Sockets Exercise:
-----------------

Change the files that were used in class in order to do the following:

1. all socket connections should happen at port 5503

2. when running the client/server application, we needed to use the IP
   address of the server, to be able to connect to it. Rewrite some parts of
   the application to be able to access the server by hostname.
   For example, instead of running:
   tcpechoclient 18.58.0.236
   you will run:
   tcpechoclient list.mit.edu

   For that part of the exercise, you may want to use gethostbyname() instead 
   of gethostbyaddr()
   Remember that you only need to pass the server name as argument for
   gethostbyname()

3. our initial client/server application uses TCP as its transport layer. We
   would like to change that in order to have UDP running instead.
   Let's explore what we need to change in order to achieve that:
   A. Remember that you have to use SOCK_DGRAM instead of SOCK_STREAM
   B. UDP is a much smaller protocol than TCP. It is connectionless, so 
      there is no need to connect/listen/accept. Delete or comment out all 
      the code that was used for those functions.
   D. We will not need any of the lines from:
      newsockfd = accept ....
      all the way to the line before:
      while (read(...)
      Also, since we do not use newsockfd in this case, reading and writing
      should happen at the sockfd socket, so change the reading/writing/closing
      to take sockfd instead.
      No need for the exit(EXIT_SUCCESS) either.
   C. Since we don't open a connection to a certain address/port, we need to 
      send the server address everytime we send packets of data. So, we cannot
      use read/write, that do not have functionality for client and server
      addresses. So, let's change read() and write() to recvfrom() and 
      sendto() respectively. The functions are as follows:

      sendto(sockfd, &outbuffer, 1, 0,  &serveraddr, sizeof(serveraddr))
      instead of:
      write(sockfd, &outbuffer, 1)

      and:
      recvfrom(sockfd, &inbuffer, 1, 0, &serveraddr, &serveraddrlength)
      instead of:
      read(sockfd, &inbuffer, 1)

      P.S: You will need to declare:
           serveraddrlength = sizeof(serveraddr);
           before using it in the client program, just like it is used in
           the server program

   Write 2-3 lines about the main differences between UDP and TCP as comments
   in your code
   To do that, put the text that you write between 
   /* text goes here */

Coding:
-------
For parts 1 and 2, make the changes in one set of files and save the files as:
for client: athena_username_client.c
for server: athena_username_server.c

For part 3, make changes to different copies and name them:
for client: athena_username_udp_client.c
for server: athena_username_udp_server.c

where you replace athena_username by your username


Submission:
-----------
submit all your code by email attachment. 

Help:
-----
Send email to: richard@list.mit.edu