It differs from broadcast television in that the signal is not openly transmitted, though it may employ point to point P2P, point to multipoint P2MP, or mesh wired or wireless links. Though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that may need monitoring such as banks, stores, and other areas where security is needed. Though Videotelephony is seldom called 'CCTV' one exception is the use of video in distance education, where it is an important tool. In industrial plants, CCTV equipment may be used to observe parts of a process from a central control room, for example when the environment is not suitable for humans. CCTV systems may operate continuously or only as required to monitor a particular event. A more advanced form of CCTV, utilizing digital video recorders DVRs, provides recording for possibly many years, with a variety of quality and performance options and extra features such as motion detection and email alerts. More recently, decentralized IP cameras, perhaps equipped with megapixel sensors, support recording directly to network attached storage devices, or internal flash for completely stand alone operation. The earliest video surveillance systems involved constant monitoring because there was no way to record and store information. The development of reel to reel media enabled the recording of surveillance footage. These systems required magnetic tapes to be changed manually, which was a time consuming, expensive and unreliable process, with the operator having to manually thread the tape from the tape reel through the recorder onto an empty take up reel. Due to these shortcomings, video surveillance was not widespread.