was fast!! Here we are in 2014 right on the verge of 100Gbit/sec networks. Four orders of magnitude increase in bandwidth is no small engineering feat, and achieving 100Gb/s network communications requires innovation at every level of the seven layer OSI model.
To tell you the truth, I never really understood the top three layers of this OSI model: I prefer the TCP/IP model which collapses all of them into a single “Application” layer which makes more sense. Unfortunately, it also collapses the Link layer and the Physical layer and I actually don’t think this makes sense to combine these two. I like to build my own ‘hybrid’ model that collapses the top three layers into an Application layer but allows you to consider the Link and Physical layers separately.
It turns out that a tremendous amount of innovation is required in these bottom four layers to achieve effective 100Gb/s communications networks. The application layer needs to change as well to fully take advantage of 100Gb/s networks. For now we’ll focus on the bottom four layers. Continue reading →