Expand used a series of compression algorithms to reduce the number of packets on the wire. Other vendors, most notably Packeteer, also used highly advanced compression schemes and began adding QoS to further allocate and manage WAN traffic flows.
File-caching provides yet another way to reduce traffic by storing a copy of recently accessed files on an appliance near requesting users. As with a browser cache, files and objects are kept closer to the remote user, helping to overcome latency and prevent excessive, redundant requests over the WAN. This is typically a “full file” cache and not made up of smaller data segments. Full-file caching isn’t nearly as effective as newer segment-caching methods, because the chance of a second or third user requesting the same file is slim. Also, if the file on the file server is renamed or changed, then it won’t match the file already in cache and must be transferred again anyway.
In with the new
In recent years, TCP acceleration has taken center stage as one way to improve performance by reducing ACKs and playing games with the TCP window size. Vendors such as Swan Labs, Peribit (now owned by Juniper Networks), Expand Networks, and Riverbed Technology have all developed solutions based on improving TCP’s performance.
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The next step beyond TCP tricks is application-specific acceleration. Some WAN optimization vendors use plug-ins in their appliances to help improve application response. Applications such as DNS, Exchange, FTP, Citrix, Notes, and CIFS/NFS can all benefit from reduced chatter on the wire. The plug-ins work much like the TCP ACK optimization in that they handle redundant requests locally instead of sending each one.
There is no quilt
The WAN optimization and acceleration space is heading toward a convergence of sorts. In the past some vendors specialized in a single technology solution, but now they are adding other technologies to solve additional pieces of the WAN problem. Orbital’s Pierce sees the multiple approaches to solving WAN problems as “patches, in the context of patches and a quilt. In the end, it’s about the quilt; it’s not about the patches themselves. Customers buy patches today because there is no quilt.” The trend is for vendors to move away from “point” solutions to a more comprehensive managed system.
Several WAN appliances include compression and TCP acceleration along with file-caching and application-specific acceleration. But not all vendors agree that such consolidation is wise. “I think more customers are more worried about just the visibility into the network,” says Allot’s Narayanan. “They want a good traffic-management company with the ability to decode any application layer properly, not falsify it.”