Which of the following is a TransmissionMedium?a) A dummy terminalb) Optical fibberc) A Modemd) IBM AS/400

The correct answer is b) Optical fiber.

Optical fiber is a type of transmission medium. It is a flexible, transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than electrical cables.

On the other hand, a dummy terminal, a modem, and IBM AS/400 are not transmission mediums. A dummy terminal is an output device that accepts data from a computer but doesn't process any data. A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. IBM AS/400 is a midrange server designed for small businesses and departments in large enterprises and now redesigned as the IBM eServer iSeries.