TCP(7P)                                                                TCP(7P)


NAME
     tcp - Internet Transmission Control Protocol

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

     s = socket(AF_INET, SOCK_STREAM, 0);

     s = socket(AF_INET6, 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 formats and, in
     addition, provides a per-host collection of "port addresses".  Thus, each
     address is composed of an IPv4 or IPv6 address specifying the host, 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 socket must be bound to the address INADDR_ANY for IPv4 or
     the address in6addr_any for IPv6.  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.

     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 IPv4 (for AF_INET sockets) or IPv6 (for AF_INET6 sockets)
     network level may be used with TCP; see ip(7P) and ip6(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, for
     IPv4 sockets, by specifying a zero-length buffer with the IP_OPTIONS
     option to setsockopt (see ip(7P)).  For IPv6 sockets, IPV6_PKTOPTIONS is
     used (see ip6(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), inet6(7F), ip(7P), ip6(7P)
     IRIX Network Programming Guide


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