Cable modem

Internet Experiment Note (IEN) 96[1] (1979) describes an early RF cable modem system.

Similar cable-bus systems are in operation at a number of government sites, e.g. Walter Reed Army Hospital, and the NASA Johnson Space Center, but these are all standalone, local-only networks.

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.

Hybrid Networks developed, demonstrated and patented the first high-speed, asymmetrical cable modem system in 1990.

This allowed CATV operators to offer high-speed data services immediately without first requiring an expensive system upgrade.

[7] Because of contractual agreements with Antec involving this joint venture, Nortel spun the LANCity group out into the ARRIS Interactive joint-venture.

The Zenith Cable Modem technology was used by several cable television systems in the United States and other countries, including Cox Communications San Diego, Knology in the Southeast United States, Ameritech's Americast service (later to be sold off to Wide Open West after the SBC / Ameritech merger), Cogeco in Hamilton Ontario and Cablevision du Nord de Québec in Val-d'Or.

[8] Zenith Homeworks used BPSK (Bi-Phase Shift Keyed) modulation to achieve 500 Kbit/sec in 600 kHz, or 4 Mbit/sec in 6 MHz.

[9] Com21 was another early pioneer in cable modems, and quite successful until proprietary systems were made obsolete by the DOCSIS standardization.

The central ComController switch was a modular system offering one downstream channel (transmitter) and one management module.

CDLP customer premises equipment (CPE) was capable of both PSTN (telephone network) and radio frequency (cable) return paths.

CDLP has been also rolled out at the French cable operator Numericable before upgrading its IP broadband network using DOCSIS.

However, the 802.14 working group was disbanded when North American multi system operators (MSOs) instead backed the then-fledgling DOCSIS 1.0 specification, which generally used best-effort service and was IP-based (with extension codepoints to support ATM[11] for QoS in the future).

MSOs were interested in quickly deploying service to compete for broadband Internet access customers instead of waiting on the slower, iterative, and deliberative processes of standards development committees.

Albert A. Azzam was Secretary of the IEEE 802.14 Working Group,[12] and his book, High-Speed Cable Modems,[13] describes many of the proposals submitted to 802.14.

Although the Internet Engineering Task Force (IETF) generally does not generate complete cable modem standards, the IETF chartered Working Groups (WGs) that produced various standards related to cable modem technologies (including 802.14, DOCSIS, PacketCable, and others).

While deployed DOCSIS RFI 1.0 equipment generally only supported best-effort service, the DOCSIS RFI 1.0 Interim-01 document discussed quality of servce (QoS) extensions and mechanisms using IntServ, RSVP, RTP, and Synchronous Transfer Mode (STM) telephony (as opposed to ATM).

In 2004, the Multimedia over Coax Alliance (MoCA) was established to develop industry standard for the connected home, using the existing coaxial cabling.

Some high-speed Internet customers may use VoIP telephony by subscribing to a third-party service, such as Vonage, MagicJack+ and NetTALK.

Some cable modems may incorporate a router and a DHCP server to provide the LAN with IP network addressing.

While this is a common occurrence and usually unnoticed, if a modem's flap is extremely high, these disconnects can cause service to be disrupted.