by Dave Jameson, Principal Architect, Fujitsu Network Communications
The world has seen rapid changes in technology in the last ten to twenty years that are historically unparalleled, particularly as it relates to mobile communications. As an example, in 1995 there were approximately 5 million cell phone subscribers in the US, less than 2 percent of the population. By 2012, according to CTIA, there were more than 326 million subscribers. Of those, more than 123 million were smartphones. This paradigm shift has taken information from fixed devices, such as desktop computers, and made it available just about anywhere. With information being available anywhere in the hands of the individual users some have started to called this the "human centric network," as network demands are being driven by these individual, often mobile, users.
But this growth has also created greater bandwidth demands and in turn has taken its toll on the infrastructure that supports it. To meet these demands we’ve seen innovative approaches to extracting the most benefit from existing resources, extending their capabilities in real-time as needed. Clouds, clusters and virtual machines are all forms of elastic compute platforms that have been used to support the ever growing human centric network.
But how does this virtualization of resources in the datacenter relate to SDN in the telecom carrier's network? Specifically how does SDN, designed for virtual orchestration of disparate computational resources, apply to transport networks? I would suggest that SDN is not only applicable to transport networks but a necessary requirement.
What is SDN?The core concept behind SDN is that it decouples the control layer from the data layer. The control layer is the layer of the network that manages the network devices by means of signaling. The data layer, of course, is the layer where the actual traffic flows. By separating the two the control layer can use a different distribution model than the data layer.
The real power of SDN can be summed up in a single word - abstraction. Instead of sending specific code to network devices, machines can talk to the controllers in generalized terms. And there are applications that run on top of the SDN network controller.
The southbound interface handles all of the communications with the network elements themselves. The type of southbound interface can take one of two forms. The first is a system which creates a more programmable network. That is to say that instead of just sending commands to the devices to tell them what to do SDN can actually reprogram the device to function differently.
The second type of southbound interface is a more traditional type that uses existing communication protocols to manage devices that are currently being deployed with TL1 and SNMP interfaces.
SDN has the ability to control disparate technologies, not just equipment from multiple vendors.
Networks are, of course, comprised of different devices to manage specific segments of the network. As seen in Figure 2 a wireless carrier will have wireless transmission equipment (including small cell fronthaul) with transport equipment to backhaul traffic to the data center. In the data center there will be routers, switches, servers and other devices.
Today at best these are under "swivel chair management" and at worst have multiple NOCs managing their respective segment. Not only does this add OpEx in terms of cost for staffing and equipment but additionally makes provisioning difficult and time consuming as each network section must, in a coordinated fashion, provision their part.
In an SDN architecture there is a layer that can sit above the controller layer called the orchestration layer and its job is to talk to multiple controllers.
Why do carriers need SDN?As an example of how SDN can greatly simplify the provisioning of the network let's take a look at what it would take to modify the bandwidth shown in Figure 2. If there is an existing 100MB Ethernet connection from the data center to the fronthaul and it is decided that the connection needs to be 150MB, a coordinated effort needs to be put in place. One team must increase the bandwidth settings of the small cells, the transport team must increase bandwidth on the NEs, and routers and switches in the data center must be configured by yet another team.
Such adds, moves, and changes are time consuming in an ever changing world where dynamic bandwidth needs are no longer a negotiable item. What is truly needed is the ability to respond to this demand in a real time fashion where the bandwidth can be provisioned by one individual using the power of abstraction. The infrastructure must be enabled to move at a pace that is closer to the one click world we live in and SDN provides the framework required to do so.
SDN ApplicationsNo discussion of SDN would be complete without examining the capabilities that SDN can bring through the mechanism of applications. There are many applications that can be used in an SDN network. Figure 4 shows a list of examples of applications and is broken down based on the type of application. This list is by no means meant to be exhaustive.
One example of an application that specifically applies to carrier networks is path computation or end to end provisioning. Over the years there have been many methods that have sought to provide a path computation engine (PCE), including embedding the PCE into the NEs, intermingling the control and data layers. But since the hardware on the NEs is limited, so the scale of the domain it manages is also limited. SDN overcomes this issue by the very nature of the hardware it runs on, specifically a server. Should the server become unable to manage the network due to size, additional capacity can be added by simply increasing the hardware (e.g. add a blade or hard drive). SDN also addresses the fact that not all systems will share common signaling protocols. SDN mitigates this issue by not only being able to work with disparate protocols but by being able to manage systems that do not have embedded controllers.
Protection and RestorationAnother application that can be built is for protection and restoration. The PCE can find an alternative path dynamically based on failures in the network. In fact it can even find restoration paths when there are multiple failed links. The system can systematically search for the best possible restoration paths even as new links are added to the existing network. It can search and find the most efficient path as they become available.
SDN and OTN ApplicationsA prime example of SDN being used to configure services can be seen when it is applied to OTN. OTN is a technology that allows users to densely and efficiently pack different service types into fewer DWDM wavelengths. OTN can greatly benefit the network by optimizing transport but it does add some complexity that can be simplified by the use of SDN.
Network OptimizationAnother area where SDN can improve the utilization is by optimizing the network so that over time, it can make better use of network resources. Again, using the example of OTN, SDN can be used to reroute OTN paths to minimize latencies, reroute OTN paths to prepare for cutovers, and reroute OTN paths based on churn in demand.
NFVIn addition to applications, SDN becomes an enabler of Network Function Virtualization (NFV). NFV allows companies to provide services that currently run on dedicated hardware located on the end user's premises by moving the functionality to the network.
ConclusionIt is time for us to think of our network as being more than just a collection of transport hardware. We need to remember that we are building a human centric network that caters to a mobile generation who think nothing of going shopping while they are riding the bus to work or streaming a movie on the train.
SDN is capable of creating a programmable network by taking both next generation systems and existing infrastructure and making them substantially more dynamic. It does this by taking disparate systems and technologies and bringing them together under a common management system that can utilize them to their full potential. By using abstraction, SDN can simplify the software needed to deliver services and improve both the use of the network and shorten delivery times leading to greater revenue.
About the Author
Fujitsu Network Communications Inc., headquartered in Richardson, Texas, is an innovator in Connection-Oriented Ethernet and optical transport technologies. A market leader in packet optical networking solutions, WDM and SONET, Fujitsu offers a broad portfolio of multivendor network services as well as end-to-end solutions for design, implementation, migration, support and management of optical networks. For seven consecutive years Fujitsu has been named the U.S. photonics patent leader, and is the only major optical networking vendor to manufacture its own equipment in North America. Fujitsu has over 500,000 network elements deployed by major North American carriers across the US, Canada, Europe, and Asia. For more information, please see: http://us.fujitsu.com/telecom