Developing Communication Concepts through Structured
Examples
Peter A. Cooper
Sam Houston State University
cooper@shsu.edu
1. Introduction
The CS 463 course is the second in a sequence of
three Networks courses (two undergraduate and one
graduate) in the Computer Science program at Sam
Houston State University. The course covers LAN and
WAN technologies including networking topologies,
responsibilities of the Physical, Data Link and Network
layers of the OSI reference model including framing and
error control, IP addressing and routing algorithms. The
course includes basic network management issues and has
a significant interprocess communications component. It is
this last component that is of interest in this paper. CS 463
students are expected to write a sequence of programs
during the course of the semester.
Initially, the examples were developed as individual
responses to concepts and issues that arose out of the
theoretical content of the course, in particular transmission
error control. However a number of problems arose that
dictated a change in the approach to providing the
examples, including:
 Some
recent
developments
including
multithreading, RMI and servlets were not being
addressed.
 Students needed greater guidance than was being
provided with the individual examples and a
tutorial document began to develop.
 System policies toward orphan processes on
university provided equipment made it difficult
for servers to be available all the time.
 Students felt they benefited from being able to run
and control sample versions of the assignments
and examine the interaction between client and
server.
As a result, the scope of the examples widened
and the need to provider a container environment to
manage all the examples became evident. In order to
do so the author had the following tasks
1. To manage multiple processes within a single
application
2. To provide both local servers for the development
stage and remote servers for the testing phase of
each assignment.
3. To provide supporting utilities for general
interprocess communication concepts including
the notion of a communications protocol and an
error detection mechanism.
4. To execute external processes including
application development environments, text
5.
6.
editors, word processors, and the server
applications
To account for platform differences between
target machines
To provide a distribution environment that
allowed students to install and manage the tutorial
application.
2 Assignments
The first block of assignments related to the
development of increasingly sophisticated clients designed
to connect to servers provided by the instructor. In order to
do so the students necessarily had to conform to protocols
employed by those servers.
Assignment 1: String communication. The client
communicates a string to an existing server. The server
stores all the strings received from clients. Clients can
request the strings to be returned.
From the first
assignment students encounter the following concepts
 Socket communication
 Binding streams
 Simple communication protocols
Assignment two extended the first assignment by
communicating java objects rather than strings, thus
allowing for the development of a packet object containing
structured data and methods for managing that data. The
server is once again provided for the students. From
assignment 2, students encounter:
 Communication of structured data
 Need for common definition of payload for
both client and server
 Embedding communication protocols within
the payload, in this case, establishing a
communication type field within the payload
object.
Assignment three examines connectionless services
through the DatagramSocket and Datagram facilities in
Java. The student is required to develop an application for
sending STMP mail information to a proxy server
(designed by the instructor) that validates the mail and
forwards. From Assignment 3 students encounter
 Connectionless communication
 Embedding protocols within the payload, in
this case structure the byte array payload to
identify source and destination addresses
and mail subject line.
Assignment four extends the DatagramSocket to
MulticastSockets. In assignment four, students develop a
multithreaded chat application that allows multiple clients
to communicate through the Multicast socket. Students
encounter:
 Multicast communication
 Multicast group management
Assignment 5 extends the conceptual work on the function
of the Data Link Layer via connectionless communication
techniques to include error management principles
including:
 Missing packets
 Duplicate packets
 Garbled packets
Student implement both stop and wait protocols and
sliding window protocols in assignment five. The results
of the assignment provide data for examining relative
performance levels under a range of conditions.
Assignment six examines the server side of client server
communication. Students develop socket-oriented servers
and the associated slave processes required for reliable and
stable systems. In assignment six, students encounter:
 ServerSockets
 Blocking processes
 Slave processes
3. Student Responses
Student responses to the tutorial have been generally
very favorable. Most comments revolve around four
issues,
 The packaging of the assignments aids students in
managing their work.
 The inclusion of working examples provides a
sense of security and gives the student an
understanding of what the assignment is supposed
to do.
 The templating of the assignments removes a lot
of the ‘noise’ associated with development of
applications in an unfamiliar environment and

language and allows them to concentrate on the
communications aspects of the problem. The
early assignments have the user interface and
much of the event handling structure in place from
the outset.
The focus is then on the
communication issues.
The ability to both control and to interrogate the
servers during the development process gives
them a clearer idea of what is happening, how the
communication-response sequence functions, and,
sometimes, where in the socket instantiation and
binding process, they are going wrong.

6. For the future
It has been said that software becomes obsolete
whenever you stop having to maintain it.
The
communication resources outlined above are a work in
progress. The instructor plans to continue to development
the tutorial. The following list represents the current
priorities:
1. Server reorganization. Currently each server is an
independent process.
Current development
revolves around the design of a single server to
service all assignment clients.
2.
A number of useful content areas have not yet
been developed including:
 Servlets
 Remote Method Invocation
References
[1] Hall, M. (1997). Core Web Programming.
Prentice Hall.
[2] Chan P., Lee R., and Kramer D. The Java Class
Libraries Second Edition vol. 1. Addison Wesley