Module 1 – Introduction to Computer Networks: Foundations of Data Communication, Network Models, Transmission Media, and Switching

Module 1 provides the essential foundation of computer networks, introducing students to the core principles of data communication systems and how devices interact within different types of networks. The module emphasizes the building blocks of networking, preparing learners to understand complex systems in later stages.

Students begin by exploring the concepts of data communication, including delivery, accuracy, timeliness, and jitter as critical criteria of effective communication. This is followed by a study of network types such as LANs, MANs, WANs, and the Internet, along with the criteria that determine network performance, reliability, and security.

A central part of this module is protocol layering and network models. Students learn the TCP/IP protocol suite, which powers the modern Internet, and the OSI reference model, which provides a systematic understanding of layered communication processes.

The module also introduces the Physical Layer, explaining the role of transmission media in networking. Both guided media (twisted pair cables, coaxial cables, optical fiber) and unguided media (radio waves, microwaves, infrared, satellite) are studied to show how signals travel across different channels.

Finally, students explore switching techniques, with a focus on packet switching (datagram and virtual-circuit approaches) and their advantages in efficient data transmission compared to traditional circuit switching.

By the end of Module 1, students gain a clear and structured understanding of network fundamentals, positioning them to comprehend higher-layer protocols and services.

1. COMPUTER NETWORKS BCS502 بسم الله الرحمن الرحيم Computer Science Department Chapter 1: Introduction

2. Chapter 1: Introduction 1.1 Data Communications 1.2 Networks 1.3 The Internet

3. Introduction Data communications and networking Change the way we do business and the way we live Business decisions have to be made more quickly Decision depends on immediate access to accurate information Business today rely on computer networks and internetworks Before get hooked up, we need to know: How networks operate What types of technologies are available Which design best fills which set of needs

4. Introduction Development of the PC changes a lot in business, industry, science and education. Similar revolution is occurring in data communication and networking Technologies advances are making it possible for communications links to carry more and faster signals Services are evolving to allow the use of this expanded capacity For example telephone services extended to have: Conference calling Call waiting Voice mail Caller ID

5. 1.1 Data Communications Communication: Means sharing information Local (face to face) or remote (over distance) Telecommunication Telephone, telegraph and television Means communication at a distance Tele is Greek for far

6. Data Communications Data : Refers to information Presented in any form Agreed upon by the parties ( creating & using) Data communication : is the exchange of data between two devices via some form of transmission medium (wire cable).

7. Data Communications Communication system made up of a combination of hardware and software Effectiveness of data communication system depends on: Delivery : The system must deliver data to correct destination. Data received by the indented user only Accuracy : The system must deliver data accurately (no change). Data changed & uncorrected is unusable

8. Data Communications Timeliness : The system must deliver data in timely manner Data arrived late are useless In the same order (video and audio) & without delay (Real time transmission) Jitter : Variation in the packet arrival time (uneven quality in the video is the result)

9. Data Communications

10. Components A data communication system is made up of five components

11. Components Message : the information (data) to be communicated Consist of text, numbers, pictures, audio, or video Sender : the device that sends the data message Computer, workstation, telephone handset, video camera, … Receiver : the device that receives the message Computer, workstation, telephone handset, television, ….

12. Components Medium : The physical path by which a message travels from sender to receiver twisted pair, coaxial cable, fiber-optic, radio waves

13. Components Protocol : a set of rules that govern data communications An agreement between the communicating devices Devices may be connected but not communicating (no protocol) Arabic speaker with Japanese speaker

14. Data Representation Text Audio Video Numbers Images

15. Data Representation Text : Sequence of bits ( s or 1 s) Different sets of patterns to represent text symbols (each set is called: code ) ASCII: 7 bits (128 symbols) common coding system today is: Unicode uses: 32 bits to represent a symbol or character in any language Unicode (4,294,967,296)

16. Data Representation Numbers : Represented by bit patterns The number is directly converted to a binary number

17. Data Representation Images : Represented by bit patterns A matrix of Resolution: size of the pixels High resolution: more memory is needed Each pixel is assigned a bit pattern 1-bit pattern (black and white dots image) 2-bit pattern (4 levels of gray) R G B (color images) pixels

18. Data Representation Audio : Continuous not discrete Change to digital signal Video : Recording or broadcasting of a picture or movie Change to digital signal

19. Data Flow Communication between two devices can be: Simplex Half-Duplex Full-Duplex

20. Data Flow Simplex (one way street) The communication is unidirectional Only one device on a link can transmit; the other can only receive Use the entire capacity of the channel to send data Example: Keyboards, Monitors Data

21. Data Flow Half-Duplex (one-lane with two-directional traffic) Each station can both transmit and receive, but not at the same time When one device is sending, the other can only receive, and vice versa The entire capacity of a channel is taken over by the transmitting device Example: Walkie-talkies Data Data

22. Data Flow Full-Duplex (Duplex) (two-way street) Both stations can transmit and receive at same time Signals going in either direction sharing the capacity of the link Sharing can occur in two ways: Link has two physically separate transmission paths One for sending and the other for receiving The capacity of the channel is divided between signals travelling in both directions Example: Telephone network Data Data

23. Exercise What mode of data flow the following exhibits shows? Answer: Full-Duplex Data Data

24. Networks Network : A set of devices ( nodes ) connected by communication links Node : computer, printer, … Distributed Processing : Most networks used it Task is divided among multiple computers instead of one single large computer

25. Networks Network Criteria Network must meet a certain number of criteria The most important of the network criterions are: Performance Reliability Security

26. Networks Performance T ransit time : A mount of time required for a message to travel from one device to another Response time : Elapsed time between an inquiry and a response

27. Networks Performance Performance depends on : 1- Number of users : large number slow response time. 2- Type of transmission medium : fiber-optic cabling faster than others cables. 3- Capabilities of the connected hardware : affect both the speed and capacity of transmission. 4- Efficiency of the software : process data at the sender and receiver and intermediate affects network performance.

28. Networks Performance Performance is evaluated by two contradictory networking metrics: Throughput (high): a measure of how fast we can actually send data through a network Delay (low)

29. Networks Reliability Reliability is measured by: Frequency of failure Recovery time of a network after a failure Network’s robustness in a catastrophe: protect by good back up network system

30. Networks Security Protecting data from unauthorized access Protecting data from damage and development Implementing policies and procedures for recovery from breaches and data losses (Recovery plan)

31. Networks Physical Structures: Type of connection Network : Two or more devices connected through links Link : Communication pathway that transfers data from one device two another Two devices must be connected in some way to the same link at the same time. Two possible types: Point-to-Point Multipoint

32. Networks Point-to-Point Dedicated link between two devices Entire capacity of the link is reserved for transmission between those two devices Use an actual length of wire or cable

33. Networks Point-to-Point Other options, such as microwave or satellite is possible Example: Television remote control

34. Networks Multipoint (multidrop) More than two devices share a single link Capacity is shared Channel is shared either spatially or temporally Spatially shared: if devices use link at same time Timeshare: if users must take turns

35. Networks Physical Topology The way a network is laid out physically Two or more links form a topology The topology of a network is the geometric representation of the relationship of all the links and linking devices (nodes) to one another. Four topologies : Mesh , Star , Bus , and Ring

36. Physical Topology

37. Physical Topology Mesh Every link is dedicated point-to-point link The term dedicated means that the link carries traffic only between the two devices it connects

38. Physical Topology Mesh To link n devices fully connected mesh has: n ( n - 1) / 2 physical channels (Full-Duplex) Every Device on the network must have n - 1 ports

39. Physical Topology Mesh Example: 8 devices in mesh has links: n(n-1) / 2 number of links = 8 (8-1)/2 = 28 number of ports per device = n – 1 = 8 –1 = 7

40. Physical Topology Mesh Advantages Each connection carry its own data load (no traffic problems) A mesh topology is robust Privacy or security Fault identification and fault isolation

41. Physical Topology Mesh: Disadvantages Big amount of cabling Big number of I/O ports Installation and reconnection are difficult Sheer bulk of the wiring can be greater than the available space Hardware connect to each I/O could be expensive Mesh topology is implemented in a limited fashion; e.g., as backbone of hybrid network

42. Physical Topology Star: Dedicated point-to-point to a central controller (Hub) No direct traffic between devices The control acts as an exchange

43. Physical Topology Star Advantages Less expensive than mesh ( 1 Link + 1 port per device) Easy to install and reconfigure Less cabling Additions, moves, and deletions required one connection Robustness : one fail does not affect others Easy fault identification and fault isolation

44. Physical Topology Star Disadvantages Dependency of the whole topology on one single point (hub) More cabling than other topologies ( ring or bus) Used in LAN

45. Physical Topology Bus It is multipoint One long cable acts as a backbone Used in the design of early LANS, and Ethernet LANs

46. Physical Topology Bus Nodes connect to cable by drop lines and taps Signal travels along the backbone and some of its energy is transformed to heat Limit of number of taps and the distance between taps

47. Physical Topology Bus Advantages Ease of installation Less cables than mesh, star topologies Disadvantages Difficult reconnection and fault isolation ( limit of taps) Adding new device requires modification of backbone Fault or break stops all transmission The damaged area reflects signals back in the direction of the origin, creating noise in both directions

48. Physical Topology Ring Each device has dedicated point-to-point connection with only the two devices on either side of it A signal is passed along the ring in one direction from device to device until it reaches its destination Each devices incorporates a Repeater

49. Physical Topology Ring Advantages Easy of install and reconfigure Connect to immediate neighbors Move two connections for any moving (Add/Delete) Easy of fault isolation Disadvantage Unidirectional One broken device can disable the entire network. This weakness can be solved by using a dual ring or a switch capable of closing off the break

50. Physical Topology Hybrid Topology Example: having a main star topology with each branch connecting several stations in a bus topology

51. Categories of Networks Network Category depends on its size Two primary categories LAN : Covers area < 2miles WAN : Can be worldwide MAN : Between LAN & WAN, span 10s of miles

52. Local Area Network (LAN) Privately owned Links devices in the same office, building, or campus Simple LAN: 2 PCs & 1 printer in home or office Size is limited to a few kilometers Allow resources to be shared (hardware, software, or data)

53. Local Area Network (LAN) An isolated LAN connecting 12 computers to a hub in a closet

54. Local Area Network (LAN) LAN is distinguished by: Size (# users of OS, or licensing restrictions) Transmission medium (only one type) Topology (bus, ring, star) Data Rates (speed): Early: 4 to 16 Mbps Today: 100 to 1000 Mbps

55. Wide Area Networks (WAN) Provides long-distance transmission of data over large geographic areas (country, continent, world)

56. Wide Area Networks (WAN) Switched WAN Backbone of the Internet Dialup line point-to-point WAN Leased line from a telephone company

57. Wide Area Networks (WAN)

58. INTERNETWORK

59. Metropolitan Area Networks (MAN) Size between LAN and WAN Inside a town or a city Example: the part of the telephone company network that can provide a high-speed DSL to the customer

60. 1.3.3 Switching An internet is a switched network in which a switch connects at least two links together. A switch needs to forward data from a network to another network when required. The two most common types of switched networks are circuit-switched and packet-switched networks.

61. Circuit-Switching In a circuit-switched network, a dedicated connection, called a circuit, is always available between the two end systems. the switch can only make it active or inactive.

62. Packet-Switched Network In a computer network, the communication between the two ends is done in blocks of data called packets. Instead of the continuous communication we see between two telephone sets when they are being used, we see the exchange of individual data packets between the two computers. This allows us to make the switches function for both storing and forwarding because a packet is an independent entity that can be stored and sent later.

63. The Internet 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. Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use An internet is 2 or more networks that can communicate with each other The Internet is a collaboration of more than hundreds of thousands of interconnected networks

64. The Internet Internet Today Made of many LANs and WANs Every day new networks area added and removed Internet services Providers (ISPs) offer services to the end users International service providers National service providers Regional service providers Local service providers Data rate

65. Hierarchical organization of the Internet The Internet

66. 2.1 PROTOCOL LAYERING In data communication and networking, a protocol defines the rules that both the sender and receiver and all intermediate devices need to follow to be able to communicate effectively. greet each other, HI, How are you..? I’ am fine, thank you.. confine their vocabulary should refrain from speaking when the other party is speaking Conversation should be a dialog, not a monolog exchange some nice words when they leave

67. Principles of Protocol Layering First Principle If we want bidirectional communication, we need to make each layer so that it is able to perform two opposite tasks, one in each direction The third layer task is to listen (in one direction) and talk (in the other direction). Second Principle Two objects under each layer at both sites should be identical. The object under layer 2 at both sites should be a ciphertext letter. The object under layer 1 at both sites should be a piece of mail .

68. Layered Architecture

69. Layers in the TCP/IP Protocol Suite

70. Description of Each Layer Physical Layer C arrying individual bits in a frame across the link. The communication between two devices at the physical layer is still a logical communication because there is another, hidden layer, the transmission media, under the physical layer. logical unit between two physical layers in two devices is a bit. Datalink layer TCP/IP does not define any specific protocol for the data-link layer. It supports all the standard and proprietary protocols. Any protocol that can take the datagram and carry it through the link suffices for the network layer. The data-link layer takes a datagram and encapsulates it in a packet called a frame.

71. Network Layer The NETWORK LAYER is responsible for creating a connection between the source computer and the destination computer. The communication at the network layer is host-to-host. The network layer in the Internet includes the main protocol, Internet Protocol (IP), that defines the format of the packet, called a datagram at the network layer. IP also defines the format and the structure of addresses used in this layer. IP is also responsible for routing a packet from its source to its destination, which is achieved by each router forwarding the datagram to the next router in its path. IP is a connectionless protocol that provides no flow control, no error control, and no congestion control services. This means that if any of theses services is required for an application, the application should rely only on the transport-layer protocol. The network layer also includes unicast (one-to-one) and multicast (one-to-many) routing protocols. A routing protocol does not take part in routing (it is the responsibility of IP), but it creates forwarding tables for routers to help them in the routing process.

72. Contd., The NETWORK LAYER also has some auxiliary protocols that help IP in its delivery and routing tasks. The Internet Control Message Protocol (ICMP) helps IP to report some problems when routing a packet. The Internet Group Management Protocol (IGMP) is another protocol that helps IP in multitasking. The Dynamic Host Configuration Protocol (DHCP) helps IP to get the network-layer address for a host. The Address Resolution Protocol (ARP) is a protocol that helps IP to find the link-layer address of a host or a router when its network-layer address is given.

73. Transport Layer The logical connection at the transport layer is also end-to-end. The transport layer at the source host gets the message from the application layer, encapsulates it in a transport layer packet (called a segment or a user datagram in different protocols) and sends it, through the logical (imaginary) connection, to the transport layer at the destination host. Transmission Control Protocol (TCP), is a connection-oriented protocol. It creates a logical pipe between two TCPs for transferring a stream of bytes. User Datagram Protocol (UDP), is a connectionless protocol that transmits user datagrams without first creating a logical connection. Stream Control Transmission Protocol (SCTP) is designed to respond to new applications that are emerging in the multimedia

74. Application Layer The logical connection at the transport layer is also end-to-end. The two application layers exchange messages between each other as though there were a bridge between the two layers. However, we should know that the communication is done through all the layers. Communication at the application layer is between two processes (two programs running at this layer). To communicate, a process sends a request to the other process and receives a response. Process-to-process communication is the duty of the application layer. The application layer in the Internet includes many predefined protocols, a user can also create a pair of processes to be run at the two hosts. HTTP HTTPS SMTP TELNET SSH SNMP DNS

75. Encapsulation and Decapsulation

76. THE OSI MODEL Established in 1947, the International Organization for Standardization (ISO) is a multinational body dedicated to worldwide agreement on international standards. Almost three-fourths of the countries in the world are represented in the ISO. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s. ISO IS THE ORGANIZATION; OSI IS THE MODEL.

77. TRANSMISSION MEDIA

78. Twisted-Pair Cable One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference. The receiver uses the difference between the two. In addition to the signal sent by the sender on one of the wires, interference (noise) and crosstalk may affect both wires and create unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relative to the noise or crosstalk sources (e.g., one is closer and the other is farther). This results in a difference at the receiver. By twisting the pairs, a balance is maintained. For example, suppose in one twist, one wire is closer to the noise source and the other is farther; in the next twist, the reverse is true.

79. Unshielded Versus Shielded Twisted-Pair Cable The most common twisted-pair cable used in communications is referred to as unshielded twisted-pair (UTP). IBM has also produced a version of twisted-pair cable for its use, called shielded twisted-pair (STP). STP cable has a metal foil or braided mesh covering that encases each pair of insulated conductors. Although metal casing improves the quality of cable by preventing the penetration of noise or crosstalk, it is bulkier and more expensive.

80. `

81. BAYONET NEILL-CONCELMAN (BNC)

82. Fiber-Optic Cable

83. 7.3 UNGUIDED MEDIA: WIRELESS

84. Radio waves, for the most part, are omnidirectional. Radio waves, particularly those waves that propagate in the sky mode, can travel long distances. Radio waves, particularly those of low and medium frequencies, can penetrate walls. AM radio can receive signals inside a building. we cannot isolate a communication to just inside or outside a building. RADIO WAVES ARE USED FOR MULTICAST COMMUNICATIONS, SUCH AS RADIO AND TELEVISION, AND PAGING SYSTEMS.

85. Microwaves Microwaves are unidirectional. Microwave propagation is line-of-sight. Very high-frequency microwaves cannot penetrate walls. This characteristic can be a disadvantage if receivers are inside buildings. The microwave band is relatively wide, almost 299 GHz. Therefore wider subbands can be assigned, and a high data rate is possible. Use of certain portions of the band requires permission from authorities.

86. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

87. Infrared INFRARED SIGNALS CAN BE USED FOR SHORT-RANGE COMMUNICATION IN A CLOSED AREA USING LINE-OF-SIGHT PROPAGATION

88. 8.3 PACKET SWITCHING If the message is going to pass through a packet-switched network , it needs to be divided into packets of fixed or variable size. The size of the packet is determined by the network and the governing protocol. No resource allocation for a packet. no scheduled processing time for each packet. Resources are allocated on demand , FCFS.

89. Efficiency The efficiency of a datagram network is better than that of a circuit-switched network; resources are allocated only when there are packets to be transferred. If a source sends a packet and there is a delay of a few minutes before another packet can be sent, the resources can be reallocated during these minutes for other packets from other sources. Delay There may be greater delay in a datagram network than in a virtual-circuit network. Although there are no setup and teardown phases, each packet may experience a wait at a switch before it is forwarded. In addition, since not all packets in a message necessarily travel through the same switches, the delay is not uniform for the packets of a message

90. 8.3.2 Virtual-Circuit Networks A virtual-circuit network is a cross between a circuit-switched network and a datagram network. Its characteristics: 1. As in a circuit-switched network, there are setup and teardown phases in addition to the data transfer phase. 2. Resources can be allocated during the setup phase, as in a circuit-switched network, or on demand, as in a datagram network. 3. As in a datagram network, data are packetized and each packet carries an address in the header. However, the address in the header has local jurisdiction (it defines what the next switch should be and the channel on which the packet is being carried), not end-to-end jurisdiction. The reader may ask how the intermediate switches know where to send the packet if there is no final destination address carried by a packet.`

91. 8.3.2 Virtual-Circuit Networks 4) As in a circuit-switched network, all packets follow the same path established during the connection. 5) A virtual-circuit network is normally implemented in the data-link layer, while a circuit-switched network is implemented in the physical layer and a datagram network in the network layer. But this may change in the future.

92. The identifier that is actually used for data transfer is called the virtual-circuit identifier (VCI) or the label . A VCI, unlike a global address, is a small number that has only switch scope; it is used by a frame between two switches. When a frame arrives at a switch, it has a VCI; when it leaves, it has a different VCI.

93. Three Phases SETUP TRANSFER TEARDOWN

94. TRANSFER

95. SETUP

96. SETUP - ACK