The Software-Defined Wide Area Network (SD-WAN) market is heating up with start-ups, traditional hardware vendors and WAN service providers competing for a slice of the enterprise deployment pie.  In 2017, we expect more enterprises to consider deploying SD-WAN onto their global networks to take advantage of the promised cost reduction and increased network agility.

There are typically two ways to get your network software defined:

1. Create an overlay network 

The first is to deploy hardware appliances or software running on a ‘white box’ to create an overlay network above the underlay network of WAN providers and ISPs. Currently, this is the most common practice as many vendors and System Integrators (SI) are pushing this model as the magic formula to reduce WAN cost by replacing expensive MPLS circuits with cheaper but higher bandwidth broadband Internet circuits.  The SD-WAN software controller works by aggregating these low-cost ISP circuits into a ‘pipe’ with improved performance and availability; and then creating an overlay WAN with applications visibility that allows enterprises to dynamically control how their applications are routed.  Enterprises can move towards a carrier neutral environment by utilizing whatever lower cost access is available on site, including wireless. This certainly sounds too good to be true and indeed by ‘disregarding’ the underlying transport layer, it does not remove the fact that the transport layer must still be monitored, managed and maintained in real-time.  Customers need to own any network outages and resolve them with multiple providers and ISPs in this deployment model, potentially increasing the IT resource requirement.   Moreover, an ‘Internet only’ network might not be suitable for all enterprises due to diverse enterprise WAN environments and requirements of business applications.

2. Managed SD-WAN as-a-Service 

The second option is to subscribe to a managed SD-WAN as-a-Service offering from existing WAN services providers. Many existing WAN providers have announced their own SD-WAN products or are in the process of doing so by partnering with SD-WAN technology vendors.  In this model, the SD-WAN provider is responsible for providing the underlay transport layer as well as the overlay network. 

Many WAN service providers, such as NTT Communications, offer hybrid networking with a core MPLS offering and multiple options for Internet-based connectivity.  A hybrid network is ideally suited to SD-WAN deployment as mission critical applications can continue to be carried over MPLS while other traffic can be offloaded to lower cost broadband Internet connections.  Cost reduction can be achieved by lowering the current MPLS circuit bandwidth while moving to an active-active WAN configuration with increased agility and applications visibility. The same service provider is responsible for monitoring, managing and maintaining both the overlay and underlay networks with higher efficiency than what the customer can achieve with their own resources.   

In addition, some WAN providers are deploying cloud-based SD-WAN gateways into their existing network to provide greater design flexibility and support a phased approach to migration for enterprises deploying SD-WAN. 

In summary, both models of deployment will continue to be offered in the market for the near future.  Enterprises looking at SD-WAN deployment must evaluate carefully the pros and cons of each model by looking at their business needs, applications requirements and available IT resources.