tcp(7)							 Miscellaneous Information Manual						    tcp(7)

NAME

       tcp - Internet Transmission Control Protocol (TCP)

SYNOPSIS

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

       The following is the socket call for AF_INET sockets:

       s = socket(AF_INET, SOCK_STREAM, 0);

       The following is the socket call for AF_INET6 sockets: 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.  The TCP protocol 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 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 function must be used after binding the socket with the bind function.  Only pas-
       sive sockets may use the accept function to accept incoming connections.  Only active sockets may use the connect function to initiate con-
       nections.

       Passive sockets may underspecify their location to match incoming connection requests from multiple networks.  This technique, termed wild-
       card addressing, allows a single server to provide service to clients on multiple networks.  To create a socket that listens  on  all  net-
       works,  the  Internet address INADDR_ANY (for AF_INET sockets) or in6addr_any (for AF_INET6 sockets) 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 to 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 the following socket options: 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 num-
       ber of clients, such as window systems that send a stream of mouse events which receive no replies, this gathering of output can cause sig-
       nificant  delays.   Therefore,  TCP  provides a Boolean option, TCP_NODELAY (from the netinet/tcp.h header file), to defeat this algorithm.
       This option takes an int value.	The maximum size of a TCP segment is based on the network MTU for destinations on local networks or  on  a
       default MTU of 576 bytes for destinations on nonlocal networks.	The default behavior can be altered by setting the TCP_MAXSEG option to an
       integer value from 1 to 65,535.	However, TCP will not use a maximum segment size smaller than 32 or larger than  the  local  network  MTU.
       Setting	the TCP_MAXSEG option to a value of zero results in default behavior.  The TCP_MAXSEG option can only be set prior to calling lis-
       ten or connect on the socket.  For passive connections, the TCP_MAXSEG option value is inherited from the listening  socket.   This  option
       takes  an  int  value, with a range of 0 to 65535.  When the SO_KEEPALIVE option is enabled, TCP probes a connection that has been idle for
       some amount of time.  The default value for this idle period is 2 hours.  The TCP_KEEPIDLE option can be used to affect this  value  for  a
       given socket, and specifies the number of seconds of idle time between keepalive probes.  This option takes an int value, with a range of 1
       to N (where N is tcp_keepidle divided by PR_SLOWHZ).  For more information on tcp_keepidle see the information on the inet  subsystem  con-
       figuration  attributes  in  the	System Configuration and Tuning guide.	PR_SLOWHZ is defined in the <sys/protosw.h> header file.  When the
       SO_KEEPALIVE option is enabled, TCP probes a connection that has been idle for some amount of time.  If the remote system does not  respond
       to  a  keepalive probe, TCP retransmits the probe after some amount of time.  The default value for this retransmit interval is 75 seconds.
       The TCP_KEEPINTVL option can be used to affect this value for a given socket, and specifies the number of seconds to wait  before  retrans-
       mitting	a  keepalive  probe.  This option takes an int value, with a range of 1 to N (where N is tcp_keepintvl divided by PR_SLOWHZ).  For
       more information on tcp_keepintvl see the information on the inet subsystem configuration attributes in the System Configuration and Tuning
       guide.  PR_SLOWHZ is defined in the <sys/protosw.h> header file.  When the SO_KEEPALIVE option is enabled, TCP probes a connection that has
       been idle for some amount of time.  If the remote system does not respond to a keepalive probe, TCP retransmits the probe a certain  number
       of  times before a connection is considered to be broken.  The default value for this keepalive probe retransmit limit is 8.  The TCP_KEEP-
       CNT option can be used to affect this value for a given socket, and specifies the maximum number of keepalive  probes  to  be  sent.   This
       option takes an int value, with a range of 1 to tcp_keepcnt.  For more information on tcp_keepcnt see the information on the inet subsystem
       configuration attributes in the System Configuration and Tuning guide.  If a TCP connection cannot be established  within  some	amount	of
       time,  TCP  will  time  out  the  connect attempt.  The default value for this initial connection establishment timeout is 75 seconds.  The
       TCP_KEEPINIT option can be used to affect this initial timeout period for a given socket, and specifies	the  number  of  seconds  to  wait
       before  the  connect  attempt is timed out.  For passive connections, the TCP_KEEPINIT option value is inherited from the listening socket.
       This option takes an int value, with a range of 1 to  N	(where	N  is  tcp_keepinit  divided  by  PR_SLOWHZ).	For  more  information	on
       tcp_keepinit see the information on the inet subsystem configuration attributes in the System Configuration and Tuning guide.  PR_SLOWHZ is
       defined in the <sys/protosw.h> header file.  These options can be retrieved with the getsockopt function and set with the setsockopt  func-
       tion.

       The option level for the setsockopt and getsockopt functions is the protocol number for TCP, available from the getprotobyname function.

       Options	at the IP transport level may be used with TCP; see ip(7).  Incoming connection requests that are source-routed are noted, and the
       reverse source route is used in responding.

ERRORS

       If a socket operation fails, errno may be set to one of the following values: The option_len parameter provided to the setsockopt  or  get-
       sockopt	function is less than sizeof(int) or the option_value parameter provided to the setsockopt function is outside the valid range for
       the option.  The socket to be connected already has a connection.  The system ran out of memory for an internal	data  structure.   Setting
       the  TCP_MAXSEG	option	is  not supported after connect or listen.  A connection was dropped due to excessive retransmissions.	The remote
       peer forced the connection to be closed.  The remote peer actively refuses connection establishment (usually because no process is  listen-
       ing  to	the  port).   An  attempt is made to create a socket with a port which has already been allocated.  An attempt is made to create a
       socket with a network address for which no network interface exists.

RELATED INFORMATION

       Functions: getsockopt(2), socket(2)

       Network Information: netintro(7), inet(7), ip(7) delim off

																	    tcp(7)