Network Operations & administration CS 4592 Lecture 13

1. Network Operations & administration CS 4592Lecture 13 Instructor: Ibrahim Tariq

2. Data Link Layer

3. Error Correction • By retransmission • flow and error control protocols • Forward Error Correction (FEC) • require more redundancy bits • should locate the invalid bit or bits • n-bit code word contains m data bits + r redundancy bits n=m+r • m+r+1 bits discoverable by r bits • 2r>=m+r+1

4. Data and redundancy bits

5. Hamming Code • Hamming codes provide for FEC using a “Block Parity” • i.e, instead of one parity bit send a block of parity bits • Allows correction of single bit errors • This is accomplished by using more than one parity bit • Each computed on different combination of bits in the data

6. Positions of Redundancy Bits

7. Redundancy Bits Calculation

8. Example

9. Error Correction using Hamming Code

10. Revision

11. Categories of topology

12. A fully connected mesh topology (five devices)

13. A star topology connecting four stations

14. A bus topology connecting three stations

15. A ring topology connecting six stations

16. A hybrid topology: a star backbone with three bus networks

17. Figure 2.2 Seven layers of the OSI model

18. Figure 2.3 The interaction between layers in the OSI model

19. Four Level of Addresses

20. Relationship of Layers & Addresses in TCP/IP

21. Communication Network Communication networks Broadcast networks End nodes share a common channel (TV, radio…) Switched networks End nodes send to one (or more) end nodes Circuit switching Dedicated circuit per call (telephone, ISDN) (physical) Packet switching Data sent in discrete portions (the Internet)

22. Figure 6.2 Categories of multiplexing

23. Figure 6.13 Synchronous time-division multiplexing

24. Figure 6.26 TDM slot comparison

25. Transmission Impairments

26. Bit Rate & Bit Interval (contd.)

27. Noiseless Channel: Nyquist Bit Rate • Defines theoretical maximum bit rate for Noiseless Channel: • Bit Rate=2 X Bandwidth X log2L

28. Example We have a channel with a 1 MHz bandwidth. The SNR for this channel is 63; what is the appropriate bit rate and signal level? Solution First, we use the Shannon formula to find our upper limit. C = B log2 (1 + SNR) = 106 log2 (1 + 63) = 106 log2 (64) = 6 Mbps Then we use the Nyquist formula to find the number of signal levels. 6 Mbps = 2  1 MHz  log2L L = 8

29. Noisy Channel: Shannon Capacity • Defines theoretical maximum bit rate for Noisy Channel: • Capacity=Bandwidth X log2(1+SNR)

30. Line Coding Schemes Data Communication & Networks, Summer 2009

31. Unipolar Encoding Data Communication & Networks, Summer 2009

32. Polar: NRZ-L and NRZ-I Encoding Data Communication & Networks, Summer 2009

33. Polar: RZ Encoding Data Communication & Networks, Summer 2009

34. Polar: Manchester Encoding Data Communication & Networks, Summer 2009

35. Polar: Differential Manchester Encoding Data Communication & Networks, Summer 2009

36. Figure 4.6 Polar NRZ-L and NRZ-I schemes

37. Figure 4.9 Bipolar schemes: AMI and pseudoternary

38. Data Communication & Networks, Summer 2009

39. ANALOG-TO-DIGITAL CONVERSION Digital signal is superior to an analog signal. The tendency today is to change an analog signal to digital data. pulse code modulation

40. Components of PCM encoder

41. Types of digital-to-analog conversion

42. Concept of a constellation diagram

43. Figure 5.13 Three constellation diagrams

44. Types of analog-to-analog modulation

45. Circuit Switching • There are three phases in circuit switching: • Establish • Transfer • Disconnect • The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent.

46. Packet Switching • In packet-based networks, the message gets broken into small data packets. • These packets seek out the most efficient route to travel as circuits become available. • Each packet may go a different route from the others.

47. Figure 9.11 Bandwidth division in ADSL

48. ADSL modem

49. DSLAM

50. Summary of DSL technologies