Network Printing

There are several options to communicate with printers over a TCP/IP network; two are presented here, the Socket API and the AppSocket. This information is from the LPRng-HOWTO.

Socket API

Widely used by most print server manufacturers.
HP’s JetDirect defines the de facto standard.
The socket API is simple:

1. Establish a TCP/IP connection to the printer.
   HP JetDirect uses port 9100 by default.
   This connection may be refused if the printer is busy printing a job.

2. Once the connection is established, send the print job. The connection is bidirectional: error messages may be returned at any time over this same connection.

3. After all job data is sent, half close the connection (the shutdown() network system call) to indicate that no more data will be sent.

4. The printer may terminate the connection immediately (no more messages will be received) or after the job finished printing (so that you may receive messages).

While still printing, the printer may refuse new connections, or it may refuse all data transfers on the connection.

The socket API can be used with the netcat (nc) command line tool, for example to send the job file.ps to the printer at IP 192.168.1.123, do:

nc 192.168.1.123 9100 < file.ps

AppSocket

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.

1. The printer has two ports for network connections:
   • a TCP port 9100 for TCP/IP stream connections
   • a UDP port for UDP packet connections

2. When a zero length UDP packet or a UDP packet containing only CR/LF is sent to UDP port 9101, the printer will return a UDP packet to the sender containing print status information. This information indicates the printer’s current status (busy, idle, printing) and any error conditions.

3. The format, reliability, and repeatability of the UDP format and information is totally undocumented.

4. To send a print job, make a TCP connection to port 9100. This connection will be refused while the printer is busy or has a connection to another host.

5. After the connection is established, send the job data.

6. When the job has been transferred, close the connection for sending (but keep it open for receiving messages). Alternatively, an end-of-job (EOJ) indication in the data stream (such as a Ctrl-D in a PostScript job) will terminate the connection.

7. Some printer models will not terminate the connection, but simply ignore any data following the EOJ indication.

8. Some printers support bidirectional AppSocket communication. They return error indications and status info while the connection is open.

9. Once all data has been received and the job has finished printing, the connection will be terminated by the printer.

(Unser Xerox Phaser 8200DP zeigt auf dem Frontpanel immer an, dass die Jobquelle ‘AppSocket’ sei, verhaelt sich aber nicht entsprechend dem eben beschriebenen Protokoll.)