August 2, 2008

The ABCs of Traffic Management

By Klein, Jay

Deep packet inspection systems let network managers control network traffic flows. Controlling network traffic requires limiting bandwidth to certain applications, guaranteeing minimum bandwidth to others, and marking traffic with high or low priorities. While this process is typically called traffic management, these activities may also be described as WAN optimization, application performance management, traffic shaping, bandwidth management, bandwidth optimization and quality of service (QoS).

There are some subtle differences among these terms. For example, traffic management uses QoS mechanisms, such as traffic classification, prioritization, queuing and rate limiting. When used informally, however, these terms all loosely describe setting rules or policies for how particular application traffic should behave and then ensuring the network automatically enforces those rules.

Advanced traffic-management systems, which usually rely on deep packet inspection (DPI) technologies, let network managers control network traffic flows based on application types, source and destination addresses, and other variables. To provide this level of granularity, traffic-management tools operate through Layer 7 (the application layer) of the OSI model.

Most organizations migrating multiple application types to an integrated packet-switched WAN service will benefit from traffic management tools like DPI. This is because the WAN is usually more bandwidth constrained than the LAN, causing potential congestion bottlenecks. Also, as a network shared among many customers, WAN performance is often less predictable.

An indication that a network could benefit from traffic management is if performance degradation does not improve much when WAN bandwidth is added. The behavior of certain protocols in a converged, packet-switched environment renders adding network bandwidth an ineffective fix, particularly for applications sensitive to latency.

For one enterprise, the main driver for implementing traffic- management controls was the migration from a time-division multiplexing network to a converged, packet-switch WAN-an IP virtual private network.

Traffic management was deployed at the WAN edge, where the high- speed LAN meets the lower-speed WAN access link. The LAN-WAN juncture is also where both Internet and intranet traffic enters and exits the enterprise, the best place to "tame" traffic and mitigate the impact of non-critical and even suspicious traffic picked up on the Internet. As a result of limiting or blocking the network resources available to undesirable traffic, the performance of the enterprise's business applications was improved.

With high-speed LAN traffic throttling back to a lower-speed access circuit, the LAN-WAN edge was where congestion occurred. LAN- optimized applications behave differently in the WAN environment. Not only is the WAN access link slower, but WAN services also can fall under the management purview of network providers.

The enterprise found that managing traffic in this network segment helped it serve remote users with centralized resources. The network administrator used a GUI to set parameters for business- critical policies. The administrator then propagated those policies to the various network segments where they were enforced.

Traffic management has become a fundamental element of network management in an era where enterprises and service providers are merging all traffic onto packet-switched networks. Converged networks afford many efficiencies and application innovation, but they also require monitoring and control to ensure the various applications-all contending for a common pool of bandwidth-do not negatively affect one another.

The behavior of certain protocols in a converged, packet- switched environment renders adding network bandwidth an ineffective fix.

Jay Klein is vice president and chief technology officer at Allot Communications, Eden Prairie, Minn.

Copyright Nelson Publishing Jul 2008

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