rporate or public data network would handle all these types Ultimately users will be transferring files, sending electronic mail, of traffic (and more). Most small private networks will only have booking holidays, home banking, home shopping, paying bills and one or two types of traffic and are often designed and tuned to those making directory enquiries all from the same (pocket) workstations! specific requirements. The list above is not intended to be conclusive, but to give an idea 40.8.6 Traffic variance of the differing traffic types that exist. Traffic type and load can vary with the time of day. This must be 40.8.3 Topology considered when estimating the performance requirements of a system. The construction of a network is very dependent on the distribution An example is that of a large company with many retail outlets. of the users and the resources. In the past large organisations During the day the traffic is almost completely local to the individ- centralised computing centres to which the users were linked to ual retail outlets, as they process data onto the local processor with using private communications circuits. Today, distributed process- just a few interactive enquiries to head office. At the end of the day's ing has created the WAN/LAN topology network structure where business the local processors up load the stock requirements for the the LANs provide high speed local connectivity between the users next day's trading to regional main frames, which arrange for the and the local computing resources such as file servers, local elec- goods to be on the shelves for the following day's trading. This Multiplexers in communications networks 40/15 change in traffic conditions needs to be calculated in the overall information can be used to check the general well being of the network design. network. 40.8.7 Load balancing 40.8.11 Error rate monitors The most basic (and most used) form of traffic balancing comes in Errors can be assigned to alarms with various levels of significance the form of local l