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
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 time intervals.
After the expiration of the time interval, one call to the specified code or address
is allowed access to the network, after which the call-gapping procedure is recycled
for another time interval.
Circuit-directionalization control changes 2-way circuits to 1-way operation.
Circuit-turndown control removes 1- or 2-way circuits from service.
Reroute controls serve in a variety of ways to redirect traffic from congested or failed
routes to other circuit groups not normally included in the route advance chain but
that have temporary idle capacity. Reroutes override the normal routing algorithms
in a switch. Reroutes can be used on a planned basis, such as on a recurring peak-
calling day or in response to unexpected overloads or failures. "Regular reroute"
affects traffic overflowing a trunk group. "Immediate reroute" (IRR) affects traffic
before hunting the trunk group for an idle circuit. Reroute controls may redirect
traffic to a single or to multiple routes. The multiple option is referred to as a "spray
Automatic Controls in Modern Digital Switches
. Current, computer-
based switches may include the following types of automatic controls:
Selective dynamic overload control (SDOC)
Selective trunk reservation (STR)
Dynamic overload control (DOC)
Selective incoming load control (SILC)
SDOC and STR are considered "selective" protective controls because they can selec-
tively control traffic to HTR points
more severely than other traffic. If the probability of
HTR (hard to reach) points have 3- or 6-digit destination codes. Calls to these points have a low probability