Bandwidth Management Face-off: Xedia

Managing bandwidth is a key component of delivering quality of service (QoS) on any network. The need to manage bandwidth arises from the desire to have many users, applications and customers share the same physical or logical link or circuit. Class-based Queuing (CBQ) was specifically designed to handle this task.

CBQ combines rate-controlled queuing techniques with real-time traffic classification in which each packet is inspected and matched against user-defined traffic policies. Once identified, the packet is placed in the appropriate traffic class, or queue. In this way, different types of traffic can receive different levels of service.

CBQ can control the delivery rate and priority for any protocol. In addition, CBQ can regulate the sender's transmission rate for any synchronous protocol, such as TCP, without causing packet loss or introducing additional latency. A sample CBQ implementation is on Lawrence Berkeley National Laboratory's Web site.

Xedia's Access Point implementation of CBQ delivers wire-speed bandwidth management for traffic classes ranging from a single TCP connection to aggregates comprising millions of flows. In contrast, TCP rate control deals only with the rate of a single TCP session. If bandwidth for one user out of 500 sessions on a link needs to be allocated, TCP rate control has to explicitly modify the individual rates of the other 499 users.

The debate between CBQ and TCP rate control gets derailed when the discussion jumps to the subject of how different traffic types are recognized or how non-TCP protocols are handled. By definition, non-TCP protocols such as User Datagram Protocol (UDP), SNA and IPX are not addressed by TCP rate control. However, CBQ, is architected to handle TCP and non-TCP protocols.

Backbone router vendors are actively developing products with CBQ features to provide QoS for the core of the Internet. Even Cisco is inching toward support for a CBQ-like feature set with incremental improvements in its IOS software. Features such as committed access rate, weighted fair queuing and access lists are primitive implementations of CBQ's rate limiting, queue scheduling and traffic classification capabilities.

Last but not least, the Internet Engineering Task Force is championing a significant working group targeting IP QoS. The effort, known as Differentiated Services, or Diff-Serv, is 100% consistent with the classification, aggregation, queuing and scheduling mechanisms of CBQ.

CBQ is a proven, scalable and tested technology adopted by many of the leading ISPs. Its nonproprietary, nonintrusive architecture is ideal for delivering IP QoS on the Internet, intranets and extranets everywhere.

Stephenson is chairman of Xedia Corp., a Littleton, Mass.-based provider of standards-based Internet access solutions. He can be reached at (978) 952-6000, Ext. 100 or ashley@xedia.com.