tcp(4p) 																   tcp(4p)

Name
       tcp - Internet Transmission Control Protocol

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

       s = 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 create a passive socket the system call must be used after binding the socket with the system
       call.  Only passive sockets can use the call to accept incoming connections.  Only active sockets can use the call to initiate connections.

       Passive sockets can ``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 that listens on all
       networks, the Internet address INADDR_ANY must be bound.  The TCP port can 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 that is set with and tested with 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 that receive no replies, this packeti-
       zation may cause significant delays.  Therefore, TCP provides a Boolean option, TCP_NODELAY (from to defeat  this  algorithm.   The  option
       level for the call is the protocol number for TCP, available from

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

       [EISCONN]	   Try to establish a connection on a socket which already has one.

       [ENOBUFS]	   The system runs out of memory for an internal data structure.

       [ETIMEDOUT]	   A connection was dropped due to excessive retransmissions.

       [ECONNRESET]	   The remote peer forces the connection to be closed.

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

       [EADDRINUSE]	   An attempt is made to create a socket with a port that has already been allocated.

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

See Also
       getsockopt(2), socket(2), inet(4f), intro(4n), ip(4p)

																	   tcp(4p)