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# Basic Concepts of Computer Networks - PowerPoint PPT Presentation

Basic Concepts of Computer Networks. Network Topology. Lesson Objectives. At the end of this lesson, the learner should be able to achieve the following three objectives: Clearly define the term network topology.

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### Basic Concepts of Computer Networks

Network Topology

At the end of this lesson, the learner should be able to achieve the following three objectives:

• Clearly define the term network topology.

• Identify the types of network topologies and their individual advantages and disadvantages.

• How to properly choose the appropriate topologyfor a given situation.

DEFINITION: What Is a Topology?

A network topology describes the arrangement of systems on a computer network. It defines how the computers, or nodes, within the network are arranged and connected to each other.

(TechTerms.com, 2007)

The most commonly used network topologies are:

• Bus

• Ring

• Star

• Mesh

• The bus topology is the simplest andmost common.

• It is often used when a network installation is small, simple, or temporary.

• It is a passive topology. This means that computers on the bus only “listen” to the data being sent. They are not responsible for “moving” the data from one computer to the next.

• In an active topology network, the computers regenerate signals and are responsible for moving the data through the network.

• On a bus network, all the computers are connected to a single cable.

• When one computer sends a signal using the cable, all the computers on the network receive the message, but only the addressee accepts it. The other computers disregard the message.

• The bus is simple and very reliable in verysmall networks.

• The bus network requires the least amount of cable to connect the computers together and is, therefore, less expensive than other cabling configurations.

• Failure of one network node does not effect the rest of the network.

• Heavy network traffic can slow a bus considerably

• A break in the cable or lack of proper termination can shutdown the entire network.

• It is extremely difficult to troubleshoot a bus if the entire network shuts down.

• The network is small.

• The network will not be frequently reconfigured.

• The least expensive solution is necessary.

• Network growth is not predicted.

• In a ring topology, each computer is connected directly to the next computer in line, forming a circle of cable.

• It uses a token to pass the information from one computer to the next.

• Each computer is connected to the next computer in the ring and retransmits what it receives from the previous computer.

• The message flow around the ring is unidirectional.

• The ring is classified as an active topology because there is no termination point in the ring.

• Token passing is a method of sending data in a ring topology.

• A small packet, called the token is passed around the ring to each computer in turn.

• If a computer has information to send, it modifies the token, adds address information and data and sends it down the ring.

• The information travels around the ring until it either reaches it’s destination or returns to the sender.

• A token can circle a ring 200 meters in diameter at a speed of around 10,000 times per second.

• Even with multiple users, network performance is balanced. There is no “bottle neck”.

• Allows for error checking and acknowledgement.

• Failure of one computer can affect the entire network. Data cannot be transmitted successfully.

• Data packets must pass through every computer. This makes the network slower in nature.

• It is difficult to troubleshoot the ring network.

• Adding or removing computers disturbs the network.

• The network must operate reasonably under a heavy load.

• A higher speed network is required.

• The network will not be frequently reconfigured.

• In a star topology, each device has a dedicated point-to-point link to a central controller, sometimes referred to as a hub, server, or host.

• Each computer on a star network communicates with the central hub that then resends the message to the appropriate computer(s).

• The hub can be active or passive in nature.

• An active hub regenerates the electrical signal and sends it to all the computers connected to it.

• The type of hub used in a star topology is commonly referred to as a multi-port repeater.

• Active hubs require electrical power to operate.

• A passive hub, such as a wiring panel, acts as a connection point and does not amplify or regenerate the signal.

• Passive hubs do not require electrical power to operate.

• A star network is easy to modify and add new computers.

• During the addition or removal of nodes, the network continues to function normally.

• The central hub can be easily upgraded when the network capacity is exceeded.

• The central hub provides for centralized monitoring and management of the network, thereby increasing security.

• A single computer failure does not necessarily bring down the entire star network.

• If the central hub fails, then the entire network ceases to operate. The attached nodes are disabled.

• There is a larger upfront cost to create a star network in terms of cabling and hardware.

• A star network requires a dedicated server.

• The network requires easy addition or removal of client computers.

• Star network topologies are recommended for easy troubleshooting ability.

• The network is large in nature.

• The network is expected to grow in the future.

• In a mesh topology, every device has a dedicated point-to-point link to every other device.

• A fully connected mesh network has n(n – 1)/2 physical channels to link n devices.

• To accommodate the many links, every device on the network must have n -1 input/output ports.

• Because there is a dedicated link, there is no traffic between computers.

• Failure of one node computer does not affect the rest of the network.

• Because of the dedicated link, privacy and security are easier to maintain.

• Point-to-point links make fault identification and fault isolation easier to determine.

• Due to the number of cables and input and output ports, it can be more expensive to establish and maintain.

• A large amount of space is necessary to run each of the cables.

• Topologies are the essence of computer network designs.

• Efficient networks can only be built based on the complete knowledge and understanding of the previously explored topologies.

• Knowledge of communication devices is of equal importance when determining the best options for network requirements.

• Resources and time can be wasted when choosing the wrong topology to fit the requirements of the network to be built.

Web References