ards for voice encoding adopted by the ITU. It is used mainly on carrier networks. Appendix Compression Standard Description In-band, on-channel broadcasting uses airwaves within the AM and FM spectrum to broadcast digital programming. IBOC is based on the Perceptual Audio Coder (PAC). There are many sounds that the ear cannot discern because they are masked by louder sounds. PAC discerns and discards these sounds that the ear cannot hear and that are not necessary to retain the observed quality of the transmission. This results in transmission with 15 times fewer bits. PAC was first developed at Bell Labs in the 1930s. Joint Photographic Experts Group is a compression standard used mainly for photographs. The International Standards Organization (ISO) and the ITU developed JPEG. MPEG-1 A Moving Picture Experts Group video compression standard that has been largely displaced by the more powerful MPEG-2 and MPEG-3. MPEG-2 An MPEG standard approved in 1993 for coding and decoding video and television images. MPEG-2 uses past images to predict future images and color. It then transmits only the changed image. For example, the first in a series of frames is sent in a compressed form. The ensuing frames send only the changes. A frame is a group of bits representing a portion of a picture, text, or audio section. MPEG-3 MPEG-3 is Layer 3 of MPEG-1. MPEG-3, also referred to as MP3, is a compression standard for streaming audio. MPEG-3 is the compression algorithm used to download audio files from the Internet. Some Internet e-commerce sites use MPEG SO that potential customers who have applications that use compression software can download samples of music to decide if they want to purchase a particular song. MPEG-4 MPEG-4 is a standard used mainly for streaming and down- loading compressed video and television. It is four times more efficient than MPEG-2. Computing and Enabling Technologies Table 1-2 OSI Layers OSI Layer Name and Number Layer Function Layer 1: Physical Layer Layer 1 is the most basic layer. Layer 1 de