Communication networks are in wide use in many technological fields including distributed computing, data exchange and telecommunication applications. Communication networks generally include a plurality of nodes, such as bridges, LAN switches, routers, cross-connections and telephone switches. The networks further include communication links, such as cables, point-to-point radio connections and optical fibers, which connect the nodes. The networks also include ports, generally within some of the nodes, for attaching external devices such as computers, terminals, handsets, and multiplexers referred to as end-points (or hosts).
Networks are becoming increasingly complex, especially due to their increasing speeds of operation, the number of units interconnected by a network and the formation of large networks from different types of sub-networks. In addition, the networks may transmit concurrently various types of data such as text, voice, video and other multimedia files. In order to allow for these different types of data, some networks are designed to provide different amounts of bandwidth and different levels of quality of service.
A major issue with newly deployed and existing communication networks is testing and trouble-shooting, i.e., checking whether the network is operating according to its specifications and, if not, determining the cause of the network's inadequate performance (for example, the identity of a faulty unit).
Simulators such as "BONeS," produced by Cadence, San Jose, Calif., and "OPNET," produced by MIL3, Washington, D.C., allow creation of models of a network, and subsequent testing of the network based on these models. An operator provides the simulator with a map of the network, which includes its components, specifications and expected data traffic patterns. The simulator provides performance estimations of the entire network, together with performance estimations of the network under various constraints, such as a non-operating node or link. Such performance estimation under constraints is referred to as "what-if" analysis. However, simulators do not usually cover all aspects of the simulated networks and are limited in the network size which may be simulated. In addition, simulators are able to detect only design faults, not operational faults.
Application performance measurement tools, such as "Chariot," produced by Ganymede, Research Triangle Park, N.C., and "Webload" and "Webexam," produced by Radview, Tel Aviv, Israel, evaluate the performance of existing or new applications as they are introduced into the network. However, they do not test the network itself independent of specific applications. In addition, they do not provide "what-if" analysis capabilities.
Dedicated point-to-point testing equipment is a commonly-used network testing tool. Such equipment is described, for example in U.S. Pat. No. 5,477,531, which is incorporated herein by reference. Usually, dedicated point-to-point testing equipment requires two users who coordinate their operations in order to identify a misbehaving component of the network. Moreover, to test a large network, the testing equipment must be moved between many ports of the network.
Passive network monitoring devices based on network management software, such as "HP-OpenView," produced by Hewlett Packard, Palo Alto, Calif., and "Soltice Enterprise Manager," produced by Sun Microsystems, Mountain View, Calif., are also in very common use. These devices are used in network troubleshooting, but they are passive and cannot test a network which is not in use.