aseband CSMA/CA network protocol. location-based online services location-based online services Services provided over a wireless infrastructure that are based on the location of the user. The location of the user can be determined through GPSs or by cellular networks. Radio signals emitted from cellular phones can be tracked from cellular towers and triangulated, yielding locations nearly as accurate as those from a GPS receiver. logical address An address used to identify a communications program by name to the pro- tocol stack. No matter where the program is put in the network, an individual's logical address will remain the same, even though the person's physical address may change. long-haul Long-distance, describing (primarily) telephone circuits that cross out of the local exchange. loop (1) A local circuit between an exchange and subscriber CPE, either residential (single- line telephone) or business (PBX). Also called a subscriber loop, local line, or local loop. (2) In programming, a sequence of computer instructions that repeats itself until a predeter- mined count or other test is satisfied. loop circuit A circuit that connects a subscriber's equipment with the local exchange switch. Also called a metallic circuit or local loop. loop signaling systems Any of the three methods of transmitting signaling information over the metallic loop formed by the trunk conductors and the terminating equipment bridges. Transmission of the loop signals can be accomplished by opening and closing the DC path around the loop, reversing the voltage polarity, or varying the value of the equipment resistance. loop start The most commonly used method of signaling an off-hook condition between an analog phone set and a switch, whereby picking up the receiver closes a wire loop, allowing DC current to flow, which is detected by a PBX or local exchange and interpreted as a request for service. loopback A diagnostic procedure used for transmission devices. In a loopback, a test message is sent to a device being tested, which th