Alternate party diversion is an optional feature of telephone services, whereby a call may be routed to a different number

Telephone number

A telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator...

 based on time-out and precedence schemes set up by the customer.

Technical definition

Alternate party: In multilevel precedence and preemption

Multilevel precedence and preemption

In military communications, Multilevel Precedence and Preemption is a priority scheme for assigning one of several precedence levels to specific calls or messages so that the system handles them in a predetermined order and time frame, for gaining controlled access to network resources in which...

, the call receiver, i.e. the destination user

Destination user

The destination user in an information transfer transaction is the user who receives information from the source, i.e., from the originating user....

, to which a precedence call will be diverted. Diversion will occur when the response timer expires, when the call receiver is busy on a call of equal or higher precedence, or when the call receiver is busy with access resources that are non-preemptable. Alternate party diversion is an optional terminating feature that is subscribed to by the call receiver. Thus, the alternate party is specified by the call receiver at the time

Time

Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 of subscription.

Source: From Federal Standard 1037C

Federal Standard 1037C

Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....

 and from MIL-STD-188

MIL-STD-188

MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...