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<h1 class="topictitle1">Example: Use the basic concepts of DDM in an APPN network</h1>
<div><p>The Advanced
Peer-to-Peer Networking<sup>®</sup> (APPN) support of an <span class="keyword">iSeries™ server</span> can
be used to allow DDM access to systems not directly connected to the local
server.</p>
<div class="example"> <div class="fignone" id="rbae5xappn1__rbae5appn1"><a name="rbae5xappn1__rbae5appn1"><!-- --></a><span class="figcap">Figure 1. Use DDM in an APPN
network</span><br /><div class="imageleft"><img src="rsll116.gif" alt="This figure is described in the text of this section." /></div><br /></div>
</div>
<div class="section"><p>Figure 1 in <a href="rbae5dirrel1.htm#rbae5dirrel1">Example: Use the basic concepts of DDM in an APPC network</a> shows
a program on the Chicago server accessing a file on the New York server. Although
the servers are shown as directly connected, the same DDM concepts apply if
the network is configured as shown in the preceding figure. When the DDM file
CUST021 in the figure is opened on the Chicago server, the APPN support finds
the remote location named NEWYORK, determines the optimal path through the
network, and establishes a DDM conversation with that location. Although there
might be several other servers (network nodes) forwarding the data between
CHICAGO and NEWYORK, the source DDM and target DDM function as if there were
a direct connection between these two servers.</p>
</div>
<div class="section"><p>If the file CUSTMAST were moved from NEWYORK to some other server
in the network (for example, DALLAS), then in this example, the DDM file at
CHICAGO needs to be changed. The remote location name would be changed from
NEWYORK to DALLAS. If a large number of servers in the network refer to the
file CUSTMAST, then movement of the file results in a change to the DDM file
at each of these servers. By using the <span class="keyword">iSeries</span> capability
to have multiple local location names, maintenance of these files is reduced.</p>
</div>
<div class="section"><p>In the preceding figure, the server NEWYORK can be given two local
location names, NEWYORK and FILELOC. The DDM file at CHICAGO uses FILELOC
as the remote location name. When access to file CUSTMAST is required, APPN
finds the location FILELOC in the system named NEWYORK, and the DDM conversation
is established as before.</p>
</div>
<div class="section"><p>If the file CUSTMAST is now moved from NEWYORK to DALLAS, the
user at NEWYORK deletes the local location FILELOC from his server, and it
is added to the server at DALLAS. This is done by using the APPN local location
list. When the program in CHICAGO now attempts to access the file CUSTMAST,
the APPN support finds the remote location FILELOC at the server in Dallas,
and the DDM conversation is established to that server. The movement of CUSTMAST
did not result in a change to the DDM file at CHICAGO.</p>
</div>
<div class="section"><p>This example shows the concept of multiple local locations and
how reduced maintenance results when files are moved from one server to another.
The example is not intended to suggest that a unique location name should
be used for every file accessed through DDM. The decision of which files should
be associated with separate local locations should be based on such factors
as the movement of these files and the number of remote servers accessing
these files.</p>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbae5partfile.htm" title="A system object with type *FILE exists on the source server to identify a remote file. It combines the characteristics of a device file and a database file. As a device file, the DDM file refers to a remote location name, local location name, device name, mode, and a remote network ID to identify a remote server as the target server. The DDM file appears to the application program as a database file and serves as the access device between a source server program and a remote file.">Parts of DDM: DDM file</a></div>
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