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OpenDarwin 7.2.1 - man page for tcp (opendarwin section 4)

TCP(4)				   BSD Kernel Interfaces Manual 			   TCP(4)

NAME
     tcp -- Internet Transmission Control Protocol

SYNOPSIS
     #include <sys/socket.h>
     #include <netinet/in.h>

     int
     socket(AF_INET, SOCK_STREAM, 0);

DESCRIPTION
     The TCP protocol provides reliable, flow-controlled, two-way transmission of data.  It is a
     byte-stream protocol used to support the SOCK_STREAM abstraction.	TCP uses the standard
     Internet address format and, in addition, provides a per-host collection of ``port
     addresses''.  Thus, each address is composed of an Internet address specifying the host and
     network, with a specific TCP port on the host identifying the peer entity.

     Sockets utilizing the tcp protocol are either ``active'' or ``passive''.  Active sockets
     initiate connections to passive sockets.  By default TCP sockets are created active; to cre-
     ate a passive socket the listen(2) system call must be used after binding the socket with
     the bind(2) system call.  Only passive sockets may use the accept(2) call to accept incoming
     connections.  Only active sockets may use the connect(2) call to initiate connections.

     Passive sockets may ``underspecify'' their location to match incoming connection requests
     from multiple networks.  This technique, termed ``wildcard addressing'', allows a single
     server to provide service to clients on multiple networks.  To create a socket which listens
     on all networks, the Internet address INADDR_ANY must be bound.  The TCP port may still be
     specified at this time; if the port is not specified the system will assign one.  Once a
     connection has been established the socket's address is fixed by the peer entity's location.
     The address assigned the socket is the address associated with the network interface through
     which packets are being transmitted and received.	Normally this address corresponds to the
     peer entity's network.

     TCP supports one socket option which is set with setsockopt(2) and tested with
     getsockopt(2).  Under most circumstances, TCP sends data when it is presented; when out-
     standing data has not yet been acknowledged, it gathers small amounts of output to be sent
     in a single packet once an acknowledgement is received.  For a small number of clients, such
     as window systems that send a stream of mouse events which receive no replies, this packeti-
     zation may cause significant delays.  Therefore, TCP provides a boolean option, TCP_NODELAY
     (from <netinet/tcp.h>, to defeat this algorithm.  The option level for the setsockopt call
     is the protocol number for TCP, available from getprotobyname(3).

     Options at the IP transport level may be used with TCP; see ip(4).  Incoming connection
     requests that are source-routed are noted, and the reverse source route is used in respond-
     ing.

DIAGNOSTICS
     A socket operation may fail with one of the following errors returned:

     [EISCONN]	      when trying to establish a connection on a socket which already has one;

     [ENOBUFS]	      when the system runs out of memory for an internal data structure;

     [ETIMEDOUT]      when a connection was dropped due to excessive retransmissions;

     [ECONNRESET]     when the remote peer forces the connection to be closed;

     [ECONNREFUSED]   when the remote peer actively refuses connection establishment (usually
		      because no process is listening to the port);

     [EADDRINUSE]     when an attempt is made to create a socket with a port which has already
		      been allocated;

     [EADDRNOTAVAIL]  when an attempt is made to create a socket with a network address for which
		      no network interface exists.

SEE ALSO
     getsockopt(2), socket(2), intro(4), inet(4), ip(4)

HISTORY
     The tcp protocol stack appeared in 4.2BSD.

4.2 Berkeley Distribution		   June 5, 1993 		4.2 Berkeley Distribution


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