Electronic security professionals necessarily work with communications protocols. Unless you are deliberately hiding in the stockroom sharpening drill bits, with your phone on ‘silent,’ you are using several protocols or standards such as USB, RS232, Wiegand and RS485 to get ‘er done.
A protocol is a system of formats and rules for exchanging data. A format is an encoding system
Historical Perspective: Actually, the first ‘security’ communication protocol in modern times was the telegraph, and first ‘widely’ adapted format was Morse Code named after one of its inventors, Samuel F. B. Morse. The technology was initially based on the transmission of electrical pulses over wire. Words were first translated into the corresponding pattern of dots and dashes, then an operator sent them using a key, and then somewhere down the line, others monitored the pulses and translated them back into words onto paper. A telegraph key is a switch that is rapidly opened and closed to create the pattern of short pulses (dots) and longer pulses (dashes). If you think about the evolution of technology, you may see the analogies between the telegraph and modern technologies. For example serial data transmission and how pulse-dial telephonic evolved. Morse Code was also used with wireless communications on ships to direct them towards icebergs and u-boats.
But this article is not about evolution or nostalgia but all about modern application.
USB 3.0 has transmission speeds of up to 5 Gbit/s, and is very reliable and used on most consumer equipment such as PCs, laptops, cameras, external hard drives and flashdrives. USB ports have replaced RS 232 DB9 as the defacto serial port. Compared to serial and parallel ports, USB is very easy to use.
RS232 was the ubiquitous serial protocol but newer laptops no longer even come with a DB serial connector. These days RS232 primary’s application is for dial-up modems which are also pretty much phased out, and it is said RS232 will soon become obsolete. The RS-232C standard imposes a cable length limit of 50 feet but in practice cable can be as long as 10,000 feet at baud rates up to 19,200 Bits if high quality well shielded cable is used. But RS232 performance suffers in noisy environments which can affect performance even with short cables, another reason why its time has past.
Wiegand is a term applied to different parameters which found its origins from the research of John R. Wiegand who was able to create a controlled data technology where tiny pieces of wire placed in a specific pattern would produce a pattern of electrical pulses when the patterned wires were placed in an RF field. In today’s nomenclature, Wiegand is used to describe protocols, formats and applications related to this original development including:
- Specially formatted and manufactured credentials,
- Card-to-reader interface
- The physical layer Interface wiring (reader-to-controller) , and
- The encoded credential data format used on many electronic access controls.
Although Wiegand credentials and readers are no longer in widespread use, the physical layer transmission topology and format are still in use because they are simple, reliable and effective for wire runs associated with card reader-to-controller wiring applications.
The Wiegand Interface uses three wires, one of which is a common ground and two of which are data transmission wires usually called DATA0 and DATA1. The voltage level is usually +5VDC and the recommended maximum cable run is 500 feet. Often other signals will also be included in reader wiring, including a shield and LED control. Wiegand operates at 500 Baud (pulses per second).
In Wiegand, the Standard or Open Format has one parity bit, 8 bits of facility code, 16 bits of ID code, and a trailing parity bit for a total of 26 bits. There are thousands of different formats in use which differentiate one manufacturer’s technology from another’s. The development of proprietary formats also improves security by reducing inoperability between formats, and increasing the total number of possible unique codes within a particular format.
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