Nortel Meridian 1 Planning And Installation Manual page 400

Appendix A – General information for the United Kingdom
Block all PSTN to PSTN connections, unless there is a specific customer
requirement for the facility. This blocking protects the customer from
possible effects of toll fraud, through use of the facility that is not authorized.
When implementing the feature, produce a restriction plan first. The plan
must address the following questions:
• When a call is incoming on a route, on which other routes can the call
terminate?
• Which routes share the same barring restrictions?
From this information, an access restriction number (ART) can be assigned
to each route on a system. Routes with identical restrictions share the same
number.
Use Overlay 56 to generate a table, which you can view as a 64-by-64 matrix.
When an incoming call arrives over a route, the ART number of the route is
obtained from the Route Data Block (Incoming ART). When the processor
determines that the call is to be extended to another trunk route, the Route
Data Block of the destination route is accessed. The route's ART number is
obtained (Outgoing ART).
Option 11C Mini Planning and Installation Guide
Page 379 of 590