172 lines
9.5 KiB
HTML
172 lines
9.5 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Socket characteristics" />
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<meta name="abstract" content="Sockets share some common characteristics." />
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<meta name="description" content="Sockets share some common characteristics." />
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<meta name="DC.Relation" scheme="URI" content="protocols.htm" />
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<meta name="DC.Relation" scheme="URI" content="routines.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/unix8.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2001, 2006" />
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<meta name="DC.Identifier" content="characteristics" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Socket characteristics</title>
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</head>
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<body id="characteristics"><a name="characteristics"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Socket characteristics</h1>
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<div><p>Sockets share some common characteristics.</p>
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<ul><li>A socket is represented by an integer. That integer is called a <dfn class="term">socket
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descriptor</dfn>. </li>
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<li>A socket exists as long as the process maintains an open link to the socket.</li>
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<li>You can name a socket and use it to communicate with other sockets in
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a communication domain.</li>
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<li>Sockets perform the communication when the server accepts connections
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from them, or when it exchanges messages with them.</li>
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<li>You can create sockets in pairs (only for sockets in the AF_UNIX address
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family).</li>
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</ul>
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<p>The connection that a socket provides can be connection-oriented or connectionless. <dfn class="term">Connection-oriented</dfn> communication
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implies that a connection is established, and a dialog between the programs
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follows. The program that provides the service (the server program) establishes
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the available socket that is enabled to accept incoming connection requests.
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Optionally, the server can assign a name to the service that it supplies
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which allows clients to identify where to obtain and how to connect to that
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service. The client of the service (the client program) must request the service
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of the server program. The client does this by connecting to the distinct
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name or to the attributes associated with the distinct name that the server
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program has designated. It is similar to dialing a telephone number (an identifier)
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and making a connection with another party that is offering a service (for
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example, a plumber). When the receiver of the call (the server, in this example,
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a plumber) answers the telephone, the connection is established. The plumber
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verifies that you have reached the correct party, and the connection remains
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active as long as both parties require it.</p>
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<p><em>Connectionless</em> communication implies that no connection is established
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over which a dialog or data transfer can take place. Instead, the server program
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designates a name that identifies where to reach it (much like a post office
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box). If you send a letter to a post office box, you cannot be absolutely
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sure the receiver got the letter. You might need to wait for a response to
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your letter. There is no active, real-time connection in which data is exchanged.</p>
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<div class="section"><h4 class="sectiontitle">How socket characteristics are determined</h4><p>When an
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application creates a socket with the <span class="apiname">socket()</span> function,
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it must identify the socket by specifying these parameters:</p>
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<div class="p"> <ul><li>The socket address family determines the format of the
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address structure for the socket. This topic contains examples of each address
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family's address structure.</li>
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<li>The socket type determines the form of communication for
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the socket.</li>
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<li>The socket protocol determines the supported protocols
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that the socket uses.</li>
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</ul>
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</div>
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<p>These parameters or characteristics define the socket application
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and how it interoperates with other socket applications. Depending on the
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address family of a socket, you have different choices for the socket type
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and protocol. The following table shows the corresponding address
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family and its associated socket type and protocols:</p>
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<div class="p">
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. Summary of socket characteristics</caption><thead align="left"><tr><th valign="top" id="d0e68">Address family</th>
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<th valign="top" id="d0e70">Socket type</th>
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<th valign="top" id="d0e72">Socket protocol</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" headers="d0e68 ">AF_UNIX</td>
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<td valign="top" headers="d0e70 ">SOCK_STREAM</td>
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<td valign="top" headers="d0e72 ">N/A</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_DGRAM</td>
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<td valign="top" headers="d0e72 ">N/A</td>
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</tr>
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<tr><td valign="top" headers="d0e68 ">AF_INET</td>
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<td valign="top" headers="d0e70 ">SOCK_STREAM</td>
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<td valign="top" headers="d0e72 ">TCP</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_DGRAM</td>
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<td valign="top" headers="d0e72 ">UDP</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_RAW</td>
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<td valign="top" headers="d0e72 ">IP, ICMP</td>
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</tr>
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<tr><td valign="top" headers="d0e68 ">AF_INET6</td>
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<td valign="top" headers="d0e70 ">SOCK_STREAM </td>
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<td valign="top" headers="d0e72 ">TCP</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_DGRAM </td>
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<td valign="top" headers="d0e72 ">UDP</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_RAW</td>
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<td valign="top" headers="d0e72 ">IP6, ICMP6</td>
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</tr>
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<tr><td valign="top" headers="d0e68 ">AF_UNIX_CCSID</td>
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<td valign="top" headers="d0e70 ">SOCK_STREAM </td>
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<td valign="top" headers="d0e72 ">N/A</td>
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</tr>
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<tr><td valign="top" headers="d0e68 "> </td>
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<td valign="top" headers="d0e70 ">SOCK_DGRAM</td>
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<td valign="top" headers="d0e72 ">N/A</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<p>In addition to these socket characteristics or parameters,
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constant values are defined in network routines and header files that are
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shipped with the QSYSINC library. For descriptions of header files, see the
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individual APIs. Each API lists its appropriate header file in the usage section
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of the API description.</p>
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<p>Socket network routines allow
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socket applications to obtain information from the Domain Name System (DNS),
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host, protocol, service, and network files. </p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="socaddr.htm">Socket address structure</a></strong><br />
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Sockets use the <strong>sockaddr</strong> address structure to pass and to
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receive addresses. This structure does not require the socket API to recognize
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the addressing format.</li>
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<li class="ulchildlink"><strong><a href="address.htm">Socket address family</a></strong><br />
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The address family parameter on a <span class="apiname">socket()</span> determines
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the format of the address structure to use on socket functions.</li>
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<li class="ulchildlink"><strong><a href="type.htm">Socket type</a></strong><br />
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The second parameter on a socket call determines the type of socket. Socket type provides identification of the type and characteristics of the connection that are enabled for transportation of the data from one machine to another or from one process to another.</li>
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<li class="ulchildlink"><strong><a href="protocols.htm">Socket protocols</a></strong><br />
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Protocols provide the network transportation of an application's data from one machine to another (or from one process to another within the same machine).</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzab6soxoverview.htm" title="A socket is a communications connection point (endpoint) that you can name and address in a network.">Socket programming</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="routines.htm" title="Socket network functions allow application programs to obtain information from the host, protocol, service, and network files.">Socket network functions</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../apis/unix8.htm">Socket APIs</a></div>
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</div>
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</div>
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</body>
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</html>
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