Assignment 1 Computer Networks (CS 456) solution

Description

1 Assignment Objective
The goal of this assignment is to gain experience with both TCP and UDP socket programming in a client‐
server environment (Figure 1). You can use any programming language (e.g., Java, Python, c++) to
design and implement a client program (client) and a server program (server) to communicate
between themselves.
2 Assignment Specifications
2.1 Summary
In this assignment, the client will send requests to the server to reverse strings (taken as a command line
input) over the network using sockets.
This assignment uses a two stage communication process. In the negotiation stage, the client and the
server negotiate on a random port () for later use through a fixed negotiation port
() of the server. Later in the transaction stage, the client connects to the server through the
selected random port for actual data transfer.
Note: The assignment description in the following assumes an implementation in Java.
2.2 Signaling
The signaling in this project is done in two stages as shown in Figure 2.
Stage 1. Negotiation using TCP sockets: In this stage, the client creates a TCP connection with the
server using as the server address and as the negotiation port
on the server (where the server is listening). The client sends a request to get the random port
number on the server where it will send the actual request. For simplicity, the client will send
an integer (e.g., 13) to initiate negotiation.
Once the server gets this request in the negotiation port, it will reply back with a random port
number where it will be listening for the actual request.
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Stage 2. Transaction using UDP sockets: In this stage, the client creates a UDP socket to the server in
and sends the containing a string. On the other side, the server receives the
string and sends the reversed string back to the client. Once received, the client will print out
the reversed string.
2.3 Client Program (client)
You should implement a client program, named client. It will take the command line inputs:
, , and in the given order.
2.4 Server Program (server)
You should also implement a server program, named server. There are no inputs to the server. Note
that, the server must print out the value that it is using so that the information can be used
in the client program.
2.5 Example Execution
 On host1: server
 On host2: client “A man, a plan, a canal—Panama!”
3 Hints
You can use the sample codes of TCP/UDP socket programming in Java from the Module 2 slides.
Below are some points to remember while coding/debugging to avoid trivial problems.
 Use port id greater than 1024, since ports 0‐1023 are already reserved for different purposes
(e.g., HTTP @ 80, SMTP @ 25)
 If there are problems establishing connections, check whether any of the computers running the
server and the client is behind a firewall or not. If yes, allow your programs to communicate by
configuring your firewall software.
 Make sure that the server is running before you run the client.
 Also remember to print the where the server will be listening and make sure that the
client is trying to connect to that same port for negotiation.
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 If both the server and the client are running in the same system, 127.0.0.1 (i.e., localhost) can be
used as the destination host address.
 You can use help on Java network programming from any book or from the Internet, if you
properly refer to the source in your programs. But remember, you cannot share your program
or work with any other student.
4 Procedures
4.2 Hand in Instructions
Submit all your files in a single compressed file (.zip, .tar etc.) using LEARN in dedicated Dropbox.
You must hand in the following files / documents:
 Source code files.
 Makefile: your code must compile and link cleanly by typing “make” or “gmake”.
 README file: this file must contain instructions on how to run your program, which undergrad
machines your program was built and tested on, and what version of make and compilers you
are using.
Your implementation will be tested on the machines available in the undergrad environment.
4.3 Documentation
Since there is no external documentation required for this assignment, you are expected to have a
reasonable amount of internal code documentation (to help the markers read your code).
You will lose marks if your code is unreadable, sloppy, or not inefficient.
4.4 Evaluation
Work on this assignment is to be completed individually.