Describe each topology in terms of how devices connect and how data travels. Explain how that arrangement affects its practical use.

A network topology describes how devices and their connections are arranged. This arrangement determines which routes data can take and what happens if equipment fails.

Star topology

Each device in a star topology has its own connection to a central device, usually a switch. Devices communicate with one another through that switch.

If a device or its connecting cable fails, normally only that device is affected. A central switch failure, however, interrupts communication throughout the star. Another device is straightforward to add, provided the switch has a spare port.

Mesh topology

In a mesh topology, devices connect to several other devices, giving data alternative routes through the network. Every device in a full mesh connects directly to every other device. A partial mesh has fewer connections.

These alternative routes improve reliability. If a link fails, data may still reach its destination, provided another usable route exists. The extra links come at a cost: equipment, installation and management all become more expensive.

Hybrid topology

A hybrid topology combines different topology arrangements in one network. For example, separate groups of devices can form stars, with mesh links between the switches that connect those groups.

Comparing the design factors

Data collisions occur when transmissions overlap on a shared communication medium and interfere with each other. Whether collisions occur depends on the connection technology as well as the topology. A modern switched, full-duplex Ethernet connection has no collisions; shared wireless communication can experience them.

No topology guarantees a particular transmission speed. The capacity of the links matters, as do traffic levels and the performance of the connecting equipment.

Practical applications

A switched star could suit a small design studio. It's affordable and easy to expand, and a damaged workstation cable does not disconnect the other workstations. If uninterrupted access is essential, though, the studio must also address the central switch's vulnerability.

A large training centre could use a hybrid, with stars inside teaching rooms and mesh connections between the switches serving different buildings. This puts the cost of alternative routes where a failure would affect the most users. The same principles apply in other settings; requirements determine the best choice, rather than the organisation's name or size alone.

Key terms: network topology, star, mesh, hybrid, reliability, transmission speed, scalability, data collisions, cost.

To describe a server, start with the service it provides. Then consider how to keep that service available, secure and responsive as demand grows.

A server is hardware or software that provides a service to other devices or programs over a network. A single physical computer can run several server services. Equally, several computers can share the work of running one service.

Types of server

Function, scalability, reliability and security

Scalability is the ability to accommodate increased demand while maintaining an acceptable service. As user numbers rise, a service may need extra processing capacity or storage. It may also need more network capacity or additional server instances.

Applying the factors

Access permissions in a shared file service prevent users from opening files they should not see. Extra storage supports growth. Backups allow lost files to be recovered, while a replacement or redundant server can reduce interruption after a hardware failure.

If DNS fails, users may be unable to locate services by name even though those services are still running. Redundant DNS provision improves availability. Protecting DNS records against unauthorised changes also helps prevent users being directed to the wrong destination.

DHCP address allocation must support the number of devices joining the network. A failure can stop new devices from obtaining configuration, although devices with valid existing leases may continue communicating for a time.

A proxy can enforce access restrictions. It can also become a bottleneck or a single point of failure, so its filtering and caching functions need sufficient capacity and reliable operation.

Key terms: domain name server (DNS), dynamic host configuration protocol (DHCP), file server, mail server, proxy server, web server, function, scalability, reliability, security.

Start by identifying what the models share. Then compare how the roles they assign affect control, cost, reliability and performance.

Clients in the client-server model request services or resources from servers, which provide them. Devices in the peer-to-peer model can take either role: they can request resources or provide them directly to other participants.

Both models let devices exchange data and share resources. What differs is how responsibility is organised, not the network's physical shape. Either model can operate over a switched star.

How the roles differ

Practical applications

Web browsing normally uses client-server communication. The browser requests a resource; the service returns it. Central control suits this arrangement because the service provider manages the content and access rules. It must, though, provide enough capacity for its users.

A peer-to-peer file-sharing application can obtain different parts of a file from several peers, spreading the transfer workload and reducing dependence on one provider. Availability still depends on peers staying connected and offering the required data.

There are other applications, and some combine the models. A system might use a central service to help participants find one another, then transfer data directly between peers. Classify the particular interaction—don't assume that an entire application uses only one model.

Key terms: client-server, peer-to-peer, client, server, peer, benefits, drawbacks.

Explain segmentation by showing how it works: separating traffic cuts unnecessary communication, while controlling communication between groups supports security and resource management.

Network segmentation divides a network into smaller physical or logical sections. Each section can be managed separately, and communication between sections can be controlled where needed.

Why segment a network?

There are several connected reasons to segment a network:

• Network performance: keeping traffic in the section that needs it reduces unnecessary processing elsewhere.
• Reduced congestion: when local traffic stays local, there is less competition on links connecting different sections.
• Security: restricting communication between sections limits access to sensitive resources and can hinder an attack's spread.
• Efficient resource management: separate groups can have different access rules and allocations of network capacity to match their needs.

Segmentation doesn't add link capacity. A busy link can still become congested. Communication between segments can also create a bottleneck at the device that connects them.

Segmenting, subnetting and VLANs

A broadcast domain is the set of devices that can receive a broadcast transmission from one another. Keeping broadcasts inside a VLAN stops them from reaching every device on the wider switched network.

Subnetting and VLANs are related, but they aren't interchangeable. A subnet concerns IP addressing; a VLAN concerns logical separation within a switched network. Networks commonly give each VLAN a different subnet and use routing to provide communication between them.

Worked application

A community workshop connects staff computers, visitor devices and shared tools to the same physical switching equipment. It sets up a staff VLAN, a visitor VLAN and a tools VLAN. Each has a separate subnet.

Visitor devices can access the internet but cannot reach staff computers or shared tools. Staff computers may communicate with the tools. These rules improve security: joining the visitor group does not automatically give a device access to the other groups.

Broadcast traffic from visitor devices stays within the visitor VLAN, so staff computers and tools receive less unnecessary traffic. Local communication within a group need not cross the router. That leaves the router's capacity available for traffic that genuinely needs to move between subnets.

Resources can also be managed by group. For example, a bandwidth limit on visitor traffic can stop it from consuming capacity needed for staff work. The benefit comes from applying an appropriate policy, not simply from naming a VLAN.

Separation needs enforcement

Creating separate subnets or VLANs does not automatically put every required security restriction in place. With unrestricted routing enabled between them, devices may still reach other groups. Access rules must allow necessary communication and block communication that is not required.

Segmentation also takes configuration and management work. Incorrect group assignments or access rules can block legitimate communication or leave unintended access open.

Key terms: network segmentation, segmenting, subnetting, virtual local area networks (VLANs), network performance, security, congestion, network resources.