t/s on conventional single and transmission with well defined boundaries at which interface mode fibre cable! Now the network need not be service restricted problems were dealt with. This need no longer be true. due to bandwidth bottlenecks. 2. Flexibility. As SDH now allows us to reach in to any multi- A typical SDH based network is shown in Figure 53.32. plexed signal and extract only the information we need it frees the The fibre optic cable can be directly connected to the switch, since network designer from a cost problem. The problem used to be that all of the SDH based bandwidth can now be managed by software back to back multiplexers had to be used to perform this add/drop control. As fibres enter the central office there would be no need for function which was very costly. As a result this tended to be avoided patch panels or cross-connects as all bandwidth assignment and or centralised to reduce costs, either of which led to difficult engin- capacity grooming will be performed throughout the network at eering rules that limited service responsiveness to the end user. each network element. Nor will it be necessary to segregate traffic 3. Control. Combined with the flexibility inherent in the SDH in the central office for management based on type of service. All network, the control available through the overhead maintenance fibres will connect to one switch capable of handling all services channels gives the telephone company the ability to respond to whether analog or digital; voice, data or video; narrowband, wide- customer service needs immediately. The software intensive design band or broadband; connection oriented or connectionless. of these new generation products also means that the telephone Traffic needing to go on into the network will do SO on very high company will be able to dialogue with individual terminals and capacity fibres again configured as rings for survivability. Service obtain status reports on performance. provisioning now becomes a keyboard entry that is interpreted and 4. Reli