tional timing signal. Maximum distance approx. Serial Transmission: Data is sent bit by bit. Suitable for long-distance transmission. Telecommunications Data is coded in such a way that timing network information is received with the data and only one channel is needed. In short-distance transmission DTE = Data terminal DCE = Data circuit additional wire may be used for timing equipment, terminating equipment, (clock signal). for example, PC for example, a modem Figure 6.1 Serial and parallel transmission. Data Communications over longer distances we want to manage with one channel and we have to use a line code to insert timing information into the data stream. This syn- chronization information enables the receiver to determine when it has to detect each individual received bit. How we implement this depends on whether we use an asynchronous or synchronous transmission mode, as described in Section 6.1.3. If a computer needs to communicate with, for example, a printer in the same room, parallel communication is often used. A special cable with several wires is provided between the computer and the printer and all 8 bits of a data word, corresponding to one character, are transferred at the same time in parallel over the cable. Parallel data transmission is much quicker than serial, but we can typically use it only over short distances. The maximum is usually of the order of 10m. Communicating terminal devices in data communications are called data terminal equipment (DTE) and the equipment that terminates the trans- mission channel that goes through the network is called data circuit- terminating equipment (DCE). A modem that we use for data transmission over a telephone network is a typical example of DCE. Many different inter- face specifications exist for DTE and DCE, and the most common standards are defined by the ITU-T and the Electronic Industries Association (EIA). One of the most common data interfaces is ITU-T's V.24/V.28, which corre- sponds to EIA Standard RS-232-C. 6.1.3 Asynchronous and Synchronou