Bus Topology

The Bus Topology is also known linear bus. It consists of several computers which are attached to a common cable called the trunk line.

Bus Network

In the bus topology, data on the network is sent to all the computers on the network. However, the data is accepted only by the computer that has the address matching the address in the signal. Only one computer at a time can send messages. The bus topology is a passive topology in which the computers on the bus are not responsible for moving data. In this, failure of one computer does not affect the performance of the network. The performance on a bus network can be affected by the following factors:

• Number of computers on the network
• Hardware capabilities of computers on the network
• Frequency of data transmission
• Types of cable used on the network
• Distance between computers on the network

Note: Every computer on the network has an address. Data that is sent from a computer that contains the address of the computer to which it is sent.

Star Topology

In the Star Topology, computers are connected by cable segments to a centralized device known as hub. Signals are transmitted from the sending computer through the controller on the central hub to the receiving computer. As each computer is connected to a central point, this topology requires a great deal of cabling. Also, if the central controller fails, the entire network is disabled. However, if one computer, or the cable that connects it to the hub fails, the rest of the network continues to function normally.

Star Network

Note: A hub is a device used to centralize network traffic through a single connection point. Hubs can be of two types: active and passive hub. An active hub regenerates and transmits the signals. It requires electrical power to run. A passive hub acts as a connection point and does not amplify or regenerate the signal. Passive hubs do not require electrical power to run. Signals after travelling some distance, become weak. Regeneration is the process by which the signals are given more power to travel further.

Ring Topology

In Ring Topology, computers are connected through a single circle of cable. There are no terminated ends. The signals travel around the loop in one direction and pass through each computer. The ring is an active topology where each computer acts like a repeater to boost the signal, and sends it on to the next computer. Failure of one computer in a ring network can affect the entire network.

Ring Network

The Advantages and Disadvantages of Each Type of Topology

Topology	Advantages	Disadvantages
Bus Topology	Uses the least amount of cable. Media is inexpensive, simple and reliable. Is easy to extend.	Hardware bugs are difficult to isolate. Does not adequately support large number of I/O requests from users. Cable break can affect many users.
Ring Topology	Networks can cover greater distances. Performance is even despite many users.	Expanding the system can be costly. Network reconfiguration disrupts operation.
Star Topology	New computers can be easily added. Cable layouts are easy to modify. Failure of one computer does not affect the rest of the network.	Uses a large amount of cable. If the centralized point fails, the network fails.

Advantages and Disadvantages of the Standard Topologies

Star Bus Topology

The Star Bus is a combination of the bus and star topologies. In a star bus topology, there are several star topology networks linked together with linear bus trunks.

If one computer develops a fault, it will not affect the rest of the network. If a hub develops a fault, all computers on that hub will be disabled.

Star Ring Topology

The Star Ring is a combination of ring and star topologies. The hubs in a star ring are connected in a star pattern by the main hub.

Designing the Network's Layout

The term topology, or more specifically, network topology, refers to the arrangement or physical layout of computers, cables, and other components on the network.

A network's topology affects its capabilities. Choosing one topology over the other can impact the:

• Type of equipment the network needs.
• Capabilities of the equipment.
• Network's growth.
• Way a network is managed.

A network's topology implies a number of conditions. For example, a particular topology can determine not only the type of cable used but how the cable is run through floors, ceilings and walls. Topology can also determine how computers communicate on the network. Different topologies require different communication methods, and these methods have a great influence on the network.

The type of network you install will depend on a number of factors, including the:

• Network budget
• Network size
• Level of security required
• Physical layout
• Type of business
• Amount of network traffic

Components of a Network

The following are the components and features that all networks have in common:

• Servers - Computers that provide shared resources to network users.
• Clients - Computers that access shared network resources provided by a server.
• Media - The way in which the computers are connected.
• Resources - Files, printers or other items to be used by network users.

Even with these shared components, networks can be divided into two broad categories:

• Server-Based networks
• Peer-to-Peer networks

Server-Based Networks

Most networks have a dedicated server. A dedicated server is a computer on a network that functions as a server, and is not used as a client or a workstation. A dedicated server is optimized to service requests from network clients.

Servers perform a wide variety of tasks. Usually, large networks have specialized servers for different tasks. Examples of specialized servers are:

• File and print servers - manage user access and use of file and printer resources.
• Application servers - make the data on the server available to clients.
• Mail servers - manage electronic messaging between network users.
• Communication servers - handle data flow and E-mail messages.

Peer-to-Peer Networks

In a peer-to-peer network, there are no dedicated servers. All the computers are equal and, therefore, are termed as peers. Normally, each computer functions as both a client and a server.

A peer-to-peer network has the advantage of simplicity in design and maintenance. It is usually less expensive to set up as compared to server-based networks. Peer-to-peer networks are also called workgroups. The term workgroup implies a small group of users.

Peer-to-peer networks are suitable for environments where:

• There are limited users (usually 10 or less).
• The users are located in the same area.
• Security is not an important issue.
• The organization and the network have limited growth.
• Users need to freely access data and programs that reside on other computers across the network

In a peer-to-peer network, there is no one assigned to be an administrator responsible for the entire network. Users administer their own computers. All users can share any of their resources.

Note: Network administration involves tasks like managing users and security, making resource available, installing and upgrading software.

Comparison between Peer-to-peer and Server-based Networks

Summarizes the features of peer-to-peer and server-based networks:

Feature	Peer-to-peer Network	Server-based Network
Size	Good for up to 10 users	Limited only by server and network hardware
Security	Users are responsible for their own security	Offers extensive user security
Administration	Is administered by the user of each computer	Is centrally administered