1. 1.1 Chapter 1 Introduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Course Information Code: IT251 Name: Data Communications Instructor: Ahmed Abo-Bakr, Ph.D. E-mail: amohamed@fci.au.edu.eg Time: Mondays 8 am – 11 am TA: TBA Office Hours : BAO Text 1: Data Communications and Networking, 4/e Behrouz A. Forouzan Text 2: Data and Computer Communications, 8/e William Stallings Prentice Hall, 2007 Course Group: DataCommunications@compit.au.edu.eg 1.2

3. Course Description Brief introduction of networking; layers and protocols, principles of data communications, the fundamentals of signaling, basic transmission concepts, transmission media, line sharing techniques, physical and data link layer protocols, error detection and correction, data compression, network security techniques, common carrier services and data networks, and the mathematical techniques used for network design and performance analysis, Potential topics include analog and digital signaling; data encoding and modulation; Shannon channel capacity; FDM, TDM, and STDM multiplexing techniques; inverse multiplexing; analog and digital transmission; PCM encoding and T1 transmission circuits; 1.3

4. Important Dates Week (1), October 13 th Warming Up, Introduction Week (9), December 8 th Mid-Term Exam Week (11), December 22 nd Last Lecture 1.4

5. Assignments Several homework sheets will be distributed throughout the term via course group e-mail. Late homework will be accepted if delivered no more than one week of its due date. However, late homework will be graded from 80%. For example, if a late assignment is graded out of 10 pts and received 7/10, the grade will be recorded as (0.8 × 7 ≈ 5.5 / 10) Homework delivered after the “one-week” allowance will NOT be accepted and will be recorded as ZERO. 1.5

6. Contacts Preferred way of getting in touch is through educational e-mails ONLY which will be answered promptly. Educational e-mails are those e-mails hosted at aun.edu.eg or compit.au.edu.eg or fci.au.edu.eg 1.6

7. Grading Students’ level will be evaluated according to the work done throughout the term and their grades will be distributed as follows: Assignments: 25 Mid-Term Exam(s): 25 Final Exam: 50 1.7

8. How to activate your.edu e-mail? http://195.246.49.215/mis/E_Mails.aspx 1.8

9. www.mail.office365.com Gear menu → Options Groups → Join Choose your group and click on Join How to join educational groups? 1.9

10. DATA COMMUNICATIONS 1.10

11. Knowledge of data communications and networking is crucial to today's IT professional. Virtually all computers are connected to some sort of network and exchange information with each other. 1.11

12. 1.12 1-1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.  Components of a data communications system  Data Flow Topics discussed in this section:

13. 1.13 The purpose of Data Communications is to provide the rules and regulations that allow computers with different operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications. For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs). The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness, and jitter.

14. 1.14 Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 3D ms. If some of the packets arrive with 3D-ms delay and others with 4D-ms delay, an uneven quality in the video is the result.

15. 1.15 Figure 1.1 Components of a data communication system

16. 1.16 Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

17. 1.17 1-2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. A link can be a cable, air, optical fiber, or any medium which can transport a signal carrying information.  Network Criteria  Physical Structures  Categories of Networks Topics discussed in this section:

18. 1.18 Network Criteria Performance Depends on Network Elements Measured in terms of Delay and Throughput Reliability Failure rate of network components Measured in terms of availability/robustness Security Data protection against corruption/loss of data due to: Errors Malicious users A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security

19. 1.19 Physical Structures Type of Connection Point to Point - single transmitter and receiver Multipoint - multiple recipients of single transmission Physical Topology Connection of devices Type of transmission - unicast, mulitcast, broadcast

20. 1.20 Figure 1.3 Types of connections: point-to-point and multipoint

21. 1.21 Figure 1.4 Categories of topology

22. 1.22 Figure 1.5 A fully connected mesh topology (five devices) Number of links?! Each node is exactly connected to (n-1) nodes n(n-1)/2 Robust Secure Throughput Installation Wiring Expensive

23. 1.23 Figure 1.6 A star topology connecting four stations Number of links?! n links Installation Less expensive Robust CPF (Central Point of Failure) Each node requires a single link to the Hub

24. 1.24 Figure 1.7 A bus topology connecting three stations Installation Less expensive Fault isolation Robustness Degradation Single line and n (Taps + Drop line) Reconfiguration Taps limitations

25. 1.25 Figure 1.8 A ring topology connecting six stations Installation Less expensive Fault tolerance Device Limitations Signals are unidirectional, repeaters regenerate bits until received by the receiver

26. 1.26 Figure 1.9 A hybrid topology: a star backbone with three bus networks

27. 1.27 Categories of Networks Local Area Networks (LANs) Short distances (normally less than 2 mi) Designed to provide local interconnectivity Wide Area Networks (WANs) Long distances (can be world-wide) Provide connectivity over large areas Metropolitan Area Networks (MANs) Provide connectivity over areas such as a city, a campus

28. 1.28 Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

29. 1.29 Figure 1.11 WANs: a switched WAN and a point-to-point WAN

30. 1.30 Figure 1.12 A heterogeneous network made of four WANs and two LANs

31. 1.31 1-3 THE INTERNET The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. Organization of the Internet Internet Service Providers (ISPs) Topics discussed in this section:

32. 1.32 Figure 1.13 Hierarchical organization of the Internet

33. 1.33 1-4 PROTOCOLS A protocol is synonymous with rule. It consists of a set of rules that govern data communications. It determines what is communicated, how it is communicated and when it is communicated. The key elements of a protocol are syntax, semantics and timing  Syntax  Semantics  Timing Topics discussed in this section:

34. 1.34 Elements of a Protocol Syntax Structure or format of the data Indicates how to read the bits - field delineation Semantics Interprets the meaning of the bits Knows which fields define what action Timing When data should be sent and what Speed at which data should be sent or speed at which it is being received.

35. Network Protocols Hello What’s the time? 2:00 TCP connection request TCP connection reply Request web page Send the file 1.35

36. Protocol “Layers” Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? 1.36

37. Organization of air travel a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing 1.37

38. ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below 1.38

39. Why layering? Dealing with complex systems: Explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion Modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Layering considered harmful? 1.39

40. Internet protocol stack application: supporting network applications FTP, SMTP, HTTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical 1.40

41. message segment datagram frame source application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn HlHl M router switch Encapsulation 1.41

42. Network Layers Physical Layer Data Link Layer Network Layer Transport Layer Application Layer 1.42

43. What is the Internet? Millions of connected computing devices: hosts = end systems Running network apps Communication links fiber, copper, radio, satellite transmission rate = bandwidth Routers: forward packets (chunks of data) 1.43

44. HOW BIG IS THE INTERNET? 1.44

45. http://news.sciencemag.org/2011/05/scienceshot- you-are-here 1.45 BOSTON—Astronomers have produced the most complete 3D map of the nearby universe to date. Using telescopes in both hemispheres, they measured distances to a whopping 45,000 galaxies out to a distance of 380 million light-years—for the astronomy buffs, a red shift of.07.

46. Outer Space 1.46

47. http://www.opte.org/ 1.47

48. 1.48

49. 1.49 http://internet-map.net/