<P> In both communications, communication is in the form of electromagnetic waves . With guided transmission media, the waves are guided along a physical path; examples of guided media include phone lines, twisted pair cables, coaxial cables, and optical fibers . Unguided transmission media are methods that allow the transmission of data without the use of physical means to define the path it takes . Examples of this include microwave, radio or infrared . Unguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and seawater . </P> <P> The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitters to receivers with no intermediate devices, other than amplifiers or repeaters used to increase signal strength . This term can apply to both guided and unguided media . </P> <P> A transmission may be simplex, half - duplex, or full - duplex . </P> <P> In simplex transmission, signals are transmitted in only one direction; one station is a transmitter and the other is the receiver . In the half - duplex operation, both stations may transmit, but only one at a time . In full duplex operation, both stations may transmit simultaneously . In the latter case, the medium is carrying signals in both directions at same time . </P>

Explain different types of transmission media used in computer network