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How wireless WAN can make SD-WAN more agile and resilient

Dec 06, 20214 mins

WWANS can augment SD-WANs with failover, redundancy, and rapid set-up.

wireless wan
Credit: Shutterstock / Peera_stockfoto

Wireless WAN has begun to rise in availability and utility, and to improve in affordability. It brings wide-area connectivity to just about any physical space and can hit speeds far in excess of older single or multiple T1 links and DSL.

It has its challenges to be sure, and the biggest ones are centered on the business model. It is hard to get a WWAN connection priced the same way a wired connection is: paying for a given speed, with no arbitrary limit on how many bits can be transferred in a billing period.

So IT teams using WWAN are typically faced with two unpleasant options: a) either pay a flat rate but, when a threshold number of bytes is hit, face a sharp decrease in speed; or b) pay a per-gigabyte overage fee for usage past the threshold. Sometimes carriers want to push both options—decreased speed and pay-by-the-drink overage costs.

SD-WAN can help IT take advantage of one of WWAN’s cardinal virtues—no lead time for service at a new location—and mitigate some of the other problems. SD-WAN and WWAN makes a potent combination, especially for businesses with aggressive strategies for opening branches, those with many small locations, and those with many locations outside metropolitan areas.

SD-WAN: Connectivity is Job 1

SD-WAN’s most basic purpose is to increase enterprise resilience by reducing the number, severity, and duration of WAN outages.

SD-WAN started with WAN virtualization that would aggregate connectivity from multiple sources and load-balance traffic across all links at once. Keeping all the links active allowed for seamless failover from a bad link to good links and, as important, provided seamless failback once service on the bad link was restored. Users might work through multiple failures and restorations of links without ever knowing anything about them. This was a huge win not just for user productivity but also for IT, as link problems could go from critical, drop-everything issues to watch-and-wait problems that usually fixed themselves.

SD-WAN + WWAN for smoother startups

Deploying an SD-WAN node equipped with a cellular modem can ensure that a new branch is functional in as little an hour. If wired connectivity is planned, as is usually the case for cost and performance reasons, new links can be connected to the SD-WAN and brought online without disrupting existing operations. Once enough wired connections have been brought in to provide the requisite level of redundancy, the WWAN can be shut down, again without disruption of services.

Capacity on-demand

Of course, the WWAN does not need to be shut down completely, and can instead be shifted to serve as bandwidth-at-need. It can function as emergency failover connectivity or as bursting capacity.

WWAN failover is useful for locations that have few options for redundant wired connectivity or little choice of service providers. The SD-WAN can keep the WWAN connection alive with a trickle of traffic that stays far under monthly caps but shift all traffic to it when the primary WAN link fails.

Similarly, prioritization settings and link-costing factors can be manipulated to allow some kinds of traffic to use the WWAN when capacity is otherwise lacking.

By bringing transparency to the utilization, and policy controls to bear on the problems of the WWAN, SD-WAN can be key to preventing less-critical traffic from creating surprise mega-bills from the WWAN provider.

Added redundancy

In many locations, it is difficult to get truly path-redundant connectivity, even from multiple service providers, without incurring additional construction costs. This is because all the wired connectivity comes via the same conduits or poles or the same hole through the foundation. One physical disaster can sever all the links. 

On the other hand, a WWAN link will almost always be unaffected by cable cuts. And in the event of a large-footprint disaster like a flood or a hurricane, cell services are almost always restored before other forms of connectivity. They can even be delivered from temporary towers.

So, while WWAN can slot into an SD-WAN as just another link, it does have some unique benefits in terms of agility and redundancy. And, with its ability to balance load across multiple connections and prioritize and limit use of WWAN links at need, SD-WAN can make WWAN more viable for more businesses.


John Burke, CTO of Nemertes, advises clients based on primary research in cloud, networks, automation, and security, and on his 30-plus years’ experience as an IT researcher, practitioner, and leader.