Introduction Mr. Oscar O. Ogwok oscarosaka25@gmail.com Ebenezer University Lira | NCIT212 - Computer Networking • INTRODUCTION • A computer network allows sharing of resources and information among interconnected devices. In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s. 2 Computer Network- Introduction • Set of devices communicating with each other. Could be a CPU, monitor and other peripheral devices connected (and exchanging data to each other). • It consists of two or more computers that are linked to share resources (such as printers), exchange files, or allow electronic communications. • Is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. • Could be a group of people …A network of friends. Ebenezer University Lira | NCIT212 - Computer Networking ADVANTAGES OF COMPUTER NETWORK Computer networks can be used for several purposes: • Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing. • Sharing hardware. In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer. 4 • Sharing files, data, and information. In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks. • Sharing software. Users connected to a network may run application programs on remote computers. 5 • Speed • It is very easy to communicate through a network. People can communicate efficiently using a network with a group of people. They can enjoy the benefit of emails, instant messaging, telephony, video conferencing, chat rooms, instantly. 6 DISADVANTAGES OF COMPUTER NETWORK • Security Issues: One of the major drawbacks of computer networks is the security issues involved. If a computer is a standalone, physical access becomes necessary for any kind of data theft. However, if a computer is on a network, a computer hacker can get unauthorized access by using different tools. In case of big organizations, various network security 7 softwares are used to prevent the theft of any confidential and classified data. • Rapid Spread of Computer Viruses: If any computer system in a network gets affected by computer virus, there is a possible threat of other systems getting affected too. Viruses get spread on a network easily because of the interconnectivity of workstations. Such spread can be dangerous if the computers have important database which can get corrupted by the virus. 8 • Expensive Set Up: The initial set up cost of a computer network can be high depending on the number of computers to be connected. Costly devices like routers, switches, hubs, etc., can add up to the bills of a person trying to install a computer network. He will also have to buy NICs (Network Interface Cards) for each of the workstations, in case they are not inbuilt. 9 • Dependency on the Main File Server: In case the main File Server of a computer network breaks down, the system becomes useless. In case of big networks, the File Server should be a powerful computer, which often makes it expensive. • Bandwidth Issues In a network there are users who consume a lot more bandwidth than others. Because of this some other people may experience difficulties. 10 Networking devices • All but the most basic of networks require devices to provide connectivity and functionality • Understanding how these devices operate and identifying the functions they perform are essential skills for any network administrator. Ebenezer University Lira | NCIT212 - Computer Networking Media • On any network, the various entities must communicate through some form of media. • Just as humans can communicate through telephone wires or sound waves in the air, computers can communicate through cables, light, and radio waves. • Transmission media enables computers to send and receive messages but do not guarantee that the messages will be understood. • There are two main groups of transmission media, namely the guided medium and the unguided medium Ebenezer University Lira | NCIT212 - Computer Networking Media cont. • For the guided medium, there’s a physical path (such as a cable) for electromagnetic wave propagation • For the unguided medium, however, the electromagnetic wave is transmitted through air, water, or vacuum. Ebenezer University Lira | NCIT212 - Computer Networking Network Components • Networking hardware includes all computers, peripherals, interface cards and other equipment needed to perform data processing and communications within the network. Network Interface Cards (NICs) - NIC provides the link between your computer and your network. It provides the physical connection between the network and the workstation. Most NICS are internal, with the card fitting into an expansion slot inside the computer ,others are built on the motherboard. Modem – Modulator/Demodulator It is a device normally provided by the Internet Service Provider (ISP) to gran access to the Internet It converts analog and digital signals between your landline and the Internet • • Hubs/Concentrators A hub is a device whose primary function is to send and receive signals along the network between the nodes connected to it. • It connect s multiple devices to the network, • It serves as a central meeting place for cables from computers, servers and peripherals. • It is usually configured with 4, 8, 12, or 24 RJ-45 ports. • The entire network shuts down if there is a problem on a hub Repeaters. • A repeater is a device that regenerates and amplifies signals to create long-distance networks. • It simply receives, amplifies and rebroadcasts the signals. Some repeaters provide basic error-checking • A repeater can be a separate device or it can be incorporated into a concentrator. It is used to overcome distance limitations. A bridge • A bridge is a device that links two homogenous packetbroadcast local networks. It accepts all packets from each network addressed to devices on the other, buffers them, and retransmits them to the other network. • It connects two or more networks using the same address method or protocol. • It can provide some addressing information. • Monitors and manages the traffic to maintain optimum performance on both sides of the network often used when LANs reach their capacity of nodes Switches • A switch is a high-speed multi port bridge. Today, switches are replacing multiport repeaters or concentrators in a UTP environment. (Unshielded Twisted Pair) • It is an intelligent hub that maintains a bridging table, keeping track of which hardware addresses are located on which network segment. • more efficient than any other type of hub • It has ability to dedicate bandwidth to each port on itself. Routers • Routers are similar to bridges in that they link two or more physically separate network segments. The network segments linked by a router, however, remain logically separate and can function as independent networks. Routers; • translate information from one network to another; similar to a super-intelligent bridge. i.e receive information from a cabled network and transmit it wirelessly. • maintain a map of the network, select the best route for data. • have information on source addresses, destination addresses and path distances. • segment bandwidth and segment status are contained in the router's routing table • can translate messages with different addressing methods • can act as firewalls (many ISP's block traffic at the router level) • direct signal traffic efficiently • can route messages between linear bus, star, and token ring topologies • can route messages across fibre optic, coaxial, and twisted-pair cabling Network Media and cabling What is a Network C able? A Cable is the medium through which information usually moves from one network device to another. There are several types of cables which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cables and how they relate to other aspects of a network is necessary for the development of a successful network. Types of Network cables. • The following are some of the types of cables used in networks . 1. Unshielded Twisted Pair (UTP) Cable 2. Shielded Twisted Pair (STP) Cable 3. Coaxial Cable 4. Fiber Optic Cable Twisted pair cable. • The twisted pair cable comes in two varieties: Shielded and Unshielded. Unshielded Twisted Pair (UTP) is the most popular and is generally the best option for school networks (See fig. below: • The quality of UTP may vary from telephonegrade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot Categories of Unshielded Twisted Pair Category Speed Use Voice Only (Telephone Wire) LocalTalk & Telephone (Rarely used) A 1 Mbps 2 4 Mbps 3 16 Mbps 10BaseT Ethernet 4 20 Mbps Token Ring (Rarely used) 100 Mbps (2 pair) 100BaseT Ethernet 1000 Mbps (4 pair) Gigabit Ethernet 1,000 Mbps Gigabit Ethernet 5 5e • Unshielded Twisted Pair Connector. • The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector . A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with which pin inside the connector. • UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current , the Shielded twisted pair may be the solution. • Shielded twisted pair cable is available in three different configurations: 1. Each pair of wires is individually shielded with foil. 2. There is a foil or braid shield inside the jacket covering all wires (as a group). 3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair). Coaxial Cable The Coaxial cable has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield . The metal shield helps to block any outside magnetic interference from fluorescent lights, motors, and other `Scomputers. Coaxial Cable Coaxial Cable • Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial. • Coaxial Cable Connectors The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector. Coaxial Cable Connector. Fiber Optic Cable • The fiber optic cable consists of a center glass core surrounded by several layers of protective materials . It transmits light rather than electronic signals eliminating the problem of electrical interference. • This makes it ideal for certain environments that contain a large amount of electrical interference. • It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting. Fiber Optic Cable • The fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. • It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. Fiber Optic Cable diagram. Wireless LANs • More and more networks are operating without cables, in the wireless mode. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. • Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.
