1. In a switched network, the time between the completion of signaling by the call originator and the arrival of a ringing signal at the call receiver.
Note: Queues may be caused by delays at the originating switch, intermediate switches, or the call receiver servicing switch.
2. In a data network, the sum of the delays between the request for service and the establishment of a circuit to the called data terminal equipment (DTE).
3. In a packet-switched network, the sum of the delays encountered by a packet between the time of insertion into the network and the time of delivery to the addressee.
Source: from Federal Standard 1037C and from MIL-STD-188