COMMUNICATIONS,NETWORKS, THE INTERNET AND E-MAIL

What is a network… A network is two or more computers, or other electronic devices, connected together so that they can exchange data. For example a network allows computers to share files, users to message each other, a whole room of computers to share a single printer etc.

Continued Network connections between computers are typically created using cables (wires). However, connections can be created using radio signals(wireless / Wi-Fi), telephone lines (and modems) or even, for very long distances, via satellite links.

Computers in a network Computers connected together to create a network fall into two categories: 1. Clients: Client computers, or workstations, are the normal computers that people sit at to get their work done. 2. Servers : Servers are special, powerful computers that provide ‘services’ to the client computers on the network.

Types of network LAN MAN WLAN WAN BLUETOOTH( personal area network) Wi-Fi( wireless fidelity)

LAN-Local Area Network A Local Area Network is a network confined to one building or site. Often a LAN is a private network belonging to an organization or business. Because LANs are geographically small, they usually use cables or low-power radio (wireless) for the connections.

LAN

TOPOLOGY

TOPOLOGY The word topology means ‘arrangement’, so when we talk about the topology of a network, we mean how the different parts are arranged and connected together. There are five common network topologies... Bus topology Ring topology Star topology Mesh topology Tree topology

VIDEO TOPOLOGY

Bus topology In this type of network, a long, central cable, the ‘bus’ is used to connect all of the computers together. Each computer has a short cable linking it to the ‘bus’. A bus network… 1. Is cheap to install (just one long cable) 2. Can be quite slow since all computers share the same cable when communicating 3. Will stop working if there is a break in the central bus cable.

Bus topology

ADVANTAGE Extending the network is very easy. Only single network cable needs to be installed.

DISADVANTAGE Any problem with the main cable may cause the whole network to malfunction. Data travels in both directions along the network cable. Packets of data may collide, which may slow down transmission speed and data may be lost.

Star topology In this type of network every computer is connected to a central device. The device passes messages between computers. At the centre of a star network you might use a hub (cheap, but slower) or a switch (more expensive, but faster). A star network is quite expensive to install (you have to buy lots of cable and the central device)

Star topology

ADVANTAGE Extending the network is straight forward. If one computer stops working, the network is not effected. If a cable stops working, only one computer is affected.

DISADVANTAGE It requires more cabling because each computer has its own cable to the hub. It may be more difficult to connect a new computer to the network because a separate cable is needed from the computer to the server and this may be difficult to install because of the physical layout of the building. A star topology requires more cable than a bus topology.

SUMMARY What is a network. Types of computer in a network i.e. client and server What is a topology. Types of topology: 1. bus topology. 2. star topology

Ring topology In this type of network each computer is connected to a loop of cable, the ‘ring’. (If you took a bus network and connected the ends of the bus cable together, you would have a ring network.) A ring network… can cope with a break in the ring cable since all computers are still joined together (it is now a bus network)

Ring topology

Mesh topology Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Mesh topology

Tree topology Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Tree topology

SUMMARY Types of topology. Ring topology. Mesh topology. Tree topology.