FAQs

RS-422 provides a balanced, full-duplex, 4-wire serial interface for point-to-point links. RS-485 offers balanced, serial 2-wire (half-duplex) or 4-wire interfacing (full-duplex) suitable for constructing a data bus. RS-485 outputs can be individually set to a high-impedance, inactive state ('tristate') and can therefore be wired in parallel.

Conventional copper-wire systems often utilize 2-wire configurations; with optical fiber modems, 4-wire connections are preferred

Not any more. Recent cost modeling completed by the Fiber Optics LAN Section and Pearson Technologies shows that when centralized cabling or fiber-to-the-zone designs are used, all fiber systems are actually less expensive than networks using fiber in the backbone and UTP copper in the horizontal.

Fiber is just as easy, and sometimes easier, to install than copper. Remember, since fiber is accepted as the standard choice for communications backbones for many years, today's installers are comfortable with the technology. In fact, new generation high-speed copper networks. such as Category 5e and Category 6 Unshielded Twisted Pair (UTP) cable -- require more stringent and time-consuming installation techniques than those of fiber. Compared to newer grades of copper cable, fewer regulations exist on the methods by which optical cable is pulled and terminated. In addition, there is no need to worry about the location of EMI/RFI sources during installation. Furthermore, optical fiber cables are stronger, lighter and smaller than comparable copper cable designs, and there are few routing restrictions, particularly in areas with other electrical power cables.

For companies that want to leverage their legacy electronics, need to upgrade only a portion of their network, or do not have the resources to upgrade their entire network at once, fiber can be installed incrementally. For these users, media conversion technology offers them a controlled migration strategy. Media converters do just what their name implies -- the devices convert the signal from one type of media to another, allowing seamless links between different media and supporting incremental upgrades to fiber. Media converters also allow users to continue to use their existing electronics, leveraging their existing investment.

Physically the two fiber types differ in the diameter of their cores, the light-carrying region of the fiber. This is signified by the numeric nomenclature. In 62.5/125 fiber, for example, the core has a diameter of 62.5 microns and the cladding diameter is 125 microns. In terms of performance, the difference lies in the fibers' bandwidth, or information-carrying capacity. Bandwidth is actually specified as a bandwidth-distance product with units of MHz·km. The bandwidth needed to support an application depends on the data rate. As the data rate goes up [MHz], the distance that rate can be transmitted [km], goes down. Thus, a higher fiber bandwidth enables you to transmit at higher data rates or for longer distances. 50 mm multimode fiber offers nearly three times more bandwidth (500 MHz·km) than FDDI-grade 62.5 mm fiber (160 MHz·km) at 850 nm. Network planners often choose 50 micron fiber when they know the network will need to carry high bandwidth applications over longer link distances, or when they anticipate running higher speed protocols in the future.