Achieving QoS in a Hybrid Cloud Implementation: Page 2 of 2

Software-Defined WAN (SD-WAN)

Another choice that’s becoming popular is SD-WAN. SD-WAN products allow enterprises to use multiple links as if they were virtually bonded together. A typical implementation might have one MPLS link for real-time traffic, one or more Internet links for bulk traffic, and a cellular Long Term Evolution (LTE) link for connection resilience. The SD-WAN devices are located at each enterprise WAN site and they build a full mesh of virtual private networks between themselves. The devices continuously measure each link for available bandwidth, latency, and packet loss. An advantage of SD-WAN is automatic resilience because if one link goes down, the other links carry the traffic for a site.

Because SD-WAN devices are constantly measuring each link, they can dynamically send traffic over whichever links are providing the best connectivity and service for each traffic class. A central SD-WAN controller defines policies regarding which path should be used for each traffic class (much like the CoS mentioned above). A policy might specify that voice and interactive video should transit the MPLS link while application traffic traverses the Internet links.

SD-WAN devices also incorporate compression technologies that minimize the total traffic volume, just as the older WAN optimization devices did. This makes them a preferred choice for upgrading a WAN optimization infrastructure.

Traffic that is directed to Internet sites can go directly to the Internet. This is an advantage for enterprises that are using software as a service, where end users are connecting directly to a hosting provider’s services over the Internet. If an enterprise has more than one Internet link provisioned, the SD-WAN controller can set policies regarding which link SaaS traffic should traverse, potentially keeping the remaining Internet links available for enterprise site-to-site traffic.


Other Factors

Other factors can influence the performance of the resulting system. For example, buffer bloat (the use of big buffers in network equipment) can cause significant performance problems at points where there are big differences in ingress and egress network speeds. A good example is a path that transits a 1-Gbps link into a router that connects to a 10-Mbps WAN circuit. If the router has big buffers, it fools a system on the 1-Gbps side into believing that it has a 1-Gbps path to the destination system. When the buffers fill, the router must drop many subsequent packets. Only after the router’s buffers empty can the sending system resume sending data. We’ve seen cases in which a 10 Gbps-to-1 Gbps path would run at an effective rate of less than 200 Mbps.

Another factor is workload placement -- best practice is to decouple cloud environments from each other instead of distributing an application across multiple data centers. Latency and WAN packet loss can have a significant negative impact on application performance. A widely distributed application will also be much more difficult to troubleshoot when it doesn’t work as designed (or expected).



If you don’t have dedicated links on which you can set QoS, you’ll need to either live with whatever your ISP delivers or you’ll need to investigate one of the other services (MPLS, on-ramp provider, or SD-WAN) to handle your real-time traffic. The SD-WAN option is generating a lot of interest in the industry since it combines WAN optimization, resilience of multiple links, and a form of traffic prioritization.

For more on this topic, please join me at Enterprise Connect, March 18 to 21 in Orlando, Fla., for the session, “Can You Ensure QoS in Your Hybrid Cloud Deployment?” It is a short time from now, but still enough time to get discounted admission, using the code SLATTERY. Register now!