File is one of the main storing units of information. There is a great need to transfer
file through computer network especially the internet. The model that is used in
Internet is the TCP-IP. The TCP-IP model consists of four layers. The lowest layer is
the host network layer, the second layer is the internet layer (IP handling); while the
third layer is transport layer which contains TCP and UDP. The last layer is the
application layer. This paper is concerned on the User Datagram Protocol (UDP). The
UDP is mainly used to transfer messages. It is asynchronous, connectionless and
unreliable protocol. The UDP is not suited for transferring files because of the error
or loose that could prevent us from reconstruct the original file. In order to overcome
this problem new field and configuration is applied in the application layer for
guarantee file sending and receiving. This field is the Cyclic Redundant Check (CRC)
which is computed for each block of data and all these checks were sent over another
port. At the end of receiving data the receiver checks the check matrix in order to
determine the error and requesting that block from the sender. The proposed protocol
is implemented using the Winsock and Visual Basic programming language