Abstract:
[n this thesis a file transfer protocol (FTP) software has been designed for transferring the computer files "data" from one location to another, Protocol has been implemented in BASIC language. The package is capable of transferring files successfully from one location to another through modems operating on existing telephone lines or through the null modem. The protocol uses checksum method for error handling. It follows asynchronous coinmul lication mode. It is a reliable protocol which takes care of almost all the requirements of the file transfer. For security purposes both the sender and the receiver must have the same copy of the protocol. It breaks the file in blocks of 132 characters. Out of these 132 characters 128 are of data and remaining four are control characters. The control fields are used for synchronisation and error detection. Each block is checked for errors, and retransmission takes place whenever an error is detected. It is a stop-and-wait protocol and therefore, a little slow, since after every block the transmitter has 10 wait for ACK from the receiver. The package keeps the user informed about the progress of the file transfer and other necessary details, since it is displayed on the monitor of the computer. Initially, the user is prompted about the connection type i.e, what type of connection is required to be established (through null modem or modems). The package dials the given telephone number if the modems are being used then it opens the line and puts the machine in terminal emulation mode i.e, whatever is typed will go through the line, to the connected computer.
After performing the necessary functions protocol then makes the data blocks of the file to be transmitted as per specifications discussed in chapter five of the thesis and then those blocks are transmitted one by one. At the end when the receiver, receives EOT (end of transmission) block from the sender; thereby meaning that there is no more transmission/transfer and thus transmission ends.
