Data Communications and Networking Terminology That You Need Know

by Gina Tina on April 30, 2013

The Network Basic for Dummies

The communication modes and channels that are provided by the various network and transfer of the data streams associated with an application can take place in one of five modes:

Simplex- This means the data associated with the application flows in one direction only. An example is the transmission of photographic images from a deep-space probe at predetermined times since this involves just a unidirectional flow of data from the probe to an earth station;

Half-duplex – This means that data flows in both directions but alternately. This mode is also known as two-way alternate and an example is a user making a request for some data from a remote server and the latter returning the requested data;

Duplex- This means that data flows in both directions simultaneously. It is also known as two-way simultaneous and an example is the two-way flow of digitized speech associated with a telephony application;

Broadcast  РThis means that the data output by a single source device is received by all the other devices Рcomputers, and so on -that are connected to the same network. An example is the broadcast of a television program over a cable network as all the television receivers that are connected to the network receive the same set of programs;

Multicast – This is similar to a broadcast except that the data output by the source is received by only a specific subset of the devices that are connected to the network. The later form what is called a multicast group and an example application is videoconferencing, which involves a predefined group of terminals or computers connected to a network exchanging integrated speech and video streams.

In the case of half-duplex and duplex communications, the bit rate associated with the flow of data in each direction can be either equal or different; if the flows are equal, the data flow is said to be symmetric, and if the flows are different, asymmetric. For example, a video telephone call involves the exchange of an integrated digitized speech and video stream in both directions simultaneously and hence a symmetric duplex communications channel is required. Alternatively, in an application involving a browser (program) and a Web server, a low bit rate channel from the browser to the Web server is required for request and control purposes and a higher bit rate channel from the server to the subscriber for the transfer of, say, the requested Web page. Hence for this type of application, an asymmetric half-duplex communications channel is sufficient.

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