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Zenith Cable Modem was one of the first proprietary cable modems. The two basic models are one operating at 500 kilobits per second (kbit/s), and the other at 4 megabits per second (mbit/s) with BPSK and approximately a 25% alpha. ==History== The Zenith Cable Modem was originally developed for a mid-split cable network in the mid-1980s. It was used as an eight-bit full-height PC/AT-type card containing an Intel 80186 dedicated CPU, connected to an external white box about 2"x12"x6". Other similar products were made by Ungermann-Bass (UB) under the 10BROAD36 standard and Vitalink. UB had models supporting RS-232 and Ethernet outputs, as well as a re-modulating frequency translator. In late 1993, Zenith Electronics and Prodigy provided 12 modified 500 Kbit "white modems" to Cox Communications in San Diego, including two with IBM Microchannel support. These modified modems were intended to support the Prodigy Cable Modem trial, which began on a 1500 homes-passed fiber node in El Cajon, CA. The modification allowed sub-split operation, with a fixed upstream frequency and a downstream at 74.75 MHz, within the 4 MHz space between analog channels 4 and 5. The initial trial consisted of a Prodigy server in the El Cajon headend, connected via the Microchannel-based cable modem to an Olsen Frequency Translator. This basic network supported the 1500 home passed fiber nodes, with six "subscribers" including one employee of Cox, who was also the head-end manager. One card was installed in rackmount PC in the Federal headend, another in the El Cajon headend. 1500 high pass filters were installed to eliminate any ingress from the drops. Service was reasonably reliable''.'' Zenith updated their white modems to a matte black case, adding the Homeworx name and marketing to cable operators at the $350 price range for 250 units. The new design used the same size external case, added LEDs to indicate power/TX/RX/activity and replaced the full sized eight-bit ISA card with a smaller 16 bit version. The new design dropped the onboard CPU. The modem connected to the card used a 15-pin D-shell connector—which exactly matched the PC's game connector. Both models were powered by the PC. The new modem was frequency agile, with a configuration utility that ran on the PC to set up US and DS frequencies. The option to configure the card's MAC address was soon dropped. However, the card's MAC address was not printed on the outside of the board, and thus was invisible once installed in the PC. Nor was the MAC address printed in a machine readable (bar code) format. Cox added these to the CM prior to installation, and tracked the subscriber to modem MAC address in an Excel spreadsheet, as the MAC address contained too many digits to fit into any fields within the customer billing system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zenith Cable Modem」の詳細全文を読む スポンサード リンク
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