Basics of COMPUTER NETWORKS

1. Book in glance Basics of COMPUTER NETWORKS Computer Engineering Faculty of Engineering Kurdistan University ( Email : ghasem.mohammadi@gmail.com)

2. Contact information سرفصل‌هاي درس • فصل 1: مفاهيم اوليه • فصل 2: لايه فيزيكي • فصل 3: لايه پيوند داده • فصل 4: لايه شبكه • فصل 5: لايه انتقال • فصل 6: لايه كاربرد • فصل 7 :‌كابل كشي ساخت يافته

3. Computer Network What’s a Computer Network? • Connecting two or more computers or other devices via a Communication media( Physical or wireless) • Categorizing networks according to size: • LAN (Local Area Network) • MAN (Metropolitan Area Network) • WAN (Wide Area Network) • Internet

4. Computer Network Types of Links Point-to-Point Multiple Access …

5. Computer Network

6. Computer Network

7. Computer Network Protocol Demultiplexing • Multiple choices at each layer FTP HTTP NV TFTP TCP UDP Network IP TCP/UDP IPX IP Type Field Protocol Field Port Number NET1 NET2 … NETn

8. Computer Network OSI Layers and Locations Application Presentation Session Transport Network Data Link Physical Hub Switch Host Router Host

9. Computer Network Network Interface Card (NIC)

10. Computer Network Hub (layer 1 device) Just knows bits

11. Computer Network Switch (layer 2 device) Knows MAC addresses

12. Computer Network Router (layer 3 device) Knows Logical addresses (IP and IPX)

13. Computer Network

14. Computer Network Twisted Pair UTP Connector STP

15. Computer Network Bad Good

16. Computer Network Connectors

17. Computer Network Fiber Optic Connectors

18. Computer Network

19. Computer Network A Fiber Optic Ring with Active repeaters

20. Computer Network Electromagnetic Spectrum

21. Computer Network Types of Propagation

22. Basic Modulation Types Computer Network

23. Computer Network Compression: • Huffman Coding • Run-length Coding • Ziv Lempel compression

24. Computer Network

25. Computer Network FDM (Frequency Division Multiplexing)

26. Computer Network WDM (Wavelength Division Multiplexing)

27. Computer Network TDM (Time Division Multiplexing)

28. Computer Network

29. Computer Network Circuit Switching

30. Computer Network

31. Computer Network Time Division Switch

32. Computer Network Packet Switching

33. Computer Network Message Switching

34. Computer Network Framing Methods Character Count Byte Stuffing Bit Stuffing

35. Computer Network Handling Errors

36. Computer Network Single bit Error Multiple bit Error

37. Computer Network Parity bit 0110100 1 1011010 0 One Dimensional Parity 0010110 1 1110101 1 1001011 0 1000110 1 Two Dimensional Parity

38. Computer Network Cyclic Redundancy Check (CRC) • Represent a (n+1)-bit message as an n-degree polynomial M(x) • E.g., 10101101  M(x) = x7 + x5 + x3 + x2 + x0 • Choose a divisor k-degree polynomial G(x) • Compute reminder R(x) of M(x)*xk / C(x), i.e., compute A(x) such that • M(x)*xk = A(x)*G(x) + R(x), where degree(R(x)) < k • Let • T(x) = M(x)*xk – R(x) = A(x)*G(x) • Then • T(x) is divisible by G(x)

39. Computer Network Hamming Code

40. Computer Network Categories of Flow Control

41. Computer Network Stop-and-Wait

42. Computer Network Sliding Window Sender/Receiver State Sender Receiver Next expected Max acceptable Max ACK received Next seqnum … … … … Sender window Receiver window Sent & Acked Sent Not Acked Received & Acked Acceptable Packet OK to Send Not Usable Not Usable

43. Computer Network Example of Sliding Window

44. Computer Network Sliding Window Go-Back-n, Damaged Frame

45. Computer Network Sliding window Selective-Repeat, Damaged Frame

46. Computer Network Media Access Control Evolution of Contention Protocols Aloha Developed in the 1970s for a packet radio network SlottedAloha Improvement: Start transmission only at fixed times (slots) CSMA = Carrier Sense Multiple Access Improvement: Start transmission only if no transmission is ongoing CSMA CD = Collision Detection Improvement: Stop ongoing transmission if a collision is detected (e.g. Ethernet) CSMA/CD

47. Computer Network • The Aloha Protocol • simple: if you have pkt to send, "just do it" • if pkt suffers collision, will try resending later

48. Computer Network • Slotted Aloha • synchronous system: time divided into slots • slot siz equals fixed packet transmission time • when pkt ready for transmission, wait until start of next slot • packets overlap completely or not at all

49. Computer Network • Carrier Sensing Protocols • Aloha is inefficient (and rude!): doesn't listen before talking! • Carrier Sense Multiple Access: CSMA • non-persistent CSMA: • sense (listen to) channel • if {channel sensed busy} • then wait random time; go to 1 • else transmit packet • p-persistent CSMA: • sense (listen to) channel • when {channel sensed idle} • transmit with probability p • else wait random time, go to 1

50. Computer Network • CSMA/CD • CSMA with collision detection(CD): • listen while talking! • stop transmitting when another pkt has collided with your pkt • wait random time before attempting to resend • worst case time to detect a collision? • performance depends (as in CSMA) on channel length