Unformatted text preview: What is meant by the terms serial and asynchronous ? (2) d) Draw a diagram, with explanation, to show the change of voltage over time when RS-232 transmits the following sequence of seven bits: 1011010. (4) e) With the aid of diagrams compare and contrast amplitude modulation , frequency modulation and phase-shift modulation . (6) f) What is a modem? Briefly describe the operation of a dial-up modem. (6) g) Explain how ADSL (Asymmetrical Digital Subscriber Line), which uses the two-wire local loop from telephone companies, achieves much higher data rates (e.g. 1.5 Mbps) than dial-up modems. (4)...
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- Spring '09
- relatively small area, microwave communications systems