 switch. In other systems, controls are available on a flexible basis, whereby any control can be assigned to any trunk group on a real-time basis. The availability of any specific control, its allowable control percentages, and the method of operation can vary with the specific type of switch. In many instances, these net- work controls can be activated with variable percentages of traffic affected (for example, 25%, 50%, 75%, and 100%) to fine-tune the control to match the magnitude of the NETWORK MANAGEMENT problem. Some switches also allow further control selectivity by the use of hard-to-reach (HTR) code-determination algorithms or specification of alternate-routed traffic, direct- routed traffic, or combined direct- and alternate-routed traffic-control choices. The most common manual controls are described below: Cancel controls consist of two variations. "Cancel From" (CANF) potentially pre- vents overflow traffic from a selected trunk group from advancing to any alternate route. "Cancel To" (CANT) potentially prevents all sources of traffic from access- ing a specific route. Some control arrangements permit CANF and CANT to be applied to alternate-routed or direct-routed traffic or both. All cancel controls are implemented on a percentage-of-traffic basis. Skip route control directs a percentage of traffic to bypass a specific circuit group and advance to the next route in its normal routing pattern. The control can be adjusted to affect alternate-routed or direct-routed traffic or both. Code-block control blocks a percentage of calls routed to a specific destination code. In most cases, a code-block control can also be specified to include the called-station address digits. Call-gapping control, like code-block control, limits routing to a specific code or station address. Call-gapping is more effective in controlling mass calling situations than the code-block control. Call-gapping consists of an adjustable timer that stops all calls to a specified code for a time interval selected from 16 different tim