protocol provides a reliable, flow-controlled, two-way
transmission of data.
It is a byte-stream protocol used to support the
TCP uses the standard
Internet address format and, in addition, provides a per-host
Thus, each address is composed
of an Internet address specifying the host and network, with
port on the host identifying the peer entity.
Sockets utilizing the TCP protocol are either
Active sockets initiate connections to passive
sockets are created active; to create a
passive socket the
system call must be used
after binding the socket with the
Only passive sockets may use the
call to accept incoming connections.
Only active sockets may use the
call to initiate connections.
Passive sockets may
their location to match
incoming connection requests from multiple networks.
This technique, termed
allows a single
server to provide service to clients on multiple networks.
To create a socket which listens on all networks, the Internet
must be bound.
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
Normally this address corresponds to the peer entity's network.
supports several socket options which are set with
and tested with
Under most circumstances,
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.
provides a boolean option,
to defeat this algorithm.
Set the maximum segment size for this connection.
The maximum segment size can only be lowered.
Use selective acknowledgements for this connection.
Use TCP MD5 signatures per RFC 2385.
to be set up, which can be done using
When a listening socket has
set, it accepts connections with MD5 signatures only from sources for which a
is set up.
Connections without MD5 signatures are only accepted from sources for which no
is set up.
The connected socket only has
set if the connection is protected with MD5 signatures.
The option level for the
call is the protocol number for
Options at the
transport level may be used with
Incoming connection requests that are source-routed are noted,
and the reverse source route is used in responding.
A socket operation may fail with one of the following errors returned:
when trying to establish a connection on a socket which
already has one;
when the system runs out of memory for
an internal data structure;
when a connection was dropped
due to excessive retransmissions;
when the remote peer
forces the connection to be closed;
when the remote
peer actively refuses connection establishment (usually because
no process is listening to the port);
when an attempt
is made to create a socket with a port which has already been
when an attempt is made to create a
socket with a network address for which no network interface