Garbled Output from Macintosh to Shared PostScript Printer

• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Server versions 3.5, 3.51, 4.0

SYMPTOMS

Print jobs from Macintosh clients may be printed incorrectly, often producing multiple PostScript error pages. The problem seems to happen only with complex print jobs that contain graphics.

CAUSE

This behavior occurs when the AppleTalk protocol is not used to connect to the printer. This is because there are two predominant binary encoding schemes, "standard protocol" and "Tagged Binary Core Protocol" (TBCP). PostScript originally supported several text encoding schemes, plus "standard protocol" binary. Other languages originally supported one or more text encoding schemes, plus TBCP. Standard protocol and TBCP are mutually incompatible; neither is a subset nor an extension of the other.

AppleTalk was designed to support PostScript printing, and although AppleTalk's Printer Access Protocol (PAP) can transmit TBCP on the wire, nearly every binary print job over PAP is PostScript using standard protocol encoding. As a result, many print devices assume that all binary data that arrives over AppleTalk is encoded with standard protocol.

Similarly, PC-based network printing protocols, such as DLC and LPR, were designed to support PC clients. When those clients send PostScript jobs, data is almost always encoded as text; when those clients send non- PostScript jobs, binary data is almost always encoded as TBCP. As a result, many print devices assume that all binary data over non- AppleTalk protocols is TBCP-encoded, even though the network protocols can correctly transmit standard-protocol-encoded data.

The Windows NT printing architecture lets you receive a print job, in any language, from any client, with any encoding scheme, and send that job over any available protocol to any network-attached print device. This flexibility lets Windows NT deliver Macintosh print jobs over an LPT port connection (both DLC and LPR). It also lets Windows NT deliver PC print jobs over AppleTalk. If this violates the print device's binary encoding assumptions, you receive incorrect output.

A Windows NT print server can receive PostScript jobs from Macintosh clients with binary data encoded in the standard protocol scheme. It can send those jobs over an LPT port connection (either DLC or LPR) to a network or locally attached print device that assumes all DLC, LPT port, or LPR jobs use TBCP encoding. In this case, jobs will be printed incorrectly.

RESOLUTION

1. Use AppleTalk to connect to the printer.

2. When you create PostScript print jobs (on any platform) that might be printed over a network, use "ASCII" or "text" encoding rather than binary encoding. This is an option in the PostScript driver made by Adobe Corporation for 16-bit Windows and Macintosh clients. The Windows NT PostScript driver always uses text encoding. Desktop publishing programs (on any platform) often generate their own PostScript code, completely independent of the operating system's driver. According to the Adobe Serial and Parallel Communications Protocols Specification, programs capable of both binary and text encoding should provide a user interface to select either scheme. The ability to switch modes can usually be found in the Printer Driver dialog box.

MORE INFORMATION

The third-party product discussed in this article is manufactured by a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this product's performance or reliability.