=> well-known port is free to receive requests for additional connections.Client makes requestthrough the well-known port, once the connection is made, server assigns a temporary port to this connection.Solution: use additional ephemeral ports.Server can use only one well-known port.Each connection requires a port and many connections may remain open simultaneously,.A connection is established between server and each client, remains open until the entire stream is processed.Connection oriented concurrent server: the ones that use TCP are normally concurrent,.Connectionless iterative server: the ones that use UDP are iterative, server uses one single port, arriving packets wait in line,.Concurrency in server: An iterative server can process only one request at a time whereas a concurrent server can process many requests at the same time – share its time.Concurrency in client: two or more clients can run at the same time on a machine – current trend, alternatively: one client must start, run, and terminate before another client may start (iterative).A server program is infinite – runs unless a problem occurs.A server program opens its door for incoming requests from clients but never initiates a service unless explicitly requested – Passive open.The client closes the communication channel with an Active close.Request-response may be repeated several times, the process is finite.
A client opens the communication channel using IP address of the remote host and the port address of the specific server program running on the host – Active open.A server program providing service should run all the time, as it does not know when its services will be needed. Generally, a client application program that requests a service should run onlywhen it is needed.Commonly server provides service to any client, not a particular client.
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