# communication channels

There are two types of communication channels:
-Simplex communication
-Duplex communication

Simplex communication is a name for a type of communication circuit. There are two (contradictory) definitions that have been used for the term. When one definition is used for “simplex” then the other definition is referred to as half duplex. a simplex circuit is one where all signals can flow in only one direction at a time.

Examples: Wireless communication in forces, Radio, televison

A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. (The term duplex is not used when describing communication between more than two parties or devices.)

Duplex systems are employed in nearly all communications networks, either to allow for a communication “two-way street” between two connected parties or to provide a “reverse path” for the monitoring and remote adjustment of equipment in the field.
A full-duplex, or sometimes double-duplex system allows communication in both directions, and unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex since they allow both callers to speak and be heard at the same time. A good analogy for a full-duplex system would be a two-lane road with one lane for each direction.

A Channel can take many forms. Examples of communications channels include:

1. A connection between initiating and terminating nodes of a circuit.
2. A buffer from which messages can be put and gotten. See Actor model and process calculi for discussion on the use of channels.
3. A single path provided by a transmission medium via either
* physical separation, such as by multipair cable or
* electrical separation, such as by frequency- or time-division multiplexing.
4. A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
5. The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head.
6. In a communications system, the part that connects a data source to a data sink.
7. A specific radio frequency, pair or band of frequencies, usually named with a letter, number, or codeword, and often allocated by international agreement.
Examples:
* Marine VHF radio uses some 88 channels in the VHF band for two-way FM voice communication. Channel 16, for example, is 156.800MHz. Seven additional channels, WX1 – WX7, are allocated for weather broadcasts.
* Television channels such as North American TV Channel 2 = 55.25MHz, Channel 13 = 211.25MHz. Each channel is 6MHz wide. Besides these “physical channels”, television also has “virtual channels”.
* Wi-Fi consists of unlicensed channels 1-13 from 2412MHz to 2484MHz in 5MHz steps.
8. A room in the Internet Relay Chat (IRC) network, in which participants can communicate with each other.

the types are wiire – Cheap, simple, compatable with old equipment, must be amplified for long distances
Optical – Fast, long distance, high bandwidth, can carry multiple data streams on one cable, expensive, can break easily
Wireless RF – Simple, no cables, expandable, no line-of-sight required, long distance
Wireless IR – Cheap, line-of-sight required

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