Question

• Consider a simple application-level protocol built on top of UDP that allows a client to retrieve a file from a remote server residing at a well-known address. The client first sends a request with a file name, and the server responds with a sequence of data packets containing different parts of the requested file. To ensure reliability and sequenced delivery, client and server use a stop-and-wait protocol. Ignoring the obvious performance issue, do you see a problem with this protocol? Think carefully about the possibility of processes crashing.

Answer 1

ANSWER:-

• Let consider a simple application-level protocol is build on the top of the UDP that allows a client to retrieve a file from a remote server exist in a well-known address. Here, UDP is User Datagram Protocol.

• The client first sends with a file name and the server responds with a sequence of data packets that contain the requested file.

•To ensure reliability and sequenced delivery,here the client and server are using the stop-and-wait protocol.

Problems occur with this protocol:-

• The given statement makes the possibility for a client system to get the wrong file.
• Let us assume that there are two clients A and B available, and the client A sends a request for a file
• "F1" and then it gets crashed.
• The client B sends same protocol to request some other file "F2";
• In this case, the client B is running on the same machine of where the client A is running and then both files F1 and F2 are using the same IP addresses.
• The client B binds its User Datagram Protocol socket to the same port of the client A was using previously.
• In case the client B's request is lost when the server's reply for the client A arrive.
• And also, client B receives it and assumes that it is a reply for its own request.
• Hence, the client system gets the wrong file, when using this approach.