This article explains what LPR/LPD is, and what it does.

Definition of LPR/LPD

LPR/LPD is a platform-independent printing protocol that runs over TCP/IP. Originally implemented for BSD unix, its use has spread into the desktop world and is a de facto industry standard. The specification for LPR is defined in Request for Comment (RFC) 1179.

Terminology

LPR: Line Printer Remote. Refers to the process that sends jobs to the printer or print queue. This is analogous to the print client software and is often called the 'LPR client'.

Apple has included an LPR client starting with the LaserWriter 8.5.1 printer driver, which shipped with Mac OS 8.1. It is also available separately. This software enables you to send print jobs to any LPD printer or print server.

LPD: Line Printer Daemon. Refers to the process that accepts print job from the line printer daemon client (the LPR client). This is analogous to the printer or the print server software and is often called the 'LPD server'.

The print server waits for the client to send it jobs. A print server may be capable of handling multiple printers and print queues at once. Since it (usually) has only a single IP address, the queue name must be used to specify the intended print queue.

LPR and LPD also refer to the protocol defined by the LPR/LPD specification (RFC 1179).

How LPR Works

LPR is a lot like sending a file, except you're sending a print job instead. Also, there are two parts to each print job: the data file (the data to be printed) and the control file (instructions that describe the data file and specify what to do with the data file).

When you click the 'Print' button in the print dialog, the computer spools the print job to disk and generates the PostScript data (the data file). It then sends the data file and control file to the IP address specified in the LPR desktop printer. Since there may be more than one queue at the destination IP address, the queue name is sent at the very beginning to identify the intended queue.

If the destination is a printer, the printer prints the job. If the destination is a print server, it may do some additional processing (for example, security checking) and then forward the job to the next destination in the path (usually the printer).

Advantages Of Using LPR

• Migration to single-protocol environments
• More cross-platform; platform-independent
• Accessible via the Internet

Advantages Of Using PAP (Printer Access Protocol, the Appletalk protocol for printing)

• Better status info (idle, busy, and so forth)
• Better error info (out of paper, tray out)
• Easier to set up (autodiscovery versus manual entry/selection)

Apple LaserWriter Printers With Built-in LPD

• LaserWriter 8500
• LaserWriter 12/640PS
• Color LaserWriter 12/660PS
• Color LaserWriter 12/600PS
• LaserWriter 16/600PS
• LaserWriter Pro 810

Other LPR clients and LPD servers

LPR and LPD have been widely adopted by other communities, including:

• Many flavors of unix.
• Windows NT: LPR client included in NT Workstation and Server. LPD server only included in NT Server.
• Windows 3.1x/95/98: LPR and LPD not included but available by third parties.