Media, Data Terminal Equipment (DTE) vs Data Communications Equipment (DCE), modems, optical and electronic transmission media, bandwidth, microwave, laser)
Data Terminal Equipment (DTE)
DTE is the equipment that allows the input, transfer and output of data in digital format. Simply, the equipment consists of a keyboard, network connection and monitor. This allows an operator to enter data and send it for another operator to receive it. The input device need not be a keyboard but any other input device such as bar code reader, microphone, mouse, and joystick. The network system can be as simple as a twisted wire pair or coaxial cable to a very sophisticated network system. The output can be a monitor, printer, load-speaker or even a device such as a robot.
In a more general sense, it is the equipment that allows the provision and distribution of digital information over a network. The network may be very local to the enterprise or a global netwok like the Internet.
(reference Data Communications, Computer Networks and OSI, Halsall, F.)
Data Communication-Terminatings Equipment (DCE)
This DCE allows the connectivity between two (or more) DTE's. A modem is an example of a DCE.
Other references state DCE as Data Circuit-Terminating Equipment and is defined under the CCITT (Comité Consultatif Intonationale de Télégraphique et Téléphonique)X.25 standard as being the "carrier equipment" meaning that equipment required to carry the data from one DTE to another. (Reference: Computer Networks Tanenbaum A). The equipment must comply with the standards as laid down by CCITT. These are more deeply explained in the Tanenbaum p108 and pp237-238).
X-25 itself defines the format and meaning of the information passed across the DTE-DCE interface and reference layers (or levels) in the OSI model - the physical layer, the frame (link) layer and the packet (network) layer.
Modem
Modem stands for modulator-demodulator. A modem is a device that allows the transmission of data over a "plain old telephone system" (POST) by using sound as the carrier and "modulating" the signal to carry the data. The modulation can be frequency Modulation or Amplitude Modulation.
In frequency Modulation, the frequency is changed to allow for a representation of Binary data. For example, a carrier of 600mHz can be modulated to 660mHz for a 1 and 560mHz for a 0.
In amplitude modulation, the volume is changed such that a louder noise is a 1 and a softer noise is a 0.
A typical modem today will transfer data at a rate of up to 56k bits per second (BPS) by special algorithms that allow frequency modulation/demodulation as well as data compression/decompression.
Places to look
Optical Transmission Media - Optic Fiber is a very thin, very long piece of glass rod that has special characteristics that allow the transfer via a laser beam along the length of the rod even though it may be bent.
electronic transmission media
Thin Ethernet - coaxial cable
Unshielded twisted Wire pair (UTP)
Bandwidth - The range of frequencies a transmission media can handle. In networking terms, it generally refers to the amount of traffic a link can handle. See page 169 and P187 Capron and
Microwave - A very high frequency radio spectrum that allows line of sight transmission of data.
Laser - Acronym for Light Amplification by Stimulated Emission of Radiation. A light source that is used for the transmission of data along an optic fiber. In brief, the frequency of the light is modulated to allow the transmission of data.
(Ref: http://www.whatis.com check here to get other definitions)
Mike Leishman