gh a modem or some other serial connection. out-of-band signaling Signaling in which the conversation and the signaling take place over different paths. A separate digital channel (called a signaling link) is created, where mes- sages are exchanged between network elements at 56Kbps or 64Kbps. Out-of-band signals run no danger of interference from speech or data, which allows signaling to take place during the conversation. However, the out-of-band signal needs extra bandwidth and extra electronics to handle the signaling band. output Data that has been processed. overflow Excess traffic, on a particular route, that is offered to another (alternate) route. overlay network A high-performance digital network that interconnects with the main pub- lic network but has its own lines, exchanges, and, often, a separate international gateway. overnet A PNAP. override To seize a circuit even though the circuit is already occupied. PABX (private automatic branch exchange) See PBX. packet A group of binary digits, including data and call control signals, that is switched as a composite whole. The data, call control signals, and error control information are arranged in a specific format. Also called block, frame, cell, or datagram. packet loss A problem that occurs when there is congestion at the packet switches or routers. Packet loss can considerably degrade real-time applications. packet overhead A measure of the ratio of the total packet bits occupied by control informa- tion to the number of bits of data, usually expressed as a percentage. packet radio A data network that uses licensed bandwidth and is specifically built for two- way data, not for voice communications. packet switching A method of transmitting messages through a communication network in which long messages are subdivided into short packets. Each packet contains the data and a des- tination address and is passed from source to destination through intermediate nodes. At each node, the packet is received, stored briefly, and then passed to the next node. T