TCP(4P)TCP(4P)NAMEtcp - Internet Transmission Control Protocol
SYNOPSIS
#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 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.
TCP supports one socket option which is set with setsockopt(2) and
tested with getsockopt(2). 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 (from
<netinet/tcp.h>, to defeat this algorithm. The option level for the
setsockopt call is the protocol number for TCP, available from
getprotobyname(3N).
Options at the IP transport level may be used with TCP; see ip(4P).
Incoming connection requests that are source-routed are noted, and the
reverse source route is used in responding.
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 ALSOgetsockopt(2), socket(2), intro(4N), inet(4F), ip(4P)4.2 Berkeley Distribution May 16, 1986 TCP(4P)
