Several Internet socket types are available:
· Datagram
sockets, also known as connectionless sockets, which
use User Datagram Protocol (UDP).
· Stream
sockets, also known as connection-oriented sockets,
which use Transmission Control Protocol (TCP).
The Transmission Control
Protocol (TCP) is connection-oriented and transports a stream of data over a
logical connection established between the sender and the receiver. As a
result, data sent from a sender to a receiver is guaranteed to be received in
the order they were sent.
The Connection-Oriented
Sockets are based on the stream-mode I/O model of the UNIX Operating System –
data is transferred using the concept of a continuous data stream flowing from
a source to a destination. Data is inserted into the stream by a sender process
usually called the server and is extracted from the stream by the
receiver process usually called the client.
The server process establishes a connection socket
and then listens for connection requests from other processes. Connection
requests are accepted one at a time. When the connection request is accepted, a
data socket is created using which the server process can write or read from/to
the data stream. When the communication session between the two processes is
over, the data socket is closed and the server process is free to accept
another connection request. Note that the server process is blocked when it is
listening or waiting for incoming connection requests. This problem could be
alleviated by spawning threads, one for each incoming client connection request
and a thread would then individually handle the particular client.
Program
Flow in the Connection Listener (Server) and Connection Requester (Client)
Processes
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Connection listener(server)
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Connection requester (client)
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Create connection socket and
listen for
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Create data socket and request a
connection
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connection request
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Accept connection
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Get an output stream for writing to
the socket
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Create data socket for reading from or
writing
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Write to stream
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to socket stream
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Get input stream for reading to the
socket
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Get input stream for reading to the
socket
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Read from stream
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Read from stream
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Get an output stream for writing to
the socket
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Close data socket
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Write to stream
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Close data socket
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Close connection socket
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