uest. If it cannot, it rejects the request until adequate bandwidth becomes available. For this reason, ATM is an ideal networking technology for interactive streaming media. Although ATM and ISDN are mistakenly thought of as separate technologies, it is ATM is, in fact, a B-ISDN implementation. Cell switching is the protocol that is used Video Communications: The Whole Picture to move packets across B-ISDN and ATM networks. B-ISDN, and its real-world manifestation, ATM, blur distinctions between circuit- and packet-switching. Digital Subscriber Line (DSL) As metropolitan cable service operators (MSO) increasingly offer VoIP telephone services, Telcos are striking back by offering video over digital subscriber line (DSL). The H.264/AVC video compression standard is making this practical. At bandwidths of up to eight Mbps, DSL exceeds the requisite two Mbps necessary for broadcast- quality MPEG-2 digital video. However, since most subscribers' bandwidth tops out at about 1.5 Mbps, they are limited to streaming MPEG-4 SP (MPEG-4 Simple Profile). Multimedia Research Group, Inc. expects worldwide IP video services subscriptions to grow to eight million by 2007, and for US revenue to reach about $6 billion in that period. H.264/AVC reduces full-screen DVD-quality digital transmission bandwidth requirements to 700 Kbps. By reflecting the adoption of a video communications standard (H.264) for video broadcast and the desire for Telcos to boost ARPU (average revenue per user) by adding IP services, this vignette illustrates the merging of broadcast video and video communications. For decades, Telcos have used HDSL to conserve wire pairs without sacrificing T1 speeds. However, in 1989, Bellcore conceived an idea for transmitting video, audio, and data, at rates of more than one Mbps over ordinary twisted-pair telephone lines. The crux of the idea was to transfer information more quickly in one direction than in the other (asymmetrically), with downstream rates of 1.5 Mbps and upstream rates of 16 or 64 Kbps. Such asymmetr