Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Distributed firewall wikipedia , lookup
Piggybacking (Internet access) wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Computer network wikipedia , lookup
Network tap wikipedia , lookup
IT2101: Communication Technology 3. Computer Networking Fundamentals Program: BSCS I (January Semester – 2014) Lecturer: Rebecca Asiimwe Email: [email protected] Learning Outcomes • • • • • Define a computer network Understand how networks operate Understand types of networks Identify network medium e.g. Coaxial, UTP Identify common hardware network components. • Introduce common network protocols 2 A Computer Network • Two or more computers connected together either (wirelessly or using cables) usually for the purpose of sharing information or other resources like printers. • A typical network consists of computers (nodes), a connecting medium, and specialised equipment to enable communication. Computer hardware & computer software. 3 Background • Motivated by the need for better communication, new networking technologies emerged and had a more immediate impact on the average person. 4 Background Cont’d • It became obvious that each organization with many computers needed to transfer / move data among them to facilitate information sharing. • The first data transfers from one computer to another involved removable media storage devices, usually magnetic tapes or disks but this was a time consuming and tiresome process. 5 Background Cont’d • In linking up computers, Circuit boards were built on computers to help link a computer to an external device for instance a printer or a video camera etc. • Once communication circuits have been plugged into the computers and connected by a cable, the computers use them to transfer data electronically 6 Communications Model • As earlier mentioned, the fundamental purpose of a communication’s system is the exchange of data between two parties – this is something that computer networks enable us achieve. • In this section we shall look at the basic model of communication as illustrated by the block diagram in the following slide. 7 Simplified Communications Model – the General Block Diagram 8 Key Elements of the Communications Model • Source – Generates data to be transmitted for example telephones and personal computers • Transmitter – Converts data into transmittable signals- Usually the data generated by a source system are not transmitted directly in the form in which they were generated, rather a transmitter transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across a transmission system. For example a modem takes a digital bit stream from an attached device such as a PC and transforms that bit stream into an analog signal that can be handled by the telephone network. 9 • Transmission System – Carries data - this can be a single transmission line or a complex network connecting source and destination • Receiver – Accepts the signal from the transmission system and coverts it into a form that can be handled by the destination device. For example a modem will accept an analog signal coming from a network or transmission line and convert it into a digital bit stream that a computer can understand and work with. • Destination – Takes incoming data from the receiver 10 Data Communications Model 11 • The figure below presents one particular example, which is communication between a workstation and a sever over a public telephone network. • Another example is the exchange of voice signals between two telephones over the same network. 12 Technical Illustration 13 Elements of a Telecommunications System [Figure 6.3] 14 Modem Linked Communications 15 Advantages of Computer Networks (Why Networks?) • Resource sharing e.g software and hardware like printers, scanners and other peripheral devices • Enable central management of resources for example, an anti virus solution can be easily deployed and managed over a network, ie security updates are installed only on one Machine (server), then all the client machines receive the updates and get protected from viruses and other types of malware. 16 Advantages of Computer Networks Cont’d • Allow many users to access programs and data concurrently. • Cost saving- e.g. Expensive Laser Jet printers can be shared. • Easier backup especially in centralized databases. • Make personal communication easier. • Security can be assured e.g. restricting user file access. 17 Disadvantages of Networking • Initial cost may be high e.g. Implementation of Large networks. • Depending on the Topology, a fault in one section on the Network may cause the entire network to be inaccessible. • If not properly secured, a network can be target for security threats like Hackers, Viruses etc. • In case the Network grows, there’s Performance degradation due to high traffic 18 Categories of Networks Two main categories: a) Client-Server Networks. b) Peer-to-Peer networks. • Note: These categories are based on the network design background rather than the geographical area it spans 19 a) Client-Server Networks Consists of two categories of Computers i.e. i. A client & ii. A server A client is usually the User’s workstation which accesses a network through a more powerful machine called a Server A client requests for resources from a server and the server responds to the client by providing the resources requested for. 20 Client-Server Networks Illustrated Image from: http://en.wikipedia.org/wiki/File:Clientserver-model.svg 21 b) Peer-to-Peer Networks • Involve the sharing of Information or resources between two or more workstations connected to each other without the use of a Server. • Are relatively easy to setup but do not take full advantage of networks since central mgt of the network is not possible. • Ideal for home use and small offices 22 Types of Computer Networks • Networks can be categorized based on the following grounds: oThe Network design (Discussed in the previous slides) oThe geographic area it spans. 23 Based on the Geographical Area Spaned • In general, Most Computer networks are classified according to the distance between individual computers that are attached to the network. • • • • • • • The classification includes the following: Personal Area Networks (PAN) Local Area Networks (LAN) Campus Area Networks Metropolitan Area Networks (MAN) Wide Area Networks (WAN) Global Area Networks (GAN) 24 1) Personal Area Network (PAN) • A computer network used for communication among computer devices that are close to a person. Devices include printers, fax machines, PDAs, scanners etc. • Note: These device examples are only relevant here if in close distance to a person’s body. 25 2) Local Area Network (LAN) • Connects network devices over a relatively short distance ie a small geographic area, like a home, office, or building. Current LANs are based on the Ethernet technology. • For example, a library will have a LAN for users to connect to the internet. 26 Characteristics of LANs • Local i.e. computers are in close proximity • Higher rate of data transmission • Privately owned by the organisation in which they are set up- network devices are privately owned by the organisation. • Characteristic of fewer devices than in CANs, MANs or WANs 27 LANs and - the Ethernet • In 1985, the Institute of Electrical and Electronic Engineers (IEEE) – www.ieee.org , developed a set of standards for LANs called IEEE 802 standards. • Originally developed by Xerox in the 1970s, the Ethernet defined in the IEEE 802.3 is the most implemented LAN in modern day Networking. 28 3) Campus Area Networks • A network that connects two or more LANs but is limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base etc. • It spans multiple LANs but smaller than a MAN 29 4) Metropolitan Area Network (MAN) • A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of an immediate town, city, or metropolitan area. • Involves connection of multiple switches & hubs to create the MAN. routers, 30 5) Wide Area Network (WAN) • A WAN is a network that covers a relatively broad geographic area (i.e. one city to another and one country to another) and that often uses transmission facilities provided by common carriers, such as telephone companies. • Are not owned by any one organization but exist under collective or distributed ownership & management. 31 Characteristics of a WAN • Data usually transmitted over leased telephone lines at lesser transmission rate than LANs. • Some WANs use circuit switching or Packet switching methods to transmit data. • WANs span over large geographic areas 32 WAN Illustrated Images from Google 33 WANs:- Leased Lines • As discussed, WANs communicate over long distances and therefore need appropriate Technology to achieve this. • A Leased line at times called a dedicated line is a private line permanently connecting two locations together. Unlike traditional Telephone lines (PSTN) , these lines don’t have telephone numbers. • In Uganda, Companies like MTN, Uganda Telecom, Warid, etc provide these services 34 WANs: - Circuit Switching • A circuit switched network is one that requires dedicated connection between the sender and the receiver before transmission can begin. Traditional phone lines use this method. • The exclusivity of the connection during communication can be time consuming which led to the development of packed switching Networks. 35 WANs: - Circuit Switching Note: – With Circuit switching, connection set up has to first be made, then information is transmitted between sender and receiver, and terminated by either party when the conversation is over. No one can use that particular line when it is busy. – Connection setup takes time 36 WANs: - Packet Switching • Packet switching involves the splitting of data into packets which are then transmitted to the receiving end (destination) over multiple channels. • At the receiving end, the data is then re-assembled to the original message and delivered. This is made possible through routing Algorithms (We shall look at routing in Computer Networks). • The robust nature of this technology has made it dominant in modern telecommunication Technology including the Internet. 37 6) Global Area Network (GAN) • Global area network (GAN)refers to any network that is composed of different interconnected computer networks (WANs) and also covers an unlimited geographical area. • It is generally a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. 38 Network Topology • In networking, the term "topology" refers to the layout of connected devices on a network. • The physical layout & configuration of computers, cables, nodes, and other peripherals on a Network is generally referred to as the physical Network topology. • Network topology may also be logical and this generally refers to the protocols used on the Network. Note: Protocols will be discussed later 39 Network Topology Cont’d • So, Network topology is the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes. • Topologies are the most important part of the network design theory. • A better network can be built if you have the knowledge of these topologies and if you know the difference between them. 40 Common Network Topologies • • • • • • • Point-to-Point Star Bus Mesh Ring Tree etc 41 1) Point-to-point • The simplest topology is a permanent link between two endpoints. • Like – A microphone to a single public address speaker. 42 2) Star Topology • The Star topology involves each node on the computer network being directly connected to the central Hub or concentrator as shown in the next slide. • Each of the nodes of the network is connected to a central node with a pointto-point link. 43 The Star Topology 44 Star Topology • Data on a star network passes through the hub or switch before continuing to its destination. • The hub/ switch manages and controls all functions of the network. It also acts as a repeater for the data flow. • This configuration is most common with twisted pair cable. 45 Characteristics of the Star Topology • Note: These can also explain the advantages and disadvantages of the Star Topology as given in the next slides 46 Advantages of the Star Topology • Easy to install, implement and extend (in the event of Network expansion). • The failure of one node does not have a major effect on the functionality of the others. • No problems with collisions of data since each node has its own cable to the switch / hub. • Security can be implemented in the concentrator for all. 47 Advantages of the Star Topology Cont’d • It is easy to modify and add new computers to the star network without disrupting the rest of the nodes. • Network faults can easily be identified centrally and parts are easy to remove. 48 Disadvantages of a Star Topology • Requires more cable length than a linear topology. • If the hub or concentrator fails, the entire network will fail. • More expensive than linear bus topologies since it involves purchase of additional hardware – the concentrator. 49 3) The Bus Topology • The Bus Topology involves the use of one Linear Backbone cable with a terminator at each end, to which all the nodes / computers are connected. • This can be – Linear Bus – Distributed bus 50 The Bus Topology Cont’d a) Linear bus: • All the nodes of the network are connected to a common transmission medium which has exactly two endpoints. • The two endpoints are normally terminated with a device called a terminator. 51 The Bus Topology Cont’d b) Distributed bus: • The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints 52 The Bus Topology Cont’d Linear Bus topology 53 Characteristics of the Bus Topology These define the advantages and disadvantages of the Bus topology. Advantages. • Cheap (probably the cheapest topology to install). • Easy to implement. • Less cable length required. 54 Disadvantages of the Bus Topology • Difficult to identify the source of a problem in case of network failure. • Limited cable length and number of stations. • A break of the main cable means a break of the entire network. • Performance may degrade as the network expands • Low security (all computers on the bus can see all data transmissions). • Terminators are required at both ends of the backbone cable. Proper termination is required. 55 4) Ring Topology • A ring Topology is one where each node is connected to two other nodes with the first and last being connected to each other to form a ring-like structure. 56 Ring Topology Cont’d 57 Ring Topology Cont’d • It uses a token to carry data from the source to the destination: Data is sent from one machine to the next around the ring until it reaches its destination then back to the origin. 58 Characteristics of the Ring Topology Advantages and disadvantages define them. Advantages: • Data transmission is relatively simple since data moves in one direction. • Logically, a token passes from one computer to another, so equal attention is given to all nodes. • Reliable and easier to manage. 59 Disadvantages of the Ring Topology • Difficult to troubleshoot. • Difficult to add or remove a computer. • A failure on one computer / node may cause disruption in the entire Network since the Token can’t be passed on. • Before the data reaches the destination, it must travel through all the nodes before it –What is the problem in this? 60 5) Mesh Topology • A Mesh Topology involves all the nodes on the network being interconnected to one another. • It is a network topology that resembles a wire mesh and involves the concept of routes. 61 a) Full Mesh Topology A mesh network in which every device connects to every other is called a full mesh. 62 • The main advantage of this continuous connection between the nodes (Full Mesh Topology) is that when one node goes down, the others remain unaffected. • However, implementing such a network is relatively expensive and difficult. 63 b) Partial Mesh Topology 64 6) Tree Topology • Tree topologies integrate multiple star topologies together onto a bus. The topology combines characteristics of linear bus and star topologies. • In its simplest form, only hub devices connect directly to the tree bus and each hub functions as the "root" of a tree of devices. 65 Tree Topology 66 Advantages of a Tree Topology • Point-to-point wiring for individual segments. (a point to point connection is also more secure that a multipoint connection where many machines are connected to one cable) • Tree topologies allow for the expansion of an existing network • Supported by several hardware and software venders. 67 Disadvantages of a Tree Topology • Overall length of each segment is limited by the type of cabling used. • If the backbone line breaks, the entire segment goes down. • More difficult to configure and wire than other topologies. 68 7) Hybrid Network Topologies • The hybrid topology is a type of network topology that is composed of one or more interconnections of two or more networks that are based upon different physical topologies 69 Hybrid Network Topologies 70 Considerations when Choosing a Topology • Funds. A linear bus network may be the least expensive way to install a network i.e no concentrators are required and not so many cables (and cable length) are required as it is in other topologies like star and mesh. • Length of cable needed. The linear bus network uses shorter lengths of cable. 71 Considerations when Choosing a Topology • Future growth. With a star topology, expanding a network is easily done by adding another concentrator. • Cable type. The most common cable in use is unshielded twisted pair, which is most often used with star topologies. 72 Q&A