ry complexity and cost to cable modem systems. MCNS members' intent was to leverage the low costs of ubiquitous Ethernet and IP networking technologies. Standardized DOCSIS cable modems started shipping in limited quantities in the third and fourth quarters of 1998. DOCSIS defines MPEG-2 transport for the downstream transmission convergence sublayer. MPEG-2 allows both video and data signals to be carried in a single multiplexed bit stream that occupies one analog channel, and thereby preserve channel capacity. The ITU recognition DOCSIS as an international standard in 1998, but the IEEE 802.14 continued its own work. In a token gesture to acknowledge the Working Group's work, MCNS indicated that it would implement IEEE 802.14's advanced PHY specification within DOCSIS. In meeting that commitment, MCNS asked the vendors whom the IEEE had selected to develop an advanced PHY for its own standard, to develop the advanced PHY for DOCSIS 1.2. Many believed that the IEEE 802.14 specification might become a standard for operators outside North America, or that the specification might apply to corporate data services, while DOCSIS would be deployed for residential services. These speculations now seem improbable. Despite good intentions and a better specification than that developed by MCNS, IEEE 802.14 was simply unable to complete a specification in time. DOCSIS 1.0, first issued on March 1997, offered support for high speed data services. It was a huge success; 30-million DOCSIS modems shipped worldwide as of Q3-2003. DOCSIS 1.1, first issued on March 1999, introduced support for telephony, gaming, and streaming media, and allowed for QoS, service security, and backward compatibility with DOCSIS 1.0. DOCSIS 2.0, first issued on December 2001, added the capacity for symmetric services, increased upstream capacity, improved robustness against interference (A-TDMA and S-CDMA), and backward compatibility with DOCSIS 1.0 and 1.1. For the downstream physical layer, DOCSIS 1.0 specifies ITU J.83B digital data distribution ov