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Aim
To design and develop a file transfer program utilising socket based
communications between two networked PCs.  The program should implement
the idle RQ protocol for error control and the BSC for transmission
control to allow a file to be transferred from a server to a client.

Basic Requirements
1.	The text file transfer program written in Stage 1 is to be
extended to include an Idle RQ error scheme.  To implement the Idle RQ
protocol, the file must be transmitted in frames of data with the
necessary fields for frame de-limiters, frame number and a frame check
sequence.  The appropriate control characters according to BSC should
be used for error control (ACK & NAK), frame de-limiters (STX, ETB, ETX
& DLE) and link management functions (EOT).
	The format of the frame should be:

	                1             	      1
128            	    1                1  or 2            bytes

2. The program will build on the program developed in Stage 1.  The
client computer will ask the user to enter the name of the file that is
to be transferred from the server.  The file name should be transmitted
to the server computer which will check to see if the file exists.  If
the file does not exist, the server computer will transmit back a
negative acknowledgment character.  If the file exists, the server will
send back an acknowledgement character.  If the client receives an ACK
character, it will open a new file and then send back a NAK character
to the server indicating that it is ready to receive.  If the client
receives a NAK it will request another file name. The major change here
is that the file contents are transmitted 128 characters at a time in
frames.

3.	The server will send the first 128 characters of the file in a
frame.  When the client computer receives a complete frame, it should
first display the received frame and then check the frame for errors by
looking at the FCS (frame check sequence). The FCS should be calculated
using the technique discussed in lectures.  Alternatively you may use a
CRC method of error checking.  Initially it is best to just place an
integer in this field and leave the implementation of the FCS or CRC
until later.

4.	If there are no errors then an acknowledgment character (ACK)
will be returned to the server computer and the client computer will
store the frame in the file that has just been created.  Upon receipt
of the ACK, the server computer will then transmit the next frame.

5.	Should an error be detected, i.e. the received FCS byte does
not equal the expected FCS byte, the client computer would return a NAK
to the server.  If the server receives a NAK, it will re-transmit the
frame.

6. This process of sending, checking and storing frames should continue
until the complete file has been transmitted and received without
error. Upon receipt of the final acknowledgement, the server computer
should transmit an EOT character to the client to terminate the
connection.

7. The program should implement both the timeout and DLE functionality
as required by the Idle RQ protocol.

Extensions ( Optional )
1.	An interface may be developed for the program that will display
the frame number, frame contents, acknowledgment messages and the FCS
as well as the line control information on both the source and
destination computers.
2.	A configuration option may be developed to allow the user to
alter the baud rate and other line control settings.
3.	A full 16 bit CRC may be developed and implemented instead of
the FCS byte.

Submission
Your submission should consist of the following:
1.	A group report detailing:
	- an introduction
	- the design of the structure of the frame
	- the modular structure of your program
	- a description of the protocols used - idle RQ and BSC
	- the extension options implemented
	- conclusions
	This report should be approximately 4 pages long .
2. A complete printout of the software with comments.
3. A disk with containing the source files

Assessment
Basic file transfer program with FCS, usable interface, appropriately
documented code and use of appropriate BSC characters - 20 marks
Extended interface - 2 marks
Full configuration option - 1 marks
Full 16-bit CRC - 2 marks
Report � 5 marks

NOTE:  Students will be required to demonstrate their programs for
assessment purposes during labs during Weeks 11 & 12




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"Graduate from the university of life and you
will have more wisdom than all PhDs put
together......"


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