The last newsletter noted that Jim participated in a recent Network World chat on the topic of application performance management and WAN acceleration. Today, we'll continue that thread by discussing how different performance problems require different optimization techniques. The point being that the questions that you should ask vendors when evaluating WAN acceleration products will depend upon the performance problems you are trying to resolve.

We recently surveyed 337 IT professionals who identified a number of categories of applications that were challenging to support from the perspective of ensuring successful application performance. This included real time applications such as software running over Citrix XenApp (formerly Citrix Presentation Server), VoIP and video conferencing. Other applications that were cited as concerns included backup and replication as well as file related applications and protocols; i.e., CIFS, NFS, FTP.

It typically does not make sense to accelerate the performance of real-time traffic, but there are some minor exceptions. Some IT organizations, for example, compress the headers that are associated with VoIP traffic. Leaving those minor exceptions aside, the primary technique that can help to improve the performance of real-time traffic is QoS. QoS refers to the ability of the network to provide preferential treatment to certain classes of traffic, such as VoIP or videoconferencing. QoS is typically implemented either by some queuing algorithm (i.e., priority queuing, class-based queuing, weighted fair queuing) or by using an MPLS service.

Many performance problems, including backup and replication, can be alleviated by protocol acceleration. For example the TCP windowing mechanism can make inefficient use of WAN bandwidth, especially over high latency paths. TCP can be accelerated by a variety of techniques that increase a session’s ability to more fully utilize link bandwidth. Some of the available techniques are dynamic scaling of the window size, selective acknowledgement, and TCP Fast Start.

For more information on how which optimization techniques are the most effective at ensuring the performance of key traffic categories, see this brief on Webtorials. In the meantime, we would like to hear from you. What has been your experience when dealing with the suppliers of application performance management and WAN acceleration solutions? Have they been straightforward with their answers or more allusive?

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