Class-Based Queuing Divvies Bandwidth

BOSTON (06/12/2000) - Network managers need better tools to help them control user access to IP services, as well as how much bandwidth any group of users can consume. Help is on the horizon with class-based queuing (CBQ) technology.

CBQ is a traffic management algorithm developed by the Network Research Group at Lawrence Berkeley National Laboratory as an alternative to traditional router-based technology. Now in the public domain as an open technology, CBQ is deployed by companies at the boundary of their WANs.

Network managers can use CBQ to easily classify traffic to meet business priorities and to ensure each traffic class has the appropriate quality of service. CBQ integrates easily with a company's existing network to protect its investment and provides IT managers with more control over the network, thus reducing bandwidth costs.

The concept behind CBQ is simple. It divides user traffic into a hierarchy of classes based on any combination of IP addresses, protocols and application types. A company's accounting department, for example, may not need the same Internet access privileges as the engineering department. Because every company is organized differently and has different policies and business requirements, it is vital for traffic management technology to provide flexibility and granularity in classifying traffic flows.

CBQ lets network managers classify traffic in a multilevel hierarchy. For instance, some companies may first identify the overall needs of each department or business group, and then define the requirements of each application or group of applications within each department. For performance and architectural reasons, traditional router-based queuing schemes are limited to a small number of classes and only allow one-dimensional classification.

By providing network managers with better control over user traffic, CBQ lets companies meet the needs of response-time-sensitive applications, supports service-level agreements and keeps inappropriate traffic off the network.

To add CBQ to an existing router network, a company would configure it on a LAN-to-LAN basis between the local network and selected WAN routers. This approach minimizes implementation costs by eliminating the need for any hardware changes in the router network.

Because it operates at the IP network layer, CBQ provides the same benefits across any Layer 2 technology and is equally effective with any IP protocol, such as TCP and User Datagram Protocol (UDP). It also operates with any client or server TCP/IP stack variation, since it takes advantage of standard TCP/IP flow control mechanisms to control end-to-end traffic.

Bandwidth is the largest cost in wide-area networking. CBQ lets net managers define bandwidth allowances in absolute terms, unlike router-based schemes, which provide a rough, best-effort percentage. As a result, net managers can better manage aggregate bandwidth purchases and map allocations directly to departmental budgets.

Consider this example: A firm with 10 sites uses a single T-1 line with a monthly network bandwidth cost of $25,000. The firm then encounters a typical problem: Response times for some critical applications become unacceptable, and new applications are expected to increase bandwidth demand by 30 percent. The company determines it needs to double its bandwidth, which will cost $300,000 per year.

However, using CBQ at one site, the company analyzes traffic flow and discovers that time-critical applications use less than 15 percent of the bandwidth. More than 20 percent of the traffic is completely unnecessary, while 60 percent could be supported by a best-effort service. The company uses this information to implement appropriate CBQ-based service policies, improving performance for critical applications without increasing bandwidth. The resulting savings:

$250,000 per year, close to the entire bandwidth budget.

Internet technologies and services are transforming the enterprise network. But companies can't accept the best-effort free-for-all that has characterized traditional IP network services. With CBQ, companies can use their enterprise IP networks to bring together all the services of the Internet age, and provide the visibility, access control and consistently high service quality of business-class service.

Schultz is director of VPN product management at Lucent Technologies Inc. He can be reached at brianschulz@

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