149 lines
9.4 KiB
HTML
149 lines
9.4 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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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Examples: Use multicasting with AF_INET" />
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<meta name="abstract" content="IP multicasting provides the capability for an application to send a single IP datagram that a group of hosts in a network can receive." />
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<meta name="description" content="IP multicasting provides the capability for an application to send a single IP datagram that a group of hosts in a network can receive." />
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<meta name="DC.Relation" scheme="URI" content="x1multicast.htm" />
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<meta name="DC.Relation" scheme="URI" content="x2multicast.htm" />
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<meta name="DC.Relation" scheme="URI" content="cmulticast.htm" />
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<meta name="DC.Relation" scheme="URI" content="x1multicast.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/close.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/socket.htm" />
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<meta name="DC.Relation" scheme="URI" content="../apis/bind.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2001, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2001, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="xmulticast" />
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<meta name="DC.Language" content="en-us" />
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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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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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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>Examples: Use multicasting with AF_INET</title>
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</head>
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<body id="xmulticast"><a name="xmulticast"><!-- --></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">Examples: Use multicasting with AF_INET</h1>
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<div><p>IP multicasting provides the capability for an application to send
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a single IP datagram that a group of hosts in a network can receive. </p>
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<div class="section"><p>The hosts that are in the group might reside on
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a single subnet or on different subnets that connect multicast-capable routers.
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Hosts might join and leave groups at any time. There are no restrictions on
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the location or number of members in a host group. A class D IP address in
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the range 224.0.0.1 to 239.255.255.255 identifies a host group.</p>
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</div>
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<div class="section"><p>An application program can send or receive multicast datagrams
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by using the <span class="apiname">socket()</span> API and connectionless SOCK_DGRAM
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type sockets. Multicasting is a one-to-many transmission method. You cannot
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use connection-oriented sockets of type SOCK_STREAM for multicasting. When
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a socket of type SOCK_DGRAM is created, an application can use the <span class="apiname">setsockopt()</span> function
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to control the multicast characteristics associated with that socket. The <span class="apiname">setsockopt()</span> function
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accepts the following IPPROTO_IP level flags: </p>
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<ul><li>IP_ADD_MEMBERSHIP: Joins the multicast group specified.</li>
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<li>IP_DROP_MEMBERSHIP: Leaves the multicast group specified.</li>
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<li>IP_MULTICAST_IF: Sets the interface over which outgoing multicast datagrams
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are sent.</li>
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<li>IP_MULTICAST_TTL: Sets the Time To Live (TTL) in the IP header for outgoing
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multicast datagrams.</li>
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<li>IP_MULTICAST_LOOP: Specifies whether a copy of an outgoing multicast datagram
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is delivered to the sending host as long as it is a member of the multicast
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group.</li>
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</ul>
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</div>
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<div class="section"><div class="p"> <div class="note"><span class="notetitle">Note:</span> i5/OS™ sockets support IP multicasting for
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the AF_INET address family.</div>
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</div>
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</div>
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<div class="section"><p><br /><img src="rzab6507.gif" alt="This graphic shows the flow of socket calls that are used for IP multicasting with AF_INET address family." /><br /></p>
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</div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Sending multicast datagrams</h4><p>The
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following sequence of the socket calls provides a description of the graphic.
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It also describes the relationship between two applications that send and
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receive multicast datagrams. The first example uses the following sequence
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of function calls:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket descriptor representing
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an endpoint. The statement also identifies that the INET (Internet Protocol)
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address family with the TCP transport (SOCK_DGRAM) is used for this socket.
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This socket sends datagrams to another application.</li>
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<li>The sockaddr_in structure specifies the destination IP address and port
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number. In this example, the address is 225.1.1.1 and the port number is 5555.</li>
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<li>The <span class="apiname">setsockopt()</span> function sets the IP_MULTICAST_LOOP
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socket option so that the sending system does not receive a copy of the multicast
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datagrams it transmits.</li>
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<li>The <span class="apiname">setsockopt()</span> function uses the IP_MULTICAST_IF
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socket option which defines the local interface over which the multicast datagrams
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are sent.</li>
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<li>The <span class="apiname">sendto()</span> function sends multicast datagrams to
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the specified group IP addresses.</li>
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<li>The <span class="apiname">close()</span> function closes any open socket descriptors.</li>
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</ol>
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</div>
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<div class="section"><h4 class="sectiontitle">Socket flow of events: Receive multicast datagrams</h4><p>The
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second example uses the following sequence of function calls:</p>
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<ol><li>The <span class="apiname">socket()</span> function returns a socket descriptor representing
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an endpoint. The statement also identifies that the INET (Internet Protocol)
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address family with the TCP transport (SOCK_DGRAM) is used for this socket.
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This socket sends datagrams to another application.</li>
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<li>The <span class="apiname">setsockopt()</span> function sets the SO_REUSEADDR socket
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option to allow multiple applications to receive datagrams that are destined
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to the same local port number.</li>
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<li>The <span class="apiname">bind()</span> function specifies the local port number.
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In this example, the IP address is specified as INADDR_ANY to receive datagrams
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that are addressed to the multicast group.</li>
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<li>The <span class="apiname">setsockopt()</span> function uses the IP_ADD_MEMBERSHIP
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socket option which joins the multicast group that receives the datagrams.
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When joining a group, specify the class D group address along with the IP
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address of a local interface. The system must call the IP_ADD_MEMBERSHIP socket
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option for each local interface receiving the multicast datagrams. In this
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example, the multicast group (225.1.1.1) is joined on the local 9.5.1.1 interface.
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<div class="note"><span class="notetitle">Note:</span> IP_ADD_MEMBERSHIP option must be called for each local interface over
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which the multicast datagrams are to be received.</div>
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</li>
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<li>The <span class="apiname">read()</span> function reads multicast datagrams that
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are being sent..</li>
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<li>The <span class="apiname">close()</span> function closes any open socket descriptors.</li>
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</ol>
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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="x1multicast.htm">Example: Send multicast datagrams</a></strong><br />
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This example enables a socket to send multicast datagrams.</li>
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<li class="ulchildlink"><strong><a href="x2multicast.htm">Example: Receive multicast datagrams</a></strong><br />
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This example enables a socket to receive multicast datagrams.</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="example.htm" title="These examples provide many sample programs that illustrate the more advanced socket concepts. You can use these sample programs to create your own applications that complete a similar task.">Examples: Socket application designs</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="cmulticast.htm" title="IP multicasting allows an application to send a single IP datagram that a group of hosts in a network can receive.">IP multicasting</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="x1multicast.htm" title="This example enables a socket to send multicast datagrams.">Example: Send multicast datagrams</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/close.htm">close()</a></div>
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<div><a href="../apis/socket.htm">socket()</a></div>
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<div><a href="../apis/bind.htm">bind()</a></div>
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<div><a href="../apis/ssocko.htm">setsockopt</a></div>
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<div><a href="../apis/read.htm">read()</a></div>
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<div><a href="../apis/sendto.htm">sendto()</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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