1. Data Communications Chapter 16, Exploring the Digital Domain

2. In this chapter... chief elements of a communications system how data is encoded and transmitted classifying the variety of computer networks getting “connected” at home You will learn about

3. Communicating Information broadcasting one sender, many receivers one-way communication networking one sender, one receiver pair (multiples) two-way communication

4. Shannon’s Data Communication Model

5. an information source generates a message a transmitter encodes the message as a signal the signal is transmitted over a communications channel— a medium that bridges the distance between the receiver extracts a signal from the communications channel and converts it back into the form of a message the destination receives the message a source of noise is usually present in the communication channel—this is a random element that modifies the signal in unpredictable ways

6. Encoding Messages messages are encoded as a stream of binary numbers (0s and 1s) signals are transmitted as electro- magnetic energy (electrical, optical, or radio waves) rate of reliable transmissions depend on the properties of the channel and the complexity of the message

7. Transmitting Digital Data analog (modulated signals) amplitude frequency phase (calibrated timing) digital Two types of signals:

8. Amplitude Modulation

9. Frequency Modulation

10. Phase Modulation

11. Bandwidth the bandwidth of a communication channel determines its capacity to transmit data—analogous to the size of plumbing pipes analog signals may contain independent waveforms of various frequencies the number of frequencies supported by a channel determines its bandwidth

12. Limiting Factors in Data Transmissions bandwidth signal strength noise, i.e., signal-to-noise ratio

13. Characteristics of Computer Networks distance or expanse covered by the network media used for transmission of signals type of signal used for transmission type of switching performed to route the signal

14. Networks Classified by Distance LAN (Local Area Network) WAN (Wide Area Network) usually a large area often owned by a single corporation internetwork

15. Networks Classified by Media bounded media copper wire optical fiber cable unbounded media “wireless” radio frequency waves

16. Networks Classified by Signal baseband (narrowband) employs entire bandwidth for one signal broadband multiple signals on the same channel simultaneously channel is divided into separate frequency bands, each capable of carrying a signal

17. Frequency-Division Multiplexing bandwidth is divided into separate channels each signal occupies a specific portion of the bandwidth

18. Time-Division Multiplexing signal occupies entire bandwidth time divided into frames, slots pieces of the signal are sent in slots

19. Networks Classified by Switching devices in a network called “nodes” arrangement of nodes and links called “topology” point-to-point connectivity vs. shared connectivity shared connectivity requires “switching” routing data over common links

20. Circuit Switching a continuous connection or circuit is made between transmitter and receiver ordinary telephone connections are made by circuit switching

21. Packet Switching the message is made of separate data packets each addressed to the destination Packets are transmitted over any available connection to the destination receiving node reassembles the message

22. Packet vs. Circuit Switching circuitpacket modesynchronous, continuous asynchronous, connectionless messageshandles lengthy suited for short processingvery littlerequired at both ends robustnessconnection- sensitive fault-tolerant

23. Analog Modems “modem” = modulate-demodulate

24. Cable Modems employ CATV communications upstream, downstream speeds differ downstream bandwidth shared

25. Digital Subscriber Line (DSL) DSL employs telephone communications DSL uses bandwidth not required for voice connection is continuous Asymmetric DSL is common today

26. ADSL maximum length (5.4 km) lines must be “DSL-ready”