 and Management the internet became more popular. However, the growth of internet services and their need for much higher transmission rate on the one hand, and the development of Digital Subscriber Links (DSL) standards on the other made ISDN as a data communications service obsolete. Meanwhile for telephony services the inter-exchange links have become digital, while the link between customers premises and a local exchange has largely remained analogue. ISDN systems failed to find a suitable application and are being phased out. Case Study Questions Why was ISDN standard developed? What were the motivations of operators in rolling out ISDN systems? What were the technology-business-policy elements necessary for ISDN success? What do you see as the reasons for ISDN failure? Could these have been foreseen? In hindsight, what would you have done differently? Data Source Coding The analogue to digital conversion process does not take into consideration the information content of an analogue signal as determined by information theory. As a result, redundancies in the discrete data stream remain and the transmitted number of bits representing a signal can be more than necessary. A number of source coding techniques have been developed that reduce the number of required bits and increase transmission efficiency. Source Coding Discrete data source coding generally requires a lossless algorithm, which can be done with either fixed length or variable length techniques. However, analogue information sources can only be represented digitally as an approximate value, since exact discrete representation requires infinite data size. The degree of information loss depends on whether the code follows the waveform of the analogue signal or analyses the analogue waveform into parts which are then encoded and synthesised at the receiver. Voice Source Coding Voice coding techniques can follow the analogue waveform or use signal synthesis. Waveform coding starts by an analogue to digital conversion and may be followed by further com