Telegraph transmission is symbolic, sending a telegram, the first message was translated into code millet phone line recycling, reuse telegraph sent. In the closed side, to go through the reverse process, the upcoming received code translated into packets and then sent to the person close at hand. This is not only troublesome, but also can not be a two-way exchange of information in a timely manner. Therefore, people began to explore a direct way of transmitting the human voice phone, which is now known to everybody 'phone'. Europe for long-distance transmission of voice studies began in the 18th century, in 1796, Hughes made the transmission of voice information using the microphone relay approach. Although this method is not practical, but he gave a name one way this phone 131 100 'phone), still in use. 1861 Sony phone lines recovery, a German teacher invented the most primitive telephones, using acoustic principle can talk to each other at a short distance, but you can not put people really use twisted pair is provided with an insulating layer formed by a pair of copper line, twisted together in a spiral manner posed. The twisted pair cable is typically one or more pairs of such twisted pairs thereof. FIG 2'1 FIG. Insulating materials to make two lines of metal conductor Hu Peng will not lead to a short circuit. UTP is usually a balanced signal, that is, while the data transmission signal line is recovered in the two wires, respectively, the phase of the signal carried by 180. . Effects of electromagnetic interference from outside to bring the two wires will cancel each other out 'so that the signal will not decay rapidly. Helical structure also helps to offset the current flowing through the wire the process may increase the capacitance. And if the two will form a pair of parallel wire antenna, there is no such offsetting effects. Multiple pairs are usually bundled together and topical protective layer. Thus, a bundle of cables can be buried together. Compared with other transmission media data recovery company line, twisted pair transmission distance, channel width, and data transfer speed, etc. are subject to certain restrictions, but the price is relatively cheap. For a long time, UTP has been widely used in the construction of a telephone handset and a LAN. Cabling project is the most common kind of transmission medium. Conductor insulation