DARCOM

DARCOM 9000 provides radio-based data communications to MOSCAD equipment that normally operates on wireline. It uses the 900 MHz frequencies available exclusively for data communications in many countries. It supports both point-to-point and point-to-multipoint (multiple address) system applications.

Darcom General Operation and Specifications:

• Point-to-Point describes a class of service where two data units exclusively share a communications channel. All messages on the channel occur between these two units. This is analogous to a wire communication channel between a terminal with modem and a host computer. DARCOM point-to-point systems frequently replace the wire communication channel in that example.

• DARCOM point-to-point equipment may also be used to link the host computer to the master-site radio in a point-to-multipoint communications system (advantageous when the host computer is located at a site that cannot directly communicate with the remote sites). The point-to-point equipment effectively connects the host computer to the now-distant master radio which, in turn, communicates with the remote data terminals.

• Point-to-Multipoint describes a class of service wherein one master data site communicates with several remote data sites over a single communications channel. Further, the remote sites communicate only with the master site, not with each other. Implicit within the multipoint system concept is addressability (the protocol employed must specify which of the many remote sites is expected to respond to the message) and non-exclusivity (the data protocol and equipment must tolerate messages on the communication channel addressed to others).

• DARCOM point-to-multipoint systems require the remote data terminals to share the single communications channel. Because they share the channel, they are not in continuous communications with the master site and typically may not initiate data message activity. Point-to-multipoint systems commonly operate in a host-controlled polling mode.

• Network Diagnostics is an increasingly essential aspect of automated communication systems. The DARCOM diagnostics system periodically measures certain parameters of the radio communications equipment to detect problems before they become system-crashing failures. The diagnostics activity may be programmed to occur automatically at infrequent intervals, thereby disrupting normal data activity as little as possible, or the diagnostics activity may be initiated manually when required.

• Testing a single remote DARCOM radio takes three to five seconds depending upon how extensive a test is conducted; the normal system data activity is suspended at all sites during a test of any single site. Data returned from the remote site includes transmitter power, received signal strength, temperature, and more. Commands may be sent to the remote DARCOM radio that adjusts its transmitter power, deviation, frequency, and more to correct detected problems. The collected data is archived within the diagnostics computer and may later be abstracted to observe any long-term trends.

• Protocol Requirements have been established to assist system designers determine if the existing data equipment will operate satisfactorily with the DARCOM radio equipment. Proper operation may be expected when the protocol uses asynchronous communications at 1200, 2400, 4800, or 9600 bps, with either 1 or 2 stop bits, provided that the data terminal waits for Clear-to-Send after asserting Request-to-Send. DARCOM will strip the start and stop bits and send the remaining data synchronously to all other DARCOM radios where the start and stop bits are replaced and the asynchronous data delivered to the connected data equipment. Half-duplex radio communications is used so the modems train (synchronize) at the beginning of every transmission.

• Synchronous data transfer at these same data speeds may also occur. The DARCOM modem will provide clock signal to, or accept clock signal from, the data terminal. The data input is not buffered but immediately transmitted in the same manner described above. And, bit-oriented protocols may be accepted at data speeds through 9600 bps.

• Existing wireline modems operating at 1200, 2400, 4800, or 9600 bps may be used with DARCOM radios (no internal modem). A special cable passes the Request-to-Send signal from the data terminal first to the radio so the keyup and training process may begin and later to the modem so it may begin the data transfer. Data Operated Key (DOX) may also be used.