most of the commercial simulators are gui driven, while some network simulators are cli driven. the network model / configuration describes the network (nodes, routers, switches, links) and the events (data transmissions, packet error etc.). output results would include network level metrics, link metrics, device metrics etc. further, drill down in terms of simulations trace files would also be available. trace files log every packet, every event that occurred in the simulation and are used for analysis. most network simulators use discrete event simulation, in which a list of pending "events" is stored, and those events are processed in order, with some events triggering future events—such as the event of the arrival of a packet at one node triggering the event of the arrival of that packet at a downstream node.<section end=transclusionlabelg20170307t1400gmt1 />