is a significant challenge to the local telephone operating companies. narrowcast A cable television or broadcast program aimed at a very small segment of the market. Typically these are specialized programs likely to be of interest to a relatively limited audience. network Interconnected computers or other hardware and software between which data can be transferred. Network transmission media can vary; it can be optical fiber, metallic media, or a wireless arrangement. Nipkow disc A disc with holes that, when rotated, permit some Video Communication: the Whole Picture light reflected from a screen to hit a photo tube. This creates a minuscule current flow; it is proportionate to the light in the image being reproduced. This was the basis of early television as pioneered by John Logie Baird in England in the 1920s. Paul Nipkow, a German physicist invented it, in 1884. Network Loadable Module. An application that resides in a Novell NetWare server and coexists with the core OS. NLMs are optimized to this environment and provide superior service to applications that run outside the core. A concentration point in a network where numerous trunks come together at the same switch. noise Any unwanted element accompanying program material. This can take the form of snow, random horizontal streaks or large smears of varying color. Network Termination 1, an ISDN standards-based device that converts between the U-Interface and the S/T-Interface. The NT-1 has a jack for the U-Interface from the wall and one or more jacks for the S/T Interface connection to the PC or videoconferencing system, as well as an external power supply National Television Standards Committee, the body formed by the FCC to develop television standards in the US. NTSC video has a format of 525 scan lines. Video is sent at a rate of 30 frames per second in an interlaced format, in which two fields comprise a frame (60 Hz). The bandwidth required to broadcast this signal is 4 MHz. NTSC uses a trichromatic color system known as YIQ. The NTSC signal's line