Business Data Communication Networking - bapp05.pdf - po ang - Januszek66

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APPENDIX E

TCP/IP GAME

INTRODUCTION

The purpose of this game is to help you better understand how messages are transmitted

in TCP/IP-based computer networks. Players are organized into five-person teams that

represent different computers in the network. Each person in the team assumes the role of

one layer of software or hardware on that computer (e.g., data link layer) and works with

the others to send messages through the network.

General Rules

1. This is a team game. The class will be broken into a set of five-member teams, with

each team being one computer in the communications network. Each person in the

team will role-play one layer in the computer, either the application layer, the trans-

port layer, the network layer, the data link layer, or the physical layer.

2. Messages will be created by the application layer and passed to the transport layer.

The transport layer will break the message into several smaller messages if neces-

sary and pass them to the network layer. The network layer will address and route

the message and pass the message to the data link layer. The data link layer will for-

mat the message and perform error control (which will involve sending ACKs and

NAKs) and pass the message to the physical layer for transmission. The physical

layer will transmit the message to the physical layer of the destination computer.

Messages are sent using the forms in Figure E.1. Be sure to make lots of copies of

the forms before the game starts.

3. Each layer will have a set of instructions to follow to ensure the messages are sent

and received properly. Follow them carefully. These instructions explain what you

are to write on the message forms. Never write anything on the message form in an

area used by another layer.

4. At some point, someone will make a mistake. If you receive a message that contains

an error, hand it back to the person who gave it to you and explain the error to that

person.

5. And remember, the game is meant to be fun, too!

524

From

Message

Sequence Number

User Data

Final Destination

Next Node

User Data

Source

Destination

Control

Message #

Error

User Data

Forms for the TCP/IP game.

FIGURE E.1

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APPENDIX E

TCP/IP GAME

APPLICATION LAYER

Activities

1. Send messages to other computers

2. Respond to messages from other computers

Tools Needed

• Several blank SMTP forms

• List of messages

• Network map (Figure E.2 shows an example; the instructor will draw one for

your class)

• A blank piece of paper

Sending Outgoing Messages

To send a message, you must:

1. Find a blank SMTP packet.

2. Write the IP address of your computer in the From box.

3. Use the network map to select a computer as the destination for this message. Write

the IP address of the destination computer in the To box. Don’t send all your messages

to one computer; we want to even out the messages. Try to send a few messages to

computers close to you and a few to computers far away.

4. Write the message you wish to send in the Message box. To make the message sim-

ple to understand, please use a hyphen (-) to indicate spaces between words. Select

a message from the list of messages (see below). Try to have at least one hyphen in

1.1.1.1

11-11

2.2.2.2

22-22

3.3.3.3

33-33

4.4.4.4

44-44

5.5.5.5

55-55

6.6.6.6

66-66

7.7.7.7

77-77

8.8.8.8

88-88

9.9.9.9

99-99

Sample network map.

FIGURE E.2

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TRANSPORT LAYER

the message (this is to help the data link layer do error control) or add one at the end

or at the start if you must.

5. Write the message and the name of the computer to which you send the message on

the blank piece of paper. This will help you understand the responses you get to

your messages.

6. Pass the message to the transport layer.

Responding to Incoming Messages

Eventually, you will receive an incoming message from the transport layer that was sent

to you by some other computer asking you a question. To respond to the message, you

will send a message that answers the question. Follow the same steps above to send a

message, but in step 4, write your answer in the Message box. For example, if the mes-

sage you received asked what your favorite color was, you might write red or blue in the

Message box.

List of Messages

Here are a list of messages you can send. Remember to use a hyphen instead of a space

to separate the words. Rather than writing the entire message, you can omit the words

What is your .

• What is your favorite color?

• What is your birthday?

• What is your phone number?

• What are your favorite holidays?

• What is your favorite car?

TRANSPORT LAYER

Activities

1. Accept outgoing SMTP messages from the application layer, packetize them, and

pass them to the network layer.

2. Accept incoming messages from the network layer and, if they are made up of

several packets, assemble the entire SMTP message before passing it to the ap-

plication layer.

Tools Needed

• TCP forms

•Tape

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APPENDIX E

TCP/IP GAME

Accepting Outgoing Messages from the Application Layer

Every few minutes, the application layer will hand you an outgoing message to transmit.

To transmit them, you must:

1. Break the SMTP message into smaller packets. Tear the SMTP packet into two parts

at the dotted line. If there is writing on both parts, then you must send each part as a

separate message. If the second half of the SMTP packet has no writing on it, throw

it away and ignore it.

2. Find one or two blank TCP packets.

3. Fill in the Sequence Number box. If there is only one part of the SMTP packet,

write “1 of 1” in the Sequence Number box. If there are two parts of the SMTP

packet, write “1 of 2” on the first TCP packet and “2 of 2” on the second TCP

packet.

4. Tape the SMTP packet(s) to the TCP packet(s) over the User Data space. (The

packet(s) will be too big to fit, but don’t worry about it.)

5. Pass the TCP + SMTP packet(s) to the network layer.

Accepting Incoming Messages from the Network Layer

Every few minutes, the network layer will hand you an incoming message. To process it,

you must:

• If the message is complete (that is, if the Sequence Number box says “1 of 1”):

1. Take the TCP packet off of the SMTP packet and throw away the TCP packet.

2. Pass the SMTP packet to the application layer.

• If the message is not complete (that is, if the Sequence Number box says “1 of 2”):

1. Wait for the second part of the message to arrive.

2. Take the TCP packets off of both SMTP packets and throw away the TCP packets.

3. Tape the two parts of the SMTP packet back together.

4. Pass the SMTP packet to the application layer.

NETWORK LAYER

Activities

1. Accept messages from the transport layer, route them, and pass them to the data link

layer.

2. Accept messages from the data link layer and, if they are addressed to you, pass

them to the transport layer; if they are not addressed to you, route them and pass

them back to the data link layer.

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