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<th colspan="3" align="center">LPRng Reference Manual: 24
Sep 2004 (For LPRng-3.8.28)</th>
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<h1 class="SECT1"><a name="APPSOCKET">11.4. AppSocket TCP/IP
Protocol</a></h1>
<p>The AppSocket interface is supported by Tektronix and some
other printer vendors. It is similar to the Socket API, with
a couple of significant differences.</p>
<ol type="1">
<li>
<p>The printer has two ports for network connections: a
TCP port 9100 for TCP/IP stream connections and a UDP
port for UDP packet connections.</p>
</li>
<li>
<p>When a 0 length UDP packet or a UDP packet containing
only <tt class="FILENAME">CR/LF</tt> is sent to UDP port
9101, the printer will return a packet to the sender
containing print status information. This information
indicates the printers current status (busy, idle,
printing) and any error conditions.</p>
</li>
<li>
<p>The format, reliability, and repeatability of the UDP
format and information is totally undocumented, and the
UPD port facility should be regarded as, at best, an
advisory function of the printer.</p>
</li>
<li>
<p>To send a job to the printer, a connection to TCP port
is made. This connection will be refused while the
printer is busy or has a connection to another host.</p>
</li>
<li>
<p>When the TCP connection is established, the
information to be printed can be sent over the TCP
connection. Bytes sent on this stream will be placed in
the input buffer of the Print Engine and processed.</p>
</li>
<li>
<p>An end of job (EOJ) sequence indication in the data
stream will cause the printer to terminate the
connection. This is different than the Socket API, where
the printer will keep the connection open. This means
that if the PostScript CTRL-D (end of job) character is
sent in a job, then the connection will be
terminated.</p>
</li>
<li>
<p>Some models of printers modify this behavior slightly
and will not terminate the connection, but will simply
ignore any data following the EOJ indication.</p>
</li>
<li>
<p>Some printers support bidirectional AppSocket
communication, and while the connection is open will
return error indications or status information.</p>
</li>
<li>
<p>Once all the data has been received and the job has
finished printing, the connection will be terminated by
the printer.</p>
</li>
</ol>
<br>
<br>
<p>The <b class="APPLICATION">ifhp</b> filter, one of the
helper programs for <b class="APPLICATION">LPRng</b>, is used
with <b class="APPLICATION">LPRng</b> to provide AppSocket
support. For details, please see the [<span class=
"CITATION">IFHP-HOWTO</span>] in the <a href=
"http://www.private/" target="_top"><b class=
"APPLICATION">ifhp</b> Distribution</a> and <a href=
"p450.htm">Tektronix P450 and Family</a> for details. The
following is a typical printcap entry for the AppSocket
protocol. The actual network connection to the printer is
made by the <b class="APPLICATION">ifhp</b> filter:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN4977"></a>
<pre class="SCREEN">
lp:
# <b class=
"APPLICATION">LPRng</b> opens a dummy connection for consistency
:lp=/dev/null
# we pass the ifhp filter options indicating that the
# Tektronics printer will need the appsocket protocol
# and to use port 35 at 10.0.0.1 to make the connection
# The ifhp filter may open and close the connection several
# times during the file transfer in order to ensure that
# the printer handles the job correctly.
:ifhp=model=tek,appsocket,dev=10.0.0.1%35
:filter=/usr/local/libexec/filters/ifhp
</pre>
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