Investigate a Client-Server Message System

Seek out a program (outside of DNS/HTTP) that might use a
client-server model. You may dig into an actual protocol or find a
client-server model in a program. Discuss three messages that make
sense for this client-server pair. What sorts of things does the
client need to send to the server. If your particular program doesn't
have 3, find another client-server pair until you have 3. Your
description of each message should range from two sentences to a
paragraph based on the complexity of the interaction. The entire
assignment should be perhaps a page single spaced.

Here's an example of one message interaction using HTTP as posed by a
student who doesn't actually know the HTTP protocol (unlike you all
who should actually know which of these parameters are required and
not and cannot use HTTP as an example):


GET 

Get is a sample message that must be parsed by a web server when doing
things with a web browser. Web browsers are natural client-server
applications because the browser is the client and it connects to the
web server. In specific, there is only one parameter that is required
by the GET message. And that is which file on the server to grab. So,
when a client makes a TCP connection to a web server, the client will
then issue a GET command along with a filename. The server then finds
the located file and sends a response. There can be many
responses. Some responses might be: "File found, here it is!" or "File
not Found!" or "No permissions for this file."  I've seen some
messages like, "File Moved" when playing with web servers before, but
I don't raelly understand them and would have to investigate HTTP
further to make this make sense with what I've provided here.

[I'll say this again, in reality there are other parameters and other
considerations for HTTP at play here. Some of which this sample
student is seeing, and not understanding and some of which this sample
student completely missed. That's okay. The point, in this assignment,
is to think about application level programming in a client - server
model more so than to get things perfectly right inside an existing
protocol.]