Data Transmission
In computer networks, data transmission is the process of sending and receiving digital information. Data are transmitted in the form of bits (binary digits). The most common type of data transmission is digital, which uses electronic signals to represent 0s and 1s. Analog data transmission uses electrical or optical signals to represent analogues of real-world phenomena such as sound or light.
The first telecommunication networks employed analog data transmission. In an analog signal, the amplitude (height) of the signal varies over time to represent the changes in a physical quantity such as sound pressure or voltage. Because analog signals are continuous, they can be susceptible to noise, which can degrade the quality of the signal.
Digital data transmission offers several advantages over analog data transmission. First, digital signals are easier to store and process than analog signals. Second, digital transmissions are less susceptible to noise than analog transmissions. Third, it is easy to convert between digital and Analog formats using special devices called modems . Finally , multiplexing techniques can be used with digital transmissions to send multiple streams of information on a single channel . This allows many users to share a limited number of communication channels .
Multiplexing is a key technology used in modern telecommunications networks . It allows numerous conversations or other types of information to be sent simultaneously over a single communications channel by assigning each message a different frequency band . This approach greatly increases the capacity of communications systems while minimizing costs .
Time-division multiplexing (TDM) is a type of multiplexing in which each connection is assigned a dedicated portion (time slot) of each frame that passes through the TDM switch . The switch reads successive time slots in sequence and sends them on their respective outgoing links . Thus , TDM effectively interleaves the messages from different input ports so that they share the bandwidth equally over time but not space (frequency) .
Statistical Time Division MultiplexingSTDM) STDM interleaves bursts(packets )of user traffic so that all users have equal access opportunityto link resources during any given intervalon average ). Information from various inputsis converted into fixed -size cells or packetsand then transmitted sequentiallyover one output link at regular intervals(a rowat atime downthe columnsof cells ).