Computer Networking Basics: What Is A Computer Network?

Defining a computer network to a computer networking basics class seems an easy job—until you try to do it. The problem is that the definition of a computer network—two or more computers connected to each other—doesn’t account for all of the nuances of real-life networks. Basic computer networking terms seem to get blurred as the years go by.

Computer Networking Basics: The Parts Of A Computer Network

The most basic computer network includes just two computers connected by one wire. (Usually the wire you see is a collection of several smaller wires that function as a unit.) In computer networking basics, we call this a two-host configuration; networks with three or more hosts we call multi-host configurations.

But there are more than just two computers and one wire in a two-host configuration: there are actually four different types of things that need to work together for the network to function correctly:

  1. The Application Layer is the programs that generate and use network traffic. Think of your Web browser, email program, or Dropbox online drive. It’s the most easy to understand of the computer networking basics layers because you see it working everyday.
  2. The Transport Layer is part of Windows that turns the data from the application layer into traffic which another computer can understand and, optionally, keeps track of which packets the other computer has received so it can resend any that were missed.The network layer is similar to postal carrier who picks up and delivers mail to your house. A good postal carrier checks outgoing email for an address and a stamp, while making sure incoming mail gets delivered to the correct address (returning any mail that can’t be delivered).
  3. The Network Layer is another part of Windows that figures out where data needs to be sent. In the case of the two-host configuration used here for computer networking basics, the data is usually all sent to the other computer.The transport layer is similar to the machines or people at the post office that sort outgoing mail by zip code and incoming mail into specific mail routes.
  4. The Link Layer is the network card in your computer. These days the link layer could be a wireless card, a wired ethernet card, or a telephone modem. The link layer turns the transmissions of the network layer into electricity that is sent over the actual wires.The link layer is similar to the truck that transports your mail. The truck is oblivious to what’s inside of it—it just carries it from one point (one end of the wire) to another point (the other end of the wire).

Computer Networking Basics

How The Four Layers In Computer Networking Basics Work Together

Let’s say you want to send an email to the second computer in your two-host configuration. You click send in the application layer and your email program tries to open a Simple Mail Transport Protocol (SMTP) connection to the other computer.

The SMTP connection is addressed to the other computer using its IP address (for example: 192.168.1.2). The transport layer creates a data packet that asks the other computer to open an SMTP port for your computer.

Then the network layer figures out where to send the packet requesting the connection. Many computers these days have both wired and wireless network devices—the network layer figures out that the computer you’re trying to talk to is using the wired network device.

Finally, the link layer turns the packet requesting the connection into electricity that travels down the 8-wire ethernet cord between your two computers.

The other computer receives that packet over its own link layer. It passes the packet on to its network layer which figures out which application is listening for SMTP connections. (If no application is listening, it returns the packet with a note that the address doesn’t exist.)

The network layer then reads the packet and turns it back into data the application understands before passing it on to the application. The application on the other computer then begins to receive the email from your computer.

Of course you’ve sent email before, so you know that this whole complicated series of steps usually takes only fractions of a second.

The Extra Parts Of A Multi-Computer Network In Computer Networking Basics

You almost never see two-computer configurations in real computer networking, whether or not it’s computer networking basics. One reason for this is that most computers these days are connected to the Internet, which makes them part of a network of billions of computers.

But most computers aren’t connected directly to the Internet. They’re connected to a home network with a router. In computer networking basics the setup you will most often see has the following three elements:

  • One or more computers connected via wires or radio to a router.
  • A router that manages two or three different networks: (1) the Internet, (2) the wired home network, and (3) the wireless home network. The router lets computers communicate across networks by adjusting packets at the network layer. See more
  • An optional extra router or switch which extends the home network to additional computers. A switch lets two or more computers communicate by managing data at the link layer. Every modern home router includes a built-in switch—that’s what lets two or more more computers on your home network communicate.

The Internet itself is built out of these same three tools: computers, routers, and switches. It doesn’t matter how big of a network you build, the tools used are the same as the ones you use in computer networking basics.

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