Students learn that large messages sent over the Internet are actually divided into individual packets and explore the challenges this creates. Students begin in a simulation similar to the one in the previous lesson, except long messages will now need to be split into smaller parts -- and these parts may be lost or delivered out of order. They then design their own protocol that addresses these challenges. At the end of the lesson students watch a video and learn and the User Datagram Protocol (UDP) and The Transmission Control Protocol (TCP), two different protocols for sending messages broken into packets.


Students will be able to:


Information on the Internet is not sent all at once, but is instead broken into smaller chunks of data called packets. Each packet is sent through the Internet individually and may actually take different paths or arrive at different times than others. Once they arrive the receiver will use the packets to recreate the original file.

Two protocols used to send data as packets are UDP and TCP. The User Datagram Protocol (UDP) simply sends all the packets. If some arrive out of order or are entirely missing there's no system to fix the errors. The Transmission Control Protocol (TCP) numbers packets before sending them so that the receiver can correctly reorder the packets and request missing packets be resent.

Only one of these two protocols will be used, depending on the situation. TCP takes longer than UDP because of the error-checking done to guarantee every packet was received. TCP is used to send information like emails, images, websites, and more where saving fractions of a second is less important than accuracy. In instances like live-streaming television or online gaming where speed is most important, UDP will be used since it is faster and there's less benefit to correcting errors.

This lesson gives students a hands-on experience with the ideas behind both protocols and helps them understand the implications of splitting large files into packets when sending them online.

Note: UDP is not covered in the video at the end of the lesson.


Warm Up

Prompt: Suppose our school library is moving to a new building on campus and the librarian has asked for your help.

Discussion Goal

This prompt foreshadows the challenge students will see in today's lesson and also the core difference between the two protocols they'll look at, TCP, and UDP. You don't need to cover either of those at this point in the lesson. Some key points to draw out:

Note this is a tight lesson with a significant wrap up. Aim to keep this warm up short and move to the main activity quickly.



Group: Place students into groups of 3-4. Assign each group a number, and then assign each individual student an "IP Address" using the same rules as in the previous lesson. (You may reuse the same numbers or give students new ones.)

Rules: Similar to last lesson, students will use index cards or other available methods to send messages to each other, with the teacher acting as the "router", delivering the messages (packets) to their final destination. Give your students these extra rules to follow during the simulation:

Teaching Tip: Here are a few key ways to simulate the instability of the Internet during this simulation:

Challenge #1: Send a Message

Do This: Have students send a multi-packet message to another classmate. They should aim for roughly 5 - 10 packets to increase the likelihood of some packets dropping or arriving out of order.

Teaching Tip: The goal of the first challenge is to let students see some of the issues that can arise due to packets being dropped, rerouted, or received in the wrong order. Once students have noticed these, you can move on. Most of the activity will be spent in the second half.


Challenge #2: Develop a Protocol

Do This: With their groups or with a partner, have students develop a protocol for reliably sending a message across an unreliable network. In particular, students should try to solve these problems with their protocol:

Teaching Tip

Encouraging Good Protocols: If students are unsure of how to write their protocols, try asking some of these questions:

More Than One Solution: There's lots of ways to solve this problem! Emphasize to students that while their protocol needs to solve the problem, there's not just one right answer and their solution doesn't need to look like their classmates.

Do This: Once students have developed their protocols, give two or three groups a chance to share their solutions with the class, either by describing it out loud or showing it on a projector at the front of the room. As a class discuss some of the shared features in their protocols. If short on time you may just ask students to raise their hands if their protocols included one of the features below.


Wrap Up


Display: Watch The Internet: Packets, Routing, and Reliability - Video

Teaching Tip

Key Video Takeaways: The video includes a lot of information about how packets move through the Internet. The most important points for students to understand are that:

Covering UDP: UDP is not covered in the video and students do not need to understand it in great detail. The depth of explanation in the activity is sufficient to explain the differences between them and why each would be used.

Assessment: Check for Understanding

Question: Which of the following is true regarding the way information is transmitted on the Internet?

Standards Alignment