Why use a network? There are many reasons such as sharing files with differnet people, accessing your own files on different computers and giving access to information on many other computers. But first, to understand networks, you must know about the concept of topologies.

There are two types of topologies. The first is a LAN - a local area network. These types of networks are used for local networks restricted to a limited area. A perfect example is the school network.

The second type of topology is a WAN - a Wide Area Network. Generally, this is a network that spans over one kilometre. The best and biggest example of a WAN is the Internet. WAN's are often made by connection smaller LAN's together.

Within a LAN, there are three main types of configurations.

In a STAR TOPOLOGY, all of the devices (e.g. computers, printers) are connected to a central HUB. This type of configuration is easy to install and manage. Bottlenecks can occur, however, because all data is connected to one point.

In a BUS TOPOLOGY, all of the devices are connected to a central cable called a bus or backbone. An example of a bus topology are ethernet systems.

In a RING TOPOLOGY, all the devices are connected to two other adjacent devices forming a loop. These networks, while hard to install and expensive, support high bandwidth connections and can span large distances.

Within all of these configurations lies a HUB. A HUB is a device connected to several other devices, much like the hub of a wheel to the spokes. In a network, this is where are all the computers plug or connect into.

All the computers that connect to the HUB are called nodes. Nodes are an addressable device attached to the network. All computers connected to a network have an address. Most networks use an IP address. (e.g. 207.164.25.3) This address is used so other computers can find you.

A key term you should know is a "bus". This is simply a set of conductors connecting various functional devices in a computer. This is much like a "bus-bar" in electronics. Why is this term important? The answer brings us to a serial and parallel transmissions.

The larger the bus, the more data can flow through it. It's like a water hose. The wider the hose, the more water can flow through it. This is exactly like data. The difference between a serial and a parallel transmission is that in a serial transmision, data is transferred bit by bit. In a parallel trasmission, several bits can be transferred simultaneously, allowing for faster connections. Why are faster connections important? If you've ever downloaded something off the Internet, you know.

So, now you know the relationships within a network. but if you have hundreds of people connecting to one server, as is often the case, how can a server handle all simultaneous connections? It does so with a token.

A token is simply something that gives a node permission to send data to the hub and to the server. There is only one token and it cannot be destroyed or duplicated.

In a network, as stated before, there are undreds of people on it. Meny of these people probably use different computer configurations and even different operating systems. To avoid problems, networks use what's called a protocol. A protocol is a set way that computers should connect and talk to each other. It's like a language where the talker and the listener know the rules of a converstation.

Between networks likes a gateway. Like real life, a gateway is a door to other netowrks, or in real life, other property. In a network a gateway handles all the issues that arise when connecting between two different networks.

DEFINITIONS:

Hardware and oftware data communication systems.

The OSI seven layer model attempts to provide a way of partitioning any computer network into independent modules from the lowest (physical) layer to the highest (application) layer. Many different specifications exist at each of these layers.

Networks are often also classified according to their geographical extent: local area network (LAN), metropolitan area network (MAN), wide area network (WAN) and also according to the protocols used.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=network

topology

1. The study of interconnections.

2. A network topology shows the hosts and the links between them. A network layer must stay abreast of the current network topology to be able to route packets to their final destination.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=topology

local area network

(LAN) A data communications network which is geographically limited (typically to a 1 km radius) allowing easy interconnection of terminals, microprocessors and computers within adjacent buildings. Ethernet and FDDI are examples of standard LANs.

Because the network is known to cover only a small area, optimisations can be made in the network signal protocols that permit data rates up to 100Mb/s.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=lan

Wide Area Network (WAN)

A network, usually constructed with serial lines, extending over distances greater than one kilometre.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=WAN

bus

A set of conductors (wires, PCB tracks or connections in an integrated circuit) connecting the various functional units in a computer. There are busses both within the CPU and connecting it to external memory and peripheral devices. The width of the bus, i.e. the number of parallel connectors, determines the size in bits of the largest data item which it can carry. The bus width and the number of data items per second which it can transmit are one of the factors limiting a computer's performance. Most current microprocessors have 32-bit busses both internally and externally.

Some processors have internal busses which are wider than their external busses (usually twice the width) since the width of the internal bus affects the speed of all operations and has less effect on the overall system cost than the width of the external bus.

The term is almost certainly derived from the electrical engineering term "bus bar" - a substantial, rigid power supply conductor to which several connections are made. This was once written "'bus bar" as it was a contraction of "omnibus bar" - a connection bar "for all", by analogy with the passenger omnibus - a conveyance "for all".

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=bus

gateway

1. protocol converter.

2. This term was previously used for a router or other kind of internetworking device but this use is now deprecated. By this definition, a router is a layer 3 (network layer) gateway, and a mail gateway is a layer 7 (application layer) gateway.

3. An interface between some external source of information and a World-Wide Web server. Common Gateway Interface is a standard for such interfaces.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=gateway

protocol

A set of formal rules describing how to transmit data, especially across a network. Low level protocols define the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream. High level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages etc.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?protocol

serial

One by one. Serial data transfer refers to transmitting data one bit at a time. The opposite of serial is parallel, in which several bits are transmitted concurrently.

http://www.zdwebopedia.com/TERM/s/serial.html

parallel

Refers to processes that occur simultaneously. Printers and other devices are said to be either parallel or serial. Parallel means the device is capable of receiving more than one bit at a time (that is, it receives several bits in parallel). Most modern printers are parallel.

http://www.zdwebopedia.com/TERM/p/parallel.html

hub

(By analogy with the hub of a wheel) A device connected to several other devices.

In ARCnet, a hub is used to connect several computers together. In a message handling service, a number of local computers might exchange messages solely with a hub computer. The hub would be responsible for exchanging messages with other hubs and non-local computers.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=hub

token

1. A basic, grammatically indivisible unit of a language such as a keyword, operator or identifier. Compare: lexeme.

2. (Or "pumpkin") An abstact concept passed between cooperating agents to ensure synchronised access to a shared resource. Such a token is never duplicated or destroyed (unless the resource is) and whoever has the token has exclusive access to the resource it controls. See for example token ring.

If several programmers are working on a program, one programmer will "have the token" at any time, meaning that only he can change the program whereas others can only read it. If someone else wants to modify it he must first obtain the token.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=token

node

1. A point or vertex in a graph.

2. An addressable device attached to a computer network. More often called a "host".

3. A hypertext document.

http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?query=node