Key Unit Competency:
    To be able to explain principles, standards and purposes of computer network

    Read the following scenario and answer to the asked questions.

    In the school computer labs, choose a classmate and send him/her an email that
    has “Computer Network “as the email subject and the email body contains names of
    previous units already covered in senior 5 computer science. Ask him/her to reply
    immediately to your email.

    After receiving the reply, answer the following questions:

    1. List all possible elements that make this communication possible

    2. What devices are used to facilitate sending email successfully?

    3. Discuss what made possible the sending and receiving of emails

    4. Do you like using email?

    5. How do you value the factor of sending and receiving an email

    6. Describe what you see in the photo below?

    3.1. Fundamental of computer Networ

    3.1.1. Computer Network Definition

    ACTIVITY 3.1

    Observe computers in the computer lab and answer the following question?

    1. Describe what you see?

    2. What are transmission media used to connect computers in the
        computer labs?

    3. Are all devices connected?

    A computer network is a system of interconnected computers for the purpose of
    sharing data and resources.

    Computers on a network are called nodes. Nodes can include hosts such as personal
    computers, phones, servers as well as networking hardware. Two devices are
    networked together when one device is able to exchange information with the
    other device. The computer can be connected to another in the two ways.

    Wired network: Computers are connected using cable media. Most commonly
    Ethernet Cable, coaxial cable and optic fiber.

    Wireless network: Computers are connected using wireless media. Radio waves are
    used in wireless mode.

    3.1.2 Properties of Computer Network

    • Easy Sharing of Resources: Computers are able to share various resources
    easily over a network. Shared resources can be Internet, files, printer, storage
    and others.

    Performance: It is achieved by measuring the speed of data transmission
    with number of network users, connectivity used and the software used. The
    commonly measured qualities in the network performance are Bandwidth
    and Latency.

    Reliability: It means that computer network provides assurance of the
    delivery of data to the intended recipient.

    Scalability: The possibility of adding new computer without affecting the
    network performance.

    Security: computer network must be secured for the benefit of the user and
    data protection. The security is achieved by protecting data from unauthorized

    Quality of Service (QoS): Quality of Service refers to the mechanism that
       manage congested network traffic.

    Fault tolerant: A fault tolerant network limits the impact of hardware or
    software failure and recovers quickly when a failure occurs


    1. Investigate what happen when a shared resource is disconnected from
    the computer network?

    2. Imagine other areas where computer network is used?

    3.1.3 Advantages and Disadvantage of Computer Networking
           The common advantages of computer network

    Activity 3.2

    1. Discuss the disadvantages of using computer network within your school?

    2. In class of senior 5 MPC, Computer Science Teacher decides to share notes
       for students to use on our school network. The mathematics teacher decides
       to print notes of 100 pages and distributes to each member of senior 5 MPC

    i. Evaluate the cost impact for both teachers

    ii. Both teachers, whom save money in giving notes.

    The common advantages of computer network

    1. Enhanced communication and availability of information: It allows access
       to a vast amount of useful information.

    Example: Population data, newsletters, online businesses, contents,

    2. Allow resource sharing: Fewer resources are needed when an organization
    uses a computer network.
    Example: only one printer is needed instead of buying a printer for each office.

    3. File sharing made easy: computer network allows people to share files, which
        helps to save more time and effort.
        Example: A teacher can share homework to all students through school

    4. Improve storage capacity: since you are going to share information, files and
        resources to other people, you have to ensure that all data and content are
        properly stored in the system.

    5. Cost efficiency: on computer network, you can share software license installed
    on the server and can then be used by various workstations.

    6. Security of information and resources: users cannot see other users' files
    unlike on stand-alone machines.

    7. Backup of data is easy as all the data is stored on the file server.

    The common disadvantages of computer networking

    1. Lack of independence: people rely on computer network and when the
    system is down, people get stack. Most of organizations depend on the
    computer networks.

    2. Security issues: huge number of people use a computer network to get and
    share their files and resources, a certain user’s security would be always at
    risk. Viruses can spread to other computers throughout a computer network.
    There is a danger of hacking, particularly with wide area networks. Security
    procedures are needed to prevent such abuse, Examples: The use of Antivirus
    and firewall.

    3. Lack of robustness: computer network’s main server breaks down, the entire
    system would become useless


    1. Investigate what happen when a shared resource is disconnected from
        the computer network?

    2. Imagine other areas where computer network is used?

    3.1.4 Types of computer networks

    Activity 3.3

    With two or more Bluetooth enabled devices available in the classroom:

    1. Turn on the Bluetooth feature on both devices

    2. Share and receive files such images and documents between the

    3. Turn off Bluetooth feature in the two devices.

    A computer network is classified basing on the size of the area covered, the number
    of users connected and the number & types of services available.

    The followings are type of computer networks:

    1. Personal Area Network (PAN)

    A personal area network (PAN) is a network that connects devices, such as mice,
    keyboards, printers, Smartphone, and tablets within the range of an individual
    person. PAN has connectivity range up to 10 meters. PAN may include wireless
    computer keyboard and mouse, Bluetooth enabled headphones, wireless printers
    and TV remotes. All of these devices are dedicated to a single host and are most
    often connected with Bluetooth technology.

    Bluetooth is a wireless technology that enables devices to communicate over short
    distances. A Bluetooth device can connect up to seven other Bluetooth devices.

    2. Local Area Network (LAN)

    Traditionally, a LAN is defined as a network that covers a small geographical area.
    However, the distinguishing characteristic for LANs today is that they are typically
    owned by an individual, such as in a home or small business, or wholly managed
    by an IT department, such as in a school or corporation. This individual or group
    enforces the security and access control policies of the network. LAN uses Ethernet
    IEEE 802.3 as its standard.

    A Wireless LAN (WLAN) is a LAN that uses radio waves to transmit data between
    wireless devices. In a traditional LAN, devices are connected together using copper
    cabling. In some environments, installing copper cabling might not be practical,
    desirable, or even possible. In these situations, wireless devices are used to transmit
    and receive data using radio waves. As with LANs, on a WLAN, you can share resources,
    such as files, printers, and Internet access. WLAN uses Ethernet IEEE 802.11 as its

    3. Metropolitan Area Network (MAN)

    A metropolitan area network (MAN) is a network that spans across a large organization
    like campus or a city. The network consists of various buildings interconnected
    through wireless or fiber optic backbones.

    A backbone is the part of the computer network infrastructure that interconnects
    different LAN networks and provides a path for exchange of data between these
    different networks

    The communication links and equipment are typically owned by a network service
    provider who sells the service to the users. A MAN can acts as a high-speed network
    to enable sharing of regional resources.

    4. Wide Area Network (WAN)

    A WAN connects multiple networks that are in geographically separated locations.

    The distinguishing characteristic of a WAN is that it is owned by a service provider.
    Individuals and organizations contract for WAN services. WAN network provides
    connectivity to MANs and LANs. The most common example of a WAN is the
    Internetwork or Internet in short. The Internet is a large WAN that is composed of
    millions of interconnected networks.

    Example: Kigali and Nairobi networks are connected through the Internet


    1. Discuss the role ISP services for LANs?

    2. Do an observation in the school computer lab and categorize the
    computer network type available at your school? Justify your answer.

    3. Using clear examples, Distinguish Personal Area Network and Local Area

    4. Using an arrow match the following in Group A with their
    corresponding in Group B

    Group A                                               Group B
    a. Radio waves                                     1. Qualities of Computer network

    b. Millions of interconnected network    2. Disadvantages of Computer network

    c. Sharing resources                             3. Wireless

    d. Hacking attacks                                 4. WAN

    e. Bandwidth and Latency                     5. Advantages of Computer network

    3.2 Computer Network Concept and Technology

    ACTIVITY 3.4

    You are browsing a website on the internet while the speed is okay and suddenly you
    find that the page is loading slowly. Investigate the reason behind slowness?

    3.2.1 Network metrics

    Network metrics are defined as standards of measurement by which efficiency,
    performance, progress, or quality of a plan, process can be assessed. Network metric
    are used by a router to make routing decisions.

    When data is sent over a computer network, it is broken up into small chunks called
    packets. Each packet contains source and destination address information. Packets
    are sent across a network one bit at a time.

          a. Bandwidth

    Bandwidth is the amount of data that can be transmitted in a fixed amount of time.
    Bandwidth is measured in the number of bits that can be sent every second.
    The following are examples of bandwidth measurements:

    • b/s - bits per second

    • kb/s - kilobits per second

    • Mb/s - megabits per second

    • Gb/s - gigabits per second

                    b. Latency
    Latency is the time between requesting data and receiving data. More simply put,
    the time it takes to establish a connection between your computer and the server
    hosting the website you requested. The important thing to take away here is that
    latency is not speed. Data is delayed by network devices and cable length. Network
    devices add latency when processing and forwarding data.

                     c. Throughput:
    Throughput is the actual rate at which information is transferred. It measures the
    amount of completed work against time consumed and may be used to measure
    the performance of a processor, memory and/or network communications.

                       d. Error rate:
    Error rate is the number of corrupted bits expressed as percentage or fraction of the
    total sent.
                        e. Jitter:
    Jitter is variation in packet delay at the receiver of information. For measuring the
    capacity of all of these metrics above, we focus on capacity of message and this one
    change into different form depending on the network devices where this message
    is located.

                   3.2.2 Data Transmission model

    The term transmission mode is used to define the direction of signal flow between
    two linked devices. The data that is transmitted over the network can flow using one
    of three modes: simplex, half-duplex and full-duplex.

    1. Simplex: it is a single one-way transmission. In a simplex transmission
    mode, the communication between sender and receiver occurs only in one
    direction. That means only the sender can transmit data, and receiver can
    receive that data. The receiver cannot transmit any information back to the

    The keyboard to monitor transmission is an example of simplex transmission
    mode. Other examples are communication between a computer and a
    printer, listening to the radio and the signal that is sent from a TV station to
    your home TV.

    2. Half-Duplex: data flows in one direction at a time. In half-duplex, the
        channel of communications allows alternating transmission in two
       directions, but not in both directions simultaneously. An Example of Halfduplex
       is the Talkie- Walkie used by the police.

    3. Full-Duplex: data flows in both directions at the same time. In a full duplex
       transmission mode, the communication between sender and receiver can
      occur simultaneously. Sender and receiver both can transmit and receive
      simultaneously at the same time.

    A telephone conversation is an example of full-duplex communication. Both people
    can talk and be heard at the same time.


    1. Examine 2 reasons that cause latency in computer network.

    2. What is your school download bandwidth and upload bandwidth?

    3. Contrast upload bandwidth and download bandwidth?

    4. Categorize following devices according to their transmission modes

                         a. TV

                         b. Radio

                         c. Walkie -Talkie

                         d. Phone

                         e. Computer

    3.2.3. Internetwork (Internet, Intranet, Extranet)

    ACTIVITY 3.5

    Using computer network, an organization’s employees can access data when
    they are inside the organization buildingand when they are physically outside.
    Investigate technologies that can be used to allow employees inside and outside
    to access organization’s data.

    A network of networks is called an internetwork, or simply the Internet. The Internet,
    extranets, and intranets all rely on Transport Control Protocol / Internet Protocol
    (TCP/IP). However, they are different in terms of the levels of access they allow to
    various users inside and outside the organization and the size of the network.

    1. An Intranet is a private computer network that uses Internet Protocol to
       securely share any part of an organization’s information or operational
       systems within that organization. Only users inside the organization are
        only allowed to access it.

    2. An Extranet is a private network that uses Internet protocols, network

    connectivity. An extranet can be viewed as part of a company’s intranet
    that is extended to users outside the company, the connectivity is made
    possible by the Internet.

    3. The Internet is a global system of interconnected computer networks that
    use the standard Internet Protocol suite (TCP/IP) to serve billions of users

    The difference between the Internet and Extranets is that while the extranet allows
    limited access to non-members of an organization, the Internet generally allows
    everyone to access all network resources.


    General supply Ltd. sell various services online and offline. It has various partners such
    as suppliers, sellers, buyers and clients in different Districts of Rwanda. Each partner
    wants to access the General supply data from its servers located at the main office in
    Ruhango District.

    Examine in details the appropriate technology for each user to access the General
    supply Ltd. data to avoid the user location problem

    3.3 Local Area Networks (LANs)

    ACTIVITY 3.6

    By definition, computer network is said to be a group of computers connected together
    and share resources. Using your school environment, observe followings:

    1. The range covered by your school network?

    2. The number of users on your school network?

    3. Resources shared on your school network?

    3.3.1 Definition

    Local Area Networks (LANs) are networks usually confined to a geographic area, such
    as a single building or a college campus. LANs can be small, linking as few as three
    computers, but often link hundreds of computers used by thousands of people.

    3.3.2 LAN Categories

    1. Peer-to-Peer Network

    A peer-to-peer (P2P) network is created when two or more computers are connected
    and share resources without going through a separate server computer. In a peerto-
    peer network, there is no hierarchy among the computers, nor are there any
    dedicated servers.

    Each device on the network, also called a client, has equivalent capabilities and
    responsibilities. A user is responsible for its own resources and can decide which
    data and devices to be shared with other computers. Because individual users are
    responsible for the resources on their own computers, the network has no central
    point of control and no central administration. Peer-to-peer networks work best in
    environments with ten or fewer computers.

    Advantages of peer to peer network are as follows:

    • The main advantage of peer to peer network is that it is easier to set up

    • In peer-to-peer networks all nodes are act as server as well as client therefore
      no need of dedicated server

    • The peer to peer network is less expensive

    • Peer to peer network is easier to set up and use this means that you can spend
     less time in the configuration and implementation of peer to peer network.

    Disadvantages of peer to peer network

    • A computer can be accessed anytime

    • Network security has to be applied to each computer separately

    • Backup has to be performed on each computer separately

    • No centralized server is available to manage and control the access of data.

    2. Client-Server Network

    In a client-server network, the client requests information or services from the server
    and the server provides the requested information or service to the client. Servers
    on a client-server network commonly perform some of the processing work for
    client machines.

    In a client-server network, resources are controlled by a centralized network
    administration. The network administrator implements data backups and security
    measures. The network administrator also controls user access to the server

    Note: In a home or small business, a single server can run multiple types of server
    software, it may be necessary for one computer to act as a file server, a web server,
    and an email server. A client computer can also run multiple types of client software.
    There must be client software for every service required. With multiple client software
    installed, a client can connect to multiple servers at the same time.

    Advantages of Client-Server Network

    • Centralization of control: Access, resources and integrity of the data are
      controlled by the dedicated server so that a program or unauthorized client
      cannot damage the system.

    • Scalability: You can increase the capacity of clients and servers separately.
      Any element can be increased (or enhanced) at any time, you can add new
      nodes to the network (clients or servers).

    • Easy maintenance: Distribute the roles and responsibilities to several
      standalone computers, you can replace, repair, upgrade, or even move a server,
      while customers will not be affected by that change (or minimally affect).

    Disadvantage of Client Server Networks

    • There is a reliance on the central server, if it fails, no work can be done

    • A network manager is required and this costs money

    • The server costs money, as does the network operating system

    • Servers are powerful, thus expensive

    • Lots of network traffic.

    Advantages of Client Server Networks over Peer to Peer Networks

    Centralization: Unlike Peer to Peer, where there is no central administration,
      Client Server Networks have a centralized control.

    Proper Management : All the files are stored at the same place. Therefore,
    management of files becomes easy and it is easier to find files.

    Back-up and Recovery possible: As all the data is stored on server it is easy to
      make a back-up of it. Also, in case of some break-down if data is lost, it can be
      recovered easily and efficiently. While in peer to peer network, we have to take
      back-up at every workstation.

    Upgrade and Scalability in Client-server set-up: Changes can be made
      easily by just upgrading the server. Also new resources and systems can be
       added by making necessary changes in server.

    Accessibility: From various platforms in the network, server can be accessed

    Security: Rules defining security and access rights can be defined at the time of
    set-up of server.

    Disadvantages of client server network over the Peer to peer network

    • Congestion in Network: Too many requests from the clients may lead to
      congestion, which rarely takes place in Peer to Peer network. Overload can
      lead to breaking-down of servers. In peer-to-peer, the total bandwidth of the
      network increases as the number of peers increase.

    • Client-Server network is not as robust as a Peer to Peer network and if the
      server fails, the whole network goes down.

    • Cost: It is very expensive to install and manage client server network.


    Respond the following questions by True or False and justify your answer

    • Peer to Peer network is only implemented by computers which run same
    operating system.

    • In Server-Client network, Server respond to service only requested by the

    • Limit number of hosts in the Peer to Peer network are 10 computers.

    • Client requests only the service available on the server in Server-Client

    • Peer to Peer network is more secure than Server-Client network.

    • There is a dedicated computer in Peer to Peer network.

    • In Client- Server network, both client and server must run the same Operating

    3.4. Physical Components

     ACTIVITY 3.7

    In the computer lab observe devices that are directly participating in the
    network. Examine the role of each device you have identified.

    3.4.1. Definition of network device

    A network host or a node is a computer or any other device that is directly connected
    to a computer network. A network host may offer information resources, services,
    and applications to users.

    i. Network Interface Card (NIC)

    Network Interface card is a component that allows the computer to communicate
    across a network. This component is frequently built into the motherboard of today’s
    computers, but it can also be a separate card for use in a PCI slot.

    Network Interface cards can be either wired or wireless. However, some cards do
    support both wireless and wired networking


    NIC Card installation in a desktop computer:

    Step 1: Shut down your Computer and disconnect it from the power source

    Step 2: Remove the case cover. Then remove the cover of the available slot.

    Step 3: Install NIC in proper slot and secure it

    Step4: Replace the case cover.

    Note: A wireless NIC has an antenna connected to the back of the card or attached
    with a cable so that it can be positioned for the best signal reception. You must
    connect and position the antenna.

         ii. Media Access Control Address

    Media Access Control Address (MAC address) of a device is a unique identifier
    assigned to network interfaces for communications at the data link layer of a
    network segment. MAC address is a physical address of Network Interface Card. In
    other words MAC addresses are linked to the hardware of network adapters. A MAC
    address is given to a network adapter when it is manufactured.
    Example of a MAC address: 00:0a:95:9d:68:16.

    iii. Modem

    A modem is a hardware device that enables a computer to send and receive data
    over a telephone line or a cable or satellite connection. Modem is used to transmit
    digital information via analog systems. The word “modem” is derived from the term
    “Modulator - Demodulator.”

    The essential functions of a modem are:

    • Modulate: an analog carrier signal to carry digital information, it means to
       convert the analog signal to digital signal.

    • Demodulate: a similar signal so as to decode the digital information from
    the analog carrier signal and it means to convert the same signal back to the
    analog signal then transmitted through telephone line.

    They are two types of modems:

    Internal modem which are circuit boards that plug into a computer’s motherboard and
    external modems which are discrete units housed in a separate case. Typically, an external
    modem is connected to the telephone line and the computer via cables or USB.


    Find the Mac address of your computer

    Step1: Click the Run button in the windows 10 Start Menu

    Step 2: Type cmd in the Open prompt of the Run menu and click OK to launch a
                 command prompt window

    Step 3: Type ipconfig /all at the command prompt to check the network card

    Step4: MAC address is listed by ipconfig under Physical Address

    iv. RJ 45 Connector and Port

    A registered jack (RJ) is a standardized physical network interface for connecting
    telecommunications or data equipment. The physical connectors that registered
    jacks use are mainly of the modular connector and 50-pin miniature ribbon connectortypes

    The RJ45 port is the network port on a computer. This socket has many names. It is
    also known as the Ethernet port, the network adapter, the network jack or the RJ45jack.

    3.5. Network Devices

    ACTIVITY 3.8

    Observe the connection between network devices that make your school network.
    Then answer following questions:

    1. Examine how computers are connected together in order to exchange

    2. Investigate how data / message is forwarded from the Computer A (as
         source) to Computer B (as destination)?

    3. The equipment used to connect devices within a LAN has evolved from
         hub to bridge to switch. Contrast both devices?

    3.5.1 Hub

    A hub is a network hardware device for connecting multiple devices together and
    making them act as a single network segment.

    Definition:A network segment is a portion of a computer network that is separated from
    the rest of the network by a network device.

    Hub receives message on one port and then send it out to all other ports, this means
    that when hub receives message, the received message is regenerated or duplicated
    and sent to all computers connected to the hub, each computer on the network
    receives the message, if it is not the destination message is destroyed, if it is the
    destination it reads the message.

    Note: Hubs are used less often today because of the effectiveness and low cost of
    switch. Hub do not segment network traffic. When one device sends traffic, the hub
    floods that traffic to all other devices connected to hub. The devices are sharing the

    3.5.2 Switches

    Switch filters and segments network traffic by sending messages only to the device to
    which it is sent. This means that when a switch receives a message do not duplicated
    it, it sends it directly to the destination computer. This provides higher dedicated
    bandwidth to each device on the network.

    A switch maintains a switching table, the switching table contains a list of all MAC
    addresses of computers on the network and a list of switch port which are used to
    reach a computer with a given MAC address.
    When message arrives that is destined for a particular MAC address, the switch uses
    the switching table to determine which port to use to reach the MAC address. Then message is forwarded to the destination.

    3.5.3 Bridge

    A network bridge is a computer networking device that creates a single aggregate
    network from multiple communication networks or network segments. This function
    is called network bridging

    Bridges keep a record of all the devices on each segment. A bridge can then filter
    network traffic between LAN segments. This helps reduce the amount of traffic
    between devices

    3.5.4 Access point

    The Access Point is connected to a switch using UTP cable, therefore it can provide
    access to the rest of the network. Instead of providing copper cabling to every
    network host, only the wireless access point is connected to the network with
    copper cabling and spread radio waves to the rest of network.
    The range (radius of coverage) for Access Point indoors is 98.4 ft (30 m) and too
    much greater distances outdoors depending on the technology used.


    1. Justify why outdoor range is better that indoor range?

    2. Discuss how a switch perform micro-segmentation?

    3. Analysis why Switch is much preferred than a HUB

    4. Examine the difference between Access Point and Bridge?

    5. Identify the purpose of switching table in the switch?

    6. Using the internet search for the diagram representation of hubs,
        switches and bridges in a network

    3.6 Network Transmission Medium

    ACTIVITY 3.9

    Draw a computer network of 10 computers
    This is the physical mean of communication between network computers.
    Data transmission media are the physical materials used to transmit data between
    computers. Packet of data can be transmitted on network as electrical signals
    in electric wire, light signal in fiber optic cables or as electromagnetic waves
    through space.
    There are two main types of data communication media used in network:

    1. Bounded or Guided media: which transmit signals by sending electricity
       or light over a cable wire. Common examples of bounded media are
      twisted cables, Coaxial cables and fiber optic cables.

    2. Unbounded media: which transmit data through the air, radio waves,
    layer or infrared signal and satellite based microwaves, etc.

    3.6.1 Guided transmission media

    A wide variety of networking cables are Coaxial, Fiber optic and twisted-pair
    cables which use electrical signals over copper to transmit data while Fiber-optic
    cables use light signals to transmit data. These cables differ in bandwidth, size, and

    It is used by both cable television companies and satellite communication systems
    and it carries data in the form of electrical signals. There are several types of coaxial

    • Thicknet or 10BASE5 - used in networks and operated at 10 Mb/s with a
    maximum length of 1640.4 ft. (500 m.)

    Thinnet 10BASE2 - used in networks and operated at 10 Mb/s with a maximum
    length of 607 ft. (185 m.)

          b. Twisted-pair copper cabling

    Twisted-pair is a type of copper cabling used for telephone communications and
    most Ethernet networks. The pair is twisted to provide protection against crosstalk,
    which is the noise generated by adjacent pairs of wires in the cable.
    The use of this cable is limited by two factors:

    a. Attenuation: the strength of signal reduces as the distance increases i.e the
    cables loose signals strength when they exceed their maximum length stated
    in network specification.

    b. Crosstalk: this refers to interference generated by cables when they are too
    close to each other. Signals from one line get mixed with signals from another.

    3.6.2. Types of twisted pair cables

    There are two types of twisted pair cables: unshielded and shielded cables

    a. Unshielded twisted-pair (UTP)

    Unshielded twisted-pair (UTP) cabling is the most common variety of twisted-pair

    UTP cable consists of four pairs of color-coded wires that are twisted together and
    then encased in a flexible plastic sheath that protects from minor physical damage.
    The twisting of wires helps protect against crosstalk. However, UTP does not protect
    against electromagnetic interference (EMI) or radio frequency interference (RFI).
    EMI and RFI can be caused by a variety of sources including electric motors and
    fluorescent lights.

    There are two different wiring schemes called T568A and T568B. Using the T568A
    and T568B wiring schemes, two types of cables can be created: a straight-through
    cable and a crossover cable.

    1. A straight-through cable is the most common cable type. It maps a wire
        to the same pins on both ends of the cable. The order of connections (the
        pin out) for each color is the exact same on both ends.

    Two devices directly connected and using different pins for Transmit and Receive
    are known as unlike devices. They require a straight-through cable to exchange
    data. For example, connecting a PC to a switch requires a straight-through cable.

    2. A crossover cable uses both wiring schemes. T568A on one end of the
    cable and T568B on the other end of the same cable.
    Devices that are directly connected and use the same pins for transmit and receive,
    are known as like devices. They require the use of a crossover cable to exchange
    data. For example, connecting a PC to another PC requires a crossover cable.

    Note: The most used cable standards are below:

    • 100Base-TX: known as Fast Ethernet, it uses category 5, 5E, or 6 UTP cable and
    it wires u to 100 meters long.

    • 1000Base-T means that the speed of the network is up to 1000
    Mbps, baseband signaling is sed, T stands for twisted-pair as UTP cable used

    b. Shielded twisted-pair (STP)

    The STP type similar to UTP cable except that there is a metal foil or braided metal-
    mesh cover that encases each pair of insulated wires. The extra covering in shielded
    twisted pair wiring protect the transmission line from electromagnetic interference
    ( EMI) leaking into or out of cable. However this can make cables quite bulky
     and harder to install.
    The basic difference between UTP and STP is that UTP is a cable with wires that are twisted
    together to reduce noise and crosstalk. On other hand, STP is a twisted pair cable confined
    in foil or mesh shield that guards the cable against electromagnetic interference.



    1. Unshielded twisted pair (UTP) patch cable

    2. Modular connector (8P8C plug, aka RJ45)

    3. Crimping tool

    4. Cable tester (optional, but recommended

    Step 1: Strip the cable jacket about 1.5 inch down from the end.

    Step 2: Spread the four pairs of twisted wire apart.

    Step 3: Untwist the wire pairs and neatly align them in the T568B orientation.

    Step 4: Cut the wires as straight as possible, about 0.5 inch above the end of the jacket.

    Step 5: Carefully insert the wires all the way into the modular connector, making sure
                that each wire passes through the appropriate guides inside the connector.

    Step 5: Carefully insert the wires all the way into the modular connector, making sure
                that each wire passes through the appropriate guides inside the connector.

    Step 6: Push the connector inside the crimping tool and squeeze the crimper all the
                way down.

    Step 7: Repeat steps 1-6 for the other end of the cable.

    Step 8: To make sure you›ve successfully terminated each end of the cable, use a cable
                tester to test each pin.


    Step 1: Open the Network and Sharing Center:

    Step 2: Select the Control Panel from the Start menu.

    Step 3: Select Open Network and Sharing Center and click Network and Sharing Center

    3.6.3 Fiber optic cables

    An optical fiber cable, also known as a fiber optic cable, is an assembly similar to an
    electrical cable, but containing one or more optical fibers that are used to carry light

    Advantages of fiber optic

    a. Since they transmit light rather than electronic signal, the problem of electrical
        interference is eliminated , therefore they are not affected by radio interference
         or cross talk

    b. They have become the standard for connecting networks between buildings due
         to their immunity the effects of moisture and lighting.

    c. Fiber optic can transmit signal over much longer distance than coaxial cable and
        twisted cables

    d. They can carry information at high rate speed between

    e. The distance can be up to 2000 meters without repeater

    f. Security: it is difficult to tap into optical fiber line. If this is happen it will be
        noticed immediately.

    g. Low transmission loss

    h. Data can be transmitted digitally

    i. They are more resistant to adverse weather conditions.

    3.6.4 Unguided transmission media

    Unguided media transport electromagnetic waves without using a physical
    conductor. This type of communication is often referred to as wireless communication.
    The mediums used in wireless communications are air, vacuum and even water. Air
    is the most commonly used medium.

          a. Wireless Transmission

    Wireless transmission can be categorized into three broad groups namely radio
    waves, microwaves, infrared

          1. Radio waves

    Radio waves are normally omnidirectional. When an antenna transmits radio
    waves, they are propagated in all directions. This means that the sending and
    receiving antennas do not have to be aligned. The omnidirectional characteristics
    of radio waves make them useful for multicasting, in which there is one sender but
    many receivers. Our FM radio stations, cordless phones and televisions are examples
    of multicasting.

         2. Infrared

    Infrared is used in devices such as the mouse, wireless keyboard and printers. Some
    manufacturers provide a special port called the IrDA port that allows a wireless
    keyboard to communicate with a PC.

    Infrared signals have frequencies between 300 GHz to 400 THz. They are used for
    short-range communication. Infrared signals have high frequencies and cannot
    penetrate walls. Due to its short-range communication system, the use of an infrared
    communication system in one room will not be affected by the use of another system
    in the next room. This is why using an infrared TV remote control in our home will
    not interfere with the use of our neighbor’s infrared TV remote control.

    The disadvantages of using infrared

    • Infrared signals cannot be used for long distance communication.

    • Infrared waves can not be used outside of a building because sun’s rays contain
    infrared waves that can interfere with communication.

           3. Bluetooth

    Bluetooth technology is designed to serve as a new way of connecting devices.
    Bluetooth technology has an advantage of being low investment and low energy
    consumption demanding.

    The difference between Bluetooth and infrared is that Bluetooth allows communication
    when there is a barrier or a wall.

    4. Wi-Fi (Wireless Fidelity)

    Wi-Fi (Wireless Fidelity) is a standard that certifies that wireless devices in Wireless
    LAN to work together. It supports IEEE802.11b Ethernet standard.

    Wi-Fi uses radio signals to transmit high speed data over the wireless network, the
    Access Point is used to connect devices and it acts as the central device for Wireless
    LAN. Wireless devices can be: smartphones, PDAs, IPad, laptop and notebook.

    General steps to connect to a WI-FI network near you
    The following steps run through the general steps that anyone needs to take to get
    connected to the internet via WI-FI. (Do this exercise and discover the corresponding
    windows for every step. What is the meaning of different icons forms that a wireless
    network take?)

    Step 1: Locate yourself in a property or public space that has a wireless router.

    Step 2: Make sure that the device you›re going to use is:

              • Capable of connecting to the internet and

             • Capable of connecting to WI-FI.

    Step 3: Find out the name of the WI-FI network that the router in your location is

    Step 4: Once you know the name of the WI-FI network, use your chosen device to find

           3.7. IP Address

           3.7. IP Address

    The fingerprint and addressed letters are ways of identifying and addressing a person.
    A person's fingerprints usually do not change. They provide a way to physically identify
    people. The mailing address of a person can change, as it relates to where the person
    lives or picks up mail. Do network devices have addresses? Justify your answer.

        3.7.1 Understand IP Addresses

    An IP address is an address used in order to uniquely identify a device on a computer

          IP Versions

    There are two versions of IP addressknown as IP version 4 and IP version 6

          a. IP version 4

    IP version 4 is the common used IP address,

        a.1 Structure of IP address

    • An IP address is simply a series of 32 binary bits. Because it is difficult for human
       to read a binary IP address, the 32 bits are grouped into fout-8-bits bytes called

    • When a computer is configured with an IP address it is entered as doted decimal
       number such as

    • When a host receives an IP address , it looks at all 32 bits as they are received by
       the NIC

    • Each octet is made up with 8 bits an each bit has a value. The four groups of 8 bits
       have same set of value.

    • Parts of the IP address
     The logical 32 bits IP address is made up two parts which are network part or network
     address and the second one is host address .

     a.2 Classes of IP version 4

    There are five classes of available IP ranges: Class A, Class B, Class C, Class D and Class
    E, while only A, B, and C are commonly used classes D and E are reserved.
    Here is a listing of these addresses:

    Class A

    In class A the first bit of the first byte is always 0

    0xxxxxxx where x stand for any value (either o or 1)

    Minimum: 00000000
    Maximum: 01111111

    The valid range in class A =

    The range of IPs 127.x.x.x is reserved for the loopback or localhost, for example, is the common loopback address. Range to

    all hosts on the local network.
    The first byte in class A represent Network address while the three remaining
    represent the host address thus class A=Network. Host-Host-Host

    Class B

    In class B the first bit of first byte is always 1 and the second bit of first byte is always


    Minimum: 10000000=128
    Maximum: 10111111=191

    Valid range[ 128-191]

    The two first byte in class B represent Network address while the two remaining
    represent the host address thus class B=Network-Network-Host-Host

    Class C

    The first bit of first byte is always 1, the second bit of first byte is always 1 and the
    third bit of first byte is always 0 i.e 1100000

    Minimum: 11000000= 192
    Maximum: 11101111= 223
    Valid range: 192-223
    The three first bytes in class C represent Network address while the last byte remaining
    represent the host address thus class C=Network. Network -Network -Host

    a.3 Subnet Masks

    A subnet mask help to know which portion of the address identifies the network
    and which portion of the address identifies the host. Class A, B, and C networks have
    default masks, also known as natural masks, as shown here:

    Class A:

    Class B:

    Class C:

    Devices that are attached to a network have two addresses that are similar to a
    person’s fingerprints and a person’s mailing address. These two types of addresses
    are the Media Access Control (MAC) address and the IP address. The MAC address is
    hard coded onto the network interface card (NIC) by the manufacturer and it does
    not change. The IP address is assigned to a host to the network and may change.

      b. Internet Protocol Version 6 (IPv6)

    IPv6 (Internet Protocol Version 6) also called IPng (Internet Protocol next generation)
    is the newest version of the Internet Protocol reviewed to replace the current version
    of IPv4. IPv6 is designed to allow the Internet to grow steadily, both in terms of the
    number of hosts connected and the total amount of data traffic transmitted.

    IPv6 shows a 128-bit address in eight 16-bitblocks separated by colons

    Example: 3ffe:1900:4545:3:200:f8ff:fe21:67cf.


      b.1 Features of IPv6

    • Supports source and destination addresses that are 128 bits (16 bytes) long.

    • No more NAT (Network Address Translation)

    • Auto-configuration

    • No more private address collisions. Requires IPSec support to provide two
       security headers which can be used separately

    • Those security headers are Authentication Headers(AH) and Encrypting
       security payload(ESP)

    • Uses Flow Label field to identify packet flow for Quality of Service handling by

    • Allows the host to send fragments packets but not routers.

    • Does not require manual configuration or DHCP.

    • Moves optional data to IPv6 extension headers.

    • Uses Multicast Neighbor Solicitation messages to resolve IP addresses to linklayer

    • Uses Multicast Listener Discovery (MLD) messages to manage membership in
       local subnet groups.

    • Uses ICMPv6 Router Solicitation and Router Advertisement messages to
      determine the IP address of the best default gateway

    Why there is no different classes in IP v6?

    In IPv4 we have class A, B, C,D and E. In IPv6 we have only global prefix and interface

    IP v6 has three types of addresses, which can be categorized by type and scope:

    Unicast addresses: a packet is delivered to one interface.

    Multicast addresses: a packet is delivered to multiple interfaces.

    Anycast addresses:a packet is delivered to the nearest of multiple interfaces (in
    terms of routing distance).

    3.7.2. IP address assignment1. Static IP assignment

     The manual configuration of a host in a network, allows to assign the static IP address
     and the following information has to be specified:

    IP address - identifies the computer on the network

    Subnet mask - is used to identify the network on which the computer is

    Default gateway - identifies the device that the computer uses to access the
    Internet or another network

    Optional values - such as the preferred Domain Name System (DNS) server
    address and the alternate DNS server address

    Note that host on the same network should have the same Network ID


    Go through all these steps to assign to your computer a static IP address

    STEP 1: Go to Network Connections.

    STEP 2: Go to the network connection your computer is currently using, then
                 select Properties.

    STEP 3: Go to Internet Protocol Version 4 (IPv4) from the list and click the Properties
    STEP 4: Choose Use the following IP address option

    NOTE: When assigning a static IP address, make sure to set a value that will not
                conflict with others on your network. You may refer to your router documentation
               for the range of IP address that it assigns to its devices.

    STEP 5: Next to the IP address field, enter the IP address value you want to assign
                  to the computer.

    NOTE: If the DHCP range of your router is from say, you can use
    any range from for example.

    STEP 6: In the Subnet mask field, enter “”

    STEP 7: In the Default gateway field, enter the IP address of your router or gateway

    NOTE: Usually, the default gateway address for most routers is Again,
    you may refer to your device documentation to determine the correct IP address
    of your router.

    STEP 8: For the Preferred DNS server and Alternate DNS server fields, you can take
                 a look for the exact DNS values that your router is getting from your ISP, which can
                 be usually found by accessing your router’s configuration page.

    STEP 9: Click OK on all windows to save your changes.

    3. Dynamic IP configuration

    A DHCP (Dynamic Host Configuration Protocol) server automatically assigns IP
    address to host. It simplifies the addressing process. DHCP server can automatically
    assign to a host an IP addres, Subnet mask, Default gateway and Optional values,
    such as a DNS server address


    Go through all the steps to assign an IP address using DHCP

    Step 1: Go to network connections

    Step 2: Select “View network connections”.

    Step 3: Locate the “Network connection” you want to view

    Step 4: After locating connection, right –click on it and select “Properties”

    Step 5: Double-click “Internet Protocol Version (TCP/IPv4)”

    Step 6: Select the followings:

              • Obtain an IP address automatically

              • Obtain DNS server addresses automatically
              • OK

    Step 7: Select “OK” and restart your computer.

    3.7.3 Some common protocols

    A protocol is defined a set of rules and procedures that control communication
    between computers or other network devices on a network.

    a. Internet control message protocol (ICMP)

    Internet Control Message Protocol (ICMP) is used by devices on a network to send
    control and error messages to computers and servers. There are several different
    uses for ICMP, such as announcing network errors, announcing network congestion,
    and troubleshooting.

    b. HTTP (Hypertext Transfer Protocol)

    e.g. http://www.reb.rw/
    http:stands for hypertext transfer protocol used to connect computer to the server.
    It provides a standard web browser to communicate with a server FTP (File Transfer

    This protocol allows you to transfer files between two computers on internet.

         c. TCP and UDP

    Transmission Control Protocol and User Datagram Protocolare most common
    transport layer both protocols that manage the communication of multiple
    applications. The difference between the two are the specification function that
    each protocol implements.

    d. SMTP (Simple mail Transfer protocol)

    The SMTP stands for Simple mail Transfer protocol is a TCP/IP used in sending and
    receiving e-mails. However, since it is limited in its ability to queue message at the
    receiving end, it is used with one of two other protocols POP or IMAP that let users to
    save messages in server mailbox and download them from the server once needed.

    e. POP (Post Office Protocol)

    Post Office Protocol is a protocol designed to allow single user computer to retrieve
    electronic mail from a POP server via TCP/IP.

    3.7.4 Commands used to verify computer connection on a network Ping

    The command Ping is commonly used to test connections between computers.
    Ping is a simple but highly useful command-line utility used to determine whether a
    specific IP address is accessible. ipconfig

    The ipconfig command is used to find out your current local IP address, default
    gateway, TCP/IP settings and more.

    All Ipconfig commands explained:

              i. ipconfig/all: it displays all current IP information for all adapters.

              ii. ipconfig /release: Used to release current IP information and obtain a
                  new IP Address from the DHCP server.

            iii. ipconfig /renew: it is used to renew IP Address if you have it set to

               obtain IP Address automatically.

     3.8. Data and device sharing

       ACTIVITY 3.10(b)

    1. Share a folder with your classmate on your school computer network

    2. Identify how resource are shared on computer network

    3.8.1 Workgroup

    A workgroup is a collection of computers and servers on a LAN that are designed
    to communicate and exchange data with one another. Each individual workstation
    controls its user accounts, security information, and access to data and resources.


    Go through the steps below in order to create a WorkGroup

    Step 1: Open the Start menu, do a search for HomeGroup and press Enter.

    Step 2: Click Create a HomeGroup.

    Step 3: Click Next.

    Step 4: Choose what to share on the network. By default Windows sets Pictures, Videos,
    Music, and Printers & Devices as Shared. However, the Documents folder is marked as
    not shared.

    Note: The sharing options you choose will only apply to devices connecting with
    different accounts. If you sign-in with the same user account on another computer,
    you will have access to all files regardless of what you chose to share.

    Step 5: Once you've decided what content to share, click Next.

    Step 6: The wizard will complete the setup, and you'll be presented with a HomeGroup
    password, which is needed to allow other computers to access files and printers. Write
    down or click the link to print the password.


    Go through these steps to add computers to a HomeGroup

    Step 1: Open the Start menu, do a search for HomeGroup and press Enter.

    Step 2: Click the Join now button.

    Note: If you don't see the Join now button, there is something wrong, make sure
    you're connected to the network and restart your computer.

    Step 3: Click Next.

    Step 4: Select the content you want to share on the network by using the drop
    down menu for each folder and click Next.

    Step 5: Enter your HomeGroup password and click Next.

    Note: If you're signed into another computer, but you're using your Microsoft
    Account, then you won't be prompted to enter a password.

    Step 6: Click Finish to complete the task.

    3.8.2 Network Resource Sharing

    First determine which resources will be shared over the network and the type of
    permissions users will have to the resources. Any device which is connected to a
    host /node is called a Network Peripheral in other word network peripheral is any
    device that is indirectly connected to the network. Examples of network peripheral
    are: printer, scanner


    Go through the steps below to add new folders to shared HomeGroup libraries

    Step 1: Use the Windows key + E keyboard shortcut to open File Explorer.

    Step 2: On the left pane, expand your computer’s libraries on HomeGroup.

    Step 3: Right-click Documents.

    Step 4: Click Properties.

    Step 5: Click Add.

    Step 6: Select the folder you want to share and click Include folder.

    Step 7: Click Apply.

    Step 8: Click OK.

    Application activity 3.17

    Go through these steps to add new folder via Windows network share to your

    Step 1: Right-click the folder you want to share.

    Step 2: Select Share with and click the Homegroup (view) option.
    Users can access the newly shared folder by:

    Step 3: Using the Windows key + E keyboard shortcut to open File Explorer.

    Step 4: Clicking Network on the left pane.

    Step 5: Double-clicking the computer name with shared content, and browsing the
                folder location.

    By default, every HomeGroup folder shared on the network are set with read only
    permissions. It has to be this way to prevent accidental deletions and modification to
    your files by other users.

    3.9. Network Topology

    ACTIVITY 3.11

    Draw a Peer-to-peer network and assign each host an IP address. Network must have 1
    switch, 8 computers, one printer which has NIC card and a printer.

    The network topology describes the configuration of network, the physical and
    logical arrangement of nodes that form a network. Network topologies are classified
    as physical, logical and signals topologies.

    Physical topology describes the mapping of network nodes and physical connection
    between them. Signal topology describes the paths which signals take while they
    pass over network that mapping of the paths taken by data as they travel over
    network. A logical topology is the way data signals pass from one device to another.

    There exist different types of network topologies which are Bus topology, Ring
    topology, Star topology, Mesh topology, Tree topology and Hybrid topology,

    3.9.1 BUS Topology

    Bus topology is a network type in which every computer and network device is
    connected to single cable. When it has exactly two endpoints, then it is called Linear
    Bus topology.

    It is the most used and employed in LAN architecture. All devices are connected to a
    central cable, called the bus or backbone. This topology is relatively inexpensive and
    easy to install for small networks.

    Features of Bus Topology

    1. It transmits data only in one direction.

    2. Every device is connected to a single cable

    3.9.2 RING Topology

    It is called ring topology because it forms a ring as each computer is connected to
    another computer, with the last one connected to the first. Exactly two neighbors
    for each device. In a Ring topology each device is connected directly to two other
    devices, one on either side of it, to form a closed loop. This topology is relatively
    expensive and difficult to install, but it offers high bandwidth and can span large

    A ring topology is a computer network configuration in which computer connections
    create a circular data path. Each networked computer is connected to two others
    like points on a circle.

    In a ring network, data travel from one device to the next until they reach their
    destination. Most ring topologies allow data to travel only in one direction called
    a unidirectional ring network. Others permit data to move in both directions called bidirectional.

    3.9.3 STAR Topology

    In this type of topology all the computers are connected to a single hub or a switch
    through a cable. This hub or switch acts as the central device and all others nodes
    are connected to the central device.

    So, in a Star topology all devices are connected directly to a central computer or
    server. Such networks are relatively easy to install and manage

    Features of Star Topology

          1. Every node has its own dedicated connection to the hub.

          2. Hub acts as a repeater for data flow.

         3. Can be used with twisted pair or coaxial cable.

    3.9.4 MESH Topology

    • It is a point-to-point connection to other nodes or devices. All the network
    nodes are connected to each other. A Mesh topology can be either a full mesh
    or a partial mesh. In the former, each computer is connected directly to each
    of the others.

    Types of Mesh Topology

    1. Partial Mesh Topology: In this topology some of the systems are connected
    in the same fashion as mesh topology but some devices are only connected to
    two or three devices.

    2. Full Mesh Topology: all devices are connected to each other which is very
    expensive but provides the best redundancy as a failure of a single does not
    affect the network connectivity.

    Features of Mesh Topology

    1. Fully connected.

    2. Robust.

    3. Not flexible.

    3.9.5 Tree Topology

    It has a root node and all other nodes are connected to it forming a hierarchy. It is
    also called hierarchical topology. It should at least have three levels of hierarchy.

    Features of Tree Topology

    1. Ideal if workstations are located in groups.

    2. Used in Wide Area Network.

    3.9.6 Hybrid Topology

    Hybrid, as the name suggests, is mixture of two different things. Similarly in this
    type of topology that integrate two or more different topologies to form a resultant
    topology which has good points (as well as weaknesses) of all the constituent
    basic topologies rather than having characteristics of one specific topology. This
    combination of topologies is done according to the requirements of the organization.

    For example, if there exists a ring topology in one office department while there is a bus
    topology in another department, connecting these two will result in hybrid topology.
    However, connecting two similar topologies cannot be termed as Hybrid topology.

    Notice that the cost of technology, network devices, and transmission mediums to
    be used in the computer network has to be considered while choosing the network
    topology to use.


    Using clear example, compare computer network devices, network peripherals
    and computer peripherals?

    1. In an organization there are 20 computers distributed into different offices
        and all offices share one printer .The managements wants to build a
         computer network that connects all the computers and printer.

         i. Identify a topology to use in this situation

         ii. Draw arrangement of computers using identified topology

    2. Draw a hybrid topology