Lecture 7 - Computer Networking.pdf

Lecture 6 Networks And The Effects of Using Them Dr. De-Graft Johnson Dei PhD. Information Science +233 - 243775571 Dr De-Graft Johnson Dei  Introduction/Subject or Session Ove...

Lecture 6 Networks And The Effects of Using Them Dr. De-Graft Johnson Dei PhD. Information Science +233 - 243775571 Dr De-Graft Johnson Dei  Introduction/Subject or Session Overview This lecture will introduce students to computer Networks and why we use them. Students will be exposed to the various types of networks and some components within a computer network. Dr De-Graft Johnson Dei  Lecture Outline The key topics to be covered in the session are as follows: 1. Introduction: defining networks 2. Network Architecture 3. Intranets and Extranets 4. The Internet Dr De-Graft Johnson Dei  Learning Objectives By the end of this lecture, you should be able to:  Understand the advantages and disadvantages of networking computers  Describe the characteristics and purpose of different types of networks, such as LAN, WAN, VPN, Client-Server, Peer-to-Peer, intranets, extranets and the internet.  Define the term internet and the WWW and discuss the difference between the two.  Understand how internet is used for communication Dr De-Graft Johnson Dei Introduction: Defining network Topic One Dr De-Graft Johnson Dei Dr De-Graft Johnson Dei  What is a Network? A single computer is known as a stand-alone computer. When we connect stand-alone computers together we create a network. A network is a set of computers and devices connected together so they can communicate and share resources. Dr De-Graft Johnson Dei  What is a Network? A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. The first instance of computers being linked together was in 1969 with the Advance Research Projects Agency Network (ARPANET) Dr De-Graft Johnson Dei  Networking Equipment  Modem.  Router.  Firewall....  Wireless Access Point....  Racks....  Bridges  Hubs  Repeaters  Gateways  Switches Dr De-Graft Johnson Dei  Modem  A modem – "modulator-demodulator" – is a hardware device that converts data from a digital format, intended for communication directly between devices with specialized wiring, into one suitable for a transmission medium such as telephone lines or radio.  A modem modulates one or more carrier wave signals to encode digital information for transmission, and demodulates signals to decode the transmitted information.  The goal is to produce a signal that can be transmitted easily and decoded reliably to reproduce the original digital data.  Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio.  A common type of modem is one that turns the digital data of a computer into a modulated electrical signal for transmission over telephone lines, to be demodulated by another modem at Dr De-Graft Johnson Dei the receiver side to recover the digital data.  Router  A router is a networking device that forwards data packets between computer networks.  Routers perform the traffic directing functions on the Internet.  Data sent through the internet, such as a web page or email, is in the form of data packets.  A packet is typically forwarded from one router to another router through the networks that constitute an internetwork (e.g. the Internet) until it reaches its destination node  A router is connected to two or more data lines from different IP networks.  When a data packet comes in on one of the lines, the router reads the network address information in the packet header to determine the ultimate destination.  Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey.  The most familiar type of IP routers are home and small office routers that simply forward IP packets between the home computers and the Internet.  More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Dr De-Graft Johnson Dei  Firewall  In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.  Firewalls are software programs or hardware devices that filter and examine the information coming through your Internet connection.  They represent a first line of defense because they can stop a malicious program or attacker from gaining access to your network and information before any potential damage is done.  A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the Internet Dr De-Graft Johnson Dei  Wireless Access Point (WAP)  A Wireless Access Point (WAP) is a device that you can place anywhere on your network (with a network cable) to provide wireless internet to other devices.  The advantage of using a WAP is that you can place it where you need it instead of in your server room or wherever your modem is installed.  Some WAP devices also are capable of bridging.  This allows multiple Wireless Access Points to create one larger wireless network.  If you have a large office in the past you would have several wireless networks to deal with bad coverage.  With bridging you eliminate the need to disconnect and reconnect to a network with a stronger signal.  Newer WAP devices can support multiple networks.  This allows you to have a private network for employees only use that accesses network resources and a separate public network for clients, etc that cannot access your network resources protecting your company data. Dr De-Graft Johnson Dei  Advantages of computer networking File sharing - you can easily share data between different users, or access it remotely if you keep it on other connected devices. Resource sharing - using network-connected peripheral devices like printers, scanners and copiers, or sharing software between multiple users, saves money. Sharing a single internet connection - it is cost-efficient and can help protect your systems if you properly secure the network. Increasing storage capacity - you can access files and multimedia, such as images and music, which you store remotely on other machines or network-attached storage devices. Site (software) licences are likely to be cheaper than buying several standalone licences. Network users can communicate by email and instant messenger. Security is good - users cannot see other users' files unlike on stand-alone machines. Data is easy to backup as all the data is stored on the file server. Dr De-Graft Johnson Dei  Disadvantages of computer networking Purchasing the network cabling and file servers can be expensive. Managing a large network is complicated, requires training and a network manager usually needs to be employed. If the file server breaks down the files on the file server become inaccessible. Email might still work if it is on a separate server. The computers can still be used but are isolated. 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, eg a firewall. Dr De-Graft Johnson Dei  Network Topology Dr De-Graft Johnson Dei  Network Topology  Network topology is  the arrangement of the elements (links, nodes, etc.) of a communication network.  the schematic description of a network arrangement, connecting various nodes(sender and receiver) through lines of connection  a network which comprises of nodes and connecting lines via sender and receiver is referred as network topology.  the structure of the network of how all the components are interconnected to each other.  Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial fieldbusses and computer networks.  No matter how identical two organizations are, no two networks are exactly alike.  However, many organizations are relying on well-established network topology models.  Network topologies outline how devices are connected together and how data is transmitted from one node to another. Dr De-Graft Johnson Dei  Network Topology  Network topology is the topological structure of a network and may be depicted physically or logically.  Physical topology is the geometric representation of all the nodes in a network  A logical network topology is a conceptual representation of how devices operate at particular layers of abstraction.  Logical and physical topologies can both be represented as visual diagrams.  A physical topology details how devices are physically connected.  It is an application of graph theory wherein communicating devices are modeled as nodes and the connections between the devices are modeled as links or lines between the nodes.  Physical topology is the placement of the various components of a network (e.g., device location and cable installation), while logical topology illustrates how data flows within a network. Dr De-Graft Johnson Dei Dr De-Graft Johnson Dei  Bus Topology  Bus topology is a network type where every device is connected to a single cable that runs from one end of the network to the other.  This type of network topology is often referred to as line topology.  In a bus topology, data is transmitted in one direction only.  If the bus topology has two endpoints then it is referred to as a linear bus topology.  Smaller networks with this type of topology use a coaxial or RJ45 cable to link devices together.  However, the bus topology layout is outdated and you’re unlikely to encounter a company using a bus topology today. Dr De-Graft Johnson Dei  Advantages of Bus topology:  Disadvantages of Bus topology: Low-cost cable: Extensive cabling: A bus topology is quite simpler, but still it requires a In bus topology, nodes are directly lot of cabling. connected to the cable without passing through a hub. Difficult troubleshooting: Therefore, the initial cost of installation is It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, low. then it would disrupt the communication for all the nodes. Moderate data speeds: Signal interference: Coaxial or twisted pair cables are mainly used in bus-based networks that support If two nodes send the messages simultaneously, upto 10 Mbps. then the signals of both the nodes collide with each other. Familiar technology: Reconfiguration difficult: Bus topology is a familiar technology as Adding new devices to the network would slow the installation and troubleshooting down the network. techniques are well known, and Attenuation: hardware components are easily available. Attenuation is a loss of signal leads to communication issues. Repeaters are used to Limited failure: regenerate the signal. A failure in one node will not have any effect on other nodes. Dr De-Graft Johnson Dei  Ring Topology Ring topology is like a bus topology, but with connected ends. The node that receives the message from the previous computer will retransmit to the next node. The data flows in one direction, i.e., it is unidirectional. The data flows in a single loop continuously known as an endless loop. It has no terminated ends, i.e., each node is connected to other node and having no termination point. The data in a ring topology flow in a clockwise direction. The most common access method of the ring topology is token passing. Token passing: It is a network access method in which token is passed from one node to another node. Token: It is a frame that circulates around the network. A token moves around the network, and it is passed from computer to computer until it reaches the destination. The sender modifies the token by putting the address along with the data. The data is passed from one device to another device until the destination address matches. Once the token received by the destination device, then it sends the acknowledgment to the sender. In a ring topology, a token is used as a carrier. Dr De-Graft Johnson Dei  Advantages of Ring topology:  Disadvantages of Ring topology: Network Management: Difficult troubleshooting: Faulty devices can be removed from the It requires specialized test equipment to network without bringing the network down. determine the cable faults. If any fault occurs in the cable, then it would disrupt Product availability: the communication for all the nodes. Many hardware and software tools for network Failure: operation and monitoring are available. The breakdown in one station leads to the Cost: failure of the overall network. Twisted pair cabling is inexpensive and easily Reconfiguration difficult: available. Therefore, the installation cost is very low. Adding new devices to the network would slow down the network. Reliable: Delay: It is a more reliable network because the communication system is not dependent on the Communication delay is directly single host computer. proportional to the number of nodes. Adding new devices increases the communication delay. Dr De-Graft Johnson Dei  Star topology Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer. The central computer is known as a server, and the peripheral devices attached to the server are known as clients. Coaxial cable or RJ-45 cables are used to connect the computers. Hubs or Switches are mainly used as connection devices in a physical star topology. Star topology is the most popular topology in network implementation. Dr De-Graft Johnson Dei  Advantages of Star topology  Disadvantages of Star topology Efficient troubleshooting: A Central point of failure: Troubleshooting is quite efficient in a star topology as compared to bus topology. If the central hub or switch goes In a bus topology, the manager has to inspect the kilometers of cable. down, then all the connected In a star topology, all the stations are connected to the centralized nodes will not be able to network. Therefore, the network administrator has to go to the single communicate with each other. station to troubleshoot the problem. Cable: Network control: Complex network control features can be easily implemented in the Sometimes cable routing star topology. Any changes made in the star topology are becomes difficult when a automatically accommodated. significant amount of routing is Limited failure: required. As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network. Familiar technology: Star topology is a familiar technology as its tools are cost-effective. Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub. Cost effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable. Dr De-Graft Johnson Dei  Tree topology Tree topology combines the characteristics of bus topology and star topology. A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion. The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node. There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy. Dr De-Graft Johnson Dei  Advantages of Tree topology  Disadvantages of Tree Support for broadband transmission: topology Tree topology is mainly used to provide broadband transmission, Difficult troubleshooting: i.e., signals are sent over long distances without being attenuated. If any fault occurs in the node, then it Easily expandable: becomes difficult to troubleshoot the problem. We can add the new device to the existing network. High cost: Therefore, we can say that tree topology is easily expandable. Devices required for broadband Easily manageable: transmission are very costly. In tree topology, the whole network is divided into segments known Failure: as star networks which can be easily managed and maintained. A tree topology mainly relies on main Error detection: bus cable and failure in main bus cable will damage the overall Error detection and error correction are very easy in a tree topology. network. Limited failure: Reconfiguration difficult: The breakdown in one station does not affect the entire network. If new devices are added, then it Point-to-point wiring: becomes difficult to reconfigure. It has point-to-point wiring for individual segments. Dr De-Graft Johnson Dei  Mesh Technology Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections. There are multiple paths from one computer to another computer. It does not contain the switch, hub or any central computer which acts as a central point of communication. The Internet is an example of the mesh topology. Mesh topology is mainly used for WAN implementations where communication failures are a critical concern. Mesh topology is mainly used for wireless networks.  Mesh topology is divided into two categories: Full Mesh Topology: In a full mesh topology, each computer is connected to all the computers available in the network. Partial Mesh Topology: In a partial mesh topology, not all but certain computers are connected to those computers with which they communicate frequently. Dr De-Graft Johnson Dei  Advantages of Mesh topology:  Disadvantages of Mesh topology  Reliable: Cost:  The mesh topology networks are very reliable A mesh topology contains a large number of as if any link breakdown will not affect the connected devices such as a router and more communication between connected transmission media than other topologies. computers. Management:  Fast Communication: Mesh topology networks are very large and  Communication is very fast between the very difficult to maintain and manage. If the nodes. network is not monitored carefully, then the communication link failure goes undetected.  Easier Reconfiguration: Efficiency:  Adding new devices would not disrupt the communication between other devices. In this topology, redundant connections are high that reduces the efficiency of the network. Dr De-Graft Johnson Dei  Hybrid Topology The combination of various different topologies is known as Hybrid topology. A Hybrid topology is a connection between different links and nodes to transfer the data. When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology. Dr De-Graft Johnson Dei  Advantages of Hybrid Topology  Disadvantages of Hybrid topology Reliable: Complex design: If a fault occurs in any part of the network will not The major drawback of the affect the functioning of the rest of the network. Hybrid topology is the design of Scalable: the Hybrid network. It is very Size of the network can be easily expanded by difficult to design the architecture adding new devices without affecting the of the Hybrid network. functionality of the existing network. Costly Hub: Flexible: The Hubs used in the Hybrid This topology is very flexible as it can be designed topology are very expensive as according to the requirements of the organization. these hubs are different from Effective: usual Hubs used in other topologies. Hybrid topology is very effective as it can be designed in such a way that the strength of the Costly infrastructure: network is maximized and weakness of the network is minimized. The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc. Dr De-Graft Johnson Dei Dr De-Graft Johnson Dei  Which Topology Should I Choose?  There is a range of factors that you need to take into account when choosing which topology to use. Before choosing a topology you’ll want to closely consider the following: Length of cable needed Cable type Cost Scalability  First, you need to take into account the length of the cable you need to provide service to all your network devices. A bus topology is the most lightweight in terms of cable needs. In this sense, this would be the simplest topology to install and buy cables for. This ties into the second factor, you need to consider the type of cable you’re going to use. Cable types range from twister pairs to coaxial cables and optical fiber cables.  The cost of installing the topology is also very important. The more complex the topology you choose is, the more you’ll need to pay in terms of resources and time to create that setup.  The final factor you’ll want to take into account is scalability. If you’re planning to upscale your network infrastructure in the future you want to make sure that you use a network that is easy to add devices to. A star topology network is ideal for this because you can add network nodes with minimal disruption. This isn’t as simple within a ring network because you will incur downtime if you add any nodes. Dr De-Graft Johnson Dei Network architecture Topic Two Dr De-Graft Johnson Dei  Network Architecture based on Geographic and Physical Nature.  When network is described by its geographic and physical architecture, there are two categories of networks: Local Area Network (LAN) Campus Area Network (CAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Others Tiny Area Network (TAN) Home Area Network (HAN) Office Area Network (OAN) Personal (Bluetooth) Area Network (PAN) Dr De-Graft Johnson Dei  Personal Area Network (PAN)  A network used for communication among computer and different ICT devices close to one person.  Designed for very short-range connections (typically just about 10 metres).  A PAN may include wired and wireless devices.  USB and FireWire  Bluetooth and infrared Dr De-Graft Johnson Dei  Bluetooth (Personal Area Network) Some Keyboard examples of Mouse devices that Headset are used in a personal computers, PAN are printers, fax machines, telephones, scanners, and even video game consoles. Dr De-Graft Johnson Dei  Home Area Network (HAN)  A HAN is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices.  HAN is contained within a user's home that connects a person's digital devices, from multiple computers and their peripheral devices to telephones, VCRs, televisions, video games, home security systems, smart appliances, fax machines and other digital devices that are wired into the network.  An important function is the sharing of Internet access, often a broadband service through a cable TV or digital subscriber line (DSL) provider Dr De-Graft Johnson Dei  Local Area Networks (LAN)  A LAN is a network that is restricted to a small geographic area.  Most LANs are confined to a single building or group of buildings.  A typical LAN will consist of a number of computers and other devices that are connected to hubs or switches.  Either the hub or switch will usually be connected to a router and a modem to allow LANs to connect to the internet. Dr De-Graft Johnson Dei  LAN Components Server Client Computer NIC (Network Interface Card) Network Cables/Hubs NOS (Network Operating System) Dr De-Graft Johnson Dei  Campus Area Network (CAN)  Campus Area Network (CAN) is a group of interconnected Local Area Networks (LAN) within a limited geographical area like school campus, university campus, military bases, or organizational campuses and corporate buildings etc.  This Campus Area Network also called as Corporate Area Network. Sometimes this network is also referred as Residential Network or ResNet as it is only used by residents of specific campus only.  Campus Area Network is network of interconnected Local Area Networks where these LANs are connected via Switches and routers and create a single network like CAN.  Campus Area Network covers areas of around 1 to 5 km range and it can be both wired or wireless connectivity.  A Campus Area Network is larger than Local Area Network but smaller than Metropolitan Area Network (MAN) and Wide Area Network (WAN).  The networking equipment such as  switches, routers and  transmission media (optical fiber, copper plant, cable, etc.) Dr De-Graft Johnson Dei  Metropolitan Area Network - MAN  A metropolitan area network (MAN) is a computer network that interconnects users with computer resources in a geographic region of the size of a metropolitan area.  The term MAN is applied to the interconnection of local area networks (LANs) in a city into a single larger network which may then also offer efficient connection to a wide area network.  The term is also used to describe the interconnection of several local area networks in a metropolitan area through the use of point-to-point connections between them A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber- optical links, and provides up-link services to wide area networks (or WAN) and the Internet.  Thus, MANs are larger than LANs but smaller than wide area networks (WAN). Dr De-Graft Johnson Dei  Wide Area Network (WAN)  A WAN is a network that covers a larger geographical area.  A WAN connects different smaller networks, including local area networks (LAN) and metro area networks (MAN).  WAN implementation can be done either with the help of the public transmission system or a private network.  The most common example of WAN is the internet. Dr De-Graft Johnson Dei  Network Architecture Based on how Data is Stored and Accessed on it. The two architectures for storing and accessing data on a network are: Client-Server Network Peer-to-Peer Network Dr De-Graft Johnson Dei  Client-Server Network A client-server network uses a dedicated computer to store data, manage resources and control user access, this computer is known as a server. A computer that connects to the server to access that data and resources it manages is known as a client. Dr De-Graft Johnson Dei  Peer-to-Peer Network A peer-to-peer network has no central server to manage the network. Each computer on the network shares its data and resources with all the others known as Peers. Dr De-Graft Johnson Dei  Activity 1 Find out what kind of internet you have in your University or home. What is the structure of it and how does it store data? Does your University network have any servers? If it does, what are they used for? Dr De-Graft Johnson Dei Intranets and extranets Topic four Dr De-Graft Johnson Dei  Intranets An intranet is a privately owned network that uses internet technologies (such as web pages) for internal use within the organization. Intranets usually use client-server architecture. An intranet is for internal use only and this increases its security and confidentiality. Many organizations use intranets. For example: Schools use Virtual Learning Environment (VLE). Dr De-Graft Johnson Dei  Extranets An extranet is an intranet that has been opened up to allow external user access. Extranets use VPN’s to allow an external user to securely access the information on them. Access to an Intranet is normally available through the organization’s website. (Through user log in using email and password) For example: A school’s VLE may allow parents to access their child marks, attendance data and reports. Dr De-Graft Johnson Dei The internet Topic Five Dr De-Graft Johnson Dei  The Internet  The term ‘internet’ originates from ‘inter-network’, meaning a network that was formed from joining networks. Network of Networks International Network  To connect to the internet we need to use an Internet Service Provider (ISP)  ISPs use public telephone systems, underwater cables, microwave transmissions via satellites and radio waves to provide connections.  Data and information on the internet is held and distributed by content providers. Dr De-Graft Johnson Dei  The Internet  A content provider is an organization, group or company that offers content on web pages.  No one company or organization runs or has authority over the internet, although various independent organizations control aspects of it: The Internet Corporation for Assigned Names and Numbers (ICANN) The Internet Engineering Task Force (IEFT) The World Wide Web Consortium (W3C) Telecommunication companies own the infrastructure that the internet uses for communication. Dr De-Graft Johnson Dei  Communication Using the Internet The Internet allows users to communicate in several ways: Instant Messaging (IM): Now a feature of many social networking sites. Voice over Internet Protocol (VOIP): Examples are SKYPE and WHATSUP voice all. News Services: An example is Google News. Dr De-Graft Johnson Dei  Discussion 1 What would your life be like if you did not have the internet? What would be different? Would your life be better or worse? Dr De-Graft Johnson Dei