Managing WAN traffic on a per-flow basis

When managing WAN bandwidth for optimal performance, there are many technologies that queue traffic, sense congestion so you can throttle back traffic to smooth out packet flows and chop up packets into more transportable sizes.

Many of these technologies are supported in traffic management appliances and sophisticated WAN access routers. When wading through the morass of technology options to invoke at the WAN edge to optimize application performance, there is no single solution that meets the requirements of all enterprises. Your choices will depend on the applications you support, how many sites you have, staff expertise and budget.

But note also that there are certain applications, such as VoIP and Citrix, which, while they may not require much bandwidth, do require a minimum amount to function at all. For these applications, you will want to configure your traffic management system so that you have control over the number of concurrent flows within a traffic class – something you should be sure your system can do.

For example, when using traffic management systems, the tendency is to allocate bandwidth based on a traffic class as a whole. A “class” is traffic you’ve deemed to be treated with the same priority (it can be an application, user group, traffic from particular site or some combination of these characteristics).

You prioritize a traffic class by allocating a certain minimum amount of bandwidth to it, putting a ceiling on how much bandwidth it can consume, marking a priority tag in it for treatment by the service provider in the WAN or by using a combination of these and other techniques.

But while 256K bits/sec of bandwidth is likely adequate, in aggregate, for 10 concurrent Citrix sessions (Citrix traffic could constitute a “traffic class”), it might not be adequate for more than 12 or 13 sessions, given that a single Citrix flow might require 20K bit/sec before dying on the vine. So one thing you might want to check out, capability-wise, in your traffic management system is your ability to allocate bandwidth within a traffic class on a per-flow basis.

Per-flow treatment can be achieved using special per-flow queuing or TCP rate control techniques. Generally speaking, traffic management appliances are ahead of the curve on per-flow bandwidth allocation compared with routers.