TERENA COMPENDIUM - Géant

TERENA Compendium of National Research and Education Networks In Europe /TrafficIn cases where links are more heavily loaded, it is possible that the bandwidth issaturated at certain times of day. Under these conditions users may experiencea real reduction in performance as congestion leads to packet loss and retries.Under these conditions the throughput per month is not a good indicator.Graph 3B.3.2 Daily traffic variations on a network displaying saturationIn this context, the term external is taken to mean all of the NREN connectionsto GÉANT, commercial peerings, direct connections to other NRENs, crossborder fibres etc. In many cases the percentage of traffic that is exchanged withcommercial networks exceeds 75% of external NREN traffic, although there aresome marked exceptions.We asked each NREN to report the total amount of external bandwidth availablein January of each year and also the total traffic that flowed over that bandwidthin the month of January.From this it is a simple matter to compute the total number of Terabytes thatthe links are theoretically able to transfer in one month and compare it with thetotal number of Terabytes actually transferred. The percentage of traffic over themaximum possible transfer is taken to be the load. actual traffic in January% LOAD =Maximum transfer capabilityOverall the NRENs’ approach to providing a good quality of service is to ensurethat links are lightly loaded, an approach known as over-provisioning. Thisapproach avoids heavy traffic engineering, that can might adversely affect thedevelopment and performance of innovative applications.For most NRENs, link utilisation is less than 10% , so for the purposes of thisevaluation it is reasonable to assume that the links are not saturated.By undertaking the measurements each January, it is has become possible to plotthe values over the years and to observe trends in loading.We have observed that most traffic to and from NREN user sites is exchangedwith sites off the home NREN network – what we here call external networks.52