A multiplexing method by which multiple low-speed incoming transmissions can share a single high speed outgoing digital circuit. An analog voice conversation requires bandwidth of 4 kHz.Although there are a considerable number of methods for converting an analog voice signal into a digital signal, the fundamental standard is pulse code modulation (PCM), which requires 64 kbps. A voice grade digital channel, therefore, is 64 kbps wide, which forms the fundamental building block for digital switching and transmission of not only voice, but all forms of data. A typical digital voice application is multi-channel in nature and involves a four-wire circuit with a TDM multiplexer, or mux, placed on each end of the circuit, as illustrated in Figure T-3. At the transmitting end of the circuit, the mux scans the buffers associated with the ports to which individual devices are attached. Each device port is allocated a channel in the form of a time slot on the aggregate line for transmission of data. Using T1 as an example, the transmitting TDM mux relieves each buffer of an 8-bit sample of data, beginning with buffer/port #1 and proceeding in sequence through buffer/port #24, and transmits the bytes, in sequence, across the circuit, interleaving them into a frame of data. The ... mux prepends the frame with a framing bit that delineates that frame from another, and is used by the multiplexers and other intermediate devices for purposes of synchronization and, in some cases, for various signaling and control purposes. This process occurs 8,000 times a second at the precise pace of 125
(1) (Target Disk Mode) A method for transferring files between two Macs. See Target Disk Mode.
(2) (Target Display Mode) An iMac feature that enables the screen to function as an external monitor for another computer. See Target Display Mode.
(3) (Time Division Multiplexing) A technology that transmits multiple signals simultaneously over a single transmission path. Each lower-speed signal is time sliced into one high-speed transmission. In the simplest example, three incoming 1,000 bps signals (A, B and C) can be interleaved into one outgoing 3,000 bps signal as ABCABCABCABC. The receiving end divides the single stream back into its original signals. TDM enabled the telephone companies to migrate from analog to digital on all their long distance trunks, and later to the local loops. TDM is widely used to combine multiple 64 Kbps streams into the 1.544 Mbps capacity of a T1 channel. For example, a channel bank converts 24 analog voice conversations into digital and then multiplexes them via TDM onto the T1. Contrast with FDM. See TDMA, circuit switching, channel bank and DS.