Last time, we discussed the fact that WAN scalability is impacted by many factors other than just the ability to increase the bandwidth of the WAN circuits. Today, we'll continue the discussion by focusing on the scalability of network and application acceleration products.

In late August, Riverbed unveiled three appliances that it claims deliver industry-leading scalability. The appliances are targeted at large offices and data centers - places that require scalable products.

Each of the appliances has a stated WAN capacity of hundreds of megabits per second. This is roughly equivalent to increasing the bandwidth of WAN circuits. While this is a good thing, there are other factors that influence the scalability of network and application acceleration products and Riverbed discussed some of that when it launched the products.

In the last WAN newsletter, we mentioned how some of the early X.25 networks could only support a very limited number of simultaneous virtual circuits and that this had limited their scalability for certain types of users. The Riverbed appliances can support tens of thousands of simultaneous TCP connections, a factor that is critical in both large offices and in data centers.

Another aspect of scalability is the ability of the appliances to scale to support new traffic types. In this regard, the Riverbed announcement was a good news/bad news situation. The good news is that Riverbed's operating system (RiOS - Riverbed Optimization System) now supports QoS enforcement for all traffic types including VoIP. The bad news is - why did it take so long to support QoS?

How scalable are the Riverbed appliances? The answer is that IT organizations looking to deploy network and application optimization need to test any potential solution in a setting that closely reflects their current and planned production environments. Only in this way can IT organizations determine if some potentially subtle limitation of the solution negates the ability of that solution to be effective in their environment.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.