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Kabel BW Modem

Kabel BW Modem – A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial (HFC) and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in Australia, Europe, Asia and the Americas.


Kabel BW Modem

IEEE 802.3b (10BROAD36)

The IEEE 802 Committee defined 10BROAD36 in 802.3b-1985 as a 10 Mbps IEEE 802.3/Ethernet broadband system to run up to 3,600 metres (11,800 ft) over CATV coax network cabling. The word broadband as used in the original IEEE 802.3 specifications implied operation in frequency-division multiplexed (FDM) channel bands as opposed to digital baseband square-waveform modulations (also known as line coding), which begin near zero Hz and theoretically consume infinite frequency bandwidth. (In real-world systems, higher-order signal components become indistinguishable from background noise.) In the market 10BROAD36 equipment was not developed by many vendors nor deployed in many user networks as compared to equipment for IEEE 802.3/Ethernet baseband standards such as 10BASE5 (1983), 10BASE2 (1985), 10BASE-T (1990), etc.

IEEE 802.7

The IEEE 802 Committee also specified a broadband CATV digital networking standard in 1989 with 802.7-1989. However, like 10BROAD36, 802.7-1989 saw little commercial success.

Hybrid networks

Hybrid Networks developed, demonstrated and patented the first high-speed, asymmetrical cable modem system in 1990. A key Hybrid Networks insight was that in the nascent days of the Internet, data downloading constitutes the majority of the data traffic, and this can be served adequately with a highly asymmetrical data network (i.e. a large downstream data pipe and many small upstream data pipes). This allowed CATV operators to offer high speed data services immediately without first requiring an expensive system upgrade. Also key was that it saw that the upstream and downstream communications could be on the same or different communications media using different protocols working in each direction to establish a closed loop communications system. The speeds and protocols used in each direction would be very different. The earliest systems used the public switched telephone network (PSTN) for the return path since very few cable systems were bi-directional. Later systems used CATV for the upstream as well as the downstream path. Hybrid’s system architecture is used for most cable modem systems today.


LANcity was an early pioneer in kabel bw modems, developing a proprietary system that was widely deployed in the U.S. LANcity, which was led by the Iranian-American engineer Rouzbeh Yassini, was then acquired by Nortel, which eventually spun the kabel modem business off as ARRIS. ARRIS continues to make kabel modems and CMTS equipment compliant with the DOCSIS standard.

Zenith homeworks

Zenith offered a cable modem technology using its own protocol which it introduced in 1993, being one of the first cable modem providers. The Zenith Cable Modem technology was used by several cable television systems in the United States and other countries, including Cox Communications San Diego, Ameritech’s Americast service (later to be sold off to Wide Open West after the SBC / Ameritech merger), and Cogeco in Hamilton Ontario. Zenith Homeworks used BPSK (Bi-Phase Shift Keyed) modulation to achieve 500 Kbit/sec in 600 kHz, or 4 Mbit/sec in 6 MHz.


Com21 was another early pioneer in kabel bw modems, and quite successful until proprietary systems were made obsolete by the DOCSIS standardization. The Com21 system used a ComController as central bridge in CATV network head-ends, the ComPort kabel modem in various models and the NMAPS management system using HP OpenView as platform. Later they also introduced a return path multiplexer to overcome noise problems when combining return path signals from multiple areas. The proprietary protocol was based on Asynchronous Transfer Mode (ATM). The central ComController switch was a modular system offering one downstream channel (transmitter) and one management module. The remaining slots could be used for upstream receivers (2 per card), dual Ethernet 10BaseT and later also Fast-Ethernet and ATM interfaces. The ATM interface became the most popular, as it supported the increasing bandwidth demands and also supported VLANs. Com21 developed a DOCSIS modem, but the company filed for bankruptcy in 2003 and closed. The DOCSIS CMTS assets of COM21 were acquired by ARRIS.


CDLP was a proprietary system manufactured by Motorola. CDLP customer premises equipment (CPE) was capable of both PSTN (telephone network) and radio frequency (cable network) return paths. The PSTN-based service was considered ‘one-way cable’ and had many of the same drawbacks as satellite Internet service; as a result, it quickly gave way to “two-way cable.” Kabel bw modems that used the RF cable network for the return path were considered ‘two-way cable’, and were better able to compete with the bi-directional digital subscriber line (DSL) service. The standard is in little use now while new providers use, and existing providers having changed to the DOCSIS standard. The Motorola CDLP proprietary CyberSURFR is an example of a device that was built to the CDLP standard, capable of a peak 10 Mbit/s downstream and 1.532 Mbit/s upstream. CDLP supported a maximum downstream bandwidth of 30 Mbit/s which could be reached by using several Kabel modems. The Australian ISP BigPond employed this system when it started kabel modem tests in 1996. For a number of years Kabel Internet access was only available in Sydney, Melbourne and Brisbane via CDLP. This network ran parallel to the newer DOCSIS system for several years. In 2004, the CDLP network was terminated and replaced by DOCSIS. CDLP has been also rolled out at the French cable operator Numeric cable before upgrading its IP broadband network using DOCSIS.


Digital Video Broadcasting (DVB) and Digital Audio Visual Council (DAVIC) are European-formed organizations that developed some kabel bw modem standards. However, these standards have not been as widely adopted as DOCSIS.

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