This lesson is the last part of a series of activities that help us understand important ideas about algorithms and the internet. It shows us how routers figure out the best ways to send data across the internet.
In earlier lessons, we learned about shortest path algorithms by looking at a complete graph. But the internet is huge, and it’s impossible for one router to know every possible path. Plus, the internet is always changing. Computers and routers can join or leave the network, connections might be lost, and routers can face security issues.
The big question here is: how do routers find the best paths to send data, and what do they do when a path they know becomes unavailable? This lesson helps us understand an algorithm that routers use to find and update the best paths through the internet.
Not all routers are directly connected to each other. Instead of knowing every path, routers keep track of the “cost” of sending data through their neighboring routers. “Cost” can mean different things like time, speed, reliability, or even money. Usually, it refers to time, which is how long it takes for data to travel from one router to another.
When a router joins a network, it knows the costs of its direct connections. It shares this information with its neighbors. Through this sharing, a router might find out that sending data through a neighbor can reach other routers it couldn’t reach before. The total cost is the cost of the direct connection plus the cost reported by the neighbor to reach the destination.
As time goes on, connection costs might change, or new, better paths might be found. Routers keep updating their tables to have the latest and best information. Each router tracks multiple paths to different destinations by watching the costs with its direct neighbors. The algorithm is simple, but because every router uses it, the process is spread out, allowing all routers on the internet to keep learning.
In this activity, you’ll act as routers, sharing information with others in a small network of eight. Each of you will connect with three classmates to share information. At first, you’ll only know the costs to your direct neighbors. As you exchange information, your routing table will grow, showing the costs of sending data through each neighbor to every other router in the network.
To set up, arrange eight students in a circle around a table and give out worksheets in alphabetical order. Each student will have a sticky note with their router name, visible to others. If the class size isn’t divisible by eight, make groups to ensure each group has as many students as possible.
Read the instructions on the handout, noting your connections to the students on either side and one across the table. You should only talk to these three connected peers. The goal is to find the cheapest routing costs, shown by numbers on the connections.
Go through examples on the worksheet to see how to calculate the cost of a path based on information exchanges. For example, if you learn from another student that the cost to reach a certain router is lower through a neighbor, update your routing table.
After a few rounds of sharing information, groups will draw their understanding of the network on a poster. Trace routes between starting and ending points, discussing the best paths and what might happen if a link fails.
Finally, think about why routers keep track of multiple paths to a destination instead of just the shortest one. Discuss scenarios like what would happen if a critical link between two routers failed. This helps us understand the importance of having backup paths to keep the internet running smoothly.
Imagine you are a router in a network. Pair up with classmates and exchange “routing information” to find the best paths to send data. Use a simple map of connections and costs to simulate how routers communicate and update their tables. This will help you understand the dynamic nature of the internet.
Work in small groups to solve a series of puzzles where you calculate the cost of sending data between different routers. Use the information shared by your “neighboring routers” to determine the most efficient path. This activity will reinforce your understanding of how routers evaluate different paths.
Create a visual map of a network using poster paper and markers. As a group, draw connections between routers and label them with costs. Update your map as you receive new information from your peers, illustrating how routers continuously adapt to changes in the network.
Simulate a scenario where a connection between two routers fails. Discuss and demonstrate how routers find alternative paths to maintain data flow. This activity will help you appreciate the importance of redundancy and multiple paths in network reliability.
Engage in a class discussion about why routers keep track of multiple paths to a destination. Consider scenarios such as network congestion or link failures. This will deepen your understanding of the strategies routers use to ensure efficient and reliable data transmission.
This lesson serves as the final part of a short series of unplugged activities focusing on the key concepts of algorithms and the internet. It connects back to the internet by demonstrating how routers learn the best ways to route traffic.
In previous lessons, students explored shortest path algorithms by analyzing a complete graph. However, the internet is vast, making it impossible for a single router to track every possible path to every location. Additionally, the internet is dynamic; computers and routers join and leave the network, connections can be severed, and routers may experience security breaches.
The central question of this lesson is: how do routers determine the best ways to route traffic, and how do they recover when a known path becomes unavailable? This lesson provides students, acting as individual routers, with insight into an algorithm for calculating and updating the best paths through the internet.
Not all routers on the internet are directly connected. Instead of tracking entire paths, routers maintain information about the cost of routing traffic through neighboring routers. “Cost” can refer to various factors, including time, speed, reliability, and sometimes money. Typically, it represents time, which is a measure of the bit rate between routers and the total time it takes for a packet to travel from one router to another.
When a router joins a network, it initially knows the costs of its direct connections. It can then exchange information about these costs with neighboring routers. Through this exchange, a router may discover that routing packets through a neighbor can lead to other routers that were previously unreachable. The total cost of routing through a neighbor is the cost of the direct connection plus the cost reported by that neighbor to reach the destination.
Over time, connection costs may change, or new, more efficient paths may be identified. Routers continuously update their internal tables to reflect the most current and optimal information. Each router keeps track of multiple paths to various destinations by monitoring the costs associated with its directly connected neighbors. The algorithm each router uses is relatively simple, but because every router is executing it, the process is effectively distributed, allowing all routers on the internet to learn continuously.
In the activity, students will act as routers, exchanging information with other routers in a small network of eight. Each student will be connected to three classmates, with whom they can share information. Initially, they will only know the costs to these directly connected neighbors. As they exchange information about routing costs, each student’s routing table will grow, showing the costs of routing traffic through each neighbor to every other router in the network.
To facilitate this activity, arrange eight students in a circle around a table and distribute worksheets in alphabetical order. Each student will have a sticky note indicating their router designation, which should be visible to others. If the class size isn’t divisible by eight, create groups to ensure each group has as many students as possible.
Students will read the instructions on the handout, noting their connections to the students on either side and one across the table. It’s crucial that they only communicate with these three connected peers. The goal is to find the cheapest routing costs, represented by numbers on the connections.
Walk through examples on the worksheet to illustrate how to calculate the cost of a path based on information exchanges. For instance, if one student learns from another that the cost to reach a certain router is lower through a neighbor, they will update their routing table accordingly.
After a few rounds of information exchange, groups will visualize their understanding of the network by drawing it on a poster. They can trace routes between starting and ending points, discussing the best paths and the implications of potential link failures.
Finally, prompt students to consider why routers keep track of multiple paths to a destination rather than just the shortest one. Discuss scenarios, such as what would happen if a critical link between two routers were to fail.
Routers – Devices that forward data packets between computer networks, directing the data along the most efficient paths. – Example sentence: The school upgraded its routers to ensure faster internet access for all students.
Internet – A global network of interconnected computers that allows users to access and share information worldwide. – Example sentence: Students use the internet to research topics for their science projects.
Algorithms – Step-by-step procedures or formulas for solving problems, often used in computer programming. – Example sentence: Learning to write algorithms is an essential part of understanding how software works.
Data – Information processed or stored by a computer, which can be in the form of text, numbers, images, or other types. – Example sentence: The app collects data on how often users log in and what features they use the most.
Costs – The resources, such as time or money, required to achieve a particular result in computing or networking. – Example sentence: The costs of maintaining a large server can be high, but it’s necessary for supporting many users.
Connections – Links between computers or devices that allow them to communicate and share data. – Example sentence: Strong connections between devices ensure that data is transferred quickly and reliably.
Paths – Routes taken by data packets as they travel across a network from the source to the destination. – Example sentence: Network engineers optimize paths to improve the speed and efficiency of data transmission.
Network – A group of interconnected computers and devices that can communicate with each other and share resources. – Example sentence: The school’s network allows students to access shared printers and files from any computer in the building.
Information – Data that has been processed and organized in a way that is meaningful and useful. – Example sentence: The program analyzes information from various sources to provide accurate weather forecasts.
Sharing – The act of distributing or giving access to resources, data, or information to others. – Example sentence: Cloud services make sharing files with classmates easy and convenient.
