Nonetheless, the question of where WAN-optimization features physically belong isn't easy to answer.

Over the next few years, Whiteley expects to see WAN-optimization technology shift from being deployed as a dedicated hardware device to being integrated as a feature on a more universal platform. "WAN optimization should not be viewed as a solution unto itself," he says. "In the long term, it's going to be built into part of the network infrastructure."

Three architectural scenarios are possible, Whiteley says. First, WAN optimization could wind up in the router or packet-layer infrastructure, an approach that such vendors as Cisco and Juniper Networks are putting their weight behind. In other cases it could become part of the application-layer infrastructure, along with load-balancers and other application-oriented technology; he expects such vendors as F5 Networks and Citrix Systems to advance this option. Third, enterprises could buy a services platform wherein WAN optimization becomes one of many services (print, file, DHCP, DNS) running on an appliance. Microsoft and Riverbed Technology are going in this direction, he says.

For enterprises, committing to an architectural model is no small decision. "Large companies must think long and hard, from an architectural perspective, about how they want to do this," says Jim Metzler, a principal at Ashton, Metzler & Associates.

Making a case for disaggregation

For Joe Skorupa, a research vice president at Gartner, the key issue is less about where optimization features will reside and more about how they can be deployed in a flexible, manageable way to accommodate different enterprise priorities.

Skorupa once thought application-delivery controllers and WAN-optimization devices would merge, "but in fact it hasn't happened to any significant degree," he says. What he is seeing instead is a trend toward disaggregation, separating WAN devices into component parts that can be deployed - in the data center, branch offices and the network - and reused as necessary. "You can place a particular function where it happens to make the most sense. And if it makes sense to have the same function, such as QoS, in two different places, then the nice thing is that you get consistent behavior in both locations," he says.

F5 is the furthest along this path, Skorupa says, citing as an example the vendor's WebAccelerator module, which is built to accelerate dynamic Web pages. "It can run on the Big-IP application-delivery platform, it can run as a stand-alone device, and with an extra lease of software, you'll actually be able to put it on one of F5's WANJets in a branch office. It brings different value depending on where it's placed," he says.

F5's TMOS common operating system unites the vendor's platform elements. Similarly, Blue Coat Systems has engineered a common operating system and platform for its acceleration devices and security-gateway products. A single box runs all Blue Coat functions, so enterprises can turn on or off the features they need, including Web filtering, logging, antivirus software and peer-to-peer blocking.