HP-UX Reference (11i v2 07/12) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

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TCP(7P) TCP(7P)
NAME
TCP - Internet Transmission Control Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.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 pro-
tocol used to support the SOCK_STREAM socket type. TCP constructs virtual circuits between peer enti-
ties. A virtual circuit consists of remote Internet addresses, remote ports, local Internet addresses and
local ports. IP uses the Internet addresses to direct messages between hosts, and the port numbers to iden-
tify a TCP entity at a particular host.
Sockets using TCP are either active or passive. connect() creates active sockets, which initiate con-
nections to passive sockets (see connect(2)). To create a passive socket, use the listen() system call
after binding the socket with the
bind() system call (see listen(2) and bind(2)). Only passive sockets can
use the accept() call to accept incoming connections (see accept(2)).
Passive sockets can underspecify their location to match incoming connection requests from multiple net-
works. This technique, called wildcard addressing, allows a single server to provide service to clients on
multiple networks. To create a socket that listens on all networks, the Internet address INADDR_ANY
must be bound for AF_INET family and in6addr_any for AF_INET6 family. The TCP port can still be
specified even if wildcard addressing is being used. If the port is specified as zero, the system assigns a
port.
Once accept() has a rendezvous with a connect request, a virtual circuit is established between peer
entities. bind() supplies the local port and local Internet address and accept() gathers the remote
port and remote Internet address from the peer requesting the connection.
The system supports four socket options: TCP_MAXSEG , TCP_NODELAY , TCP_ABORT_THRESHOLD
,
and
TCP_CONN_ABORT_THRESHOLD
(defined in the include file <netinet/tcp.h>).
TCP_MAXSEG option can only be used with getsockopt() , while TCP_NODELAY ,
TCP_ABORT_THRESHOLD
, and TCP_CONN_ABORT_THRESHOLD can be set with setsockopt()
and tested with getsockopt() (see getsockopt(2)). These four options require level to be set to
IPPROTO_TCP in the getsockopt/setsockopt
call.
TCP_MAXSEG (non-boolean option) lets an application to receive the current segment size
of the TCP SOCK_STREAM socket. The current segment size will be
returned in optval.
TCP_NODELAY (boolean option) causes small amounts of output to be sent immediately.
TCP_ABORT_THRESHOLD
(non-boolean option) sets the second threshold timer for the connections
that are in ESTABLISHED state. The option value is the threshold time in
milliseconds.
When it must retransmit packets because a timer has expired, TCP first
compares the total time it has waited against the two thresholds, as
described in RFC 1122, 4.2.3.5. If it has waited longer than the second
threshold (R2), TCP terminates the connection. The default value for this
option is the current value of the ndd tunable parameter
tcp_ip_abort_interval. Refer to ndd(1M) online help for details on
the tcp_ip_abort_interval default value.
TCP_CONN_ABORT_THRESHOLD
(non-boolean option) sets the second threshold timer during connection
establishment. The option value is the threshold time in milliseconds.
This option is the same as TCP_ABORT_THRESHOLD, except that this
value is used during connection establishment. When it must retransmit
the SYN packet because a timer has expired, TCP first compares the total
time it has waited against the two thresholds. If it has waited longer than
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