Extending your reach with media converters

Instead of retrofitting an entire cabling system, install a media converter to meet your bandwidth needs.

Jan 1st, 2002
Th 81517

Instead of retrofitting an entire cabling system, install a media converter to meet your bandwidth needs.

Are you looking to extend the distance that your copper-based network covers? Is using optical fiber the only way to do it? If so, what would be the cost and disruption of changing your whole infrastructure to fiber? Is there a solution? Yes: media converters.

Media converters (see table, page 58) actually describe a range of different devices, but the most common is copper-to-fiber and then back from fiber-to-copper. This form of media conversion is typically used to increase the distance that installed, legacy copper systems can handle. By taking the signal from the copper cable and converting it to a format suitable for optical fiber, it is possible to significantly extend data transmission distances without going to the expense and trouble of ripping out the copper infrastructure and replacing it with a complete fiber-based solution.

Other types of media converters include multimode-to-singlemode fiber. Various speeds are also available, typically 10- and 100-Mbit/sec, and also increasingly 1-Gbit/sec, with even 10-Gbit/sec in the pipeline.

In a sense, media converters are quite simple products, and where there is simplicity there is less potential for anything going wrong.

Just passing through

"Media converters are strictly pass-through devices; that is, when signals coming from a hub or a switch are sent via a converter, the converter will handle them without regenerating or re-timing them in any significant way," explains Mark Benevento, senior product manager for MiLAN Technology (www.milan.com), producers of media converters, and a division of Digi International. "Any time-delay effect that might happen is in the order of nanoseconds-far less than a hub or switch," he says.

Media converters have never gone through the process of becoming an Institute of Electrical and Electronics Engineers (IEEE-www.ieee.org)-specified product, and some see them as rather an ad hoc, perhaps not very elegant or long-term solution.

With Transition Networks' Point System Conversion Center, distances of up to 65 km are possible, extending bandwidth to those outside the reach of the 1000BASE-T standard. The converters allow a mixed network of copper and fiber ports, so the exact number of fiber ports can be deployed as needed.
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"Media converters are somewhat of a band-aid," says Stephen Montgomery, president of ElectroniCast (www.electronicast.com), a consultancy that tracks and analyzes the optical fiber industry, claiming they are a temporary answer to the question of whether a company should upgrade to fiber. "But of course, band-aids can last 20 years if you don't wash them," Montgomery adds.

Nevertheless, the most frequently used type of media converters-copper to fiber-have proved increasingly popular over the last few years because of their cost advantages and flexibility.

"Typically, many manufacturers still do not design the basic networking products like network interface cards (NICs), switches and hubs with the idea of fiber connectivity in mind," Benevento says. "So, if you need to go over a greater distance than 100 meters, a media converter can be a simple, cost-efficient way of doing it."

A media converter using multimode fiber makes it possible to achieve a distance of 2 km at 100 Mbits/sec, and with singlemode, up to 100 km is feasible. A typical environment in which media converters are used would be a small office, say a two-story structure, housing 250 to 500 employees. Here, the 2 km made possible by multimode fiber would be sufficient.

An example of where longer distances are needed using singlemode fiber is provided by developments in China, where the major telecommunications points of presence (PoPs) need to provide links out to the many rural provinces, frequently requiring a reach of up to 70 km. "To do this," says Benevento, "the telecommunications companies are using a media converter that takes its input from the copper-based switch at the PoP and sends the data at 100 Mbits/sec to perhaps another fiber ring at the distant village, where a second converter is used to supply the signals to the copper network." This approach is happening elsewhere, in the US and also in Europe-notably in Helsinki, Finland, where a major home networking project is using media converters.

Default drawbacks

A potential problem is that converters can fail to work properly in an automated negotiation system. For example, with a 10/100 hub at each end and a converter in between, the converter might default to half-duplex operation when full-duplex is required. This could happen in an unmanaged environment, where the devices do not have DIP switches to force the system into the required mode.

The MiLAN MIL-9100 is a 1U 19-inch, rack-mountable unit that lets you mix-and-match up to eight system modules for converting UTP copper to fiber.
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"The IEEE specifications call for switches and hubs to have DIP switches, in order to force negotiation, if need be," Benevento says. "However, to save costs, many manufacturers, such as those from Taiwan, have removed these DIP switches, so there could be a problem."

Clearly, if we ever move to an all-fiber world, copper-to-fiber converters would be unnecessary. But nobody believes that will happen for the next decade, and possibly not beyond that. This is partly because of the huge installed copper base, partly because we have hardly yet begun to see widespread use of the most advanced copper cable now available-Category 6 and 7-and partly because the cost of complete fiber solutions is still significantly higher than copper. Analysts are predicting demand for media converters will continue for at least the next five years.

One change that has occurred recently is much greater competition, as a result of several Chinese and Taiwanese manufacturers entering the market and producing stripped-down converters with only basic functionality. The effect has been a virtual price war. Today, typical cost for a 10-Mbit copper-to-multimode fiber converter is now about $85, and for 100-Mbit, about $170. These represent major price reductions compared with a few years ago.

Increasingly, converters are be coming available with a degree of management capability. This lets users perform actions such as enabling/disabling ports, or monitoring what is happening at either end of the link-copper or fiber. This is particularly useful for service providers managing the sort of long-distance environment referred to earlier, where the remote end may be many tens of kilometers from the central point. "Converters will play a major role in areas like fiber-to-the-home, and service providers will need to know what is happening at the end node and exercise some control," Benevento says. "So, instead of pure converters, I think we will see simple 2-port switches emerging, because you can do a lot more in terms of management with a switch application-specific integrated circuit (ASIC) than you can with a converter ASIC. The result will be anything you can now do with a 24-port switch, you will be able to do with the 2-port device."

MiLAN's latest introductions are gigabit-level media converters: the MIL-C611x series of 1000BASE-T to 1000BASE-LX and 1000BASE-T to 1000BASE-SX. The MIL-C611xs convert unshielded twisted-pair (UTP) copper signals to fiber, and can extend network distances from 220 meters using multimode, and up to 70 km using singlemode. These media converters are suitable for linking enterprise networks or connecting campus backbones with bandwidth intensive applications. "Using the converters with low-cost 1000BASE-T switches allows users to upgrade their network to gigabit speeds in an economical manner," Benevento says.

The MIL-C611x series are designed with a wide variety of fiber connector types and distance specifications, including SC connectors for distances of 220 meters, 5 km, 20 km, 50 km, or 70 km; MT-RJ for distances of 10 km; and LC in 5 km or 50 km. Each converter comes with auto-detection MDI/MDI-X capability on the UTP port, letting users insert 8-pin modular Category 5 cable without concern about straight-through or crossover recognition. A full complement of LEDs, including link, receiving, and transmit on both the fiber and copper ports provide port status information, simplifying installation and troubleshooting.

VF-45-based converters

A Fast Ethernet range of media converters is available from Volition (www.volition.com), a division of 3M that principally supplies fiber-based systems. Its media converters, based on 3M's VF-45 interface, include the Volition VOL-M100FX workstation media converter, which is a standalone unit with a single-port configuration for desktop use; while the Volition VOL M100FX-12 is a 12-port, 19-inch rack-mount unit for use in wiring closets. Both connect with standard protocols and comply with IEEE 802.3u.

Typical situations for which Volition supplies media converters are when a customer has migrated to an advanced fiber-based installation, but wants to continue using their existing copper active equipment (such as NICs and switches) that may have been installed only a short time ago. "They will typically have a 10-Mbit copper switch and use a rack-mount media converter on the 19-inch side to convert to fiber," explains Jörg Reinhardt, market development manager for Volition Network Solutions Europe, based in Neuss, Germany. "It is usually a switch rather than a hub, because with fiber and a hub, you lose too much performance. Then at the workstation, there is an existing copper NIC card, and a media converter is located there to use that."

Reinhardt concludes, "Media converters give a simple solution-they are literally plug-and-play. There is no need for any configuration, or to open up the computer, as you have to do it if you want to install a fiber NIC."

With a large installation containing hundreds or thousands of ports, replacing copper NICs with fiber NICs in every individual PC could take weeks. With media converters, however, it can be done in a day. Then, in perhaps 2 to 3 years time, when the copper NICs are due for renewal, fiber NICs can be installed to create a complete fiber-to-the-desk implementation. Given the expense associated with fiber-to-the-desk, most installations today are going into market areas like the financial industry, where the funds are available, and where demands for bandwidth are so critical that only fiber can provide it (such as medical, computer design, multimedia, etc.). A major Volition installation using media converters is at the world's second largest insurance company, Allianz, based in Munich. The company has implemented a huge fiber-to-the-desk system, comprising more than 20,000 ports throughout its offices across Germany. But since media converters are about half the price of a fiber NIC, the company wanted to continue to use the copper NICs in its PCs. Also, many of Allianz's PC users do not yet need more bandwidth than the 10 Mbits they have now. So, while Allianz has installed fiber switches on the cabinet side, it has used media converters to avoid having to re-fit all its PCs.

Some claim the long-term lifetime of copper-to-fiber media converters is limited. But that is clearly not the view of one of the leading converter makers, Transition Networks, which has introduced a range of devices intended to provide a cost effective migration path to Gigabit Ethernet. With the converters, distances of up to 65 km are possible, extending bandwidth to those outside the reach of the 1000BASE-T standard, Transition says. They allow centralization of the network by consolidating equipment in one location. Rather than be dependent upon a pre-packaged port count of fiber or copper connections, Transition says its converters allow a mixed network of copper and fiber ports, so the exact number of fiber ports can be deployed where and when needed. The converters are available in a standalone form-factor or as a chassis card for Transition's Point System Conversion Center. These converters feature a range of management facilities, including auto negotiation, link pass through, and pause.

"As networking speeds increase, the need for media converters that are adapted to solve specific problems is becoming ever more acute," says Cheri Podzimek, vice president of marketing for Transition Networks. "The Gigabit Ethernet converters are perfect for enterprise networks or connecting campus backbones with bandwidth-intensive applications, such as large file transfers and multimedia."

David Boothroyd is a veteran technical journalist in the United Kingdom, covering the cabling industry. He has served as technical editor for Cabling Installation & Maintenance Europe. You can contact David via e-mail at: d.boothroyd@btinternet.com.

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