Chapter 8 Data and Network Communication Technology

1. Chapter 8Data and Network Communication Technology

2. Chapter 8Data and Network Communication Technology Chapter Outline Communication Protocols Encoding and Transmitting Bits Transmission Media Channel Organization Focus – Serial and Parallel Storage Connections Focus – Infiniband Clock Synchronization Error Detection and Correction Focus – 802.11 Wireless Network Standards Focus - Upgrading Storage and Network Capacity (Part I)

3. Chapter Goals • Explain communication protocols • Describe signals and the media used to transmit digital signals • Compare and contrast methods of encoding and transmitting data using analog or digital signals • Describe methods for efficiently using communication channels • Describe methods for detecting and correcting data transmission errors

4. Data and Network Communication Technology

5. Communication Protocol Set of rules and conventions for communication • Message content and format • Bit encoding • Signal transmission • Transmission medium • Channel organization Includes procedures for coordinating flow of data • Media access • Clock synchronization • Error detection and correction

6. Communication Protocol Components

7. Communication Protocol Components

8. Encoding and Transmitting Bits • Carrier waves • Modulation methods • Data bit encoding • analog signals • digital signals • Signals • Electrical, optical, or radio • Capacity and errors

9. Carrier Waves • A sine wave with encoded bits • transports bits from one place to another • Characteristics of sine waves • amplitude • frequency • phase • Importance of waves in communications • Travel through space, wires, and fibers • Can have patterns encoded in them

10. Carrier Waves

11. Modulation Methods • Techniques used to encode bits in sine waves • Frequency modulation (FM) • Amplitude modulation (AM) • Phase shift modulation • Multilevel coding

12. Amplitude Modulation (AM) represents bit values as specific wave amplitudes

13. Frequency Modulation (FM) represents bit values by varying carrier wave frequency while holding amplitude constant

14. Phase Shift Modulation represents bit values by making a sudden shift in signal phase which can be detected and interpreted as data

15. Multilevel coding embeds multiple bit values within a single wave characteristic

16. Analog Signals • Use full range of carrier wave characteristics to encode continuous data values • Can represent any data value within a continuum of values

17. Digital Signals • Can contain one of a finite number of possible values • Pulse code modulation (PCM) • Binary data transmission via square waves • Square waves preferred over short distances

18. Pulse Code Modulation (PCM)

19. Digital Threshold A digital signaling scheme defines a range of wave characteristic values to represent each bit value.

20. Signal Capacity and Errors

21. Signal Capacity and Errors • Analog signals compared with digital signals • Carry more information • Are more susceptible to transmission error

22. Transmission Media • Communication path that transports signals • copper wire • optical fiber • Characteristics • Raw data transfer rate • speed • capacity • Bandwidth • Susceptibility • noise • distortion • external interference • and attenuation

23. Communication Channel A communication channel consists of a sending device, receiving device, and the transmission medium that connects them.

24. Speed and Capacity • Interdependent • jointly described as data transfer rate (raw versus effective data transfer rate) • Factors that account for transmission speed differences among media • Length of media • Ways in which multiple media segments are interconnected • Rate at which bits are encoded in signals and recognized by the receiver

25. Frequency and Bandwidth • Carrier wave frequency • Fundamental measure of data-carrying capacity (i.e., limits capacity) • Bandwidth • Difference between maximum and minimum frequencies of a signal • High-bandwidth channels can carry multiple messages simultaneously

26. The Electro-magnetic Spectrum The range of electromagnetic frequencies Subsets of that range are known as “bands”

27. Modem Protocols Modulator-demodulator (modem) technology sends digital signals over voice-grade telephone channels by encoding them in an analog carrier wave. Current rates are as high as 56,000 bps.

28. Signal-to-Noise (S/N) Ratio • Measure of the difference between noise power and signal power • Effective data transfer rate can be much lower than raw data transfer rate due to • Electromagnetic interference (EMI) • Attenuation • Distortion • Internal or external noise

29. In this channel, S/N ratio is positive for distances up to 5 kilometers

30. Electrical Cabling • Transmits signals through copper wire • Two types • Twisted pair • Relatively cheap • Limited in bandwidth, S/N ratio, and transmission speed • Axial (coaxial and twin-axial) • More expensive • Offers higher bandwidth, greater S/N ratio, and lower distortion • Resistant to EMI

31. Optical Cabling • Provides very high bandwidth, little internally generated noise and distortion, immunity to EMI • Requires amplifiers and repeaters for long distances to increase signal strength and remove noise and distortion • Two types • Multimode • Older • Surrounded by relective cladding • Single-mode (up to 10 Gbps) • Core density varies • forces signal to stay centered • Faster and much more expensive

32. Common Cable Connectors

33. Wireless Data Transmission Transmit data through the atmosphere or space Uses shortwave radio or infrared light waves Advantages • Higher bandwidth than hard wire transmission • Avoids wired infrastructure • Simultaneous broadcast transmission Disadvantages • Susceptibility to external interference • Cost • High demand for unused radio frequencies • Ability to be “overheard”

34. Communication Protocol Components

35. Communication Protocol Components

36. Channel Organization • Configuration and organization issues • Number of transmission wires or bandwidth assigned to each channel • Assignment of those wires or frequencies to carry specific signals • Sharing, or lack thereof, of channels among multiple senders and receivers • Three types: simple, half-duplex, full duplex

37. Channel Organization

38. Channel OrganizationSimple

39. Channel OrganizationHalf-duplex

40. Channel OrganizationFull Duplex

41. Parallel and Serial Transmission

42. Parallel Transmissionof a Byte

43. Serial Transmissionof a Byte

44. Channel Sharing • Uses available capacity by combining traffic of multiple users • For use when no single user or application needs a continuous supply of data transfer data capacity • Techniques • Circuit switching • Packet switching • Frequency division multiplexing (FDM)

45. Channel Sharing Techniques

46. Packet Switching, or TDM(Time Division Multiplexing) Packets are sent to their destination as channel capacity becomes available.

47. Channel Sharing, or FDM(Frequency Division Multiplexing) Signals are transmitted within each subchannel at a fixed frequency or narrow frequency range.

48. Technology FocusInfiniband • A data interconnection standard developed by a consortium of digital communications companies. • Uses a switched fabric which interconnects multiple devices with multiple transmission pathways and a mesh of switches • A matrix-like interconnection • Allows any sender and any receiver to connect • Supports many simultaneous connections

49. Communication Protocol Components

50. Communication Protocol Components