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1.1 root 1: .\" Copyright (c) 1983 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)tcp.4p 6.2 (Berkeley) 5/16/86
6: .\"
7: .TH TCP 4P "May 16, 1986"
8: .UC 5
9: .SH NAME
10: tcp \- Internet Transmission Control Protocol
11: .SH SYNOPSIS
12: .B #include <sys/socket.h>
13: .br
14: .B #include <netinet/in.h>
15: .PP
16: .B s = socket(AF_INET, SOCK_STREAM, 0);
17: .SH DESCRIPTION
18: The TCP protocol provides reliable, flow-controlled, two-way
19: transmission of data. It is a byte-stream protocol used to
20: support the SOCK_STREAM abstraction. TCP uses the standard
21: Internet address format and, in addition, provides a per-host
22: collection of \*(lqport addresses\*(rq. Thus, each address is composed
23: of an Internet address specifying the host and network, with
24: a specific TCP port on the host identifying the peer entity.
25: .PP
26: Sockets utilizing the tcp protocol are either \*(lqactive\*(rq or
27: \*(lqpassive\*(rq. Active sockets initiate connections to passive
28: sockets. By default TCP sockets are created active; to create a
29: passive socket the
30: .IR listen (2)
31: system call must be used
32: after binding the socket with the
33: .IR bind (2)
34: system call. Only
35: passive sockets may use the
36: .IR accept (2)
37: call to accept incoming connections. Only active sockets may
38: use the
39: .IR connect (2)
40: call to initiate connections.
41: .PP
42: Passive sockets may \*(lqunderspecify\*(rq their location to match
43: incoming connection requests from multiple networks. This
44: technique, termed \*(lqwildcard addressing\*(rq, allows a single
45: server to provide service to clients on multiple networks.
46: To create a socket which listens on all networks, the Internet
47: address INADDR_ANY
48: must be bound. The TCP port may still be specified
49: at this time; if the port is not specified the system will assign one.
50: Once a connection has been established the socket's address is
51: fixed by the peer entity's location. The address assigned the
52: socket is the address associated with the network interface
53: through which packets are being transmitted and received. Normally
54: this address corresponds to the peer entity's network.
55: .PP
56: TCP supports one socket option which is set with
57: .IR setsockopt (2)
58: and tested with
59: .IR getsockopt (2).
60: Under most circumstances, TCP sends data when it is presented;
61: when outstanding data has not yet been acknowledged, it gathers
62: small amounts of output to be sent in a single packet once
63: an acknowledgement is received.
64: For a small number of clients, such as window systems
65: that send a stream of mouse events which receive no replies,
66: this packetization may cause significant delays.
67: Therefore, TCP provides a boolean option, TCP_NODELAY (from
68: .IR <netinet/tcp.h> ,
69: to defeat this algorithm.
70: The option level for the
71: .I setsockopt
72: call is the protocol number for TCP,
73: available from
74: .IR getprotobyname (3N).
75: .PP
76: Options at the IP transport level may be used with TCP; see
77: .IR ip (4P).
78: Incoming connection requests that are source-routed are noted,
79: and the reverse source route is used in responding.
80: .SH DIAGNOSTICS
81: A socket operation may fail with one of the following errors returned:
82: .TP 20
83: [EISCONN]
84: when trying to establish a connection on a socket which
85: already has one;
86: .TP 20
87: [ENOBUFS]
88: when the system runs out of memory for
89: an internal data structure;
90: .TP 20
91: [ETIMEDOUT]
92: when a connection was dropped
93: due to excessive retransmissions;
94: .TP 20
95: [ECONNRESET]
96: when the remote peer
97: forces the connection to be closed;
98: .TP 20
99: [ECONNREFUSED]
100: when the remote
101: peer actively refuses connection establishment (usually because
102: no process is listening to the port);
103: .TP 20
104: [EADDRINUSE]
105: when an attempt
106: is made to create a socket with a port which has already been
107: allocated;
108: .TP 20
109: [EADDRNOTAVAIL]
110: when an attempt is made to create a
111: socket with a network address for which no network interface
112: exists.
113: .SH SEE ALSO
114: getsockopt(2), socket(2), intro(4N), inet(4F), ip(4P)
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