A Study of VBR Traffic Treatment in a Diffserv Domain

The unreliable network layer in the Internet has been a cause of concern for network managers and users. The unreliability manifests itself in terms of lost or delayed packets due to congestion or failure in the network. One of the causes of congestion is the inherent burstiness of network traffic. Traffic includes unpredictable large file or web page transfers as well as variable-rate media streams. “Traffic shaping” means smoothing the traffic as a function of time. Many different schemes to perform shaping have been proposed. The target of such schemes is to increase the amount of traffic that can be supported while maintaining the required quality of service and reducing the amount of congestion in the network. This article presents the results of an investigation into the effects of using various shapers and markers on VBR streams in a Diffserv domain. Simulations are conducted using NS–2 simulation platform applying VBR streams that are shaped using TB and dual-TB shapers followed by srTCM, trTcm, and tswTCM markers. The shaped traffic is applied across a Diffserv domain under unloaded and loaded traffic conditions to determine the effect on the level of congestion due to a particular scheme. Generally, in TB shapers, changing the bucket size affects the burstiness of the traffic and changing the queue length affects the delay of the traffic. Applying different traffic parameters (w.r.t. applications) and connecting them to various shapers provides a suitable burst size and delay for each application and allows different colouring of packets. The most suitable shapers generate a maximum number of green packets, thus reducing the potential for congestion in the network.