This Clear Choice Roundup of four products that trim WAN links presents details from three vendors - Expand Networks, Silver Peak Systems and XRoads Networks. Optimizing WAN links can reduce telco charges in either of two ways. For mature links with fairly steady use (neither growing nor shrinking), you can use WAN-optimization devices to compress the data and then tell your telco to dial back the bandwidth you're leasing. You pay less for the link, yet the same information flows through it.For links with rapidly increasing bandwidth use that you plan to upgrade soon, WAN-optimization devices can compress the data and thus let you defer the upgrade to a much later date. A WAN link that was near maximum capacity suddenly can handle present and future traffic with ease.Compressing the data flowing across a WAN link is just one of the techniques these devices employ. They also accelerate traffic by compensating for TCP\/IP inefficiencies, caching frequently accessed data and prioritizing business-critical packets.These tools are appropriate for virtually every kind of network traffic, with two obvious exceptions - already compressed data and encrypted data. These data types lack repeated strings of characters and thus are poor candidates for compression.Initially, we intended to run a full comparative test of WAN-optimization tools but found that several vendors were working on new versions (which should be announced around now). We intend to run a full comparative test later this year.In the meantime, we present details on four products from three vendors - Expand Networks, Silver Peak Systems and XRoads Networks. If you can't wait until later this year to start slimming down your WAN links, these tools can give you immediate relief. Think of this article as the WAN link appetizer for the full meal to come.One final note: We decided to provide individual scorecards for these products, as opposed to comparing them in a combined scorecard. The scores are not meant to be compared with each other in our typical fashion but are to be used to judge the products on their own merits. See "How we tested WAN environments."Barry Nance runs Network Testing Labs and is the author of Introduction to Networking, 4th edition and Client\/Server LAN Programming. His e-mail address is firstname.lastname@example.org. Nance is also a member of the Network World Lab Alliance, a cooperative of the premier reviewers in the network industry, each bringing to bear years of practical experience on every review. For more Lab Alliance information, including what it takes to become a member, go to www.networkworld.com\/alliance.