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<h1 class="topictitle1">Communications in the QFileSvr.400 file system</h1>
<div><p><span>The QFileSvr.400 file system communicates
in the following ways.</span></p>
<div class="section"><ul><li>TCP connections with the file server on a target server can be established
only if the QSERVER subsystem on the target server is active.</li>
<li>SNA LU 6.2 connections are attempted only if there is a locally controlled
session that is not in use (for example, a session specifically established
for use by the LU 6.2 connection). When establishing LU 6.2 connections,
the QFileSvr.400 file system uses a mode of BLANK. On the target system, a
job named QPWFSERV is submitted to the QSERVER subsystem. The user profile
of this job is defined by the communications entry for the BLANK mode. For
more information about LU 6.2 communications, see <a href="../books/sc415443.pdf" target="_blank">APPC Programming</a> <img src="wbpdf.gif" alt="Link to PDF" />.
</li>
<li>File server requests that use TCP as the communications protocol are performed
within the context of the job that is issuing the request. File server requests
that use SNA as the communications protocol are performed by the <span class="keyword">i5/OS™</span> system job Q400FILSVR.</li>
<li>If a connection is not yet established with the target server,
the QFileSvr.400 file system assumes that the first-level directory represents
a TCP/IP host name. The QFileSvr.400 file system goes through the following
steps to establish a connection with the target server: <ol><li>Resolve the remote location name to an IP address.</li>
<li>Connect to the host server's server mapper on well-known port 449 using
the resolved IP address. Then send a query to the server mapper for the service
name <span class="q">"as-file."</span> One of the following occurs as result of the query: <ul><li>If <span class="q">"as-file"</span> is in the service table on the target server, the server
mapper returns the port on which the <span class="keyword">i5/OS</span> file
server daemon is listening.</li>
<li>If the server mapper is not active on the target server, the default port
number for <span class="q">"as-file"</span> (8473) is used.</li>
</ul>
<p>The QFileSvr.400 file system then tries to establish a TCP connection
with the <span class="keyword">i5/OS</span> file server
daemon on the target server. When the connection is established, QFileSvr.400
exchanges requests and replies with the file server. Within the QSERVER subsystem,
the QPWFSERVSO prestart requests take control of the connection. Each prestart
job runs under its own user profile.</p>
</li>
<li>If the remote location name is not resolved to an IP address, the first-level
directory is assumed to be an SNA LU 6.2 name. Therefore, an attempt is made
to establish an APPC connection with the <span class="keyword">i5/OS</span> file
server.</li>
</ol>
</li>
<li>The QFileSvr.400 file system periodically (every 2 hours) checks to determine
if there are any connections that are not being used (for example, no opened
files associated with the connection) and those connections had no activity
during a 2-hour period. If such a connection is found, the connection is ended.</li>
<li>The QFileSvr.400 file system cannot detect loops. The following path name
is an example of a loop: <pre> /QFileSvr.400/Remote2/QFileSvr.400/Remote1/QFileSvr.400/Remote2/...</pre>
<p>where <samp class="codeph">Remote1</samp> is the local system. When the path name that contains a loop is specified,
the QFileSvr.400 file system returns an error after a brief period of time.
The error indicates that a time-out has occurred.</p>
<p>The QFileSvr.400
file system will use an existing free session when communicating over SNA.
It is necessary to start the mode and establish a session for the QFileSvr.400
to successfully connect to the remote communications system.</p>
</li>
</ul>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaaxrfsfs.htm" title="The QFileSvr.400 file system provides transparent access to other file systems that reside on remote iSeries servers. It is accessed through a hierarchical directory structure.">i5/OS file server file system (QFileSvr.400)</a></div>
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