2002 - cesnet

3.6 Statistical Traffic Analysis3.6.1 Average Long-term Utilization of BackboneNetwork CoreFrom a long-term perspective, the core of the CESNET2 backbone network hasthe character of an over-provisioned network. In this case the QoS (Quality ofServices) parameters are guaranteed by sufficient free capacity of the backbonelines and sufficient free processing capacity of active network devices (routers,switches). In addition to other aspects, this is a positive feature with respectto services operating on a real-time basis. Their quality depends on the timeand time-capacity parameters of the network, e.g. absolute one-way or two-waydelay, jitter, absolute current available free capacity, etc. From a global point ofview, the rate of the CESNET2 backbone network core utilization reaches from10 to 13 % of the overall available capacity.3.6.2 Utilization of Backbone LinesAccording to the outcome of long-term empirical monitoring, the average longtermrate of use reaches around 15 %, as a frequently mentioned limit for theover-provisioned networks. Even though the long-term average load of the CES-NET2 backbone core is below this value, this does not mean in any case, thatthe network capacity is not used as it may seem at first sight.When reviewing the results, it is necessary to take into account the method ofoperational long-term measurements.The basic parameter influencing the results of measurement is the time intervalbetween two successive measurements of a particular item – the time-step ofmeasurement. In the operating mode, these measurements are usually carriedout with a time-step of several minutes. As regards the CESNET2 backbone, theconfigured time-step is usually 5 minutes.The results of such measurement express just the average utilization of a particularline during the entire time-step, i.e., for us, this means an average utilizationduring a five-minute interval. Having in mind that the range of hundreds ofseconds is in fact an infinity from the point of view of short-term perspective inhigh speed networks, there is no chance to estimate the real usage of the linecapacity within that time interval.The two diagrams below demonstrate the dependence of the results on themeasurement time-step. The measurement was provided during the same timeinterval with different time-steps. The Figure 3.7 shows utilization of the Prague–High-speed National Research Network and its New Applications 200229