n the congested switching system, but it can also cause connected switching systems to become con- gested. Therefore, NTM controls are available that can remove the ineffective attempts to a congested switching system. These controls will result in inhibiting the switching congestion and preventing its spread to adjacent switching systems. Telcordia, in Ref. 12, defines a message as a call that has a high probability of completion. NETWORK MANAGEMENT 21.6.4 Network Traffic Management Functions The following are several types of overloads for which network traffic management con- trols can provide complete or partial relief. 1. A general network overload is caused by changes in traffic patterns and/or increased traffic load. These changes may be generated by a reduced business week (heavier calling before and after an extended weekend), holiday traffic, local or seasonal changes such as an increase in tourist traffic, unanticipated growth, and natural or man-made disasters. In cases of general network overload, a large amount of the network capacity may be used to switch calls that have a poor chance of completing. These calls are often regenerated many times by both the calling customers and switching systems before they are completed. This results in contention between the "poor completers" and those calls having a better chance of completing. Because of the volume of regeneration to the poor completers, much of the available trunking and switching capacity is used in switching these calls to an overflow condition. As NTM personnel identify poor completers, appropriate measures are instituted, when necessary, to control congestion and remove some or all of these calls from the network. This is done by using code-blocking, call-gapping, and protective trunk group controls. The control of poor completers can greatly increase the number of messages handled by the network. Figure 21.4 illustrates the typical network performance under a general overload. This figure shows the decrease of completed traffic when the of