Backward Explicit Congestion Notification Research Articles

Quality of Service: Part 2 Route at the Edge, Switch at the Core

Almost any network can take advantage of QoS techniques, whether it's a small independent LAN, an enterprisewide layout, or an internet service provider. Obviously the larger the network, the more QoS options there are. The level of complexity also rises with larger networks. We've managed to just barely skim the surface of QoS in this two-part series. Table 3 is offered as a quick summary of this discussion. Cranking through some of the details can be time consuming, but very interesting. Understanding QoS details can sometimes get burdensome due to the extent of rules-based routing described above and the few billion acronyms. One of my favorites that I came across was backward explicit congestion notification (BECN). I can just envision saying to our network manager, "Using the Orbison Model, I think that my backward explicit congestion notification is set too high." Of course, then you must be ready when they ask, at do you mean by that?" (Especially since I made up the "Orbison M odel".

Ping-pong flow control for ATM ABR traffic

In this paper, we propose an improved technique for congestion control, named as ping-pong flow control (PPFC), for asynchronous transfer mode (ATM) available bit rate (ABR) traffic. This is a rate-based flow control scheme, in which the rate regulation is achieved by directly adjusting the transmission rate in the source end station. The proposed algorithm uses a bipolar feedback strategy, which employs positive and negative feedbacks to control the transmission rate for different switch states. These states are determined using the traditional threshold-based method. We also introduce state early detection (SED), which enables the PPFC to control traffic flows more precisely and accurately at critical moments. The simulation results show that the proposed algorithm provides a higher throughput and lower cell loss ratio when compared to the well-known backward explicit congestion notification (BECN). Furthermore, these results also show that PPFC is robust against feedback losses.

Modeling and control of VBR H.261 video transmission over frame relay networks

Examines the transmission of variable bit-rate (VBR) H.261 video over a mixed traffic (video/inter-LAN) integrated services frame relay (FR) network. We introduce a modified H.261 codec that produces VBR output and show that parsing of the video bit stream at group of blocks (GOB) boundaries produces variable length FR packets well suited to the network. We demonstrate that GOB-level video traffic requires a more sophisticated statistical model of the resulting data stream than the frame-level models. The transform expand sample (TES) method is used to obtain an accurate model of the autocorrelation and the marginal probability distribution of the bit-rate variations at the GOB level. A simple and effective methodology is introduced for capturing the periodic components that are present in the GOB-level autocorrelation. The methodology is extended to permit simulations of VBR codecs in which the codec quantization step size is adjusted in response to prevailing network conditions. We show that the quality of service requirements of VBR video can be met by using the FR backward explicit congestion notification (BECN) facility in conjunction with a modified H.261 codec whose rate is controlled by the congestion notification. We also show that the performance of the control mechanism is significantly influenced by a subset of network threshold and codec control parameters which are identified using 2/sup k/ factorial analysis techniques. We obtain optimal ranges of values for these parameters using mean field annealing. Variable quantization rate control may be more effective for this purpose than variable frame rate control.