Data Transmission Media & Modes
Transmission Modes
The direction in which information can be transmitted over a channel depends on whether the channel is simple, half-duplex or full-duplex.
» Simplex transmission
Simplex transmission is unidirectional data transmission. Of the two linked devices, only one of them can send data and the other one can only receive data.
» Half–duplex transmission
Half–duplex transmission is bi-directional data transmission, but the linked devices cannot send and receive at the same time. When one device is sending data the other can only receive.
» Full-duplex transmission
Full-duplex transmission is bi-directional and the linked devices can send and receive data simultaneously. The linked devices can send data and at the same time receive data.
Data Transmission Media
The data is sent from one computer to another over a transmission medium. The transmission media can be grouped into guided media, and unguided media.
Guided Media
In the guided media, the data signals are sent along a specific path, through a wire or a cable. Copper wire and optical fibers are the most commonly used guided media. Copper wire transmits data as electric signals. Copper wires offer low resistance to current signal, facilitating signals to travel longer distances. To minimize the effect of external disturbance on the copper wire, two types of wiring is used—
1. Twisted Pair
2. Coaxial Pair
3. Optical fibers
Unguided Media
In the unguided media, the data signals are not bounded by a fixed channel to follow. The data signals are transmitted by air. Radio, microwave, and satellite transmissions fall into this category.