TCP(4N)                 COMMAND REFERENCE                 TCP(4N)



NAME
     tcp - Internet Transmission Control Protocol

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

     s = socket(AFINET, SOCKSTREAM, 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 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.

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;




Printed 4/6/89                                                  1

TCP(4N)                 COMMAND REFERENCE                 TCP(4N)



     [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.

CAVEATS
     It should be possible to send and receive TCP options.  The
     system always tries to negotiate the maximum TCP segment
     size to be 1024 bytes.  This can result in poor performance
     if an intervening network performs excessive fragmentation.

SEE ALSO
     inet(4n) and intro(4n).




























Printed 4/6/89                                                  2

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