Ethernet Interface

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Ethernet

Ethernet is the most common computer network technology, other network standards such as Token Ring and AppleTalk are no longer common.

Large printers are expensive machines and are almost always shared between many users. One of the original driving forces behind networking was the ability to share printers.

Printer manufacturers often included an Ethernet interface as standard on their business -oriented models. Older fast laser printers generally have an "option slot" in which an Ethernet "print server" card can be fitted. In addition, most printers have a parallel interface into which an external "print server" can be plugged.

Ethernet was intended as a general-purpose standard, but it presents a couple of significant difficulties for printer support –

Ethernet needs a fairly powerful microprocessor to support it. Furthermore the processor handling Ethernet must be able to handle network events whenever they happen. Printers often have a powerful processor - the Raster Image Processor (RIP). However this is usually dedicated to building the page-image in memory and cannot be interupted by the network. Printers with an Ethernet interface have a dedicated processor to support it.

Several control parameters have to be set up. Printers with an Ethernet interface do not usually just accept and print anything sent to the correct Media Access Control address (MAC). They generally expect data to obey a protocol. There are two in common use:

IPX – a semi-proprietary Novell protocol now sliding into obsolescence
TCP/IP – an open standard but one that requires several parameters to be set - notably an IP address.

Ethernet is rather unusual amongst printer connection standards because it is "scalable". If 10mbps Ethernet is too slow plug in a switch and run part of the network at 100mbps. If 100mbps is too slow use gigabit Ethernet.

Since Ethernet is so flexible and can scale up to meet users demands the surprise has been that it was not included in more printer designs. The key problem seems to be the cost of the control processor. Printer manufacturers historically charged as much as £300 extra for what amounts to an Ethernet adapter. (The HP JetDirects are examples)

Alternative Print Servers

If Ethernet connection seems like a good idea but the printer either doesn’t have the option or it is overpriced an alternative is to use an external print-server. External print-servers do pretty much the same job as an internal interface but use a standard parallel cable or on more recent models USB in order to connect to the printer.

Some Ethernet to parallel interfaces are built into a large version of the Centronics plug - so the print server may take little or no space and cost as little as £50. Multi port models tend to cost a bit more and feature rich devices more still.

The problem can be that print protocols are quite complicated and network protocols to support printing still more so. Users need to know which protocols they will use and there's quite a choice. For instance this is the list for the HP JetDirect 625n which is one of the older EIO Ethernet cards. this is an excerpt from the brochure :

"TCP/IP (IP direct mode, LPD, FTP, IPP), IPX/SPX, DLC/LLC, AppleTalk, Auto-IP, Apple Rendezvous compatible, NDS, Bindery, NCP, Telnet, SLP, IGMP, BOOTP/DHCP, Network protocols: WINS, SNMP v 1 and v 2c, HTTP"

If you know what those protocols are and what they do there isn't much of an issue. Lots of users don't, so buying anything other than the original network card could be a steep learning curve. Just for information most users set network printers and external print servers up to boot using DHCP at a fixed address programmed into the local router and use IP Direct mode (aka port 9100 printing). It's true that the IT department could wireshark data on the network to get confidential files like payroll so you might prefer a JetDirect 635 with SSL. (However if they're that keen they could intercept keypresses, run VNC or RPC from your machine, or decrypt you password.)

Multifunction printers with scanners pose particular problems because traditional print protocols don't support a back channel from the printer to the PC. Most network print servers come with a long compatability list but many of the recent printers won't be on it.

Choices, Choices.

Experience suggests that most users play it safe and replace internal print servers with the same model or an upgrade rather than experiment with anything different. IT departments are quiter busy enough without messing about with print servers.

Print server vendors will obviously advise people on what to buy but the average network vendor's external print server retails for under £60. With my retailer hat on I'd say technical support on making a recalcitrant print server work with a multifunction printer is going to be limited.

Protocol Converters

Print servers can do considerably more than connect Ethernet into printer parallel ports. Protocol converters can translate between computer systems that have little in common. The most common protocol converters link low-cost printers into IBM mainframe systems. Axis sell the most popular line of devices.

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© Graham Huskinson 2010

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