Routing in circuit-switching networks has traditionally involved a static routing strategy with the use of（  ）paths to respond to increased load. Modern routing strategies provide more adaptive and flexible approaches. The routing function of a packet-switching network attempts to find the least-cost route through the network , with cost based on the number of（  ）,expected delay, or other metrics. In virtually all packet-switching networks, some sort of adaptive routing technique is used. Adaptive routing algorithms typically rely on the（  ）of information about traffic conditions among nodes. In most cases, adaptive strategies depend on status information that is（  ）at one place but used at another. There is a tradeoff here between the quality of the information and the amount of（  ）. The exchanged information is itself a load on the constituent networks, causing a performance degradation.