SD-WANs are not WAN optimization. They solve a different problem from WAN optimization. And yet walking along the floors at the ONUG conference hearing about SD-WANs and service chaining, I couldn’t help but think that software-defined WANs (SD-WANs) are the death of WAN optimization in branch offices.
WAN Optimization
We started using WAN optimization at a time when the fundamental challenge facing TCP application performance was the distance between the branch office and the data center. The latency incurred in long distance connections limited TCP throughput regardless of the bandwidth of connection. As a result, two connections – 10 Mbps and 100 Mbps — between New York and Los Angeles will still deliver the same amount of TCP bandwidth. (It’s the Mathis algorithm and to better understand why that’s the case see this post.) Add in packet loss and the situation on becomes worse.
WAN optimization corrects for these challenges dramatically increasing the data that can be delivered over distances. Throughput is improved by a combination of reducing the effects of latency through various techniques, such as optimizing TCP, and increasing the amount of data that can be sent over the wire with compression and data deduplication. Packet loss can be eliminated or reduced by aggressively retransmitting TCP packets and reconstructing lost packets on the fly using forward error correction (FEC). Other technologies address traffic shaping, security and more.
New World, New Rules
Today’s world brings a different set of the challenges to application performance. I’ve seen latency become less of an issue as my customers go to the cloud. No longer do branch offices need to access resources in data centers far, far, away (Yes, that’s a nod to The Force Awakens.) Cloud operators replicate data sets and applications so they’re closer to their users. Latency has shrunk at a time when the bandwidth has grown and packet loss rates have continued to drop (see figure).
Instead, we need to find ways to make our routing smarter. BGP and OSPF other modern day routing protocols do not factor application requirements into their shortest path metrics. Router hops are counted, but ignored are the latency and loss on those paths. This says nothing about how routing policies are aligned to service provider economics and not necessarily enterprise performance.
SD-WAN’s Are Innocent
SD-WANs address the routing problem. A smart SD-WAN solution should be policy-based and aware of the underlying network. Tolerances and conditions should be defined for applications in policies. The overlay fabric should gather loss and latency statistics on the various paths between the sites participating in the SD-WAN. By aligning the two, the SD-WAN can steer application traffic along the optimum path to the destination.
Some data flows will continue to need the performance benefit of WAN optimization. These cases include applications or data resident in distant data centers or “elephant” data flows, such as with data replication, backup or large trans-global file transfers. For such flows, enterprise can locate WAN optimization within regional headquarters and rely on service chaining to direct the necessary flows from the branch to the optimization function in the regional location. Service chaining decouples application services from the underlying network. Data flows can be directed as necessary through network functions, such as WAN optimization, even when those functions may lay out-of-path.
So suppose, for example, your company has sites in China and in North America. The old world would have called for WAN optimization devices to be located at each office across both continents. The new approach? Deploy an SD-WAN and locate WAN optimization in the regional headquarters of either region. Most flows are sent across the Internet to the cloud. The inter-regional flows or those requiring optimization are first steered across the virtual overlay to the optimization devices in the regional headquarter. They’re optimized and then sent on to their destinations, where low latency paths do not impede the speed. Pretty cool, right?
SD-WAN Flexibility
The combination of changing conditions and the flexibility of SD-WANs suggest to me that organizations will be less dependent on WAN optimization in their branch offices. To find out how to migrate your branches to SD-WANs, consider using the free The Ultimate WAN RFP template. It’s a great guide for how to evaluate all things WAN. Contact us at 212-203-7310 x150 for a free network assessment and to discuss how to adapt the RFP to your needs.
