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Working with some key suppliers of digital technology, Cable Television Laboratories, Inc., and its members, have agreed upon a specification establishing the basic building blocks of digital services, allowing set-top terminals and data modems built by different manufacturers to work together on the same cable system. CableLabs expects that many of its members will purchase equipment that complies with this specification. The specification covers how cable television systems will transport digital video and data in standard 6 MHz cable channels. In the specified digital transmission systems, the payload data rate will be between 27 and 40 Mbit/s.
"This specification will advance the industry's ability to deploy digital set-top boxes and cable modems in a cost-effective manner", says Time Warner Cable chief technician James Chiddix according to a press release. "That will benefit the cable customer and the cable operator dramatically, with lower price points and more choice." This inter-operable digital cable specification will allow the simultaneous co-existence in the same cable system of set-top terminals and data modems from a variety of manufacturers.
Ongoing research on high-speed cable modems at American CableLabs indicates that cable operators in one data channel on a single node will be able to support 100s of users simultaneously with no noticeable degradation of performance. Cable Labs is advancing quickly with its evaluation of high-speed cable modems, including activities that explore a series of architectures-related questions involving applications, testing and modelling.
The applications being tested vary widely in their function, given that high-speed cable modems are used for a wide range of applications which vary in bandwidth intensity and quality of service. These include, but are not limited to, Web surfing, electronic mail, file transfer-protocol, streaming audio and video, videoconferencing, Internet phone, and "cable telecommuting".
These specific applications were chosen for testing cable modems because "they are the most realistic of residential Internet access in the Cable environment", says Bob Cruickshank, director of data applications at Cable Labs. "There is an incredible pent-up demand for Internet access - applications are changing and becoming more exciting for users."
Testing experience shows that most cable modems differentiate themselves in performance. The testing is being conducted to assess the performance of each vendor's cable modem system in several important areas such as:
By examining various applications via testing and modelling, Cable Labs is looking for answers to three questions:
The next part of our series on high-speed data communications will focus on cable modems. But please, dear reader, let us hear from you about what is going on in Europe for a change!
By Paul Devoldere, BBN, 01.11.1996