Data Networking-Concepts and Technology

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Managing Network Printers and Print SpoolersPatrick Powell Astart Technologies, 9475 Chesapeake Dr., Suite D San Diego, CA 92123 619-874-6543


Part 1- Printer Hardware and FirmwarePrinter Mechanisms Host/Printer Connections Serial, Parallel, Network Configuration and Problems Network Printer Support Print Job Formats for Vintage Printers Print Job Formats for Modern Printers Page Description Languages PostScript and PCL Job Control and Format Languages PostScript, PCL, and PJL


Part 2-BSD Print SpoolersPrint Spooler Basics Print Spooler Client-Server Structure BSD, SVR4, Novell, MS RFC1179 BSD Print Spoolers LPRng Printing Process Printcap Files Filters Printcap Examples


Part 3 - Managing Print Spooler Operations Management Facilities lpc, printcap Adding New Printers checkpc (lprng) Installation replacing print spooling system Diagnostics Load Sharing and Printer Pools Bounce Queues Routing Host Specific Printcap Entries


Part 4 - Horrible ProblemsPermissions Security and Authentication Accounting SNMP


Part 5 - Multi-platform Printing and GatewaysNetwork Print Spooling Drivers and Print Spoolers Printer Gateways Microsoft Print Spooler Windows 95 Wslpr


Part 5 - Cont’dNT LPR Support Novell Print Spooler PCNFS (Sun Microsystems) PCNFSD LPR Support Samba Samba LPR Support Desperate Measures


ReferencesPostScript Tutorial and Cookbook, Adobe Systems, Addison-Wesley 1985 PostScript Language Program Design, Adobe Systems, Addison-Wesley 1985 PostScript Language Reference Manual, 2nd Edition, Adobe Systems, Inc. Addison-Wesley, 1990 Portable Document Format Reference Manual, Adobe Systems, Inc. Addison-Wesley, 1993 Web Site for Adobe and more documents:


SoftwareLPRng ftp site: unless otherwise indicated, all software can be obtained from the site. See the README and INDEX file GNU software can be obtained from many mirror sites. Try and look for MIRRORS PostScript Utilities psutil31.tgz More PostScript Utilities psutilmore2.tgz GhostScript GNU GhostView GNU Adobe Acrobat PDF viewer/tools LPRng LPRng distribution FILTERS_LPRng collection of filters, patched for LPRng


Part 1 Printer Hardware and Firmware


Basic Printer OperationA Printer is a peripheral device, usually attached to a host computer The host computer transfer print files to the printer over the communication channel


Printer Communication ChannelsPrinter must be connected to source of print jobs Channel determines the rate at which text (characters) are delivered to printer Also determines the reliability Also determines the availability of error messages and diagnostics Simple and Cheap is not always best


Serial PortSlowest and most error prone Older printers had a very slow transfer speed (9600 bits/second) due to the real time requirements of handling paper Newer ones can go up to 115 Kbps Data transmissions errors VERY common Printer does not have a large buffer to store input so flow control is absolutely required Hardware (RTS/CTS) flow control almost mandatory Software flow control (DCON/DCOFF or CTRL-S/CTRL-Q) can be used over networks Watch out for buffering in network!


Advantages of Serial PortError and Status messages available from printer Most systems have multiple serial ports, can attach multiple printers Can be put on terminal server (watch out for flow control, enable RTS/CTS) Cables can be up to 50 feet long Cheat and they can be up to 200 feet long


Disadvantages of Serial PortVery very slow Did I mention flow control problems? This is a major headache Errors in data transmissions can have interesting effects Note: Software Flow Control Headaches Some software flow control tries to accommodate errors by restarting transmission when ANY character is received from the other end after a time-out period. When you get a printer error, the printer sends CTRL-S to stop job and then later reports status, you lose rest of job. (Headache #27)


Parallel Port - AdvantagesTransfers data 8 bits at a time Flow control implicit because it uses a hardware handshake for data transfer. Very low error rate on data transfer


Parallel Port - DisadvantagesHas limited bi-directional capability Out of Paper, Error indication Bi-directional support limited on most interfaces May not be able to indicate error condition when flow control enabled Surprisingly low throughput due to interrupt per byte on most PCs and workstations Games played at OS level to improve this Real pain is getting status back using bi-directional mode Real cheap folks can even use print sharing boxes You get what you pay for Don’t call me when they lock up


Network InterfaceUsually supports various protocols IPX (Novell and Microsoft) NETBUI (Microsoft) TCP/IP (LPD + RAW Connection) Printer builders are (or did not use to be) network aware Has changed tremendously over last couple of years Configuration of interface is now usually pretty simple once you understand the various options Front panel configuration is really quite simple HP Jetdirect has BOOTP/DHCP configuration


Network DisadvantagesAnybody can print on the printer Leads to the mysterious print job from nowhere In spite of being on the network, only one person can actively use the printer at a time Yes, yes, I know what the documentation says and I am telling you what REALLY happens Multiple users can/will/have locked up the interface (this is a known problem with HP Jetdirect interfaces) Multiple users trying different protocols can/will/have locked up the interface When the printer dies there is usually no handy way to reset it without powering it down


Network AdvantagesVery high throughput, and has built in flow control Very low transfer error rate Ethernet has CRC Higher level protocols also do checking at transport level Can be configured using BOOTP/DHCP Status can be obtained by using SMTP on most systems If DHCP working, can even reboot printer Printer sharing becomes very simple, in principle For shared system resource, may actually be the cheapest interface as it does not require host for support (see LPR/LPD later for details)


Hybrid SolutionsPrint Server Boxes Has network interface, supports parallel port and serial ports for printers and/or modems I have used several different ones with various levels of success Lantronics - works, configuration tricky, good functionality Rose - works, configuration simple, limited functionality Dumb Network Interface (LPserver UNIX/NT/W95) Extremely stupid program that turns your PC into a TCP/IP raw socket connection to the printers serial (bi-directional) or parallel (unidirectional) port This has its place when doing accounting, very tricky printer operations


HP Jetdirect ConfigurationSimilar in principle to most printer network interfaces Front Panel Configuration Enable basic network protocols IPX/Novell Print Spooler DCP/Microsoft TCP/IP Set IP address, netmask, syslog server Enable BOOTP/DHCP configuration BOOTP/DHCP Configuration BOOTP/DHCP supplies IP configuration information Specifies a TFTP server and file that has detailed printer configuration information


Jetdirect Configuration File# Administration Info name: picasso location: 1st floor, south wall contact: Phil, ext 1234 # Only allow connections from network/netmask or host allow: allow: idle-timeout: 120 syslog-facility: local2 # SNMP Configuration get-community-name: blue set-community-name: yellow trap-community-name: red trap-dest: trap-dest: authentication-trap: on


Jetdirect RestrictionsThe “allow” configuration parameter enables you to restrict access to the printer from the specified network/subnetmask addresses This is essential to controlling access to your printer You need to use the BOOTP/DHCP to set the IP address, gateway, and syslog server Note: Setting up the BOOTP/DHCP server can be tricky. You will need to either have a DHCP server on each subnet, run a ‘forwarder’ process on a host on the subnet, or have your router forward requests to a server. (Hint: if you have Cisco router, use the “ip helper” command to specify the DHCP server address.)


Direct ConnectionsTCP/IP Port 9100 on the Jetdirect card is a direct connection to the print engine This is a bi-directional connection, and error messages will be written on it Other network support cards have similar facilities; if they do not, then DON’T USE THE CARD Usually only one connection at a time can be active; this can cause problems if trying to share the printer among several different hosts


SNMPSimple Network Management Protocol provides a common interface to obtaining information about the status of network devices. An “agent” process resides in the network device, spies on the activities of the device, and provides information when queried. Agents can also generate messages (traps) when a specific activity is detected A “manager” process queries agents for status Agents can also “write” information to the network device when requested by a manager. This allows configuration management to be done by a manager.

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Last Updated: 8th March 2018

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