bed the Specialists Group on Coding for Visual Telephony, it was a genuinely international effort that included North American members, enjoyed strong European support, and was chaired by a representative from Japan. Working on two standards simultaneously, the group met more than ten times between late 1984 and 1988. One of the standards was referred to as Mx384; M stood for multiples, the X was pronounced by (i.e., M-by-384), and the 384 represented transmission speed in Kbps. The group expected Mx384 to leverage the internationally-available ISDN HO standard for switched 384 Kbps digital dialing. The second standard was known as Nx64 in which "N" referred to a variable per- second frame rate from 1-30, and "64" referred to the 64 Kbps ISDN B-channel over which a compressed video signal would travel. Standards for Videoconferencing By September 1988, the Specialists Group had completed the Mx384 standard. Unfortunately, it was already obsolete. One year earlier, an American manufacturer had introduced a product that delivered adequate picture and sound quality at 224 Kbps. Although the Specialists Group recommended that the CCITT General Assembly formally ratify Mx384, none of the world's codec manufacturers ever built products that conformed to it. Instead, they waited for the Nx64 standard (which was later renamed Px64). During the process of developing Px64 (pronounced P times 64), Study Group XV (the term Study Group replaced the term Specialists Group) had to consider many alternative compression algorithms. No single method offered the efficiency and flexibility to meet the group's goals, SO they combined techniques. Unable to afford the time or expense required to model every coding iteration, the Group used computer-based simulation systems that consisted of digitally sampled video sequences. To simulate picture-coding algorithms, they applied various computer programs to the sequence. After compression, they viewed and evaluated the results, made changes, and re-applied the simulated coding process. Ev