Types of Networks – LAN, WAN, Intranet, and the OSI Model

What Is A LAN?

Local area networks (LANs) are created to provide networking services to a group of computers that are relatively close to one another. A LAN can serve a single floor in an office building or a classroom in a school. The size of a given LAN can vary from one room to one building or even to a group of buildings, depending on the users’ needs. When using TCP/IP networking, LANs are most commonly set up as a single subnet with a clearly defined mask. LANs can be created based on wired or wireless connections. Today, wireless is most commonly used because of its convenience and ease.

What Is A WAN?

Wide area networks (WANs) span much larger geographical distances than LANs. The largest WAN of all is the Internet, which has a global reach. Multiple LANs often co-exist inside a WAN. Each subnet mask is connected to the WAN through a router or switch. A lot of devices can be used to create a WAN, from satellite dishes and radio towers to regular telephone lines. A WAN can use many different data link layer protocols, which hold the protocols for each LAN.

Internet Vs. Intranet

The Internet is a global “network of networks,” capable of connecting any computer on earth to any other computer. An intranet, by contrast, uses Internet Protocol technology to securely transmit data between computers located on a private network. Intranets use Ethernet, Wi-Fi, browsers and servers, but they are firewalled and not connected to any other network. Intranets are growing in popularity because they cost much less than proprietary protocols on private networks. An example of an intranet is an internal email network such as the ones used by businesses to allow employee communication.

What Is A VPN?

The need to reliably share information securely from multiple remote locations has given rise to virtual private networks (VPNs). A private network of computers is created through the Internet with “virtual” connections. The connections between nodes are virtual because they are secured from the Internet itself and merely pass through it. Thus, virtual private networks are completely secure even though they use the Internet. The VPN acts as a private tunnel through the Internet, safely transporting data between users. VPNs encapsulate data packets; that is, they place one data packet within another, ensuring the internal packet’s safe transport.

Peer-to-peer Vs. Client-server networks

The traditional Internet model is client-server. A client, usually a web browser, requests data from a server, which stores and hosts web pages. The server must authenticate each browser through certificates, even if no secure connection is being used. A peer-to-peer network is wholly different. Each computer stores and shares files and data equally. Peer-to-peer networks became well-known due to the phenomenon of online music piracy. Peer-to-peer networks cost next to nothing to create, but they have no security. The danger from viruses, worms and Trojan horses on a peer-to-peer network is infamous.

The OSI (Open Systems Interconnection) Model

The OSI (Open Systems Interconnection) model is a complex model that implements protocols in seven layers within a given network.  Unlike the types of networks we’ve discussed thus far, OSI is not a type of network.  However, now that we’ve covered a few basic types of networks, it is useful to begin putting the pieces together by examining the OSI model.

The model defines what path data has to travel through to get from one device to another in a network. The layers are divided into two sets: transport and application. The transport set consists of physical, data, network and transport. The application set contains session, presentation and application. The Physical layer defines the characteristics of network hardware such as connections and timing. In Data, a specific Physical protocol is assigned to data. Packet sequencing is also defined. Network figures out how the data will be sent to recipients. Finally, Transport is responsible for flow control, error checking and data recovery.

The seven layers of the OSI model

The Session layer handles all aspects of connecting to the device used by the data recipient. The Presentation layer takes information provided by the seventh and last layer, Application, and makes it intelligible to the lower layers. Lastly, Application interfaces with the operating system and thus the user whenever he chooses to carry out activities on the network.

Satirical OSI Model
Flickr user lumachrome created this humorous interpretation of the OSI model: Olive, Sauce, Lettuce, Cheese, Beans, Guacamole, Rice. Photo credit: Christopher Chen.


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