Media converters help deliver fiber where it's needed

Aug. 1, 2000

There are a lot of factors driving fiber deeper into LANs. And media converters are becoming an important part of the delivery system.

By Cheri Podzimek and Bob Brocklehurst

Media converters do exactly what their name implies-they convert data signals on one cabling medium (defined by cable or connector type and bandwidth) to signals that can be transported over another medium. They can also be used for speed conversion, allowing network managers to transition between different transmission speeds for individual parts of their networks.

These characteristics make them ideal for network managers who need to upgrade their copper systems with fiber but don't have the luxury of undergoing a wholesale replacement effort. Media conversion also allows you to cost-effectively install new fiber networks. Cost has kept many network managers from making the transition to fiber, but those costs can be significantly reduced when

the network infrastructure is viewed in sections. By allowing incremental upgrades, or buying copper electronics teamed with media conversion to provide the needed fiber connections, media converters facilitate the migration of a network to fiber by allowing network managers to decide when and where they need fiber.

Media converters can be used to support connections to and from switches, hubs, routers, and even directly to servers. Because they can be used to connect many kinds of devices, anywhere they are needed in the network, media converters give network managers the flexibility to enhance the performance of their networks by taking advantage of speed, bandwidth, and security enhancements as they become available.

Using media converters in a 100Base-TX-to-100Base-FX back-to-back configuration, for instance, provides a single method of extending the distance between a full-duplex switch and a file server up to 2,000 m. The same strategy will work between two switches. In fact, media converters can function in either half-duplex or full-duplex mode. Full-duplex Ethernet over UTP runs at 20 or 200 Mbits/sec, while half-duplex Ethernet over UTP runs at either 10 or 100 Mbits/sec. Full-duplex Ethernet is especially valuable in linking two switches or connecting a switch to a file server. No adjustments are necessary when using either mode. A media converter will automatically sense which mode is in operation. In short, media converters enable network managers to:

  • Take advantage of the longer distances supported by multimode and singlemode fiber by allowing the integration of fiber-optic cable into copper-based networks.
  • Incorporate add-on devices, making it possible to connect the newest, high-end, high-bandwidth switches and hubs, regardless of connector restrictions.
  • Maximize the efficiency and economy of networks by enabling a high-bandwidth fiber-optic backbone to feed lower-speed fiber or copper cables to workgroups and desktops.
  • Increase network flexibility, because media converters can be inserted almost anywhere in the network.

Media converters are an ideal tool to link high-speed fiber backbones to lower-speed desktop cabling. In fact, currently, the most commonly used media converters support twisted-pair-to-fiber connections.

Media conversion offers a mainstream solution for providing fiber connectivity in a twisted-pair-dominated environment. The guidelines laid out in the proposed 100Base-SX standard add a new twist to this proposition.

The draft 100Base-SX standard defines an affordable migration strategy for 10-Mbit/sec copper or fiber to 100-Mbit/sec fiber by using 850-nm optics, rather than the 1,300-nm optics called out for 100Base-FX. The benefits are two-fold: an 850-nm light-emitting diode (LED) is compatible with 10Base-FL and costs less than a 1,300-nm LED. While the standard offers an excellent pathway to Fast Ethernet, media converters make it possible to convert the legacy copper-based system to fiber without replacing all the electronics.

The proposed 100Base-SX standard implements auto-negotiation by adopting the IEEE 802.3 1998 edition's clause 28 (the portion of that standard that defines auto-negotiation for 100Base-TX) and defining how it needs to be converted for use on fiber. As a result, the information passed and the state machine used (a state machine is just the sequence of events and the logic that controls them) are compatible with all the existing 10/100 equipment and installations.

Because of the cost savings it offers, media conversion has been used aggressively to bring fiber closer to the end user. For example, when the school system in Gary, IN, wanted to bring fiber to the classroom, its reseller, JDL Technologies, suggested they team media conversion with Cisco switches and routers rather than buy dedicated fiber blades. The goal was to bring fiber into 42 buildings and 2,400 classrooms.

By using media conversion, JDL reported a nearly 40% savings in the cost of the electronics. The district did not have to sacrifice any functionality on the Cisco equipment, simply changed the choice of physical media from fiber to copper. In fact, the school district was able to reassign the funding for the project and could expand the project definition to include more advanced features, including voice-over-IP support.

Although it continues to play a supporting role on the fiber-optics stage, media conversion has been instrumental in the explosive growth of the fiber industry. As the market continues to evolve, network architects, traditional system integrators, and the new wave of "convergence" experts will surely continue to use media conversion to help enhance and expand fiber networks to deliver high-bandwidth applications to end users.

Cheri Podzimek, vice president of marketing at Transition Networks Inc. (Minneapolis), wrote this column on behalf of the TIA Fiber Optic LAN Section (FOLS). She can be reached at [email protected]. Bob Brocklehurst is product marketing manager-media products at Allied Telesyn.

Fols member companies include 3M, AMP, Allied Telesyn, Berk-Tek, Belden Wire & Cable, Comm Scope, Corning, LANCAST, Lucent Technologies, MicroLinear, Ortronics, Panduit, Siecor, Siemon Co., SpecTran, Sumitomo Electric Lightwave, and Transition Networks. For more information from FOLS, please visit

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