1. Computer communications
Types of Computer Network

2. Why network computers?
Networking computers can be complex and requires managing, so why go through the hassle?
Sharing resources like Internet connection and printers as well as a shared data stores.
Easier to manage multiple computers. This includes installing software and settings across multiple computers remotely.
Users no longer need to be tied to a single computer to access their data and programs.

3. Network Topology
Topology is the mathematical study of shapes and nodes.
In computing devices are nodes and they can be connected together in different ways.
The structure of the underlying nodes and connections for a network is known as its topology.
There are three types of topology that we need to study. There are some others however.

4. Network Topology Bus network
A bus network has a central cable that all devices connect to.
Only one device can access the bus at a time.
There are terminators at each end of the bus network.
If a device wishes to communicate on the network it first checks to see if there is any traffic on the network. If there is it waits a random period of time and tries again. If it can communicate then it will send the message to the device it wants to communicate with.

5. Network Topology Bus network
Advantages
Less cable need than other types.
Relatively cheaper and easier to install and maintain.
Easy to add new nodes by removing terminator
If a workstation/terminal goes down the others will continue.
Disadvantages
Heavy traffic can cause network failure and delays
Heavily dependent upon the cable backbone and cable damage can cause network failure.

6. Network Topology Ring network
A ring has no central host computer and none of the nodes need to have overall control of access to the network. Messages in the ring flow in one direction from node to node.
An imaginary token is continuously passed around the ring. A token is a small packet that contains bits of data which passes around the ring (Always the same way around).
If a computer is waiting to transmit, it catches a token and with it the authority to send data. It attaches its data. The packet will contain the destination address. As long as one device has a token no other device can send data. Once the sending workstation has received acknowledgement that the message has been received the token is free for use by another device.

7. Network Topology Ring network
Advantages
There is no dependence upon a central computer as data transmission is supported by all devices on the ring. Each node has sufficient intelligence to control the transmission of data from and to its own node.
Very high transmission speeds are possible.
Routing between devices is simple because messages normally travel in one direction.
As data is in one direction it can transmit large volumes of data
Disadvantages
Systems depends upon the reliability of the ring repeater. If one node malfunctions this can affect the operation of the network.
Cabling costs can be high.
Difficult to extend the ring

8. Network Topology Star network
The Star network is the most commonly used network topology in use today.
Each device is connected directly to a central computer (usually through a switch).
Your home network is a star, connecting through the wifi router.

9. Network Topology Star network
Advantages
Suitable for WANs where large organisations rely on a central computer for the bulk of data processing tasks
Central control of message switching allow a high degree of security
Each spoke is independent upon the rest. If one spoke breaks down the others can continue and the central CPU can identify any faults.
Data transmission speeds can vary from spoke to spoke so one can use a high-speed device and another a low speed e.g. disc drive.
Saves cabling.
Disadvantages
Network is vulnerable to central hub failures.
As a distributed system, some processing is still possible at the nodes but internode connection is lost.
If servicing a WAN a mini or mainframe system is needed for control of messaging. So hardware and software is expensive.

10. Other ways to describe a network
Topology is only one way to describe a network.
Another way is to use the relationship between the computers that make up the network.

11. Peer to Peer Networks
All stations are joined together in the network have equal status.
If you have a number of computers at home on sharing a wireless router then this is the type of network you will probably have.
Each device shares the connection to the Internet, whether that is a tablet, games console or computer.
Each computer can give rights of access to other computers, so data or devices can be shared.

12. Client - Server networks
A client-server network has different types of computers.
A powerful central computer called a server manages the client computers the users use.
The data is stored centrally. This means that it does not matter which client computer the user logs on to, they can still access all their work.
The client machines can be controlled and managed from the central computer.
Data can be backed up centrally.

13. Local Area Networks
A Local Area Network (LAN) describes a network that is on one location such as a building or campus.
All the devices are connected together physically or with wifi.

14. Wide Area Networks
Some large organisations have more than one site, but still need to communicate between sites.
These separate LANs are joined together through the telephone networks to create a Wide Area Network or WAN.
The Internet is the biggest WAN, joining together millions of computers.