WAN optimization is a set of techniques that make applications and file transfers run faster over a wide area network, the links that connect offices, data centers and clouds over long distances. It works by sending less data across the link and by reducing the impact of latency on protocols that were designed for local networks. It is usually delivered as a pair of appliances or software instances, one at each end of the link, or as a feature of some SD-WAN and cloud networking services.
At a glance
- WAN optimization targets two problems: limited bandwidth and high latency between sites.
- Common techniques include deduplication, compression, caching, TCP optimization and application-specific protocol acceleration.
- Most methods need cooperating devices or software at both ends of the link.
- Results depend heavily on the traffic: repetitive, uncompressed data benefits most; already encrypted or compressed data benefits least.
- Some SD-WAN products include optimization features, but many SD-WAN deployments do not.
What problem it solves
Many business protocols were built for a local network, where a round trip takes a fraction of a millisecond. Stretch the same protocol across a country or an ocean and each round trip can take tens or hundreds of milliseconds. An application that makes hundreds of small requests before showing a screen can feel unusable even when the link has plenty of bandwidth. Buying a bigger circuit does little, because the delay comes from distance, not capacity.
Bandwidth itself can also be the limit, especially at international or remote sites where circuits are expensive. When the same files, images or backup blocks cross the link again and again, sending them in full every time wastes capacity. WAN optimization addresses both problems: it cuts repeated data and reduces how many round trips an application needs.
How it works
Deduplication. Devices at each end keep a store of data patterns they have already seen. When a chunk repeats, the sending side transmits a short reference and the receiving side rebuilds the original from its own store. This can cut traffic sharply for repeated files and backups.
Compression. Data that has not already been compressed is shrunk before it crosses the link.
Caching. Frequently requested content is kept close to users so it does not need to cross the WAN each time.
TCP optimization. Standard TCP behavior can underuse long, high-latency links. Optimizers adjust window sizes, acknowledge data locally and recover from loss more efficiently.
Protocol acceleration. For chatty protocols such as some file-sharing and older business application protocols, the device can answer or batch requests locally, reducing round trips. Support for specific protocols varies by vendor.
Traffic shaping. Many products also include quality of service (QoS) features that prioritize important traffic when the link is busy.
Optimization can run on physical appliances, virtual machines, cloud instances, or inside a provider’s network. Encryption limits what can be done: compression and deduplication gain little on encrypted traffic unless the device is configured to decrypt it.
For guidance on combining optimization with modern WAN designs, see our SD-WAN solution page.
When it matters for buyers
- International or remote sites. High latency to headquarters or a data center makes optimization most valuable.
- Data center replication and backup. Moving large, repetitive data sets between sites within a set window.
- Replacing MPLS with SD-WAN. Check whether the SD-WAN you are evaluating includes optimization, and whether you need it, before retiring existing appliances.
- Expensive bandwidth. Where circuits are costly, such as satellite or some overseas locations, reducing data sent can delay an upgrade.
- Appliance refresh. End-of-life optimization hardware is a natural time to ask whether the traffic that justified it still exists.
Questions to ask vendors
- Which of our applications and traffic types will benefit, and can you show results from a trial on our own traffic?
- How do you handle encrypted traffic, and what decryption, if any, is required?
- Do we need an appliance or instance at each site, or can one end sit in your cloud or point of presence?
- Is optimization included in the SD-WAN license, or sold separately?
- How is the deduplication store sized, and what happens to performance when it fills?
- What happens to traffic if the optimization device fails: does it pass through unoptimized or stop?
How it differs from SD-WAN
SD-WAN manages several links as one network and steers each application onto the best available path based on policy and measured performance. WAN optimization changes the traffic itself so it uses less bandwidth and fewer round trips on whichever link it crosses. The two solve different problems and can work together: SD-WAN picks the path, and optimization makes better use of it. Some vendors bundle both, so compare what each product actually includes. Older private WANs built on MPLS often paired the circuits with dedicated optimization appliances.