Routing calls destined for inaccessible destinations

• US 5,404,350 A
• Filed: 11/05/1993
• Issued: 04/04/1995
• Est. Priority Date: 04/22/1993
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: DeVito, Nicholas M., Hagerman, William E., Moulos, Ted
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): VU, HUY DUY
• Application Number:
  US08/147,680
• Time in Patent Office: 515 Days
• Field of Search: 370/16, 370/16.1, 370/13, 379/272, 379/273, 379/274, 379/279, 379/269, 379/45, 379/37, 379/221, 379/211, 379/212
• US Class Current: 370/217
• CPC Class Codes: H04M 2207/12 intelligent networks
• CPC Class Codes: H04M 3/5116 for emergency applications
• CPC Class Codes: H04M 3/5237 Interconnection arrangements between ACD systems
• CPC Class Codes: H04Q 3/0016 Arrangements providing connection between exchanges

Abstract

An arrangement for selectively routing traffic to alternate destinations. If the network or switch for accessing the primary destination is inaccessible (i.e., out of service), as opposed to simply being busy, calls are routed to an alternate destination; however, if the primary destination is simply busy, calls are not routed to any alternate destination. This is useful, for example, for emergency (E911) calls which are routed to alternate emergency bureaus only if the network or switch for accessing the home bureau is out of service. Alternatively, the tandem switch can select an alternate toll carrier on the basis of allocation of traffic to different alternate toll carriers. The same general kind of arrangement can be used to route calls to an alternate toll carrier if the preferred toll carrier selected by the customer is not accessible.

Claims

1. In a telecommunications network a method of routing a call to an alternative destination, said method comprising the steps of:

receiving said call in said telecommunications network;

if a primary circuit switching system for serving a primary destination becomes inaccessible, receiving in a circuit switching system for routing said call, or in a routing data base for providing data for routing said call to said circuit switching system for routing said call, an indication from said network of primary circuit switching system inaccessibility;

subsequently, responsive to receipt of a request to route said call to said primary destination, testing, in said circuit switching system for routing said call, or in said routing data base, whether said primary circuit switching system is accessible;

if said primary circuit switching system is accessible, attempting to route said call only to said primary circuit switching system; and

if said primary circuit switching system is not accessible, attempting to route said call to an alternate circuit switching system for serving an alternate destination, said alternate circuit switching system different from said primary circuit switching system;

wherein said network comprises at least one Signal Transfer Point, STP, and wherein said receiving an indication comprises;

receiving a message from an STP for signaling to said primary circuit switching system indicating that said at least one STP cannot communicate with said primary circuit switching system.

2. The method of claim 1 wherein said step of receiving a message comprises the step of receiving at least one transfer prohibit message.

3. In a telecommunications network a method of routing a call to an alternative destination, said method comprising the steps of:

receiving said call in said telecommunications network;

if a primary circuit switching system for serving a primary destination becomes inaccessible, receiving in a circuit switching system for routing said call, or in a routing data base for providing data for routing said call to said circuit switching system for routing said call, an indication from said network of primary circuit switching system inaccessibility;

subsequently, responsive to receipt of a request to route said call to said primary destination, testing, in said circuit switching system for routing said call, or in said routing data base, whether said primary circuit switching system is accessible;

if said primary circuit switching system is accessible, attempting to route said call only to said primary circuit switching system; and

if said primary circuit switching system is not accessible, attempting to route said call to an alternate circuit switching system for serving an alternate destination, said alternate circuit switching system different from said primary circuit switching system further comprising;

responsive to receiving said call, said circuit switching system for routing said call requests routing data for said call from said routing data base; and

wherein said circuit switching system for routing said call receives said routing data from said routing data base.

4. In a telecommunications network, comprising a plurality of toll carrier networks each comprising ingress circuit switching systems for receiving calls from a local carrier and egress circuit switching systems for transmitting calls to a local carrier, a method of routing a toll call to a toll carrier network, said method comprising the steps of:

if an ingress circuit switching system for a toll carrier network becomes inaccessible, receiving in said telecommunications network an indication of toll carrier ingress circuit switching system inaccessibility for said toll carrier network;

receiving said toll call in said telecommunications network;

determining a preferred toll carrier network of said plurality of toll carrier networks for said toll call;

testing whether a toll carrier network ingress circuit switching system is accessible for said preferred toll carrier network;

if the toll carrier network ingress circuit switching system for said preferred toll carrier network is accessible, attempting to route said toll call only via said preferred toll carrier network; and

if said preferred toll carrier ingress circuit switching system is not accessible, attempting to route said call via an alternate toll carrier network accessed via an ingress circuit switching system of said alternate toll carrier network;

wherein prior to attempting to route said call via said alternate toll carrier network an announcement is made to a caller of said call indicating a change of toll carrier network.