Content delivery networks make a lot of sense if you need to accelerate the delivery of video, content, and applications over the public Internet, but what about internal corporate WANs? “CDNs and ADNs are for folks who need to leverage the Internet as a business-grade network,” says Robert Whitely, senior analyst, enterprise networking, at Forrester Research. “For private networks using frame relay, MPLS [multiprotocol label switching], or an IPSec intranet, where one company owns both ends of the network connection, appliance- and/or software-based approaches to WAN optimization may be the answer.”(Read also about content distribution networks in Your Web site’s secret weapon.)

In fact, the issues affecting today’s corporate WANs are not all that different from those involving the Internet. On the one hand, more business is being conducted at widely distributed branch offices and other remote sites. On the other, trends in consolidation and compliance have removed applications, servers, and IT staff from those sites and centralized them in better-managed and more-secure datacenters. The result: longer distances between the user and the applications and data. The problem is exacerbated by the growth of latency-sensitive applications such as VoIP and streaming video, which compete with other applications for limited WAN bandwidth. “You don’t have the same congestion issues that you have on the Internet,” says Melanie Posey, IDC research director for telecom markets, “but you do have bandwidth competition from the other applications running over the company’s WAN.”

WAN-optimization appliances from Riverbed, Blue Coat, Cisco, Juniper, Packeteer, Citrix, and Expand Networks take several approaches, similar in many ways to those used by CDNs, to speed the delivery of content and applications across corporate WANs. Many use compression and byte and object caching to reduce traffic on the WAN pipe.

QoS methods prioritize applications such as VoIP over less time-sensitive applications such as e-mail. Protocol-optimization techniques speed inefficient protocols such as TCP and HTTP to reduce latency. Other solutions use their own WAN-optimized transport protocol to overcome the inefficiencies of TCP.

Solutions from Riverbed and Blue Coat require dropping appliances at each end of the WAN connection. Cisco’s WAAS (Wide Area Application Services) integrate directly into its integrated services routers.

Cisco and Riverbed also offer some application-specific acceleration capabilities that use tricks such as intelligent message suppression, data and metadata caching and validation, message prediction, read-ahead techniques, and transaction prediction to optimize certain application flows. Which WAN-optimization solution you choose depends to a large extent on the types of applications you must accelerate and who your networking vendor is.