aviour. External stimulate (i.e. information, com- G.781/2/3 were created primarily to describe different types of drop mands, etc.) trigger an object to behave in a certain way e.g. change and insert multiplexers, however, the general principles and indeed, its attributes, transmit information, commands etc. The claim is that much of the detail, are just as applicable to LTEs and large cross a standardised object could be looked upon as the software equival- connects. Moreover, the formalism required to describe complete ent of a hardware integrated circuit. One of the biggest areas of SDH networks was produced very much with this same functional disagreement in generating an agreed standard set of SDH objects, decomposition in mind. We shall see, later, how these atomic func- is the questions of whether an object should represent a piece of tions may be paired between network elements on opposite sides of a network to produce a complete traffic path, that is sufficiently well Management of a service defined for a computer to recognise. SERVICE LAYER eg. 2 Mbit/s leased lines, ISDN service Management of paths across a complete network Control and management NETWORK LAYER requires an understanding of network topology Control and management within any type of telecommunications Management of network (not just an SDH one) can best be viewed in terms of a ELEMENT LAYER individual network elements eg. multiplexers and cross series of layers (See Figure 42.23). At the lowest level, there is connects internal control of an individual network element, which performs internal housekeeping functions and deals in alarm and control Internal management of EQUIPMENT LAYER the network elements primitives. CCITT G.783 has rigorously defined a minimum set of control and alarm primitives for each of the SDH atomic functions, and these are the basis of all SDH management. However, beyond this CCITT G.784 describes how such primitive information should Figure 42.23 Network management layering for the be processed and ordered to pro