networks

Networks

A network connects computers together so that they can share information and resources, such as printers, scanner, internet access, servers etc. The end devices on a network are referred to as "nodes."


 * Network Categories**

There are two main categories of networks. LAN which stands for Local Area Network and WAN which is Wide Area Network.

A LAN is a network that connects servers and nodes that are within a close geographic proximity, such as a school, business office, your home network even.

A WAN is a network that connects two or more LAN's into one big network known as a WAN. An example of a WAN is each banks computer system. Each branch has it's own LAN, which is a part of a WAN.


 * Network Types**

Like network categories, there are two network types. These are client server networks and the other peer-to-peer networks (Also called P2P).

In a client server network, there is a server (Which is like a master computer) or servers which handle such tasks as:
 * User authentication - Users will try and login on the computer/workstation then the credentials they have provided are checked against that stored on the server.
 * File server - The role of a file server is to share and store files in a central location. An example of this is the S and H drives on the local Salesian College Network. The H drive is a location where your files are located on the server, which can be access through whichever computer you login to.
 * Enforce restrictions - On a windows network you have something called Group Policy. What group policy does is restrict what the user can do on the client computer. Evidence of this on our Salesian network is not having access to the control panel, the clock on the work station (Changing it), not having write access to the local computers C drive. etc.

The server in a client server network is "superior" to that of the client. Servers run software called a Network Operating System. A network operating system is a piece of software that is designed for computers that are servers. They have the additional features that managing networks easy. They also have more advanced security features in comparison to the standard operating system (A standard operating system is Windows 7, Vista, XP, Mac OS X etc.). An example of a NOS is Windows Server 2008 R2:

More information on Software can be found on Steve Madi's Software page by clicking here.


 * Network Topologies**

Networks come in all different shapes and forms and are connected through different mediums. The design/shape of a network is referred to as a topology. The three main network topologies are:
 * 1) Bus
 * 2) Ring
 * 3) Star

Bus topologies are not so common these days due to their unreliability and slowness. A bus topology connects all "nodes" in the network by them attaching onto one central cable known as the "bus". Consider the diagram below.
 * //Bus Topology//**



This image shows the nodes (in this case computers) being connected to one single bus. With a bus network, if one node wants to send something or communicate that something to another node, the message is sent to all nodes along the bus until it reaches the one it is destined for. e.g. If the computer in the top left, wants to send something to the computer at the top right, the message would visit all computers in-between before reaching the destination computer. This makes the network slow down. At the end of the bus, a terminator must be in place. Without a terminator, the data is going to bounce back along the able until a node accepts it. If no node accepts it, then the data is just going to go around and around, taking up bandwidth.

Advantages Costs - To build a bus network is cheap. Traditional bus networks used coaxial cable (The type of cable which is used for TV antenna points. The black one). This type of cable was slow and didn't offer much room for scalability.

Disadvantages Can be easily broken - If a single cable on a bus network is broken, the whole network goes down.


 * Ring Network**

A ring network is very similar to that of a bus network, that is each node is connected to one another via coaxial cable. If a node in a ring network wants to send information from one to another, they have to wait for a gap in the network to send their message. If there is already data in the network, they can't send it until it's gone.

Advantages Costs - To build a ring network is fairly cheap.

Disadvantages Can be easily broken - If a single cable on a ring network is broken, the whole network goes down. Can be hard to set up - A ring network can be hard to set up because of the fact the cable needs to form a ring. That is it must connect all computers in a loop/ring formation with attempting to keep the length of the cable between the nodes to a minimum.

Star Network

A star network is the most popular for of network due to their scalability and reliability. A star network differs from that of the ring and bus networks because they have a switch or hub to that connect all nodes (As shown below). The image below states that it's a client server network and it is, that is because **all most** every client server network is a star network!



What is a switch and or hub? A switch and a hub are not the same thing, don't make this mistake! Though their functions are similar. As you can see above, all the nodes are connected to one another via cords to the hub. To understand how it all works, I will give an example, as it can be complex if you have not learnt about networks before. Gates-1 Workstation wants to retrieve a file from the server. Gates-1 Workstation then sends out a request asking for that file from the server. The request travels along the cord from Gates-1 Workstation to the hub and then from the hub, it sends out the request to all nodes connected to it seeing if they contain the requested information. Only the server would respond because that's who it's intended for. The server would then send the information to the hub, which would then send out the requested information to all nodes, and only Gates-1 Workstation would respond. Saying that I'm here and I want it.

The different between a switch and a hub is that, if a switch was to be placed in that network diagram instead of a hub. The process would be:
 * 1) Gates-1 Workstation sends out request
 * 2) Switch sees the request and sees it's for the server
 * 3) The switch sends the request to the server only
 * 4) The server then gets the request
 * 5) Sends the requested information back to the switch
 * 6) The switch then sees the information is intended for Gates-1 Workstation.
 * 7) The switch sends the information to Gates-1 Workstation only.

As can be seen, a switch is basically a smart hub. It knows what is connected to it on each port so it knows where to send the information, instead of sending it out to all nodes and clogging up the network.

There are two main categories of communication mediums for networks. These are wired and wireless.
 * Communication Mediums for Networks**

//Wired communication// Wired communication is the fastest of the two categories of communication mediums, though there are different types of cords. The different types of cords offer different speeds and expandability. They are:
 * 1) UTP (Unshielded twisted pair) - This cable is the blue one you see in most computer labs. Inside them, they have 8 copper cables, twisted in pairs to reduce interference. This cable comes in a variety of different speeds. The current standard is CAT (Category) 5e. Which offers speeds of 100Mbps as standard though can offer up to 1000Mbps. Though this isn't common. CAT6 is the next up category and is now just becoming standard. It offers speeds of 1000Mbps (1Gbps). There are some restrictions on UTP cable, it's signal starts to deteriorate after 100m use due to the copper cable.
 * 2) Fibre-optic - Fibre-optic is the fastest cable around. Instead of using copper to transmit data along it uses light.
 * 3) Coaxial - Not used basically anymore as it's pretty much crap.