 start-stop format, but the ends of the link are both ments transmitted over a channel. clocked. Line hit. Unwanted signals introduced onto a transmission line Isotropic antenna. An omni-directional antenna which is used as a due to electrical interference. reference against which the performance of other antennas is Line of sight transmission. Transmission which occurs between measured. two systems having a clear unobstructed view of each other. Example of line of sight transmission is microwave. Line turnaround. The delay between the sending of data in one Jamming. Deliberate interference of a signal by generating an- direction, and its receipt at the other end, and sending data in other signal at greater power and close to the transmitted the other direction. frequency of the first signal. Link budget. The process of considering all factors affecting the Jitter. Small and random variations in time or phase of a trans- signal on a transmission line (usually a satellite radio link), in mitted signal which can result in errors or loss of synchronisa- order to determine the signal to noise ratio. tion. Link by link signalling. Signalling system in which signals are Junction. Name sometimes applied to the link between two ex- processed in each intermediate point when passing from one changes. end to the other of a system. Junctor. Refers to the circuit connecting networks within the same Link layer. The layer in the ISO OSI model which is responsible office. It is also sometimes referred to as an intraoffice link. for transmission of data between communicating nodes. Justification. The method used to change the rate of a transmitted Listener echo. Echo received by listener, where the listener or signal to allow it to match with a system having a different rate. receiver hears the wanted signal together with a delayed, atte- nuated version of the original signal. Load balancing. The process of distributing the traffic over trans- Ka band. Electromagnetic spectrum in the 12GHz to 30GHz fre- mission lines so that they