2002 - cesnet

queues, for the division of output interface bandwidths to various classes oftraffic. An advantage of the WRR algorithm – compared to the WFQ algorithm(Weighted Fair Queuing), used by the Cisco 7500 router for the same purpose – isthe lower computation complexity, together with a lower processor load. A disadvantageis that the WRR algorithm will systematically prefer data flows witha higher content of longer packets, compared to data flows comprising mostlyshorter packets (e.g., transmission of files is preferred to voice communication).However, this preference is not too strong and it is therefore irrelevant in practicalterms.Referenced traffic sourceWS1195.113.147.10/29rude -s script.cnfBackground traffic source100BASE-TXfe1/1/0fe1/1/1WS2100BASE-TX195.113.147.18/29rude -s script.cnfTraffic destination100BASE-TX WS3fe1/1/2195.113.147.26/29Juniper M10crude -p 2000 -l crude.logJUNOS5.0Figure 9.1: Configuration of experiments with Juniper routersSome Cisco routers, for example the GSR series, solve this problem with a DRRalgorithm (Deficit Round Robin), adding any unused capacity of a certain trafficclass from one queue cycle to the next cycle, thus eliminating the preferencesto longer packets.Figure 9.2 (left) shows the development of throughput in two data flows, competingfor a capacity of 100 Mbps in one output interface, without any QoSconfiguration. The first data flow includes 1,500-Byte packets (dotted line); thepackets of the second one are 256 Bytes long (full line). The second data flowwas applied over a period of 5 to 25 seconds. We can see that the developmentof throughput was pseudo-random.The right side of the figure depicts the development of throughput after WRRactivation, i.e., each data flow was allocated a bandwidth of 50 Mbps. The seconddata flow was applied at 5 to 10 seconds. We can see the development ofthroughput settling down and the data flow of 1500-Byte long packets reports aslightly higher throughput than the data flow of 256-Byte long packets.Juniper routers provide a programming interface (API), allowing for the sendingof configuration commands and receiving their responses over the network.Commands and responses are structured as XML documents. Connection canbe provided through SSH.122 High-speed National Research Network and its New Applications 2002