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Tandem Switching Feature

Description

Network Calls Routed via the Local System

When non-local users access ARS to dial out over PSTN facilities connected to your local system or to another system connected to yours, your system uses a special form of the Remote Access feature to accommodate these calls. Because calls are routed from one system to one or more other systems, the Remote Access settings for this purpose are distinct from the Remote Access feature used by individuals who enter a barrier code in order to reach an extension or place an outgoing call on the system.

Non-local users who access your PSTN trunks via ARS and private network trunks do not dial a Remote Access barrier code. For security purposes, the system applies the default COR calling restrictions that you assign to all tie (T1-emulated voice or data, or analog) or non-tie (PRI) trunks, ignoring the barrier code requirement setting. If remote users connect to your system via tandem PRI facilities, the non-tie restrictions apply; otherwise, the tie restrictions apply. Non-tie restrictions apply to tandem PRI trunks only, and tie restrictions apply to tandem tie trunks only. You can program both types of COR if needed, using the following system programming procedure (refer to System Programming for detailed instructions).

SYS PROGRAM LINES/TRUNK Remote Access NONTIE/TIELINES RESTRICTIONS

When programming the default COR, change the Calling Restriction option to unrestricted (the factory setting is outward restricted). You should assign Disallowed List 7 to include; 900, 976, and other types of calls that users should not be allowed to call. When a call is received at a non-local system that routes it to another network system, the FRL assigned to the default COR is compared to the local UDP or ARS route FRL to permit or forbid the routing of the call. For a call to go through, the route FRL must be equal to or less than the default COR FRL.

	SECURITY ALERT:
	Networked systems require special attention to security issues. Follow the rules below when setting up and planning your system for network use.

• Ensure that barrier codes are required for incoming Remote Access calls received on PSTN PRI dial plan routed and DID facilities, as well as those calls that are made from the local system by dialing the Remote Access code (889, for example). When you program the default COR, turn the barrier code requirement on. This setting is ignored for ARS calls and calls to non-local extensions across the network. It is still applied to DID and PRI dial plan routed Remote Access calls, however, as well as to calls received on a tandem trunk and routed to a Remote Access code. Because the COR Calling Restriction must be set to unrestricted for network calling, using barrier codes on these facilities is essential in order to apply security measures. When a Remote Access code is included in the non-local dial plan of the calling system, the caller's barrier code FRL on the called system is compared to the UDP or ARS route FRL on the called system. see Class of Restrictions (COR) for details.
  
  
• Extension and ARS FRLs should be carefully and stringently assigned in order to prevent unauthorized trunk-to-trunk transfers to local PSTN facilities.

To implement this operation where ARS calls are routed to or via your system, consult System Programming and Class of Restrictions (COR) in the section about Remote Access.

The following general steps outline the procedures:

• Do not assign the private trunks for remote networked users to Remote Access.
  
  
• Set the options listed below for the Remote Access default COR on your system. If your system is linked to the private network by tandem tie facilities (analog,T1-emulated voice and/or data), assign the settings to all tie trunks. If only tandem PRI trunks link your system to the private network, assign the settings to all non-tie trunks. If both tandem tie and tandem PRI trunks link your system to the private network, assign the Remote Access default CORs to their respective types of trunks.
  
  
• In a network, this setting should be turned on in order to require barrier code entry on calls that arrive from the PSTN over DID or PRI dial plan routed facilities or that are made by dialing a Remote Access code included in the non-local dial plan. When barrier codes are not required, the remaining default COR settings apply to PSTN calls as well as network calls. This poses a security risk and does not allow adequate protection against toll fraud. The barrier code requirement is ignored for calls on tandem trunks, but the remaining default COR setting does apply to such calls.
  


• This setting determines whether local and/or toll calls are allowed. The factory setting is outward- and toll-restricted. To allow call routing to the PSTN or to another system in the network, this setting should be changed to unrestricted, allowing the routing of all such calls.

• Use this FRL setting by assigning a restriction level from 0 to 6, 0 is the most restrictive, and 6 is the least restrictive. The FRL value assigned here is the opposite of the FRL value assigned to an ARS route, where a value of 0 is the least restrictive, and a value of 6 is the most restrictive. The factory setting is 3. To restrict calls from using selected UDP or ARS routes, assign a value that is lower than the FRL assigned to the route. Network call routes (UDP or ARS) use this default COR FRL and do not use barrier codes. As long as you require barrier codes for the default COR setting, the barrier code FRL and not the default COR FRL, is applied to Remote Access calls that arrive on PSTN dial plan routed PRI facilities or on DID trunks or that are made by dialing a Remote Access code included in the non-local dial plan.
  
  
• Do not assign any Allowed Lists.
  


• Disallowed Lists should be used for the default COR. You should use Disallowed List 7, which prohibits a variety of calls often made by toll fraud abusers. Review and add to this list as needed. When a Disallowed List is assigned, ARS calls cannot reach the specific numbers included on the list. When barrier codes are required for the default COR, Disallowed Lists should be assigned to individual barrier codes.
  


• Modify ARS as required. Using the example outlined earlier, a remote user might dial the 617 area code preceded by a 1. If the call would be routed as a local call on your local system, the digits 1617 would be absorbed. If not, they might be retained and then absorbed by a networked system connected to your own and located in the 617 area code. For additional information, see System Programming and Automatic Route Selection. For more information refer to the Network Reference.

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