Tandem Switching Feature

Description

Local Calls Routed to Other Systems

Local system users may use ARS to route calls over tandem trunks to the PSTN facilities connected to a non-local system.

This arrangement can provide toll cost savings when users need to reach outside numbers that are not in their own local calling area but are local to other systems in a network. It also means that in some cases, a MERLIN MAGIX Integrated System may have only one or two PSTN trunks connected to it for emergency purposes only. Under normal circumstances, the system uses PSTN facilities connected to another system in the network, which can provide call-volume advantages when buying PSTN services such as domestic long-distance calling.

For intersystem calls among network extensions and for routing of DID and PRI dial plan routed calls that are sent across the network, UDP routing is used. It is much like ARS routing, only simpler. Details are provided in Uniform Dial Plan Features.

To accommodate certain types of calls, enhance security, and make system programming simpler, the systems in a network should all use the same ARS access code. This code then cannot be included in the non-local dial plan of any networked system, because system programming of the local ARS access code into the non-local dial plan is blocked. If ARS access codes are not all the same, great care must be taken not to program a non-local ARS access code into the non-local dial plan. For example, if the ARS access code is 9, extension ranges such as 9000-9050 should not be programmed. Programming the ARS access code into the non-local dial plan can allow inadvertent access to ARS on a remote system.

For detailed information on modifying ARS in order to allow calling out on PSTN facilities connected to a non-local system in a network, refer to the Network Reference. The general rules are listed below:

Assign tandem trunks to a pool or pools including only one type of trunk (PRI, T1-emulated tie programmed for voice and/or data, or analog tie). For information about assigning trunks to pools, see Pools.

For 10xxx and 101xxxx equal access Interexchange Carrier (IXC), Dial 0, and N11 calls from a collocated networked system that is not connected to the PSTN, the tandem trunks must be assigned to the main pool so that these calls can be routed across the network to another system's public switched telephone network PSTN trunks. For equal access calls, the system automatically prepends the local ARS access code, which must match the ARS code of the non-local system.

CAUTION:

Unless networked systems are collocated, each system should have at least one loop-start line connected to the PSTN. The line is required to allow connection of a power-failure telephone to the Power-Failure Transfer (PFT) jack on a module as a power outage backup and for correct routing of emergency and other N11 calls. To ensure that the correct services are reached, if the loop-start line is used for emergency or other N11 calls, it should be assigned to the main pool. In this case, IXC calls determine the number of loop-starts required. Refer to the Feature Reference guide for details on the PFT feature.

At the system where calls originate, use one or more ARS tables for routing network calls. The type of table required depends upon how users in your system will employ networked lines. Typically, you might need an Area Code table. For example, if the remote system is in the 617 area code and your local system is in the 908 area code, the Area Code Table that you set up might include the entry 617.

All tables that specify tandem trunk pools must prefix the ARS access code of the remote system.

For all fully programmable ARS tables, ARS tables 17 & 18, Dial 0 table, and Special Numbers table, the Remote Access code must not be programmed in the prepended digits attributes table of each table.

At the system where calls are delivered to the PSTN, digit manipulation may also be required. In the example above where calls are routed from the 908 area code to the 617 area code, the system in the 617 area code absorbs 1617. ARS tables can be used, under some circumstances, to send calls to yet another networked system. It may be necessary to add or absorb digits for further routing. For more information refer to the Network Reference.

At the system where calls originate, set up the subpatterns for the table. In doing so, you may wish to check with the non-local System Manager to ensure that the local system routes associated with the primary time period (sub-pattern A) take advantage of non-local system routes associated with the secondary time period (sub-pattern B). If the non-local system is in a different time zone from your own, you may need to take this into consideration as well. For more information refer to the Network Reference.

At the system where calls originate, assign appropriate FRLs to the routes and to the extensions that will use the networked lines. Factory settings do not restrict toll calls. At the system where calls reach the PSTN, assign an FRL to the default COR for the type of tandem trunk (non-tie for PRI and tie for all others). See "restrictions" in the ARS topic and Uniform Dial Plan Features. For more information refer to the Network Reference.
FRLs are assigned to extensions. These FRLs apply not only to ARS but to non-local UDP routing as well. Plan UDP, ARS, and extension FRLs carefully so that extension users can reach non-local extensions as needed and still be subject to required limitations on toll calling. For more information about UDP routing, see Uniform Dial Plan Features. For more information refer to the Network Reference.
Assign absorbed and other (prepended) digits as required by ARS at each switch. The local ARS feature must prepend the ARS access code of the remote system.

Topics

Description

	Switch Identifiers
	ARS, UDP Routing and Remote Access
	Local Calls Routed to Other Systems
	Network Calls Routed via the Local System

At a Glance

System Programming

Feature Interactions