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23.5 Network Printers
A network printer can support various protocols, some of them even concurrently. Al-
though most of the supported protocols are standardized, some manufacturers expand
(modify) the standard because they test systems that have not implemented the standard
correctly or because they want to provide certain functions that are not available in the
standard. Manufacturers then provide drivers for only a few operating systems, elimi-
nating difficulties with those systems. Unfortunately, Linux drivers are rarely provided.
The current situation is such that you cannot act on the assumption that every protocol
works smoothly in Linux. Therefore, you may have to experiment with various options
to achieve a functional configuration.
CUPS supports the socket, LPD, IPP, and smb protocols.
socket
Socket refers to a connection in which the data is sent to an Internet socket without
first performing a data handshake. Some of the socket port numbers that are com-
monly used are 9100 or 35. The device URI (uniform resource identifier) syntax
is socket://IP.of.the.printer:port, for example,
socket://192.168.0.202:9100/.
LPD (Line Printer Daemon)
The proven LPD protocol is described in RFC 1179. Under this protocol, some
job-related data, such as the ID of the printer queue, is sent before the actual print
data is sent. Therefore, a printer queue must be specified when configuring the
LPD protocol for the data transmission. The implementations of diverse printer
manufacturers are flexible enough to accept any name as the printer queue. If nec-
essary, the printer manual should indicate what name to use. LPT, LPT1, LP1, or
similar names are often used. An LPD queue can also be configured on a different
Linux or Unix host in the CUPS system. The port number for an LPD service is
515. An example device URI is lpd://192.168.0.202/LPT1.
IPP (Internet Printing Protocol)
IPP is a relatively new (1999) protocol based on the HTTP protocol. With IPP,
more job-related data is transmitted than with the other protocols. CUPS uses IPP
for internal data transmission. This is the preferred protocol for a forwarding queue
between two CUPS servers. The name of the print queue is necessary to configure
IPP correctly. The port number for IPP is 631. Example device URIs are
ipp://192.168.0.202/ps and ipp://192.168.0.202/printers/ps.
Printer Operation
443
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Troubleshooting
