The only other issue that i will touch on is the use of the ethernet industrial switches and hubs. I've always being a little sceptical about using office grade equipment in an industrial enviroment and as such i have always used an industrial type. Hey, a lot of people might disagree, which would be an interesting digression.
Why choose Industrial Ethernet Units over office-grade equipment?
Temperature - Office-grade equipment is typically specified over a +5°C to +40°C temperature range, while industrial controllers such as programmable logic controllers (PLCs) are rated from 0° to +60°C. Ethernet equipment should have equal or better temperature ratings as the equipment to which it is connected. Many outdoor applications require that the equipment perform over a wider -40°C to +75°C range. These two ranges are beyond the capabilities of office-grade equipment, but generally are covered by the industrial unit without the use of fans which are undesirable in industrial applications.
Mounting - Control devices are usually mounted onto sub-panels, which are installed into industrial control panels. Devices are secured by mounting tabs or snapped onto DIN-rails. Industrial units can be mounted in this way. Office-grade equipment is intended for tabletop installation and seldom has provisions for secure mounting. Frequently, the units are left unmounted or attached using Velcro®, duct tape or a special shelf is fabricated at additional cost for their mounting. Office-grade equipment is out of place in an industrial control panel.
Power Supply - Industrial systems are usually powered from a common low-voltage control transformer or low-voltage DC power supply. Industrial ethernet units will generally operate over a wide-range of AC or DC voltages compliant to the needs of most any type of control application. A wide-range DC-to-DC converter, which can operate during brownout conditions utilizing a large input capacitor to ride-out spikes and dropouts that can frequently occur with factory power sources, is generally used in the power supply design. Additional connections are provided for redundant power schemes to ensure the greatest amount of uptime. Office-grade equipment is usually mains-powered or requires a wall-mounted plug-in transformer that is inconvenient in a control panel and susceptible to inadvertent disconnection, compromising the reliability of the system.
Regulatory Requirements - The movement of industry in embracing Ethernet standards does not remove the requirement to conform to various agency regulations not required in the office. Seldom does office-grade Ethernet equipment meet the unique requirements of industrial automation or even building automation. Generally Industrail Ethernet products are designed and tested to the higher electromagnetic compatibility (EMC) immunity standards required for industrial equipment. All the products are UL 508 Listed for use in industrial control panels and some are listed under UL 1604 for Class I, Division 2 hazardous locations. Still others are UL 864 recognized for smoke and fire protective applications. All the products carry the CE mark for installation in the European Union.
Extended Product Life Cycle - Original Equipment Manufacturers (OEMs) require a stable bill-of-material (BOM) without the additional expense and effort to requalify a replacement for an obsolete device. This is especially true when the OEM equipment has been qualified for agency approvals and subject to factory surveillance. This is not the case with office-grade equipment that is frequently changed without notification making it difficult to specify and procure the same item even over a short time span.
Responsive Technical Support - A decent supplier of indurtrial ethernet equipment will back there product.
FINALLY, you might want to check this thread out if you are interested in learning more about ethenet.
Indutrial Ethenet Course
Oh, and i am waiting to see if Bobb gets on and throws his comments about ethernet...(Bob, I'll catch up with u before Xmas hopefully)