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meaning please

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In Asymmetric encryption, how does the recipient receive the private key in order to decipher the data? LM

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Sir What is Defragmentation and fragmentation?

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Sir What is Defragmentation and fragmentation?

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'Topology' refers to the physical layout of the network, normally with a particular aim in mind.  The main topologies you need to be aware of for GCSE Computer Science are star and mesh topologies. You can find more information here:

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'Topology' refers to the physical layout of the network, normally with a particular aim in mind.  The main topologies you need to be aware of for GCSE Computer Science are star and mesh topologies. You can find more information here:

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Network Toplogies

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What is network topology?

Network topology is the description of the arrangement of nodes (e.g. networking switches and routers) and connections in a network, often represented as a graph.

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.

A logical network topology is a conceptual representation of how devices operate at particular layers of abstraction. A physical topology details how devices are physically connected. Logical and physical topologies can both be represented as visual diagrams.

A network topology map is a map that allows an administrator to see the physical network layout of connected devices. Having the map of a network's topology on hand is very useful for understanding how devices connect to each other and the best techniques for troubleshooting.

Types of network topology

There are many different types of topologies that enterprise networks have built on today and in the past. Some of the network topologies we're going to look at include bus topology, ring topology, star topology, mesh topology, and hybrid topology.

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.

Advantages

Bus topologies were often used in smaller networks. One of the main reasons is that they keep the layout simple. All devices are connected to a single cable so you don't need to manage a complex topological setup.

The layout also helped make bus topologies cost-effective because they can be run with a single cable. In the event that more devices need to be added then you could simply join your cable to another cable.

Disadvantages

However, relying on one cable does mean that bus topologies have a single point of failure. If the cable fails then the entire network will go down. A cable failure would cost organizations a lot of time while they attempt to resume service. Further to this, high network traffic would decrease network performance because all the data travels through one cable.

This limitation makes bus topologies suitable only for smaller networks. The primary reason is that the more network nodes you have, the slower your transmission speeds are going to be. It is also worth noting that bus topologies are limited in the sense that they are half-duplex, which means that data can't be transmitted in two opposite directions simultaneously.

See also: Network, Server and Application Monitoring for SMBs

Ring Topology

In networks with ring topology, computers are connected to each other in a circular format. Every device in the network will have two neighbors and no more or no less. Ring topologies were commonly used in the past but you would be hard-pressed to find an enterprise still using them today.

The first node is connected to the last node to link the loop together. As a consequence of being laid out in this format packets need to travel through all network nodes on the way to their destination.

Within this topology, one node is chosen to configure the network and monitor other devices. Ring topologies are half-duplex but can also be made full-duplex. To make ring topologies full-duplex you would need to have two connections between network nodes to form a Dual Ring Topology.

Dual Ring Topology

As mentioned above, if ring topologies are configured to be bidirectional then they are referred to as dual ring topologies. Dual ring topologies provide each node with two connections, one in each direction. Thus, data can flow in a clockwise or counterclockwise direction.

Advantages

With ring topologies, the risk of packet collisions is very low due to the use of token-based protocols, which only allow one station to transmit data at a given time. This is compounded by the fact that data can move through network nodes at high speeds which can be expanded on when more nodes are added.

Dual ring topologies provided an extra layer of protection because they were more resistant to failures. For instance, if a ring goes down within a node then the other ring can step up and back it up. Ring topologies were also low cost to install.

Disadvantages

One of the reasons why ring topologies were replaced is because they are very vulnerable to failure. The failure of one node can take the entire network out of operation. This means that ring topology networks need to be constantly managed to ensure that all network nodes are in good health. However, even if the nodes were in good health your network could still be knocked offline by a transmission line failure!

Ring topologies also raised scalability concerns. For instance, bandwidth is shared by all devices within the network. In addition, the more devices that are added to a network the more communication delay the network experiences. This means that the number of devices added to a network topology needed to be monitored carefully to make sure that the network resources weren't stretched beyond their limit.

Making changes to a ring topology was also complicated because you need to shut down the network to make changes to existing nodes or add new nodes. This is far from ideal as you'll need to factor in downtime every time you want to make a change to the topological structure!
See also: Tools To Monitor Throughput
Star Topology

A star topology is a topology where every node in the network is connected to one central switch. Every device in the network is directly connected to the switch and indirectly connected to every other node. The relationship between these elements is that the central network hub is a server and other devices are treated as clients. The central node has the responsibility of managing data transmissions across the whole network and acts as a repeater. With star topologies, computers are connected with a coaxial cable, twisted pair, or optical fiber cable.

Advantages

Star topologies are most commonly-used because you can manage the entire network from one location: the central switch. As a consequence, if a node that isn't the central node goes down then the network will remain up. This gives star topologies a layer of protection against failures that aren't always present with other topology setups. Likewise, you can add new computers without having to take the network offline like you would have to do with a ring topology.

In terms of physical network structure, star topologies require fewer cables than other topology types. This makes them simple to set up and manage over the long-term. The simplicity of the overall network design makes it much easier for administrators to run troubleshooting when dealing with network performance faults.

Disadvantages

Though star topologies may be relatively safe from failure, if the central switch goes down then the entire network will go down. As such, the administrator needs to manage the health of the central node closely to make sure that it doesn't go down. The performance of the network is also tied to the central node's configurations and performance. Star topologies are easy to manage in most ways but they are far from cheap to set up and use.

Tree Topology

As the name suggests, a tree topology network is a structure that is shaped like a tree with its many branches. Tree topologies have a root node that is connected to another node hierarchy. The hierarchy is parent-child where there is only one mutual connection between two connected nodes. As a general rule, a tree topology needs to have three levels to the hierarchy to be classified this way. This form of topology is used within Wide Area Networks to sustain lots of spread-out devices.

Advantages

The main reason why tree topologies are used is to extend bus and star topologies. Under this hierarchical format, it is easy to add more nodes to the network when your organization grows in size. This format also lends itself well to finding errors and troubleshooting because you can check for network performance issues systematically throughout the tree.

Disadvantages

The most significant weakness of tree topology is the root node. If the root node fails then all of its subtrees become partitioned. There will still be partial connectivity within the network amongst other devices such as the failed node's parent.

Maintaining the network system is not simple either because the more nodes you add, the more difficult it becomes to manage the network. Another disadvantage of a tree topology is the number of cables you need. Cables are required to connect every device throughout the hierarchy which makes the network layout more complex when compared to a simpler topology.

Mesh Topology

A mesh topology is a point-to-point connection where nodes are interconnected. In this form of topology, data is transmitted via two methods: routing and flooding. Routing is where nodes use routing logic to work out the shortest distance to the packet's destination. In contrast, flooding is where data is sent to all nodes within the network. Flooding doesn't require any form of routing logic to work.

There are two forms of mesh topology: partial mesh topology and f ull mesh topology. With partial mesh topology, most nodes are interconnected but there are a few which are only connected to two or three other nodes. A full mesh topology is where every node is interconnected.

Advantages

Mesh topologies are used first and foremost because they are reliable. The interconnectivity of nodes makes them extremely resistant to failures. There is no single machine failure that could bring down the entire network. The absence of a single point of failure is one of the reasons why this is a popular topology choice. This setup is also secure from being compromised.

Disadvantages

However, mesh topologies are far from perfect. They require an immense amount of configuration once they are deployed. The topological layout is more complex than many other topologies and this is reflected by how long it takes to set up. You'll need to accommodate a whole host of new wiring which can add up to be quite expensive.

Hybrid Topology

When a topology is composed of two or more different topologies it is referred to as a hybrid topology. Hybrid topologies are most-commonly encountered in larger enterprises where individual departments have network topologies that different from another topology in the organization. Connecting these topologies together will result in a hybrid topology. As a consequence, the capabilities and vulnerabilities depend on the types of topology that are tied together.

Advantages

There are many reasons why hybrid topologies are used but they all have one thing in common: flexibility. There are few constraints on the network structure that a hybrid topology cannot accommodate, and you can incorporate multiple topologies into one hybrid setup. As a consequence, hybrid topologies are very scalable. The scalability of hybrid setups makes them well-suited to larger networks.

Disadvantages
See also: Network Discovery Tools and Software
Unfortunately, hybrid topologies can be quite complex, depending on the topologies that you decide to use. Each topology that is part of your hybrid topology will have to be managed according to its unique network requirements. This makes administrators' jobs more difficult because they are going to have to attempt to manage multiple topologies rather than a single one. In addition, setting up a hybrid topology can end up being quite costly.

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:

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.

Network Topology Mapping Software

Now that we know the different types of topology, it is time to consider how to design your network from scratch. There are several software products that allow you to create your own network topology diagrams. Network topology diagrams show you a diagram of how your network connects together and helps you to create an efficient network design. It also provides you with a reference point that assists you when you attempt to run troubleshooting to fix faults.

Our methodology for selecting network topology mapping software

We reviewed the market for network topology mapping software and analyzed the options based on the following criteria:

Automatic network discovery

Live topology map creation for up-to-date

Device identifiers and statuses displayed on the map

Options for different layout formats

Options to manually redesign the network layout within the mapper

A free assessment period or money-back guarantee

Value for money, represented by a price that represents a good deal for the number of tools the package includes

There are many different network topology mapping products out there but one of the most widely used is Microsoft Visio.

With Microsoft Visio, you can draw up your network by adding network elements to a canvas. This program allows you to design a topology diagram that details your network. Of course, drawing up your own network isn't always ideal particularly when you're attempting to map a larger computer network.

As a result, you might want to consider using another tool like SolarWinds Network Topology Mapper which can autodiscover devices connected to your network. Autodiscovery comes in handy because it means that you don't have to draw up your network structure manually.

SolarWinds Network Topology Mapper Download 14-day FREE Trial

Faddom, until recently, called VNT is a mapping system that automatically creates a network topology map through a scanning routine. As well as mapping physical networks, this tool can identify servers and VMs within a hypervisor and map the links between them.

You can examine this tool with a 30-day free trial.

Choosing Network Topology Mapping & Diagram Software

The network topology you choose for your enterprise should be deeply rooted in your usage requirements. The number of nodes you have in your network will determine whether you can make it by using a bus topology or whether you're going to need to deploy a more complicated mesh or hybrid setup.

Remember that all topologies have their advantages and disadvantages depending on the environment they're applied within (even those that have become obsolete!).

Once you've given some thought to what topology you want to use you can make the move to deploy it. You can also learn more about Documenting a Network Topology Using CDP.

One good way to plan ahead is to use a network topology mapping tool to draw up the network layout that you're going to use. Using a tool like SolarWinds Network Topology Mapper will allow you to plot your network on a diagram to view your topological structure in one place.

Network Topology FAQs

Related: The Best Network Monitoring Tools

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6 Best Network Topologies Explained - Pros & Cons [Including Diagrams]

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Network topology is the description of the arrangement of nodes (e.g. networking switches and routers) and connections in a network, often represented as a graph. No matter how identical two organizations are, no two networks are exactly alike. However, many organizations are relying on well-established network topology models.

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Replicate means to repeat or copy something.

Example:

https://mote.com/m/dbrj68m

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If you hear a word in your lessons, or when doing your work and you are not sure of the meaning, use this board to ask and find out...

- You don't need to log in if you don't want your name on it.
- just write out the word you want to know and I will get back to you and explain it.
- this will be on your Google Classroom so you can keep coming back to it if you forget.

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What does the word "specific" mean?

Specific means special or unique to something.