Using QoS for WAN optimization

With all the new IP applications traversing wide-area nets, industry experts speculate that past QoS measures need to be carefully balanced against WAN optimization and application acceleration technologies.

According to a December research report by Forrester Research analyst Robert Whiteley, QoS efforts aren’t so simple when it comes to ensuring the performance of IP-based applications over the WAN. And with advanced traffic, such as multi-media applications crossing the lines, previous efforts at QoS could be foiled in the future, the report says.

“QoS is a necessary – and often evil – component for multi-service networks. Its goal is to guarantee that not all traffic is treated equally,” Whiteley states. “It’s important to note that QoS is not a technology, but rather an attribute of your network defined across many technologies like routers, switches, and appliances.”

Whiteley details how QoS helps network managers first mark traffic by classes of service and then shape traffic based on available bandwidth. A QoS-enabled network essentially puts traffic into various buckets that represent classes of service (CoS). This involves distinguishing traffic that gets top priority down to that traffic with less importance, based on business needs or preset policies. Whiteley says when it comes to differentiating traffic, network managers need to be sure not to get too granular, because doing that makes QoS “exponentially harder to administer.”

Secondly, traffic shaping works with the preset buckets, or classes, of traffic to “throttle back excess packets” and “prevent one particular class from hogging” bandwidth. The main difference between CoS and shaping is the more dynamic nature of traffic shaping technologies, from vendors such as Packeteer (see Packeteer’s recent release of Packeteer 7.0), which provide products to help address bursting traffic loads.

QoS requires ongoing maintenance and attention, to work effectively according to Whiteley. “Every time a company adds a new enterprise app, touches a significant network component, or adds and subtracts nodes – QoS must be revisited. Similar to any network policy, it has to be treated as an ongoing project subject to audits and regular refreshes,” he writes in the Forrester report.

Whiteley advises that if companies cannot eliminate QoS in their networks they should opt to have it performed by a service provider as a managed service. He explains that applications often perform worst on the WAN, so there isn’t as pressing a need to implement QoS on the LAN.

“To mitigate the WAN complexity, Forrester recommends managed service providers like AT&T and MCI,” Whiteley advises.