Networking Client-Server Lab Exercise (Projects 1-7)

 

Items Necessary to Download and Install (if not already on the computer)

Java Developer Kit/Java 2 Platform

Java Plugin for Browser

 

Java Files
IPFinder.java
MyLocalIPAddress.java
TCPEchoClient.java
TCPEchoServer.java
UDPEchoClient.java
UDPEchoServer.java
PortScanner.java
GetRemoteTime.java
GetWebPage.java

 

The purpose of this lab is to provide you with some insight into how the client-server architecture actually works. In this lab you will experience a simulated client-server relationship on your local PC. Later, we will move into creating the same client-server relationship among multiple computers. Most of this simulation will take place utilizing java programs that run in the MS-DOS command console. It will not be necessary to understand or learn Java programming to complete this exercise. However, you will need to have an understanding of certain DOS commands and the directory file structures that exist on your computer.

 

Introduction to Java/DOS/File Directories

The way in which you give instructions to a computer and receive feedback from the computer is called a user interface. Java’s user interface may take on many forms. In its simplest state, the user interface is a command line that displays input and output on a blank screen, which is called console mode or stand-alone mode. Java programmers may also view the output of applet programs using a Java tool called the Applet Viewer. The Applet Viewer, which comes with the JDK and Java 2 Platforms, is like a mini-browser that can display the applet on the desktop. It loads and executes applets, but does not contain the menus and buttons that display in a full version of a browser. For all of these projects you will be utilizing the MS-DOS Prompt window.

 

Setting up the Desktop

There are two ways to open up the MS-DOS prompt window.

 

First, you can click on the Start button, Select Programs, Select Accessories, and then Select Command Prompt.

 

Or you can click on the Start button, Select Run, and type in CMD. Either way will produce the following screen:

 

 

Intro to Dos

The following discussion is an abbreviated version from the author Chuck Scharmann, the full version can be found at http://pages.map.com/~freek/dos.html .

 

DOS is an acronym for (D)isk (O)perating (S)ystem. It is the brains of your computer and very powerful. Without it your computer wouldn't work. There are several different types and versions of DOS that basically operate the same way.

 

The command syntax is what you type in to make things work. The computer processes what you type, into special code so that it knows what to do. This code is then sent to the computers interrupter and then performs the tasks that were programmed to do.

 

This code is unreadable to you, unless you can read hexadecimal. If you view this program with an editor you'll see nothing but gibberish. This gibberish, when loaded into a code editor becomes readable to the programmer.

 

Learning the DOS Syntax

There are two types of DOS commands. Those that load in when your system boots, and those that are in a directory called DOS on your hard drive and can be identified with an eight letter filename and a three letter extension. The commands that automatically load when your system boots are called internal commands, and those that you see in the DOS directory called external commands.

 

Most of the commands are external, however there are several that must load when the system boots. The reason is so if your operation system isn't present on the hard drive you will have some control.

 

 

 

 

 

Listed below are the most common DOS commands

 

DIR – this command allows you to view the files and subdirectories in the directory that you specify

CD – this command allows you to change to another drive or directory

FORMAT – this command creates a new root directory on your drive or disk. It will also erase all your files as well.

COPY – this command allows you to make copies of your files or directories

RENAME – this command allows you to change the name or extension of your files

DEL – this command allows you to delete files
UNDELETE – this command allows you to recover files that were deleted (NOTE MAY NOT ALWAYS BE ABLE TO RECOVER YOUR FILES)

 

USING DOS COMMANDS

This can initially appear tricky as there are in some cases multiple option that you can employ, not to mention DOS commands in base syntax forms can be very confusing. See Below

 

COPY [/A|/B] source [/A|/B] [+ source [/A|/B] [+ ...]][destination [/A|/B]] [/V]

/A Indicates an ascii text file.
/B Indicates a binary file.
/V Verifies that new file was written correctly

 

USED IRL

 

COPY oldfile.txt newfile.txt 

 

For purposes of this exercise the two main commands you will use will be DIR and CD.

 

For the CD (change directory command) simply type

CD [drive] [path]

So CD C:\java  will make the java folder the current directory (providing it exists)

CD ..  (with two periods) will move up one folder from the current directory

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DIR [drive:][path][filename] [/P] [/W]

[drive:][path]filename Specifies the drive, directory and the filename for which you want to see a listing.

Switches:

/P Displays one screen of the listing at a time.
/W displays the listing in a wide format.
/A[:] attributes Displays only the names of those directories and files with the attributes you specify.

H

Hidden files

 

-H

Files that are not hidden

S

System Files

 

-S

Files other that system files

D

Directories

 

-D

Files only *no Directories*

A

Files ready for archiving

 

-A

Files that have not changed since the last backup

R

Read only files

 

-R

Files that are not read-only

 

 

/O controls the sort order

 

 

N

Alphabetical order

 

-N

Reverse Alphabetical order

E

Alphabetical order by extension

 

-E

Reverse alphabetical order by extension

D

By date & time, earliest first

 

-D

By date & time, latest first

S

By size, smallest first

 

-S

By size, largest first

G

With directories grouped before files

 

-G

With directories grouped after files

C

By compression ratio, lowest first

 

-C

By compression ratio, highest first

/S Lists every occurrence in the specified directory and all sub directories of the specified filename
/B Lists each directory name or filename one per line
/L Displays unsorted directory names and filenames in lowercase

Examples:

DIR /a Lists all files on drive A
DIR /s/w/o/p alphabetizes with wide format and pauses after each screen.
DIR /s/w/o/p/a:-d Same as above but omits the directory names
DIR > list.dir Sends the directory to a file name called list.dir

 

For more details on options, syntax, or how a command works in DOS you can always type in the word HELP followed by the DOS command.

File Directories

DOS and UNIX both utilize a tree structure for directories. At the top of the tree is your root directory followed by subdirectories or folders. It is very important that you attempt to create some sort of logical ordering sequence for your files and folders as it will ease the locating process in the future. Listed below is an example of a directory structure on your local computer.

 


 


Setting up the Java Development Kit (JDK) in MS-DOS

In order to begin to execute Java Programs in MS-DOS it is important to set the path to where the Java Complier resides. The compiler is a programming language that translates source code that is closer to English, to executable code that is closer to machine language. The files with the .java extension are all source code for running networking programs. The Java compiler that you downloaded actually turns the source code into bytecode that is denoted by .class. Bytecode is the code that can be interpreted on any machine. The name of the interpreter is called the Java Virtual Machine (JVM). To set the path of the java compiler you can type in the following command (if you downloaded it off the website or you are in the lab)

 

Path=c:\jdk1.2.2\bin

 

The next step is to change into the directory that you downloaded all of your .java source code files. If you have not already done so, you should create a folder called ajava in the C directory. Typing cd ajava will change your current directory to where your java programs are, if you do not change your directory the compiler won’t know where or how to find your files.

 

Once this step is completed you are all set to start compiling your programs and creating your client and server relationships. Now, you might be wondering how you compile your programs? Good question—this is easily done by knowing and remembering the command javac. The exact syntax is javac FILENAME.java. If everything is executed correctly you will see a return to a blank C:\ prompt. If there is an error in the code you will see an error message. See below:

 

 

Now we’re ready for some networking!
Utilizing Some Java Networking Programs

Prior to this lab exercise we have discussed fundamental network protocols and techniques. This lab will illustrate how these protocols and techniques can be used and implemented. There are many useful classes written in the JDK that will allow us to communicate with other servers on the internet, or internally on your own server. Again, you will not need to have programming knowledge to write or debug java networking programs save for the previous items covered.

 

Project One – IP FINDER

Download IPFinder.java

This simple program is a tool that can be used to find the IP address of a particular host. The ‘guts’ of this program utilize the DNS server to make a match of URL name to its listed IP address. To run this program, you must first compile the program by typing javac IPFinder.java. Then to actually execute the program type java IPFinder. You will then be prompted to enter in a host name, enter in www.msn.com. Your end result should look like the screen below:

Rerun the program to find the IP addresses for the following hosts:

  1. www.cnn.com
  2. www.espn.com
  3. www.sandiego.edu

 

Make a screen shot of your results (hint hold down ALT & PRINT SCREEN) and paste the picture (CONTROL+V) into a Word Document under the heading Project One Results.

 

Project Two MY LOCAL IPADDRESS

Download and use MyLocalIPAddress.java

Sometimes we would like to retrieve our local IP address. This program will do this for us. Repeat the same steps as in project one to compile and execute the program. Upon completion, take a screen shot and paste into the same word document—except this time placing the picture under Project Two Results.

 

Project Three- Client/Server relationships in TCP/IP

For this project you will need to download the following:

TCPEchoClient.java

TCPEchoServer.java

 

These programs should help reinforce not only the client-server relationship, but the concepts of ports and sockets. Remember that a port is a logical connection to a computer (not physical) and is identified by a number in the range 1 to 65,535. These numbers have no correspondence with the number of physical connections to the computer, of which there may only be one. Ports are implemented upon all computers attached to a network, but we are only concerned with port numbers that refer to server programming running on them. For example port numbers 1 to 1023 are normally set aside for “well-known” services, like port 80 which is typically used by a web server. For each port supplying a service there is a server program waiting for any requests. These programs run in parallel on the host machine (server). Then a client attempts to make a connection with a particular server program, it supplies the port number of the associated server.  The host machine will examine the port number and pass the client’s transmission to the appropriate server program waiting for processing.

 

However, in most applications there are likely to be multiple clients wanting the same service at the same time. A common example of this requirement is that of multiple browsers (potentially 1,000’s) wanting web pages from the same server. The server needs some way of distinguishing between clients and keeping their dialogues separate from each other, hence this is what sockets do. Now keep in mind that a socket is an abstract concept and NOT an element of computer hardware. Basically a socket refers to the two ends of a communication point between client and server.

 

Here is a little bit more on how it works, when a client wishes to make a connection to a server it creates a socket on its end and basically asks the server to do the same. The server then will create a new socket on its end that will be dedicated to communication with that client on the specific port number. This process can be repeated many times over, so that port 80 could have 1,000’s of sockets associated with it.

 

Lets see how this concepts works in our networks. This example will utilize a TCP socket, which is a connection-oriented link. This means that the connection between server and client remains open until it is formally broken by one of the two parties. To run this example you will need to open two MS-DOS command prompt windows. In the first window compile the TCPEchoServer.java program. In the second window you will need to compile the TCPEchoClient.java program. Once both programs have been compiled you will be ready to execute the programs. To execute the connection, first run the server java program (NOTE THAT IF YOU DO NOT RUN THE SERVER PROGRAM FIRST IT WILL CRASH), followed by switching to the second window and running the client program. In this example the server will accept a single line text message from the client and reply with an echo. This dialogue will continue until the client sends the ***CLOSE*** message to the server, to which the server will reply with a confirmation message.

 

Once both programs are running, type three messages in the client window—with the third one being ***CLOSE***. Then rerun the client program and type two more messages with the second message being ***CLOSE***. Upon completion make a screen shot of both server and client windows and paste in your word document under Project Three Results.

 

Project Four – Client/Server Relationships in UDP

For this project you will need to download the following:

UDPEchoClient.java

UDPEchoServer.java

 

We have discussed in class how TCP/IP sends multiple packets and actually makes a connection, whereas UDP (datagram) sends a packet(s) but it does so in an isolated transmission. As such UDP is a connectionless link. As noted in class UDP can provide a faster means of transmitting data, but they can be unreliable. This example will provide you with a more visual representation of the differences between TCPIP and UDP. Repeat the same steps as you did in Project Three, but this time using the two different UDP java programs. Create screen shots of the two windows and paste under the heading Project Four Results. Also under your screen shots provide a brief discussion of the differences between your results in Project Four versus Project Three.

 

Project Five Moving towards GUI’s and obtaining remote information

For this project you will need to download the following

GetRemoteTime.java

 

This project seeks to show how the java network programs can be transported in to more graphical user interfaces. It also illustrates how programs can be created to obtain information from other hosts. This program uses the Daytime protocol to obtain the date and time from port 13 of a user-specified host. However, you should note that it may be difficult to actually obtain this information as many hosts have firewalls that prevent this information. Compile and run this program. Test the following URL’s isec.sandiego.edu, www.sandiego.edu, and 192.195.154.13 (or 192.168.10.4 if in the lab). Create a screen shot of your results and paste them into your word document under Project Five Results.

 

Project Six Checking for Open Ports

For this project you will need to download the following

PortScanner.java

This is an example of a program that checks a range of ports on a specified host and reports those ports that are providing a service. Compile and execute the program. Make a screen shot and paste your results in your word document under Project Six Results.

 

Project Seven Viewing a Simple Browser

For this project you will need to download the following

GetWebPage.java

This program displays the contents of a file at a user-specified URL and actually displays the results similar to a web browser. The only difference is the applet viewer does not contain any of the buttons as in other types of browsers. Also the size of the browser is pre-set so some pages may have both vertical and horizontal scroll bars. Compile and run the program. Type in the URL http://www.sandiego.edu . Create a screen shot and paste your results in your word document under Project Seven Results. Save your word doc as YOUR_LAST_NAME_CS_LAB1_7. Print out and email to Carl.