Packets

Packets

Here is what we know about how the internet works so far:

The internet is a network of devices that are connected by a huge system of hardware, such as submarine internet cables.
Each device that is connected to the internet has a unique IP address. This enables computers to find each other and share data.
Routers determine the path data takes as it travels across networks. There are many different paths data can take as it travels, and routers work to balance a network and avoid traffic jams.

There is just one more thing we need to learn about to understand how data travels through the internet. Let's start with a real world scenario. Let's say that you go to a restaurant to pick up a quick snack and a drink. When you get inside, there is one person ahead of you in line. They begin to order, and you realize that they are ordering lunch for a large group of people. Slightly annoyed, you have to wait for them to complete their entire order before you can put your order in. Finally, they finish their order and you are able to get your snack and drink.

Let's look at the network version of this scenario when two computers are trying to send a message at the same time:

While this works, it is incredibly inefficient. Imagine if you wanted to send an email and it took minutes or even hours to get to its recipient. Luckily there is a solution!

Packets

To solve this problem, data is broken down into packets. A packet is the unit of data that is sent over a network. Let's say that you score tickets to a Taylor Swift concert, and you want to share a picture with your friend. As we know, digital images require thousands and thousands of bits of data! To decrease the amount data being transmitted at one time, your image is first broken down into packets.

Picture of Taylor Swift performing at a concert. She is holding a guitar and holding her hands in heart shape above her head. To the right is an arrow that shows the image broken into four pieces.

Each packet has a header and data. The layout of the header is defined by the Internet Protocol. It includes the IP address of the source and the destination along with some other information to correctly route the data. The packet data is the actual message being sent. In this case, it is the pixel data of your image; however, it could be strings of an email or the content of a webpage.

Image of one packet. One piece of the Taylor Swift image is at the top. Underneath is a table titled Header. Under the header is a to and from field, each with an ipv6 address. Under this is a row with 0s and 1s that represent the data of the file.

Once your data has been broken into packets, it is then sent over the network based on the path determined by the routers. Once all of the packets have arrived, they are pieced back together.

Activity: Command Line Interface

The command line interface is an important tool that network administrators use to gather information about the status of a network. You are able to perform a wide variety of tasks in the command line interface, and in this activity, we will focus on one networking command: ping.

The ping command sends packets to a specific IP address and waits for a response. It measures the round-trip time for the response to return, and then provides a summary of the number of packets sent and the number of packets received.

Use the two simulations below to practice your network administrator skills and explore the ping command! Each simulation is followed by a set of questions, which you will answer in the following free response activity.

Exploration #1: CodeHS

Use this command line interface to ping codehs.com. Press "Run." Then, click into the simulated command line interface and enter this command: ping www.codehs.com. Note: You may need to scroll back down to the CLI after you click into it.

Use these questions to analyze the results:

How many packets did your device send to the target IP address?
How many bytes were in each packet?
How many packets were successfully received?
What does this report reveal about the connection between your device and the target IP address?

Exploration #2: Wikipedia

Use this command line interface to ping wikipedia.org. Press "Run." Then, click into the simulated command line interface and enter this command: ping www.wikipedia.org. Note: You may need to scroll back down to the CLI after you click into it.

Use these questions to analyze the results:

How many packets did your device send to the target IP address?
How many bytes were in each packet?
How many packets were successfully received?
What does this report reveal about the connection between your device and the target IP address?