[转帖]Cable Modem 标准和规范简介(英文)

Two international standards have emerged for cable modem products: DOCSIS, which is the standard in North America and in other International markets, and DVB/DAVIC EuroModem, which is the emerging standard in Europe.<br>
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The DOCSIS Standard<br>
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The Institute of Electronic and Electrical Engineering (IEEE) 802.14 Cable TV Media Access Control (MAC) and Physical (PHY) Protocol Working Group was formed in May 1994 by vendor engineers to develop an international cable modem standard. The group set a publication goal of December 1995, but missed that target by more than two years. <br>
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Tired of waiting for IEEE 802.14, cable operators combined their purchasing power to jumpstart the standards process. In January 1996, MSOs Comcast, Cox, TCI (now AT&T), and Time Warner formed a limited partnership called Multimedia Cable Network System Partners Ltd. (MCNS) to research and publish their own cable modem system specifications. MediaOne Group, Rogers Cablesystems and Cable Television Laboratories Inc. also signed on to the initiative. <br>
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MCNS released its draft standard, called the Data Over Cable Service Interface Specification (DOCSIS 1.0), to the manufacturing community in March 1997. Vendors immediately began building prototype products and the first public interoperability demonstration of DOCSIS equipment was held in December 1997. <br>
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In early 1998 CableLabs began a formal certification program for DOCSIS equipment to ensure products built by different manufacturers are indeed compatible. In March 1998, the International Telecommunications Union (ITU) accepted DOCSIS as a cable modem standard, called ITU J.112. <br>
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To deliver DOCSIS data services over a cable television network, one 6 MHz radio frequency (RF) channel in the 50 - 750 MHz spectrum range is typically allocated for downstream traffic to homes and another channel in the 5 - 42 MHz band is used to carry upstream signals. <br>
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A headend cable modem termination system (CMTS) communicates through these channels with cable modems located at the customer premise. Most cable modems are external devices that connect to a personal computer through a standard 10Base-T Ethernet card and Category 5 wiring, although external Universal Serial Bus (USB) modems and internal PCI modem cards are also becoming available. <br>
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CableLabs manages a certification process to ensure DOCSIS cable modems manufactured by different vendors comply with the standard and are interoperable. Those products that pass the tests earn the right to affix a seal marked &quot;CableLabs Certified&quot; to their DOCSIS cable modem packaging, informing buyers that the product is guaranteed to interoperate with other certified products. <br>
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CableLabs is not formally certifying DOCSIS headend CMTS products since the equipment is purchased directly by cable operators, however it is &quot;qualifying&quot; CMTS units. Although the qualification process is less rigid than modem certification, the label is an indication of CMTS product stability and interoperability. <br>
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In April 1999 CableLabs issued a second-generation specification called DOCSIS 1.1, which adds key enhancements to the original standard, such as improved QoS and hardware-based packet-fragmentation capabilities, to support IP telephony and other constant-bit-rate services. In short, DOCSIS 1.1 provides the bandwidth and latency guarantees required to offer toll-quality voice, dedicated business-class data services and multimedia applications across a shared cable modem access network. The next-generation standard is designed to be backward compatible, enabling DOCSIS 1.0 and 1.1 modems to operate in the same spectrum on the same network. <br>
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In addition to 1.1, CableLabs is eyeing a third-generation DOCSIS standard, tentatively called DOCSIS 1.2, which would add an advanced PHY to the core specification to increase upstream transmission capacity and reliability. The plan is to use frequency-agile time division multiple access (FA-TDMA) technology advocated by Broadcom and synchronous code division multiple access (S-CDMA) technology developed by Terayon Communication Systems. <br>
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More than 30 vendors are now building DOCSIS cable modem products. Additional information on the DOCSIS standard is available online at <a target=_blank href=http://www.cablemodem.com/>http://www.cablemodem.com/</a><br>
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DVB/DAVIC EuroModem<br>
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Digital Video Broadcast (DVB) and Digital Audio Video Council (DAVIC) technology is the incumbent European standard for digital set-tops and is now starting to gain momentum for cable modems. With support by more than 15 vendors, DVB/DAVIC is challenging DOCSIS for dominance in Europe. <br>
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EuroCableLabs (ECL), operating under the direction of the European Cable Communications Association (ECCA), has championed a DVB/DAVIC-based &quot;EuroModem&quot; as an alternative to DOCSIS. DVB cable modems meet the preference of some European operators for a standard that better fits their set-top architectures. There is also a desire to support home-grown Euro products, rather than importing solutions from American suppliers. <br>
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The DVB 2.0 specification has been formally adopted by the European Telecommunications Standards Institute (ETSI) as ETS 300800. The standard describes the out-of-band and in-band transmission options applicable to interactive set-top boxes and cable modems, respectively, enabling the deployment of interactive TV, data and voice services over a common platform. ETS 300800 has also been selected by DAVIC to be the DAVIC 1.5 specification for cable modems. <br>
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ECCA/ECL issued its DVB/DAVIC-based EuroModem product specification on May 12, 1999. Shortly thereafter, an ECCA-affiliated EuroModem Consortium of 13 cable operators issued a tender to purchase 250,000 to 500,000 cable modems for delivery between by December 2000. These operators serve a combined 25 million cable subscribers in nine European, including Cablecom (Switzerland), Cablelink (Ireland), Deutsche Telekom (Germany), France Telecom Cable, Helsinki Media (Finland), NV Casema (Netherlands), NV CasTel (Netherlands), O.tel.o. (Germany), Palet Kabelcom (Netherlands), StjarnTV (Sweden), Tele Danmark (Denmark), Telenor Avidi (Norway), and Telia InfoMedia TeleVision (Sweden). <br>
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A total of 24 vendors replied to the modem tender. From this group, the consortium selected a &quot;short list&quot; of preferred EuroModem equipment suppliers, as follows: Thomson Multimedia and Thomson Broadcast, Com21, Hughes, COCOM (acquired by Cisco Systems), The Industree, Netgame, DeltaKabel, ECI Telecom, Hirschmann, Kongsung, Kathrein, Telsey, and Sagem. <br>
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The DVB/DAVIC Interoperability Consortium, a vendor group formed to foster open standards and compatibility for EuroModems, plans to implement an interoperability initiative that involves decentralized vendor testing at a University lab. Results will be documented and submitted to a review board and published on a public Web site starting in the first quarter 2000. <br>
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More information on the EuroModem standard is available online at <br>

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