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<th colspan="3" align="center">LPRng-HOWTO: 8 Feb 2002
(For LPRng-3.8.6)</th>
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<td width="80%" align="center" valign="bottom">Chapter
11. Printer Communication and Protocols</td>
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<h1 class="SECT1"><a name="AEN5138">11.8. Problems With
Network Print Servers</a></h1>
<p>Most of the Network Print Servers are implemented using
extremely simply software. The following is a list of some
problems and what options the <b class=
"APPLICATION">LPRng</b> software uses to handle them.</p>
<div class="SECT2">
<h2 class="SECT2"><a name="AEN5142">11.8.1. Network Print
Server Not Responding</a></h2>
<p>Only a single TCP/IP connection is accepted at a time.
This means that when one user is sending a job then the
unit will not accept other connections. There is another
side effect of this problem, which is that some
implementations will accept a network connection but not
read any data from the connection until the previous
connection is finished.</p>
<p>The deal with these problems the <tt class=
"LITERAL">connect_timeout</tt>, <tt class=
"LITERAL">send_job_rw_timeout</tt>, and <tt class=
"LITERAL">send_query_rw_timeout</tt> are used to control
job transfer and lpq status gathering. See <a href=
"printingjob.htm">Printing Job Files</a> and <a href=
"opendevice.htm">Opening the Output Device</a> for
details.</p>
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<div class="SECT2">
<h2 class="SECT2"><a name="AEN5151">11.8.2. Network Print
Server Does Not Handle LPQ, LPRM</a></h2>
<p>Some Network Print Servers do not respond to <tt class=
"LITERAL">lpq</tt> or <tt class="LITERAL">lprm</tt> queries
correctly. The <tt class="LITERAL">remote_support</tt>
option can be used to solve this problem by specifying what
operations the remote print server can handle:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN5157"></a>
<pre class="SCREEN">
:remote_support=RMQVC
R = lpr, M = lprmg, Q = lpq, V = lpq -v, C = lpc
:remote_support=R # printer only handles LPR
</pre>
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<br>
<br>
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<div class="SECT2">
<h2 class="SECT2"><a name="AEN5159">11.8.3. Incomplete Job
Transfers</a></h2>
<p>This is the result of a defective or buggy TCP/IP
stacks. A common problem is the habit that some Network
Print Servers occaisionally discard data at the end of a
print job when a network connection is <i class=
"EMPHASIS">half-closed</i>. A <i class=
"EMPHASIS">half-closed</i> connection is one where one end
of the sending connection indicates that no further data
will be sent. Unfortunately, the Network Print Server will
then try to close the connection in the other direction.
When this does not immediately succeed, it will terminate
the network connection, discarding any unprinted data.</p>
<p>The <tt class="LITERAL">half_close</tt> flag can be used
to solve this problem. See <a href="normalterm.htm">Normal
Termination</a> for more details.</p>
<div class="INFORMALEXAMPLE">
<a name="AEN5167"></a>
<pre class="SCREEN">
lp:lp=lp@remote # shutdown(fd,WRITE) connection, wait for end
lp:lp=lp@remote:half_close@ # close() connection and do not wait
</pre>
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