This content is part of the Essential Guide: What is SD-WAN? Future, challenges, benefits of SD-WAN technology

The far-reaching benefits of SD-WAN improve network edge to inner layers

The benefits of SD-WAN could work inward from the network edge to improve network infrastructure efficiency, anticipate network service needs and maybe emerge as NFV's killer app.

The tech industry has always been known for generating new acronyms, but networking seems to be outdoing other...

areas in recent years.

For example, a partial acronym list includes the following: SDN, network functions virtualization (NFV), Open Networking Foundation (ONF), Open Network Operating System (ONOS), Open Daylight (ODL) and finally, software-defined wide area networking (SD-WAN).

The good news is the last acronym on the list, SD-WAN, may offer us a networking vision that will define and position all the other acronyms for emerging technology efforts, because the benefits of SD-WAN start at the top of the service delivery chain. SD-WAN sits at the network service edge and defines what the service looks like to users. In contrast, technology for most services starts at inner network layers and works its way up the service chain until it finally meets service users.

But network users don't buy technology; they buy services. The major focus of network initiatives -- and the source of the other networking acronyms -- has been on technology changes to infrastructure. Sure, those changes could percolate their way to the edge and create something users could see, but an effort focused on services directly would start right where the market and the money are.

That's what SD-WAN is about. SD-WAN may stand for software-defined wide area network, but that is neither particularly descriptive nor helpful. SD-WAN is more about service than software, and it's not limited to the WAN.

SD-WAN's work at the network edge

Network layers build on one another, as we've known since the '70s, when the Open Systems Interconnection model came along. In brief, the model outlines that you can build connectivity up in layers from the physical wires. A byproduct of that layering ability is  you can build connectivity from a tunnel that looks like a wire, as well, that can be built over almost any network service available -- from IP and Ethernet to fiber.

SD-WAN's original mission was to combine private-network VPN tunnels, like MPLS, and tunnels over the internet to build a VPN that could cover sites too small and numerous to be served by MPLS VPNs alone.

Because of this combined virtual-wires mission, SD-WAN must sit at the network edge. An SD-WAN product usually has several network-side connections and one connection to the user's on-premises network. An SD-WAN device on the customer's premises takes on several popular forms: The original combines internet and MPLS VPN; another uses multiple internet service provider connections or internet pathways. One of the benefits of SD-WAN is to tie all the pathways together to create a tunnel network that links all of the sites on an organization's network. It also uses a forwarding table at each location to send traffic to the correct tunnel and service.

SD-WAN's edge position has led vendors to enhance SD-WAN products with other features ranging from security to application acceleration and traffic prioritization to WAN optimization, where needed. Businesses tend to like these extended features, because many SD-WAN sites are too small to warrant local technical support, and having one device that serves many missions simplifies things for headquarter operations staff that supports the smaller sites.

SD-WAN works from the outer network edge to benefit inner network layers
SD-WAN's position at the top of the service delivery chain can improve infrastructure efficiency for technology efforts in deeper network layers.

SD-WAN in the cloud and as NFV killer app

In most cases, SD-WAN is provisioned as a set of physical devices. But the benefits of SD-WAN include its availability as software, which gives it two additional and vital capabilities. First, it can be deployed as part of an application inside the cloud. Cloud providers normally don't let customers locate physical devices in the cloud, and in any case, a physical device might not make sense given the cloud's ability to host applications in many different places. Second, SD-WAN can be deployed as a virtual network function as part of an NFV deployment.

Virtual customer premises equipment (vCPE) contains a hidden challenge for NFV. The vCPE application is expected to be promising in the near future, but it focuses on enterprise VPN connections and delivers security and related services that most of these connected sites already provide through other on-premises devices. If SD-WAN targets sites not yet on a VPN, and if SD-WAN and extended features can be packaged and delivered through NFV, it might be the killer app NFV supporters have been looking for. If so, that could jump-start all the open source NFV activities out there, including Open Source MANO, Open-Orchestrator Project and ONOS.

If operators had access to SD-WAN data, they could correlate service conditions with network conditions.

NFV isn't the only networking effort SD-WAN could save. If you build a thin SD-WAN shell around changing network infrastructure, service users within the network are insulated from the technology effects of those infrastructure changes. The SDN transformation would be easier, because service users wouldn't have to do anything different, which would help the ONF and ODL projects. MEF's Third Network notion builds services from a combination of IP and Ethernet elements that depend on SD-WAN to unite all the pieces.

Benefits of SD-WAN on service management

Even service-level agreements (SLAs) with customers could be enhanced by SD-WAN. One of the challenges that has dogged network operators is that users want service-wide guarantees. Network management tools deliver the capability. SD-WAN could deliver end-to-end statistics on a service no matter what technology elements were involved. 

In fact, service management at all levels could be improved by having end-to-end statistics. If operators had access to SD-WAN data, they could correlate service conditions with network conditions. This could improve their ability to anticipate situations where network changes would create SLA violations, or where changes in end-to-end delay or packet loss indicate something is happening to the infrastructure below. Managed service providers have already learned about these benefits of SD-WAN and are building businesses on stable services that span multiple operators' networks. Operators themselves are now adopting similar approaches, though more slowly.

Network evolution in any form has to support both the current service models and new service models. It's often difficult to reconcile technical changes in the network with a requirement for stable service behavior at the edge. But SD-WAN does that, and it opens the door for a new and more competitive VPN model. In all, SD-WAN could be the critical step in letting future networks hit two moving targets -- service needs and infrastructure efficiency.

Next Steps

How SD-WAN and MPLS work together

SD-WAN increases the value of SDN and NFV

SD-WAN's effect on the edge router market

This was last published in August 2017

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