OSI Model

• OSI network model
  
  The Open Systems Interconnection (OSI) seven-layer network model is a comprehensive explanation of the different pieces used to form a network. The seven layers are defined as the following:
  
  ApplicationLayer 7End user processes
  PresentationLayer 6Network or application encryption and decryption layer
  SessionLayer 5Connects end user and network applications
  TransportLayer 4Provides transfer of data among hosts on the network
  NetworkLayer 3Switching and routing of data for efficiency and speed
  Data LinkLayer 2Packages data into packets for transmission/reception
  PhysicalLayer 1Hardware
  
  Sometimes the model is further broken down as shown in the diagram. Here, the data link layer and the physical layer have been further subdivided to include information about different data link methods and different physical devices and protocols. This complex model is interesting to know and may sometimes assist in identifying the source of a problem, however it is rarely necessary to remember it because all of the complexity of a network has been made easy by the software developers and hardware manufacturers. You will need to know about two of the layers to start using a network.
  
  

Physical Layer

• The hardware needed for a network is built into most computers via a Network Interface Card (NIC). Ethernet or 802.11 are a couple of the ways the manufacturers describe their network hardware. Each computer attached to the network needs an NIC. There must also be a physical way for the information to be transferred from the computer to the network. This is done either with a cable such as CAT 5 or CAT 6 cables, or via Wi-Fi, which does not require cables.
  
  

Data, Network and Transport Layers

• These layers are encapsulated in a physical device called a hub. Hubs require a router and most hubs today are also routers. The cable from the NIC is connected to the router or in the case of Wi-Fi, the NIC connects to the router without cables by broadcasting and receiving radio waves. The router also has a connection to another network. This other network is usually a larger network of other networks such as the Internet. Usually a modem is needed to connect the router to the Internet. Most all modems require a cabled connection to the router for security reasons.
  
  

Software

• The computer with the NIC, the router and the modem may all have software that comes with a product that needs to be installed so that the hardware can be set up. The computer with the NIC will most likely already be network ready and as soon as the router and modem are set up, it will start the software on the computer with the NIC so that a connection to the network can be established.
  
  

Summary

• To create a network in a small office or at home we need a computer with an NIC, a hub/router and a modem. If the NIC and the router are Wi-Fi capable, then you can set up a network without cables except for the cable between the router and the modem. The computer with the NIC will recognize that the network is available and allow you to connect whether via cables or Wi-Fi. A computer network is an interconnected network of computers. The Internet, in simple terms is a network of networks that allows a computer with an NIC to connect to another computer with an NIC. You can use the Internet without knowing how it all works together, but now that you know about networks you can understand what is happening when you type in a URL, hit enter and your computer shows you a web page.