nown as stray capacitance or leakage capacitance. Parity bit. An additional bit which is added to a transmitted data Object code. Executable machine code. Source code which has frame to perform a very basic error checking function. been compiled. Party line. Telephone line shared by two or more subscribers. This Off-hook. A line state which informs the central office that the is also known as shared service, whilst one subscriber per line subscriber requires service. This is the opposite of on-hook. is called exclusive service. On-hook. The unused state of a telephone circuit. The opposite of Passivation. A covering on top of a semiconductor die which off-hook. protects it from contaminants. When this protective layer is Offset antenna. An antenna which is front fed and in which the made from glassy materials this process is known as glassiva- feed is not directly on the axis of the reflector. It is offset to a tion. side to reduce signal blocking. Passive component. A component which is not made from semi- One-stop shopping. Usually refers to the facility provided by a conductor material. PTT whereby all services (including international) can be ob- Peer entity. Usually refers to a layer in the OSI seven layer refer- tained from a single source. ence model, located in an end system, which corresponds to an One way trunk. A trunk circuit which can only be seized at one equivalent layer in another end system with which it is com- municating. Operating system. Software within a computer which controls Peer to peer communication. A communication system in which basic functions, e.g. input/output, file management, etc. items performing the same functionality communicate directly Optical budget. Parameter used in the design of optical trans- with each other. Commonly used in systems based on a layered mission system. It is the difference (in dB) between output architecture, where the layers at the same level communicate power level of the source and the receiver sensitivity. directly with each other, although they use