2002 - cesnet

GÉANT 1.2 Gbps line. The left diagram represents the measurement with fiveminute time-step, the right one measurement with three-second time-step. Yousee that the average load is not significantly different, however, the differencesin peaks are considerable. The permanent peaks of 500 –700 Mbps will completelychange our idea of a load on what seem to be fairly free line.Figure 3.7: Influence of time step on line statistics – time step of 5 minutes(left) and 3 seconds (right)At a certain point the 1.2 Gbps capacity of the line was even exceeded. The reasonis that the physical capacity is 2.5 Gbps in fact and the 1.2 Gbps limitationis provided by the router. Statistical algorithms based on short-term history ofinterface load are used and therefore the short peaks may exceed the configuredlimit.Even more significant differences can be seen in the comparison of a five-minutetime-step with a one-second one. For the Prague–Liberec line, see Figure 3.8.The envelope peak curve is almost four times higher than the average values.3.6.3 Development Tendencies in the Operationof Backbone NetworkThe rate of utilization concerning the backbone network core has reported anevenly increasing character. The increase in the utilization of individual backbonelines is similar and the average values of December 2002 are approximatelytwice or three times higher than the average values of January 2002.The following diagrams of the backbone lines load depict both average valuesand the maximum peaks. These limit values are based on the highest valuesof an average five-minute load during a time interval representing a time uniton a time axis. For example, as regards year-long curves, this is the value of thehighest average five-minute load during 24 hours therefore these values do notcorrespond with the real short-time load as it was described in the previousmeasurement analysis.The first example worth mentioning is the Prague–Brno line, 2.5 Gbps. Wewould like to point out the peak utilization (a continuous flow of 2 Gbps for aperiod of two hours) of this line in the direction of Prague, reported in November2002, caused by the traffic of a MetaCentrum from Brno to Baltimore (Mary-30 High-speed National Research Network and its New Applications 2002