Fiber Optic Communications for the Premises Environment

CHAPTER 6

SERIAL DATA COMMUNICATIONS OVER FIBER OPTIC CABLE


In the premises environment the most common form is serial data communications. This is the situation where data embarks from the Source at a serial interface and enters the User at a serial interface. Serial data communications is everywhere in the office, campus or industrial environment. It is found, on the factory floor, in the hospital, in the retail establishment and out in the oil patch. This list goes on and on.

In this chapter we consider premises serial data communications carried out using fiber optic data links. Products are introduced that support this type of communications. Some of these products have been introduced in previous chapters. Others are new. All of these products are available from Telebyte.

Model 271 Fiber Optic Auto Powered Line Driver

The Model 271 Fiber Optic Auto Powered Line Driver is pictured as a stand-alone unit in Figure 6-1.

 
Figure 6-1: Model 271 - Fiber Optic Auto Powered Line Driver


The Model 271 Fiber Optic Auto Powered Line Driver is a short haul modem that employs an RS-232 data interface and transmits the data on a fiber optic cable. This modem provides, full duplex, asynchronous, data communications over two fiber optic cables. The length of the fiber optic cable can be up to 2 km and the data rate as high as 56 KBPS. Performance of the unit is optimized for 62.5/125-fiber optic cable. However, the modem can also be used with fiber optic cable having other dimensions.

The operating power for the Model 271 Fiber Optic Auto Powered Line Driver is derived from the transmit data line. This is a real convenience when an electrical outlet is not readily available. The Model 271 is equipped with a DTE/DCE switch that reverses pins 2 and 3 of the RS-232 connector. This allows the modem to support terminals, printers, computers or any other RS-232 based device. The fiber port of the unit employs ST connectors.

One application of the Model 271 is illustrated in Figure 6-2. Notice while this application deals with the factory environment there is no card cage. Rather, the application is dealing with the situation where there is the need for a data communication link between a mini-computer located in the front office of a company and a PC located on the company's factory floor. Both the front office and the factory floor are in the same building.


Figure 6-2: Example Application of the Model 271


Data communication carried out strictly in the front office may be quite reliable over copper cable. However, because the data communication link in this application traverses the boundary to the factory floor there is a need for the extra reliability provided by fiber optic cable.

Model 274 RS-232 Single Fiber, Sync/Async Line Driver

The Model 274 RS-232 Single Fiber, Sync/Async Line Driver is pictured as a stand-alone unit in Figure 6-3.


Figure 6-3: Model 274 - RS-232 Single Fiber, Sync/Async Line Driver


The Model 274 is a unique short haul modem for use on a fiber optic data link. To achieve full duplex communication it only requires one multi-mode 62.5/125-fiber optic cable. Most fiber optic data communication networks require two cables to achieve full duplex operation. In fact, if standard duplex fiber optic cables have been installed the Model 274 can be used to double the capacity.

The Model 274 receives and delivers data through an RS-232 interface. This unit supports nine synchronous data rates up to a maximum of 256 KBPS. It supports asynchronous data rates up to 38.4 KBPS. Furthermore, it supports two pairs of handshake control signals, RTS/CTS and DTR/DSR.

The Model 274 has operator selectable, built-in diagnostics. These include Local Loop-back and Remote Loop-back.

The data interface to the modem is a female DB25 connector. The fiber port interface is a ST connector. LED's for TD, RD, control signals and loop-backs allow the unit to assist in verifying link operation.

The four illustrations in Figure 6-4 indicate how the Model 274 may be employed in typical applications.


Figure 6-4: The Model 274 employed in typical applications

 

Model 279 Multi-Mode to Single-Mode Fiber Optic Converter

The Model 279 Multi-Mode to Single-Mode Fiber Optic Converter provides such conversion. It is pictured in Figure 6-5.

The Model 279 Multi-Mode to Single-Mode Fiber Optic Converter provides transparent conversion between multi-mode fiber optic cable signals and single-mode fiber optic cable signals. As alluded to above single-mode fiber optic cable can transmit data over much longer distances than multi-mode fiber optic cable. Single-mode operation is at a 1310 nm wavelength. Multi-mode operation is at 850 nm wavelength.


Figure 6-5: Model 279 - Multi-Mode to Single-Mode Fiber Optic Converter


There are many applications for the Model 279. This unit can be employed as an individual converter. A pair of these units can also be employed as single-mode, fiber optic cable, and short haul modems in order to signal over long link distances. The unit can also be used when the optical fiber type of the equipment is not compatible with the installed type of fiber optic cable e.g., you have a modem transmitting multi-mode signals but the installed fiber optic cable is single-mode.

The Model 279 operates at speeds from DC to 2.5 MBPS over links that can be as much as 15 km long. Since operation at DC is possible there is no signal that can be used to perform automatic gain control. However, the unit allows the needed control, to be executed manually, by a Line Loss Switch.

The Model 279 is illustrated in one of many possible applications in Figure 6-6. This is an application in an industrial environment. There are two manufacturing facilities in the company associated with this application. These two facilities are remotely located from one another. They are 15 km apart. The process control computer located on the floor of one facility needs to communicate with the local controller in the other facility. Both the process control computer and the local controller employ the RS-422 interface. As shown in Figure 6-8 both the process control computer and the local controller have data converted to fiber optic signals using the Telebyte Model 272A. However, these signals are multi-mode. In order to cover the large 15 km distance between the two facilities single-mode fiber optic cable must be employed. Placing a Model 279 at the fiber output of each Model 272A allows the conversion to the needed single-mode signals.


Figure 6-6: Model 279 shown in an application where process control computer is quite remote for a Local Controller

Please make a selection.