System and method for communicating pre-connect information in a digital communication system

Abstract

The present invention is directed to method, and associated system, for communicating pre-connect information between a calling endpoint and a called endpoint in an Integrated Services Digital Network (ISDN) system. In accordance with one aspect of the present invention, the method includes the steps of dialing the called endpoint from the calling endpoint, and setting a calling party's subaddress information element to a value that allows the contents of a subaddress information field to be user specified. The method further includes the steps of specifying the contents of the subaddress information field, and transmitting the message of information to the called endpoint, the message of information including the calling party's subaddress information element. In accordance with the preferred embodiment of the invention, the system is a digital communication system that is compatible with the Open Systems Interconnection (OSI) seven layer model in communication at the network layer of the OSI model is defined by ITU-T Q.931 specification. As defined by that specification, the subaddress information element can be user-defined by a subaddress specifying field, which is a three-bit field. The subaddress information element, itself, is encoded to define a message of information that includes information as to why the calling endpoint is placing the call. This information can include reasons such as the requested call is a dialed backup link, it is a forwarding or redirected call, it is informing the called party that a previously received call placed by the called end point was interrupted do to a fault condition on the interconnecting network link, etc. As is defined by the ISDN's specification, the foregoing information and information specifying elements are contained within a call SETUP message.