er-based media, whether twisted wires or coaxial cables, have long been used to connect customer premises to sources of information. The rise of the internet and a need for connec- tivity from home and office spurred research on telecommunications systems which use this existing copper infrastructure. DSL and hybrid fibre cable systems use a combination of optical fibre and copper media to provide connectivity rates in the order of 100 Mbps or more. Additionally all-fibre systems promise 1 Gbps connectivity. Fixed broadband telecommunica- tions system are capable of satisfying typical connectivity needs. Review Questions 1. In ADSL: a. What medium is used to transmit signals in ADSL? b. What is the frequency spectrum range? C. What is the role of the splitter? d. What is the role of the DSLAM? 2. What is the maximum downlink throughput of an ADSL system assuming the system uses 256 subcarriers, each with an effective bandwidth of 4 kHz, with received SNR = 12 dB, 10 dB, 8 dB, and 6 dB for 64 subcarriers each? 3. If 10% of resources are used for uplink transmissions, which carriers are used? What would be the uplink maximum capacity? 4. What is the difference between ADSL2+ and VDSL systems? 5. What are FEXT and NEXT? 6. How does 'vectoring' reduce the FEXT? What is the resulting benefit? 7. How does the discrete multi-tone (DMT) technique help with the frequency response model of the twisted copper wires? 8. Draw an architecture model for a hybrid fibre cable system. Why is optical fibre used here? 9. What is WDM and how is it valuable? 10. What determines the capacity of an optical fibre strand? Optical fibre communications use a special form of binary ASK, where the presence of a light pulse in the transmission period represents a 1 and lack thereof a 0. Why do you think multi-level ASK is not used? List four different fibre-to-the-x systems. How do optical fibre systems complement copper-based DSL systems? 13. What are the typical nodes in a fibre-to-the-premises (FTTP) network? 14. What are the main costs in 