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Software-defined WAN is the latest craze in enterprise WAN connectivity -- so can it work for unified communications and collaboration?
WAN accelerators have been useful tools to squeeze more performance out of expensive WAN links. These tools have morphed into software-defined WAN (SD-WAN) products, which promise to reduce costs further and improve network reliability and efficiency.
Functionally, an SD-WAN uses smart controllers to collect a set of WAN links to provide greater aggregate bandwidth, improve reliability and lower costs. They are called SD-WAN devices because they use centralized policy definitions in their control plane to dictate how the forwarding plane handles packets, much like how the SDN controller programs the forwarding plane of network switches. An SD-WAN implementation creates a single smart link abstraction from multiple physical links.
The cost savings come from two main aspects. The first has been proven in WAN accelerators, as they compress data transiting the WAN links, which effectively increases their bandwidth. Secondly, SD-WAN controllers can intelligently send data streams over multiple WAN links, creating a multilink path that provides greater aggregate bandwidth. Traffic can be segregated on individual links and can be prioritized on the aggregate link.
Managing UC traffic over an SD-WAN
Running unified communications and collaboration (UCC) over an SD-WAN offers several benefits -- some of which may not be readily apparent. The first is probably clear: an increase in aggregate bandwidth. More bandwidth means less congestion for a given traffic volume with potentially better loss and jitter characteristics. However, there are other benefits.
The SD-WAN controllers are smart about inspecting traffic and determining which links should be used to forward the traffic, as well as automatically applying quality of service. So, the UCC traffic can take the low-latency link, while bulk data can be forwarded on the higher latency, higher bandwidth link. As link characteristics change, the controller can adapt. This setup is much better than the complicated policy routing configurations that were formerly required.
Historically, policy routing configurations required identifying the traffic that should take a different path, then modifying the forwarding information (next hop) for the packets that were matched. It was a lot of configuration that had to be exactly right to function correctly. And when something changed, like adding another link, the configuration had to change.
Another benefit is derived from changes in WAN usage patterns. Application traffic formerly traveled from a remote site to the data center. However, software as a service deployments -- provided by cloud companies -- modify the traffic patterns.
Remote UCC traffic may travel from the remote site to a cloud provider's infrastructure. Forcing that traffic to the corporate data center then out to the Internet simply adds latency and increases the potential for packet loss. Connectivity between members of a distributed corporate workforce creates similar traffic patterns.
Since the SD-WAN controller can measure the path characteristics, it can dynamically decide which path is best. Think of this as a form of dynamic policy-based routing without the complexity that was formerly required.
Finally, a traditional redundant WAN design uses a primary and a backup link in which the backup path sits idle most of the time, providing real value only when the primary path fails. Policy routing configurations can make use of the backup path, but at the cost of significant complexity.
Since SD-WAN can use multiple links -- up to eight, in one vendor's case -- network reliability and resilience are increased. The loss of a single link has much less impact on the aggregate bandwidth.
But beware of a hidden risk with the link aggregation part of the technology. You can have more traffic than the remaining operational links can handle when the failure of a single link occurs. The SD-WAN controller needs to provide policy controls to automatically determine which traffic gets priority when the aggregate bandwidth is less than the offered load.
Creating more reliable UC functions
SD-WAN is an incremental technology that provides good value and is relatively easy to implement. A year ago, Greg Ferro, a network engineer and Ethereal Mind blogger, predicted SD-WAN as an important technology. He had some rational arguments in its favor, none of which seem to have changed.
The use cases for running UCC over SD-WAN are compelling. Some UCC functions are high-bandwidth, such as video, and gaining transport efficiency means those functions will be more reliable, consistent, and most importantly, usable.
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