TCP(7P)                                                                TCP(7P)



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 left unspecified by
     setting it to 0, 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 two socket options which can be tested with getsockopt(2),
     and manipulated with setsockopt(2).  These options are defined in
     <netinet/tcp.h>.

     TCP_NODELAY
          Under most circumstances, TCP sends data when it is presented; when
          outstanding 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 packetization may cause significant delays.
          Therefore, TCP provides a boolean option, TCP_NODELAY, to defeat
          this algorithm.



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TCP(7P)                                                                TCP(7P)



     TCP_FASTACK
          For certain applications, TCP's default behavior of delaying
          acknowledgements may produce poor performance.  Therefore, it is
          possible to turn delayed acknowledgements off using the TCP_FASTACK
          option.  Use of this option is not generally recommended, as it will
          cause more traffic than is normally desirable.

     N.B. Starting with IRIX 6.5, both TCP_NODELAY and TCP_FASTACK are
     inherited across an accept(2) system call.  In previous IRIX releases
     this was not the case.

     Options at the IP transport level may be used with TCP; see ip(7P).
     Incoming connection requests that are source-routed are noted, and the
     reverse source route is used in responding. The source route may be
     disabled by specifying a zero-length buffer with the IP_OPTIONS option to
     setsockopt (see ip(7P)).

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(3), inet(7F), ip(7P)
     IRIX Network Programming Guide









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