1

OVERVIEW
Introduction
Rationale
Subject
Grade Level
Time Requirement
Objectives
Content
Inquiry
Design
Ethics
Illinois State Standards
Assumed Prerequisite Knowledge
4
4
4
4
4
4
5
6
MATERIALS 6
LESSONS 7
Activity 1 What Does an Engineer Do? 7
Activity 2 Introduction/vocabulary 16
Activity 3 Pass the Packet 21
Activity 4 Let’s Go to the Conservatory 24
Activity 5 Designing Routes, Part 1 29
Activity 6 Designing Routes, Part 2 31
2

ASSESSMENT
Assessment Matrix
TEACHER RESOURCES
35
36
3

OVERVIEW
Introduction:
“Network Routing Algorithms” is a learning module that provides upper elementary students with the opportunity to understand, simulate, and design network routing. This module meets mathematics, scientific, fine arts, and ethical criteria. Students will use the basic Engineering Design Process that integrates scientific inquiry and the following process skills: problem solving, communication, team work, and decision-making.
Rationale:
Although students are familiar with computers, very few, if any of them understand how information is passed from one computer to another. In order to compete in today’s technological society, students need to become familiar with technological jargon and processes. They also should be exposed to career paths in technology. This module endeavors to meet these goals for 21 st century students.
Subject: Math/Science/Health/Technology
Grade Level: 5 th – 6th Grade
Time Requirement: (6) 40 minute sessions
Objectives:
Content – Students will gain an understanding of network routing and how information is communicated using routing algorithms. This will encompass language arts, math, science, and technology.
Inquiry/Problem Solving
– Students will be guided to a determination of best cost routes through hands on activities.
Design - Students will use the engineering design process to design a network route using the IRV Tool.
Ethics - Students will understand the ethics issues involved in various engineering disciplines and network routing.
4

Illinois Learning Standards
1. A.3b
Analyze the meaning of words and phrases in their context.
1. C.3d
Summarize and make generalizations from content and relate them to the purpose of the material.
5. A.3b
Design a project related to contemporary issues (e.g., real-world math, career development, community service) using multiple sources.
5. B.3a
Choose and analyze information sources for individual, academic and functional purposes.
7. B.3
Select and apply instruments including rulers and protractors and units of measure to the degree of accuracy required.
8. A.3b
Solve problems using linear expressions, equations and inequalities.
8. D.3b Propose and solve problems using proportions, formulas and linear functions.
9. D.3
Compute distances, lengths and measures of angles using proportions, the Pythagorean Theorem and its converse.
10. A.3c
Test the reasonableness of an argument based on data and communicate their findings.
10. B.3
Formulate questions (e.g., relationships between car age and mileage, average incomes and years of schooling), devise and conduct experiments or simulations, gather data, draw conclusions and communicate results to an audience using traditional methods and contemporary technologies.
11. B.3a
Identify an actual design problem and establish criteria for determining the success of a solution.
11. B.3b
Sketch, propose and compare design solutions to the problem considering available materials, tools, cost effectiveness and safety.
11. B.3c
Select the most appropriate design and build a prototype or simulation.
11. B.3d
Test the prototype using available materials, instruments and technology and record the data.
13. B.3c Describe how occupations use scientific and technological knowledge and skills.
13. B.3f Apply classroom-developed criteria to determine the effects of policies on local science and technology issues (e.g., energy consumption, landfills, and water quality).
26. B.3d Visual Arts: Demonstrate knowledge and skills to create 2- and 3dimensional works and time arts (e.g., film, animation, and video) that are realistic, abstract, functional and decorative.
5

Assumed Pre-requisite Knowledge
Mathematics: Basic mathematical operations, measurement, standard units of measurements, solving equations, and comparing numbers
Scientific Inquiry: Make observations, record, organize, and analyze data
Technology: Basic use of calculators and computers
MATERIALS
Calculators
Centimeter rulers
Computers and Internet access
Projector
Assessment Pre/Post Tests
Software: IRV Tool, http://www.cs.princeton.edu/~wayne/cs423/dijkstra/DijkstraApplet.html
Art supplies
Notebooks
Handouts of map of Garfield Park, including Marconi
6

LESSONS
Activity 1: What Does an Engineer Do?
Objectives:
 Identify different types of engineers
 Identify ethics issues in engineering
Materials:
 Pretest
 Engineering assessment notebooks
 notebooks

PowerPoint presentation
Time required: one 40 minute period
State Goals:

5. B.3a
Choose and analyze information sources for individual, academic and functional purposes.

13. B.3c Describe how occupations use scientific and technological knowledge and skills.
Investigation:
Administer Pre Test. Collect. Open discussion by asking students what they know about engineers. Write notes on what they say, if anything, on the board. Show PowerPoint presentation What Does an Engineer Do?
. Students will write the types of engineers and what they do in their notebooks. As you go through the presentation, ask what ethics issues would come up in each field. When finished, administer assessment on engineers.
7

What Does an Engineer Do?
Civil Engineers
• Civil Engineers plan, design, and supervise the construction of buildings, roads, bridges, and other structures.
Architectural Engineers
• Architectural engineers work with architects, focusing on the safety, cost, and construction methods used in constructing a building.
Chemical Engineers
• Chemical Engineers work with petroleum, plastics, and other raw materials. They turn them into products that we use every day including soft drinks, make-up and prescription medicine.
Agricultural Engineers
• Agricultural engineers help farmers by designing machines that harvest crops and experimenting with indoor farming techniques, among many other things.
Biomedical Engineers
• Biomedical engineers work with doctors and biologists to develop medical instruments, artificial organs, and prostheses for those who have lost an arm or a leg.
Aerospace Engineers
• Aerospace engineers design rockets, space telescopes, airplanes and jets, and even help design race cars and golf balls.
Electrical Engineers
• Electrical engineers take energy from various sources and move it to homes, factories and businesses. They design and work with
TV’s, cell phones, and satellite transmissions.
8

Mechanical Engineers
• Mechanical engineers design and develop machines of all sizes.
They also influence products such as doors and shoes.
Some mechanical engineers work in robotics, automotives, and air conditioning.
Environmental Engineers
• Environmental engineers prevent environmental damage and fix existing problems.
They look for new ways to reduce pollution and keep modern society earth friendly.
Mining Engineers
• Mining engineers figure out how to get valuable resources out of the ground.
They also find ways to mine safely without destroying the land and return it to its natural state when the mining is finished.
What kind of engineer will YOU be?
9

Network Routing Algorithms
Pre Test
Name: _____________________________________
Date: _____________________________________
1. Circle the examples of engineering:
2. Name two kinds of engineers. _________________________
_________________________________________________
3. A computer engineer designs a system for sending credit card numbers over the internet, but there is a way that the numbers can be read by other people. Is there an ethics issue here? If so, what is it? ______________________________________
__________________________________________________
__________________________________________________
4. An environmental engineer designs a way to clean up an oil spill. It only kills mosquitoes. Is there an ethics issue here? If so, what is it? _____________________________________
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________________________________________________
________________________________________________
5. How do you compare two numbers? ___________________
________________________________________________
6. Give an example of routing.___________________________
_________________________________________________
7. How are routes determined? __________________________
_________________________________________________
8. What is an algorithm? _______________________________
_________________________________________________
9. What factors are involved in finding a good route? _________
_________________________________________________
10. What happens when part of a route can’t be used? ________
_________________________________________________
11. Explain how routing is used in computers.
__________________________________________________
__________________________________________________
12. Starting at node C draw the best cost path to node E.
What is its cost? _________
What are the costs of other paths from node C to node E?
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Network Routing Algorithms
Pre Test Answers
Name: _____________________________________
Date: _____________________________________
1. Circle the examples of engineering: Correct answers are underlined
2. Name two kinds of engineers. _ answers may vary _________
______________________________________________
3. A computer engineer designs a system for sending credit card numbers over the internet, but there is a way that the numbers can be read by other people. Is there an ethics issue here? If so, what is it? __ yes, students should indicate that piracy of numbers is a crime.
__________________________________
4. An environmental engineer designs a way to clean up an oil spill.
It only kills mosquitoes. Is there an ethics issue here? If so, what is it? yes, students should indicate the balance of nature is upset.
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5. How do you compare two numbers? ________ determine which is larger by subtracting______________________ ______________
6. Give an example of routing. ___ answers will vary ____________
_________________________________________________
7. How are routes determined? __ someone calculates what the best way would be_______________ __________
8. What is an algorithm? __ a step by step way of doing something
_________________________________________________
9. What factors are involved in finding a good route? __ distance, time, cost___________________________________ _______
10. What happens when p art of a route can’t be used?
__ you need to detour ________________________________
11. Explain how routing is used in computers.
____ packets(messages) are sent from one computer to another using routers____________________________________
12. Starting at node C draw the best cost path to node E. C-G-F-E
What is its cost? _11 (3+6+2)________
What are the costs of other paths from node C to node E?
13

Assessment on Engineers
Name ____________________________ Date ______________
Write the letter of the correct engineer on the line that is associated with the given activities.
1. I design machines and can work in robotics and engineering.
_______________________________
2. I experiment with indoor gardening techniques and design machines to help farmers. _________________________
3. I work with others to construct new buildings safely and cost effectively. ____________________________
4. I design rockets, jets, and help design race cars and golf balls.
___________________________________
5. I work to prevent damage to the environment and fix problems in the environment when they occur. ________________________
6. I design prostheses for amputees and develop artificial organs.
______________________________________
7. I design bridges and roads. _________________________
8. I work with raw materials and turn them into everyday products like make-up and medicines. __________________________
9. I design cell phones and work with different energy sources.
______________________________
10. I design good ways to get coal and minerals out of the ground.
___________________________ civil engineer architectural engineer chemical engineer aerospace engineer electrical engineer agricultural engineer environmental engineer biomedical engineer mining engineer mechanical engineer
14

Assessment on Engineers answer sheet
Name ____________________________ Date ______________
Write the letter of the correct engineer on the line that is associated with the given activities.
1. I design machines and can work in robotics and engineering.
_____ mechanical engineer ____________
2. I experiment with indoor gardening techniques and design machines to help farmers. ___ agricultural engineer _______
3. I work with others to construct new buildings safely and cost effectively. _____ architectural engineer ________________
4. I design rockets, jets, and help design race cars and golf balls.
________ aerospace engineer _______________
5. I work to prevent damage to the environment and fix problems in the environment when they occur. __ environmental engineer ____
6. I design prostheses for amputees and develop artificial organs.
_______ biomedical engineer ___________________
7. I design bridges and roads. ____ civil engineer ___________
8. I work with raw materials and turn them into everyday products like make-up and medicines. ___ chemical engineer _________
9. I design cell phones and work with different energy sources.
_____ electrical engineer __________________
10. I design good ways to get coal and minerals out of the ground.
_______ mining engineer ____________________
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Activity 2: Introduction/vocabulary
Objectives:

Understand what a network is
 Understand routing
 Understand and use new vocabulary using context clues
Materials:
 Notebooks
 Vocabulary transparency

Handouts of map of Garfield Park, including Marconi
 Assessment
Time required: one 40 minute period
State Goals:
 1. A.3b
Analyze the meaning of words and phrases in their context.
 1. C.3d
Summarize and make generalizations from content and relate them to the purpose of the material.
Investigation:
Show PowerPoint Presentation Map. Ask students why the truck might be going the way it did. Possible answers may include that it was lost, there was construction, someone told it to go that way, etc. Tell them it is a delivery truck. See if this changes their answers. Ask questions and write key vocabulary on the board as it is said. Work with students to find working definitions of the words to write in their notebooks. When students have written vocabulary and definitions, distribute map handout of West Garfield Park.
Discuss how students could go from school to Garfield Park
Conservatory.
16

Questions for discussion:
What routes could they take? Why?
Which do you think is the shortest route?
Why might you not take it?
Introduce slide 2 and ask why the first route could not be taken.
Is it ethical to go through people’s yards?
Have students draw a route to the conservatory. They may only use streets. Compare routes using slides 3 and 4.
Draw the route in as student describes it. Discuss the merits for each route.
When students have discussed the maps and the vocabulary and have written definitions, administer the Vocabulary
Assessment.
Accommodations/Modifications:
For students with learning disabilities, distribute the map and the assessment before starting the discussion. Students may work in pairs.
network, path, route, road, link, car, packet, time, cost, traffic, algorithm, router
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Name________________________
Date_________________________
Circle the word that best fills in the missing word.
1. Heavy___________ can make your travel go slower. packet traffic router
2. A piece of information that is sent from one computer to another is called a ________________.
network time packet
3. A ___________ is another name for a route.
path cost algorithm
4. A step by step way of doing something is called an
____________.
algorithm traffic router
5. A _________ is the distance from one point to another. cost link packet
6. A set of connections between computers is called a ________. car time network
7. A _____________ is a special computer that tells packets where to go on a network. router cost path
8. The expense of traveling on a route is the _______. traffic algorithm cost
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Name________________________
Date_________________________
Circle the word that best fills in the missing word.
1. Heavy___________ can make your travel go slower. packet traffic router
2. A piece of information that is sent from one computer to another is called a ________________.
network time packet
3. A ___________ is another name for a route.
path cost algorithm
4. A step by step way of doing something is called an
_____________.
algorithm traffic router
5. A _________ is the distance from one point to another. cost link packet
6. A set of connections between computers is called a ________. car time network
7. A _____________ is a special computer that tells packets where to go on a network. router cost path
8. The expense of traveling on a route is the _______. traffic algorithm cost
19

20

Activity 3: Pass the Packet
Objectives:

Understand routing
 Find good routes
Materials:
 envelopes
 sticky notes
 seating chart handout
Time required: one 40 minute period
State Goals:
 10. A.3c
Test the reasonableness of an argument based on data and communicate their findings.

10. B.3
Formulate questions (e.g., relationships between car age and mileage, average incomes and years of schooling), devise and conduct experiments or simulations, gather data, draw conclusions and communicate results to an audience using traditional methods and contemporary technologies.
 11. B.3a
Identify an actual design problem and establish criteria for determining the success of a solution.
Investigation:
Distribute sticky notes and a seating chart to each student.
Numbers should be in order, so that students see a logical pattern. Instruct students to put their number on each of 2-3 sticky notes. Pose the following problem:
“I want an envelope to go from desk 2 to desk 24. Passing only forward, backward, left, or right, you must pass the envelope and place your sticky note on the front, starting from left to
21

right.
” Watch to see that students follow the directions.
When the envelope reaches desk 24, have the student read out the numbers from the sticky notes. Write them on the board so that students can trace the path on their seating charts in pencil.
Ask students if there was a shorter route. Try this a few times so that they can become familiar with routing. Try removing a few students in the middle so that they can see what happens when the route needs to be changed.
To assess, ask students to use their seating chart to plot out a route that has at least five stops. Then have them answer the following questions on notebook paper:
"What is the shortest route between these two points?"
"How do you know this is the shortest one?"
"Is there more than one path that would require the same number of stops? What are they?"
"When you need to reroute around a location, how many extra stops does this usually require?"
"What would be an example of a bad route in this case?"
"What makes it so bad?"
Grade responses using Rubric 1.
Accommodations/Modifications:
For students with learning disabilities, only plot out three stops on the assessment. Work in pairs.
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Rubric 1
Pass the Packet Rubric
CATEGORY
Content
4 3 2 critical, indepth thought specific examples higher level thinking with good examples surface level thought
1 did not address the question
Answering
Questions
Fully
All questions are answered fully
5 or 6 questions answered fully
3 or 4 questions answered fully
Less than 3 questions answered fully
Mathematical
Reasoning
Uses complex and refined mathematical reasoning.
Uses effective mathematical reasoning
Some evidence of mathematical reasoning.
Little evidence of mathematical reasoning.
Conventions Paper is neatly written with no distracting corrections.
Paper is neatly written with 1 or 2 distracting corrections (e.g., dark cross-outs; bumpy white-out, words written over).
The writing is generally readable, but the reader has to exert quite a bit of effort to figure out some of the words.
Many words are unreadable OR there are several distracting corrections.
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Activity 4: Let’s Go to the Conservatory
Objectives:

Find shortest route
 Find fastest route
Materials:
 Map of West Garfield Park handout
 Centimeter rulers
 Assessment rubric
 Routing worksheet
Time required: one 40 minute period
State Goals:
 7. B.3
Select and apply instruments including rulers and protractors and units of measure to the degree of accuracy required.

8. A.3b
Solve problems using linear expressions, equations and inequalities.
Investigation:
Students may work alone or in pairs for this activity.
Distribute maps of West Garfield Park to students. Stop signs and traffic lights will already be marked. Use a transparency on the overhead so that students will see what to do. Direct students to find Marconi on the map. Place a
“1” there. Direct students to find Garfield Park Conservatory on the map. Place a “2” there. Explain to students that traffic lights add one minute to their travel time and stop signs add thirty seconds to their travel time. Each centimeter takes ten seconds. Students will use a colored pencil or marker to draw a line on the map from point 1 to point 2 using only streets. They will measure each “link” on
24

the “path” to the conservatory by measuring the length of each street on their path till they make a turn. Students will then add all their measurements and calculations for stopping to get the total time. When they finish one route, they need to plan another route using different streets.
Students will mark them on the map using a different color.
They will then find the length of the second route and the time it would take by adding their measurements and calculations. At this point they will write an explanation of which path is the shortest, which path is the fastest and how they made that determination.
25

26

L
3
L
4
L
5
L
6
Routing Worksheet
Name: ________________________ Date: ___________
Link
L
1
L
2
Distance Time in
Route 1
In cm seconds
Stop signs
Stop lights
L
7
L
8
Total
Route 2
L
1
L
2
L
3
L
4
L
5
L
6
L
L
7
8
Total
Circle the route with the shortest distance.
Circle the route with the shortest time.
How did you know? ______________________________
______________________________________________
______________________________________________
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Let's Go to the Conservatory
Teacher Name: Mrs. D ésiré
Student Name: ________________________________________
CATEGORY 4 3 2
Shortest/Fastest Shortest
Route route and fastest route is indicated.
Shortest route or fastest route is indicated, but not both.
Many errors in routing.
1
No route is indicated.
Mathematical
Reasoning
Mathematical
Errors
Uses complex and
Uses effective
Some evidence of
Little evidence of refined mathematical mathematical reasoning reasoning. mathematical reasoning. mathematical reasoning.
90-100% of the steps
Almost all
(85-89%) of and solutions the steps
Most (75-
84%) of the steps and
More than
75% of the steps and have no mathematical have no errors. and solutions mathematical solutions have no mathematical solutions have mathematical errors. errors. errors.
Explanation Explanation is detailed and clear.
Explanation is clear.
Explanation is a little difficult to understand,
Explanation is difficult to understand and is but includes critical missing several components. components
OR was not included.
28

Activity 5: Designing Routes, Part 1
Objectives:
 Design a network using software
 Understand routing
Materials:
 Computers, desktops or laptops
 Assessment
 http://www.cs.princeton.edu/~wayne/cs423/dijkstra/D ijkstraApplet.html
 IRV Tool software loaded on computers
Time required: one 40 minute period
State Goals:
 11. B.3a
Identify an actual design problem and establish criteria for determining the success of a solution.
 11. B.3b
Sketch, propose and compare design solutions to the problem considering available materials, tools, cost effectiveness and safety.

11. B.3c
Select the most appropriate design and build a prototype or simulation.
 11. B.3d
Test the prototype using available materials, instruments and technology and record the data.
Investigation:
Using the computer and projector, open http://www.cs.princeton.edu/~wayne/cs423/dijkstra/DijkstraA pplet.html
.
29

This site shows how Dijkstra’s routing algorithm works. Start by clicking on the workspace four or five times. This places nodes on your workspace. Click on node A and draw a line to connect to another node. Connect the modes in this manner until they are connected to each other the way you want. Move the arrows on the links to change the numbers.
You can connect on both directions, if desired. When all nodes are connected to your satisfaction, click on ‘step’ on the right hand side. This will show the path to the first nodes that connect with ‘A’. When you click a second time, the node with the lowest cost turns yellow, and the next connections turn red. The next click shows the next lowest cost link and node turn yellow. This continues until all paths are computed. Discuss what happened.
Clear the first example and start a new one. This time the students should predict which nodes will turn red first. This is done by looking for the lowest cost from node ‘A’. Then, using a calculator if necessary, students will predict which links will turn yellow next. This gives them a preliminary understanding of algorithms.
Open the IRV Tool and let students work with it, similar to the previous activity.
To assess,
30

Activity 6: Designing Routes, Part 2
Objectives:

Design a network
 Design various routes using specific costs
 Create a 2 dimensional work of art
Materials:
 9” x 18” Construction paper
 pencils, markers, crayons
 Assessment rubric
Time required: one 40 minute period
State Goals:
 11. B.3a
Identify an actual design problem and establish criteria for determining the success of a solution.

11. B.3c
Select the most appropriate design and build a prototype or simulation.
 11. B.3d
Test the prototype using available materials, instruments and technology and record the data.

26. B.3d Visual Arts: Demonstrate knowledge and skills to create 2- and 3-dimensional works and time arts (e.g., film, animation, and video) that are realistic, abstract, functional and decorative.
Investigation:
Introduce assignment to students by reviewing what they have learned about network routing and algorithms. Make sure the following points are covered:

Networks connect computers (hosts) with each other.
31


Messages are sent in packets to their destinations.

Routers forward packets in a network.

Routing algorithms choose the path of least cost.

Routers forward the packets using the path of least cost.

Hosts connect to one router, but routers can connect to many other routers.

The connection between two devices is a link.

Each link has a cost associated with it.
Today they will use art materials to design a network on construction paper. Students will design a ‘best cost’ path from a starting host to a destination host, passing through at least four routers. They must design this by placing cost values on each link. They must also make a longer path the best cost path.
Distribute handout “Design Project” to students. Also distribute art paper, colored markers or pencils, rulers and rubric. Go over rules and rubric so that students are aware of what is expected.
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Name ________________________ Date ____________
Design Project
Rules of Design:
 There must be 2 hosts.
 Each host must be connected to only one router.

There must be at least 7 routers.
 There must be cost values on each link that are greater than 2 and less than 11.
 All routers must be connected to at least one other router.

The best cost path must be longer than the shortest path (the path with the least number of routers).
33

Marconi Community Academy
Network Routing Algorithms
Name: ________________________
Date: _________________________
Teacher: Mrs. P. Desire
Title of Work: ___________________
Criteria
Explanation
4
A complete response with a detailed explanation.
3
Good solid response with clear explanation.
2
Explanation is unclear.
1
Misses key points.
Use Of
Visuals
Requirements
Clear diagram or sketch with some detail.
Clear diagram or sketch.
Inappropriate or unclear diagram.
No diagram or sketch.
Mechanics No math errors.
Shows complete
Demonstrated
Knowledge understanding of the questions, mathematical ideas, and processes.
May be some
No major math serious math errors or serious flaws in reasoning.
errors or flaws in reasoning.
Major math errors or serious flaws in reasoning.
Shows substantial
Response shows understanding of the problem, some ideas, and processes.
understanding of the problem.
Response shows a complete lack of understanding for the problem.
Goes beyond the requirements of the problem.
Meets the requirements of the problem.
Hardly meets the requirements of the problem.
Does not meet the requirements of the problem.
Total---->
Teacher Comments :
Points
____
____
____
____
____
__
20
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8
9
10
11
12
Question
Number
1
Pre/Post Test Assessment Matrix
Illinois State
Standards
Content Problem Solving/
Scientific Inquiry
13. B.3c X
2 13. B.3c X
3
4
5
6
7
13. B.3f
13. B.3f
8. D.3b
13. B.3f
13. B.3f
X
X
X
8. A.3b
11. B.3b
10. A.3c
10. B.3
10. B.3
X
X
X
X
X
X
Design Ethics
X
X
X
X
X
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Background information:
All computer information travels through routers. Routers are specialized computers that send your messages and those of every other Internet user speeding to their destinations along thousands of pathways. Routers are the crucial devices that let messages flow between networks.
The router is the only device that sees every message sent by any computer on either of the company's networks.
One of the tools a router uses to decide where a packet should go is a configuration table . A configuration table is a collection of information, including:
 Information on which connections lead to particular groups of addresses
 Priorities for connections to be used
 Rules for handling both routine and special cases of traffic
A router, then, has two separate but related jobs:
 The router ensures that information doesn't go where it's not needed. This is crucial for keeping large volumes of data from clogging the connections of
"innocent bystanders."
 The router makes sure that information does make it to the intended destination.
In performing these two jobs, a router is extremely useful in dealing with two separate computer networks. It joins the two networks, passing information from one to the other and, in some cases, performing translations of various protocols
(sets of rules) between the two networks. It also protects the networks from one another, preventing the traffic on one
36

from unnecessarily spilling over to the other. As the number of networks attached to one another grows, the configuration table for handling traffic among them grows, and the processing power of the router is increased. Regardless of how many networks are attached, though, the basic operation and function of the router remains the same. Since the Internet is one huge network made up of tens of thousands of smaller networks, its use of routers is an absolute necessity.
Routers are one of several types of devices that make up the
"plumbing" of a computer network. Hubs, switches and routers all take signals from computers or networks and pass them along to other computers and networks, but a router is the only one of these devices that examines each bundle of data as it passes and makes a decision about exactly where it should go. To make these decisions, routers must first know about two kinds of information: addresses and network structure .
When a friend mails a birthday card to be delivered to you at your house, he probably uses an address that looks something like this:
Joe Smith
123 Maple Street
Smalltown, FL 45678
The address has several pieces, each of which helps the people in the postal service move the letter along to your house. The ZIP code can speed the process up; but even without the ZIP code, the card will get to your house as long as your friend includes your state, city and street address.
You can think of this address as a logical address because it describes a way someone can get a message to you. This logical address is connected to a physical address that you
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generally only see when you're buying or selling a piece of property. The survey plot of the land and house, with latitude, longitude or section bearings, gives the legal description, or address, of the property.
The first and most basic job of the router is to know where to send information addressed to your computer. Just as the mail handler on the other side of the country knows enough to keep a birthday card coming toward you without knowing where your house is, most of the routers that forward an email message to you don't know your computer's MAC address, but they know enough to keep the message flowing.
Routers are programmed to understand the most common network protocols. That means they know the format of the addresses, how many bytes are in the basic package of data sent out over the network, and how to make sure all the packages reach their destination and get reassembled. For the routers that are part of the Internet's main "backbone," this means looking at, and moving on, millions of information packages every second. And simply moving the package along to its destination isn't all that a router will do. It's just as important, in today's computerized world that they keep the message flowing by the best possible route .
In a modern network, every e-mail message is broken up into small pieces. The pieces are sent individually and reassembled when they're received at their final destination.
Because the individual pieces of information are called packets and each packet can be sent along a different path, like a train going through a set of switches, this kind of network is called a packet-switched network . It means that you don't have to build a dedicated network between you and your friend on the other side of the country. Your e-mail
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flows over any one of thousands of different routes to get from one computer to the other.
Depending on the time of day and day of the week, some parts of the huge public packet-switched network may be busier than others. When this happens, the routers that make up this system will communicate with one another so that traffic not bound for the crowded area can be sent by less congested network routes. This lets the network function at full capacity without excessively burdening already-busy areas.
Above is from howstuffworks.com.
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