COMPUTER NETWORKS

1. COMPUTER NETWORKS Types & Topologies

2. What is a network? In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software. Networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. compnetworking.about.com

3. Types of Networks • Local Area Network • Metropolitan area Network • Wide Area Network lo'calar'eanet'work a system for linking private telecommunications equipment, as in a building or cluster of buildings. a system for linking a number of microcomputers, terminals, work stations, etc. with each other or with a mainframe computer in order to share data, printers, information, programs, disks, etc.; usually confined to one office or building. dictionary.infoplease.com This network size falls intermediate between LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings or as large as the North of Scotland. It is not generally owned by a single organisation and often acts as a high speed network to allow sharing of regional resources. It is also frequently used to provide a shared connection to other networks using a link to a WAN. www.erg.abdn.ac.uk A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet. www.webopedia.com

4. Where is a LAN used? • A school campus • Homes • An office building • A single department of an organization

5. M.A.N. • Think of a Metropolitan area network as a network for a campus-like cluster of buildings, or two or more buildings within a short distance of each other in a city, as illustrated below. • Of the three types of networks, the MAN is the least common. • They’re found in situations where sites are too far apart to use LAN technology exclusively (since LAN technology has limits on the distance it can run), but close enough together that high-performance can be achieved in a more cost-effective way than with typical WAN technology. www.certiguide.com

6. When is a WAN used? • To connect LANs • To provide links from an internal network to some system outside that campus/ site • To give voice, video and data networking capabilities to a large area • Why not use a LAN in these situations? • Too small • Limited number of connections • Small physical distance

7. Exam type questions: • Will ask what is the difference between a MAN and a LAN? • Will require you to compare the types of networks for a particular situation... • Will give you a scenario and ask you to suggest AND JUSTIFY a particular network type that is appropriate...

8. What is a topology? In computer networking, topology refers to the layout of connected devices. Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. compnetworking.about.com

9. Network topologies: Firstly, the devices in a topology are referred to as a node regardless of their actual function. When we look at devices, we will explore these differences. The types that we are concerned about for our syllabus are: • Star • Ring • Bus • Hybrid

10. RING • Uni-directional • Bi-directional • One of the three principal topologies for a LAN, in which all nodes are arranged in a circle. • Each node in this topology connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. • Data travels from node to node, with each node along the way handling every packet. www.answers.com One cable linking two nodes, all messages passed in one direction Each node has two cable paths for sending data

11. WHY A RING?? WHY NOT A RING? • Every device has the opportunity to transmit a message (send a packet, token) • Performs better than a star topology under heavy network load • Needs no server to manage the connectivity between the computers • One malfunctioning workstation or connection can create problems for the entire network • Moves, adds and changes of devices can affect the network www.answers.com

12. STAR • With a star topology, the workstations, fileservers, printers etc. are attached via drop cables to a central hub. • The hub is central to a star topology and the network cannot function without it. doit.ort.org

13. WHY A STAR? WHY NOT A STAR? • Once installed, they are easy to maintain and expand. • New devices are easily added. • A fault in a cable only affects the computer or node it is attached to. • Faults are easy to locate. doit.ort.org • Star topologies are difficult to install • Every node is fully dependant on the hub. • Typically needs more cable www.exforsys.com/tutorials

14. BUS • Uses a common vehicle for transmissions and thus it is categorized as shared communication. • The nodes are hooked together like stops on a Public Bus route, one after the other. • All hosts/nodes on the bus will ‘see’ data placed there by others, but only the intended destination will accept it. www.thebryantadvantage.com

15. WHY A BUS? WHY NOT A BUS? • Use less cable than other topologies (cost effective) • Simple to set up. If there is an urgent need to set up a network to be used on a short term basis then the Bus network is the best possibility. • If one computer fails in the network the others are still not affected and they continue to work. www.exforsys.com • When one host transmits data, the other hosts must not do so or a collision will result, resulting in all data involved becoming unusable. • Bus topologies don't react well to more hosts being added. The most hosts we have on a bus, the more collisions we have. • Has a single point of failure. www.thebryantadvantage.com

16. HYBRID • Hybrid topologies are a combination of any two or more network topologies in such a way that the resulting network does not resemble any of the original topology types used to create it. • Two common examples for Hybrid network are: star ring network and star bus network. A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub. A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone). www.mcmcse.com/glossary/h.shtml

17. Topology • Ring • Star • Bus • Hybrid • Collision Terminology so far... Network LAN WAN MAN Link Hub Node

18. ASSIGNMENT Ashley-Jade - VoIP Kadeen – TCP/IP Jodi-Ann – hub/ switch Chamica – FTP Shaneka – FDDI Chantal – ANSI Kerine - CSMA Shaniece – OSI model • You will each have the pleasure of making a video, prezi, skit or soundfile on the networking topics at left • Tomorrow we will have one class on memory management and the other hour for IA work

19. ONE MORE THING!!! There will still be graded work for you as we approach exams, there is no getting around that...