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Commercially successful application of data communications technology to coaxial cable distribution networks requires the creation of systems useful to large numbers of subscribers sharing common communications procedures. Furthermore, it is desirable, particularly in entertainment CATV networks, that subscriber ownership of some or all terminal equipment and peripheral attachments be possible since such ownership enables the sharing of capital costs between the network operator and the subscriber. Systems designers are led inescapably to the need for standard interfaces and protocols. The paper describes some of the major types of cable data systems currently under development for both institutional and entertainment network applications. Common to both is the concept of a local interface unit to act as a link between the subscriber's terminal equipment and the cable drop. The design of the drop-side interface of this unit raises some major standardization issues. Another important issue is that of compatibility between data and video channels where both types of services are offered on the same cable television plant. The major thrust of present standardization activity has been founded upon the open systems interconnection (OSI) reference model and has taken place within a joint CVCC/EIA committee on teletext and within the IEEE Project 802.6 subcommittee on metropolitan area networks. The paper reviews this activity and explains the principal issues to be resolved.