1. The overall length of time required to establish a circuit-switched call between users. 2. For data communication, the overall length of time required to establish a circuit-switched call between terminals; i.e., the time from the initiation of a call request to the beginning of the call message. Note: Call set-up time is the summation of: (a) call request time--the time from initiation of a calling signal to the delivery to the caller of a proceed-to-select signal; (b) selection time--the time from the delivery of the proceed-to-select signal until all the selection signals have been transmitted; and (c) post selection time--the time from the end of the transmission of the selection signals until the delivery of the call-connected signal to the originating terminal.