COMP 4320 AUBURN UNVERSITY. execution of the UDP C/C++ client and UDP C/C++ server programs.

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

Due by the 27th and could use all the help i can get

 

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COMPUTER SCIENCES AND SOFTWARE ENGINEERING

AUBURN UNVERSITY

COMP 4320

Introduction to Computer Networks

Fall 2021

Project 1

Implementation of a Simple Web Service

over the UDP Transport Service

Due in Canvas: 11:55pm Oct 28, 2021

Objective

The purpose of this assignment is to implement a simple Web service over the UDP

transport service. You will write the Web client and server programs that will

communicate over your own computer or the College of Engineering LAN. You will also

learn other important functions in computer networks: (1) implementation of

segmentation and re-assembly of long messages, (2) detecting errors in the received

packets, and (3) emulation of packet errors generation and detection.

Overview

In this project you will implement a simple web client application and a simple web

server application that must be written in C or C++ and execute correctly either in your

own computer(s) or in the COE tux Linux computers. Submission of these client-server

programs written in any other languages will not receive any credit. You must also

implement segmentation and re-assembly functions, an error detection function and a

gremlin function (that can corrupt packets with a specified probability). The overview of

these software components is shown in Figure 1 below. 

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Figure 1. Overview of the Software Components

The Web client initiates the communication by sending an HTTP request to the Web

server. This outgoing HTTP request is not processed by the segmentation and reassembly, error detection or the Gremlin function. The HTTP request is sent through the

transport UDP datagram socket to the Web server.

At the Web server host, the HTTP request is also not processed by those functions at the

Web server host. The Web server will then process the request, e.g. GET command, by

reading the file requested by the Web client. Since the requested file may be large, the

server application will use the segmentation function to partition the file into smaller

segments that will fit into a packet of size allowable by the network. Each segment is

then placed into a 512-byte packet that is allowed by the network. The packet must

contain a header that contains information for error detection and other protocol

information. You may design your own header fields that are of reasonable sizes.

Another field that must be in the header is a sequence number. The packet is then passed

to the error detection function which, at the server (sending process), will compute the

checksum and place the checksum in the header. The packet is finally sent via the UDP

socket to the Web client.

When the packet is received by the Web client host UDP socket, the packet will be

processed by the Gremlin function which may randomly cause errors in some packet.

This will emulate errors that may be generated by the network links and routers. The

packet is then processed by the error detection function that will detect possibility of error

based on the checksum. The packet is then processed by the segmentation and reassembly function that re-assembles all the segments of the file from the packets received

into the original file. The file is then displayed by the Web client application using a

display software or browser.

Descriptions 

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This project introduces you to network programming in your own computer or the

College of Engineering Unix computing environment (tux Linux workstations). In both

cases, all communication between the client and the server must be through the socket

API with real IP addresses, i.e. you cannot use the 127 loopback IP addresses, e.g.

127.0.0.1. Your computer must be connected to the Internet and you must be able to find

the real IP address assigned to your computer. Use that real IP address for creating your

sockets and for all communication between the client and the server.

Use the UDP C/C++ client and server programs presented in class. You need to modify

the programs to ensure that they run correctly in your environments. For example, you

must change the server IP address to the address of the machine in which you will be

running the server program. Also make sure that the correct ports are used.

Now, modify the programs to implement a simple Web service as follows:

1. Modify the client program so that it will send a HTTP request to a simple Web

server to retrieve a data file. The HTTP request message will be of the form:

GET TestFile.html HTTP/1.0

The server will send HTTP response messages in 512-byte packets until the end

of the file (see below). The client will then receive each 512-byte packet in a loop

and writes them into a file sequentially. When it reads a 1-byte message with a

NULL character that indicates the end of the file, it will then close the file. Add

print statements in the client program to indicate that it is sending and receiving

the packets correctly, i.e. print the messages that it sends and receives.

2. Modify the server program so that it responds to clients' HTTP requests. The

server constructs HTTP response messages by putting header lines before the

object itself that is to be sent. The 4 header lines are supposed to be of the form:

HTTP/1.0 200 Document Follows\r\n

Content-Type: text/plain\r\n

Content-Length: xxx\r\n

\r\n

Data

(note: \r is a carriage return, \n is a line feed, xxx is the number of bytes in

the HTML file being sent and data is the requested HTML file)

The server then reads the requested HTML file (an ASCII file, must be at least 50

Kbytes), put them in a buffer and sends the content of the buffer to the Web

client who made the request. The HTTP response messages are sent in 512-byte

packets until the end of the file. At the end of the file, it transmits 1 byte (NULL

character) that indicates the end of the file. It will then close the file.

Add print statements in the server program to indicate that it is receiving and

sending the packets correctly, i.e. print the messages that it receives and sends.

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Gremlin Function

Your program must allow the probability of damaged packets to be input as an argument

when the program is executed. This packet damage probability is passed to your Gremlin

function. You will implement a gremlin function to simulate two possible scenarios in the

transmission line: transmission error that cause packet corruption and correct delivery.

When the receiving process receive each packet, it first pass the packet to a gremlin

function which will randomly determine whether to change (corrupt) some of the bits or

pass the packet as it is to the receiving function. The gremlin function uses a randomnumber generator to determine whether to damage a packet or pass the packet as it is to

the receiving function.

 

If it decides to damage a packet, it will decide on how many and which byte to change.

The probability that a given packet will be damaged, P(d), is entered as an argument of

the client program at runtime. If the probability of damaging a packet is .3, then three out

of every ten packets will be damaged. If the packet is to be damaged, the probability of

changing one byte is .5, the probability of changing two bytes is .3, and the probability of

changing 3 bytes is .2. Every byte in the packet is equally likely to be damaged.

The packet is then passed from the gremlin function to the error detection function that

will check for errors in the packet.

Error Detection Function

The sending process, e.g. the Web Server, will compute the checksum for the packet that

is to be sent. The checksum is calculated by simply summing all the bytes in the packet.

The checksum is then inserted into the checksum header field of the packet.

The receiving process, e.g. the Web client, will then use the same algorithm for

computing the checksum that the sending process used. It will calculate the checksum by

summing all the bytes in the received packet. It then compares the computed checksum

with the checksum received in the packet. If the two checksums match, then it assumes

that there is no error, otherwise there is at least an error in the packet.

When the receiving process detects an error in a packet, it will print out a message

indicating the packet’s sequence number and that there is an error in the packet.

In this project, you must not try to correct for errors in the packet using any network

protocol or scheme; you are required only to indicate that a packet is in error.

Testing

Run the modified UDP C/C++ client and UDP C/C++ server programs, with the

segmentation and re-assembly, error detection and gremlin functions, either on your own

computer or the College of Engineering tux Linux workstations. In both cases, all

communication between the client and the server must be through the socket API with 

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real IP addresses, i.e. you cannot use the 127 loopback IP addresses, e.g. 127.0.0.1.

Your computer must be connected to the Internet and you must be able to find the real IP

address assigned to your computer. Use that real IP address for creating your sockets

and for all communication between the client and the server.

If you use Auburn University’s tux Linux workstations you should use different tux

Linux computers for the client and the server processes. The tux computers that are

available for you use through remote access are tux050-tux065, tux237-tux252.

Altogether, there are 32 tux machines. If you are using the tux computers, send me email

with all your group members and I’ll assign to you open port numbers for the tux

computers so that you can avoid interfering with each other’s message transmission.

In both environments that you use for your execution environment, capture the execution

trace of the programs. In Linux, use the script command to capture the trace of the

execution of the UDP C/C++ client and UDP C/C++ server programs.

Print the content of the input file read by the server program and the output file received

by the client program.

Submission

Submit your source codes, the script of the execution traces of the programs, the file that

was sent by the server and the file that was received by the client. Submit these in Canvas

on or before the due date. 

Attachments:

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