222 Chapter 24 Dialing plansNN40020-603NN40020-603A set of default Public DN lengths is included with the default template. In most cases it is notnecessary to change the default values.About the Public DN lengths tableIn the public DN lengths table:• You can define up to 30 entries.• Each entry consists of a DN prefix string (1 to 10 digits) and a length value (two digits,1 to 25).• Several entries are predefined in the North America profile. These defaults can handle mostregions in North America without the need for additional programming. If required, you canremove or modify these entries.• The table always contains one default entry. You cannot remove this entry. You can onlymodify the length parameter associated with this entry. The default entry specifies the lengthof any dialing string that does not match one of the other table entries.Outgoing call routingOutgoing calls require line pool access codes or destination code (with defined routes) to leave thesystem.• Access codes provide direct, unscheduled access to an analog, digital (T1).• Destination codes also provide access to line pools, but they also allow more flexibility indialing, which allows for more complex routing options, such as scheduling, fallback routing(VoIP trunks), call definition, and multiple routing (least-cost routing). Routing also allowsyou to minimize the dialout for the user, especially to systems on the same private network.Outgoing calls can be either public or private, which is defined by the route. The public or privatedesignation determines which dialing plan is used to determine the validity of the call. Normally,public calls are routed over PSTN trunks and private calls are routed over a private network.However, MCDN trunks can also pass calls designated as public to allow remote nodes on thenetwork to call out of the PSTN of a local node. This is called tandem dialing.• If the outgoing call is designated as private, the system checks the beginning of the string for adestination code that routes to a private network. It also checks that the dial string is the correctlength. The destination code routing determines what the final dial string will be, adding orremoving digits, as required.
