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Lifting the Cloud Over SDN

Sunil Khandekar

Software-defined networking (SDN) must be magic. Why else would researchers, educators, vendors, customers -- practically everyone and anyone connected to the networking industry -- be so high on SDN?

The answer, of course, lies in the promise of SDN. After all, isn't it supposed to completely transform networking? Isn't it the innovation that has finally rescued the networking industry after a decade-long drought? And, most importantly, isn't the SDN market forecast to generate tens of billions of dollars -- an estimate being raised every month? (See Defining SDN & NFV.)

The cloud over SDN
Interestingly, everyone has their own definition of SDN and their own take on how it will reshape the networking industry. That's not entirely surprising. The term is broad enough to allow everyone's convenient interpretation to stand. The industry has made progress in moving beyond hype, and customers are now asking how SDN will help them, rather than what SDN is. Nevertheless, there is still a fair amount of confusion, which causes doubt and constricts the real progress that SDN stands to deliver. It is time to lift the cloud over SDN.

The ultimate goal of an SDN solution is to massively simplify network operations, increase agility, and accelerate deployment of new services without sacrificing security and control.

The four key tenets of an SDN solution are abstraction, automation, control, and visibility.

SDN bridges the gap between applications and networks to enable the rapid consumption of network services such as bandwidth, QoS, security, firewall, and load balancing by providing visibility and control to the applications. It is about providing abstraction of network capabilities, and it is about the automation of network provisioning. It is about separating what applications need from how the network implements its capabilities.

In order to lift the cloud over SDN, we need to understand how various implementations of "SDN" currently promoted across our industry measure up against these defining characteristics of SDN.

1. Does SDN = OpenFlow?
Discussion of separating the control and data planes took off when the Open Networking Foundation introduced the OpenFlow protocol version 1.1 circa 2011. Normally, the control and forwarding planes are part of the same network switch or router. But the ONF advocated separating and logically centralizing the control plane from the forwarding plane. The forwarding plane would remain part of the network element -- in other words, the switch or router. The ONF introduced OpenFlow as the southbound protocol used by the control plane to program reachability information in the forwarding elements.

Separating the control plane and the forwarding plane was not new. It had been done a decade ago in routers, though both functions still resided in the same physical device. The idea of physically separating the two planes and logically centralizing the control plane is not new, either. It had been already proposed in prior work, such as IETF ForCES initiative. But the industry took note of the revived efforts this time around, and the idea opened up interesting possibilities. Benefits included the ability to conduct control plane upgrades that did not disrupt network forwarding, centralizing the control plane to enable traffic optimizations based on a network-wide view (vs. network-element views), and removing the burden of processor-intensive distributed control protocols from lightweight network elements: virtual switches, CPEs, etc.

However, the overt focus on the separation of the control and forwarding planes and the shiny new OpenFlow protocol diverted attention away from SDN. The separation of the control and forwarding planes created the notion that all forwarding elements could be made simpler and cheaper. It is absolutely true that the networking requirements in campus and data center networks have traditionally not been nearly as stringent as required in the WAN. As a result, the premium attached to these devices have not been justified. The "white-box" discussion that ensued in the industry and drove down the cost of networking devices commensurate with networking requirements has been great for customers. This change has been long overdue. It was tempting for some to apply the same broad brush everywhere and suggest that all networking elements, including WAN core and edge routers, could also be simplified. This caused some confusion in the industry, which has largely settled now.

To be clear, this approach -- separating the control and forwarding planes -- falls short when measured against the four tenets of SDN discussed before. Though it provides control over forwarding elements under the OF controller domain, it does not deliver against the other three tenets: visibility into applications, abstraction of networking capabilities, and network automation.

However, the long-overdue change that caused pricing structures to change in the networking industry is nothing but goodness, and the ONF deservedly gets the credit for this.

2. Does SDN = traffic engineering?
The often-cited case study of Google's SDN implementation for the purpose of traffic engineering the network is certainly interesting. The Google implementation is about computing optimal paths for the network using an offline compute tool and then programming these paths in network elements using OpenFlow. This approach affords Google full control and visibility over the network infrastructure. But it is not the first such implementation, nor is it new by any means.

The (former) MCI network team members must get a chuckle out of this, because they did exactly the same thing 14 years ago. The one difference? They did not use OpenFlow as the southbound protocol. Instead, they used MPLS labels for traffic engineered paths computed with an offline traffic engineering (TE) engine, now called a path computation element (PCE) server, which were programmed using SNMP in their network elements. Yes, this was back in Y2K.

Next: A new approach

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User Rank: Light Beer
7/22/2014 | 8:45:09 PM
Thanks Sunil for distilling the buzzword into clear capabilities and characteristics.

I think the network is following the demands of the server and storage virtulization in the data center/enterprise and is responding to the economy of scale from the cloud computing.

I liked how you net the final goal of the network to be the "application delivery" with the abstraction of what from how, provisoning the network based on the application characteristics, and the visibility and control of the (App) delivery.

I see the similarities on OpenFlow with the other standards (and initiatives) and its possible fate (example SMI-S by SNIA from storage side of the world), as I see ONF has added conformance testing and vendor extenstions which reminds me of how fragmented the storage industry was in adopting the standards and the high expectation from customers and sysemintegrators. 

For reference http://snia.org/ I can't even find the SMi-S links now on the site. I wonder how is OpenFlow different from the other standards to lead a better outcome.




User Rank: Blogger
7/22/2014 | 12:08:32 PM
Re: Let's not forget the business angle..
Thanks Steve.  

Couldn't agree more on the business benefits.  Indeed, massively simplying operations translates to OPEX savings, increasing agility and quicker TTM translates to capitalizing on opportunity, flexibility in the network infrastructure translates to CAPEX savings. 

Yes, my focus in the article is on the network and how to it is made consumable by SDN for applications running on top.  The applications running on top certainly are important on how they are architected for deployment and deliver efficiency and automation at that layer.
User Rank: Blogger
7/22/2014 | 11:56:45 AM
Re: Bit quick to dismiss multi-vendor OSS
Definitely Ray - to the extent multi-vendor EMS helps right now to manage the existing mult-vendor networks, this is only goodness.  Was simply keeping focus on what SDN ultimately stands to deliver.
Steve Hateley
Steve Hateley,
User Rank: Light Beer
7/22/2014 | 9:28:26 AM
Let's not forget the business angle..
Great article Sunil.

From the Nuage position, your observations are good and well captured however I sense that there is still understandably an air of hardware vendor, "from the network up" perspective. But if the aim is to give an unbiased view on what SDN means to the industry across the board we should be throwing in the all-important business perspective. 

"The ultimate goal of an SDN solution is to massively simplify network operations, increase agility, and accelerate deployment of new services without sacrificing security and control."

Increasing agility (to build, configure and create new market-facing services) and accelerating deployment (shortening the time from lead-to-activate) are two goals that translate well into the concept of simplifying business automation. This requires a holistic ability to not only understand virtual networks and virtualised services, but to properly orchestrate their delivery from the sales process right through to the VNF manager and virtual machines. In many cases this sales automation is now driven from SaaS/Cloud based applications.

New startups with lightweight provisioning tools are a small part of the fully automated process, and provisioning is only one capability of the traditional EMS. In fact comprehensive orchestration needs to encompass technical catalog abstraction of available resources and logical services. In turn this is dependant upon a federated inventory perspective that reigns in not only the virtual resources but also logical and physical connectivity necessary to "connect" the cloud. Then of course there is "provisioning" but we mustn't forget the logical ordering of the necessary processes to activate requested services. So provisioning is just a cog in a larger machine.

SDN certainly brings an evolutionary change that impacts network vendors, CSPs, ISVs and customers all in one go - something that previous service and infrastructure enhancements have never fully done. Importantly though it's not just a network vendor play. To make it a success, NEMs, ISVs and CSPs need to find common ground and make it work. 

Best regards, Steve



User Rank: Blogger
7/22/2014 | 3:32:52 AM
Bit quick to dismiss multi-vendor OSS
Good article Sunil, though I have to point out a slight tension in your argument.


You state early on that:

'The industry has made progress in moving beyond hype, and customers are now asking how SDN will help them...'

Indeed -- network operators want to know how SDN, and indeed ANY technology or strategy, will help them perform better, provide a better service and make (more/any) money.


Then later, when discussing 'next-generation element management systems', you rightly allude to the fact that a next-gen EMS does not equal SDN (and I think we all know who you're referring to here...) you state:

'Does [a multi-vendor EMS] provide business agility? Not really. At best, it enhances the present mode of operations, to an extent.'

I think there's a good argument that any multi-vendor EMS that works NOW and is also relevant to future network evolutionaryy developments is providing operational and business agility -- after all, the operators want to know HOW any technology can help them, and for most telcos SDN is something they are looking at for the future, whereas a multi-vendor EMS is something that can help them right now.

A multi-vendor EMS does not = SDN, but it can sure make a difference to companies struggling to maximize efficiencies and meet customer demands, something that an SDN implementation cannot do for them with such immediate impact.

So - I am not saying an EMS = SDN, or that SDN isn't going to transform networking, I'm just highlighting that you've maybe been a bit quick to dismiss something that COULD provide great value AND act as a stepping stone towards a virtualization strategy just because it doesn't tick your SDN boxes.  

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