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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 | .\" | |
7787ae36 | 5 | .\" @(#)tcp.4 6.2 (Berkeley) %G% |
ded36191 | 6 | .\" |
9205d69a | 7 | .TH TCP 4P "" |
ded36191 KM |
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. | |
7787ae36 MK |
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. | |
ded36191 KM |
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 | |
7787ae36 | 114 | getsockopt(2), socket(2), intro(4N), inet(4F), ip(4P) |