us Optical Networks and Synchronous Digital Hierarchy Multiple Service Networks, (require high-performance transport layer) N-ISDN B-ISDN WBLLN Transport Network: Multiplexing, Transmission, Grooming, Consolidation, Routing, Capacity Allocation, Network Management Fig. 10.24 Managed transmission network; SDH network as a bearer for other services. This flow of management information among network elements, element managers, and yet more managers at the network and service levels gives rise to the concept of a Telecommunications Management Network (TMN). The main recommendation concerning the TMN is ITU-T M.3010, which attempts to define a series of interfaces between different management entities in such a network. It is not confined purely to SDH networks, but SDH networks were the first to implement an M.3010-style TMN. SDH-Based Networks Until a few years ago, SDH-based networks were viewed as the transmission bedrock sup- porting all other terrestrial telecommunications services (see Figure 10.24). As already mentioned, the main advantages of such a network are the ease and preci- sion with which the available network bandwidth can be partitioned among the higher-layer services, together with accurate monitoring of the quality of the transmission links. Despite this, the control and management of complete national networks is a difficult problem that requires some degree of standardization in the way such networks are functionally decom- posed, in much the same way as the individual network elements have already been func- tionally decomposed into their atomic elements by ITU-T G.783. The basic idea behind the functional decomposition described in ITU-T G.803 and G.805 is that a transport network can be stratified into a number of layers. Each layer provides a service to the layer above it, and is in turn a client of the layer below it, in much the same way the ISO seven-layer information transfer model consists of layers that participate in client-server relationships with their vertical nearest neighbors (s