TCP(7P)TCP(7P)NAMEtcp - 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
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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 ALSOgetsockopt(2), socket(2), intro(3), inet(7F), inet6(7F), ip(7P), ip6(7P)
IRIX Network Programming Guide
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