mission, in which the position of each frame can be determined Management hierarchy. Usually refers to the different levels by a multiframe alignment signal covering the group of frames. within network management systems, where the higher levels Multimode fibre. An optical fibre which is designed to carry light obtain a more global view of the managed network than lower at two or more different wavelengths at the same time. (See levels. Examples are element level management, network level monomode fibre.) management, and service level management. Multiple access. Techniques by which several users can gain ac- Manchester code. A transmission signal encoding technique. cess to a common transmission channel. Mapping. The logical association of one or more parameters in Multiplexer. Equipment for multiplexing several signals onto a different networks. common transmission channel. Market capitalisation. Usually measured by the product of the Multiplexing. The process of enabling several users to share a number of quoted shares in an organisation and the share price common communication channel. Several techniques may be at that time. used, such as frequency division and time division multiplex- Master clock. The clock which acts as the prime source within a network and from which all other clocks derive their synchroni- Multiprocessor. A group of processors which are interconnected sation. and co-operate in performing a task. Meridian. The line passing through the point being considered on Multitasking. The execution of several simultaneous jobs by a the earth's surface, and the earth's axis. computer. Mesochronous. The state in which two signals have their corre- Mutually synchronised network. A network in which each clock sponding significant instants occurring at the same average exerts a degree of control over all other clocks. rate. Message switched network. Network which is primarily carrying text based data, e.g. telex. Narrowband channel. A channel which can carry a limited range Message switching. Transmissio