Edit filter log

'{{Refimprove|date=August 2010}} [[File:SBV6120E.jpg|thumb|right|[[Motorola]] SURFboard SBV6120E EuroDOCSIS 3.0 cable modem]] A '''cable modem''' is a type of [[network bridge]] and that provides bi-directional data communication via [[radio frequency]] channels on a [[hybrid fibre-coaxial]] (HFC) and [[radio frequency over glass]] (RFoG) infrastructure. Cable modems are primarily used to deliver [[broadband Internet access]] in the form of [[cable Internet]], taking advantage of the high [[Bandwidth (signal processing)|bandwidth]] of a HFC and RFoG network. They are commonly deployed in [[Australia]], [[Europe]], [[Asia]] and the [[Americas]]. ==History== ===MITRE Cablenet=== [[Internet Experiment Note|Internet Experiment Note (IEN)]] 96<ref name="IEN 96">[ftp://ftp.rfc-editor.org/in-notes/ien/ien96.txt IEN 96] - The [[MITRE]] Cablenet Project</ref> (1979) describes an early [[Radio frequency|RF]] cable modem system. From pages 2 and 3 of IEN 96: <blockquote>The Cable-Bus System The MITRE/Washington Cablenet system is based on a technology developed at MITRE/Bedford. Similar cable-bus systems are in operation at a number of government sites, e.g. [[Walter Reed Army Medical Center|Walter Reed Army Hospital]], and the [[NASA]] [[Lyndon B. Johnson Space Center|Johnson Space Center]], but these are all standalone, local-only networks. The system uses standard [[Cable television|Community Antenna Television]] (CATV) [[coaxial cable]] and microprocessor based Bus Interface Units (BIUs) to connect subscriber [[computer]]s and [[Terminal (telecommunication)|terminals]] to the cable. ... The cable bus consists of [[Four-wire circuit|two parallel]] coaxial cables, one inbound and the other outbound. The inbound cable and outbound cable are connected at one end, the [[Cable television headend|headend]], and [[Electrical termination|electrically terminated]] at their other ends. This architecture takes advantage of the well developed [[Simplex communication|unidirectional]] CATV [[Distribution amplifier|components]].<ref name="RF Micro Devices, Inc. Whitepaper Describing Historical CATV Components">{{cite web|url=http://www.piedmontscte.org/resources/CATV+Hybrid+Amplifier+Modules+Past$2C+Present$2C+FutureWP.pdf|format=PDF|title=RF Micro Devices, Inc. Whitepaper Describing Historical CATV Components|website=Piedmontscte.org|accessdate=2016-08-03|quotation=Amplifiers are one of the common components used in CATV system}}</ref> The [[Network topology|topology]] is dendritic (i.e. [[Tree topology|branched like a tree]]).<br/> ...<br/> The BIUs contain [[Radio frequency|Radio Frequency]] (RF) modems which [[Modulation|modulate]] a [[Carrier signal|carrier]] [[Signal (electrical engineering)|signal]] to transmit [[Digital signal (electronics)|digital]] [[Information theory|information]] using 1 [[Hertz|MHz]] of the available [[Bandwidth (signal processing)|bandwidth]] in the 24 MHz frequency range. The remainder of the 294 MHz bandwidth can be used to carry other information [[Channel (communications)|channels]], such as [[Terrestrial television|off-the-air]] [[NTSC|TV]], [[FM radio|FM]], [[Closed-circuit television|closed circuit TV]], or a [[Voice frequency|voice]] [[Digital Telephony|telephone system]], or, other digital channels. The [[Bit rate|data rate]] of our test-bed system is 307.2 [[Data rate units|kbps]].</blockquote> ===IEEE 802.3b (10BROAD36)=== The [[Institute of Electrical and Electronics Engineers|IEEE]] [[IEEE 802|802 Committee]] defined [[10BROAD36]] in [[10BROAD36|802.3b-1985]]<ref name="IEEE 802.3b (10BROAD36) Standard">[http://standards.ieee.org/findstds/standard/802.3b-1985.html IEEE 802.3b-1985 (10BROAD36)] - Supplement to 802.3: Broadband Medium Attachment Unit and Broadband Medium Specifications, Type 10BROAD36 (Section 11)</ref> as a 10 [[Bit rate|Mbit/s]] [[IEEE 802.3]]/[[Ethernet]] broadband system to run up to {{convert|3600|m}} over CATV coax network cabling. The word ''[[broadband]]'' as used in the original IEEE 802.3 specifications implied operation in [[Multiplexing#Frequency-division multiplexing|frequency-division multiplexed]] ([[Frequency-division multiplexing|FDM]]) [[Channel (communications)|channel]] bands as opposed to digital ''[[baseband]]'' [[Square wave|square-waveform]] [[modulation]]s (also known as [[Line code|line coding]]), which begin near zero [[Hertz|Hz]] and [[Fourier series|theoretically]] consume [[Square wave#Fourier Analysis|infinite]] [[Bandwidth (signal processing)|frequency bandwidth]]. (In real-world systems, higher-order [[Signal (electrical engineering)|signal]] [[Square wave#Fourier Analysis|components]] become indistinguishable from background [[Signal-to-noise ratio|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#Baseband Ethernet|baseband]] standards such as [[10BASE5]] (1983), [[10BASE2]] (1985), [[Ethernet over twisted pair|10BASE-T]] (1990), etc. ===IEEE 802.7=== The [[Institute of Electrical and Electronics Engineers|IEEE]] 802 Committee also specified a broadband CATV digital networking standard in 1989 with [[IEEE 802.7|802.7-1989]].<ref name="IEEE 802.7-1989 Standard">{{cite web|url=http://standards.ieee.org/findstds/standard/802.7-1989.html |title=IEEE SA - 802.7-1989 - Local Area Networks: IEEE Recommended Practice: Broadband Local Area Networks |website=Standards.ieee.org |date=1990-03-09 |accessdate=2016-08-03}}</ref> 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=== LANcity was an early pioneer in cable 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 cable modem business off as [[Arris Group|ARRIS]]. ARRIS continues to make cable modems and [[CMTS]] equipment compliant with the [[DOCSIS]] standard. ===Zenith homeworks=== [[Zenith Electronics|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, Knology in the Southeast United States, [[Ameritech]]'s Americast service (later to be sold off to [[Wide Open West]] after the SBC / Ameritech merger), and Cogeco in Hamilton Ontario.<ref>{{cite news|title=Americast Places $1-Billion Order for Set-Top Boxes |publisher=''[[Los Angeles Times]]''|author=Sallie Hofmeister|url=http://articles.latimes.com/1996-08-23/business/fi-36983_1_set-top-boxes|accessdate=2010-08-28 | date=1996-08-23}}</ref> Zenith Homeworks used BPSK (Bi-Phase Shift Keyed) modulation to achieve 500 Kbit/sec in 600&nbsp;kHz, or 4 Mbit/sec in 6&nbsp;MHz.<ref>{{cite book|title=Network Design: Principles and Applications|author=Gilbert Held|year=2000|page=765|publisher=Auerbach Publications|url=https://books.google.com/books?id=06uBL8vGpoIC&pg=PA765&dq=zenith+cable+modem#v=onepage&q=zenith%20cable%20modem&f=false|isbn=978-0-8493-0859-8}}</ref> ===Com21=== {{main|Com21}} [[Com21]] was another early pioneer in cable 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 cable 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 [[VLAN]]s. 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 Group|ARRIS]]. ===CDLP=== CDLP was a proprietary system manufactured by [[Motorola]]. CDLP [[customer premises equipment]] (CPE) was capable of both [[PSTN|PSTN (telephone network)]] and [[cable network|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." Cable 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 cable modems. The [[Australia]]n ISP [[BigPond]] employed this system when it started cable modem tests in 1996. For a number of years [[cable 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 [[Numericable]] before upgrading its IP broadband network using DOCSIS. ===DVB/DAVIC=== [[Digital Video Broadcasting]] ([[Digital Video Broadcasting|DVB]]) and [[DAVIC|Digital Audio Visual Council]] (DAVIC) are European-formed organizations that developed some cable modem standards. However, these standards have not been as widely adopted as DOCSIS. ===IEEE 802.14=== In the mid-1990s the [[IEEE 802]] committee formed a subcommittee (802.14)<ref name="IEEE 802.14 WG Homepage">{{cite web|url=http://walkingdog.com/ |title=WalkingDog.com |accessdate=2012-05-13 |deadurl=bot: unknown |archiveurl=https://web.archive.org/web/19961226193928/http://walkingdog.com/ |archivedate=1996-12-26 |df= }} The IEEE 802.14 Working Group used WalkingDog.com as its web site.</ref> to develop a standard for cable modem systems. IEEE 802.14 developed a draft standard, which was [[Asynchronous Transfer Mode|ATM-based]]. However, the [[IEEE 802.14|802.14]] working group was disbanded when North American [[multiple system operator|multi system operators]] ([[multiple system operator|MSOs]]) instead backed the then-fledgling [[DOCSIS|DOCSIS 1.0]] specification, which generally used [[Best-effort|best efforts service]] and was [[Internet Protocol|IP-based]] (with extension [[Code point|codepoints]] to support [[Asynchronous Transfer Mode|ATM]]<ref name="DOCSIS RFI 1.0-I01">[http://www.cablelabs.com/specifications/SP-RFI-I01-970326.pdf DOCSIS RFI 1.0-I01 (March 26, 1997)] {{webarchive|url=https://web.archive.org/web/20110525094347/http://www.cablelabs.com/specifications/SP-RFI-I01-970326.pdf |date=May 25, 2011 }} (See section 6.2.3 for the DOCSIS [[Asynchronous Transfer Mode|ATM]] codepoint. See sections 6.1.2.3, 6.2.5.3, 6.4.7, 9, and 9.2.2 for DOCSIS 1.0 [[Quality of service|QoS]] mechanisms.)</ref> for [[Quality of service|QoS]] in the future). [[multiple system operator|MSOs]] were interested in quickly deploying service to compete for [[Internet access|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,<ref name="IEEE 802.14 WG Officers">{{cite web|url=http://www.walkingdog.com/catv/officers.htm |title=IEEE 802.14 WG Officers |accessdate=2012-05-13 |deadurl=bot: unknown |archiveurl=https://web.archive.org/web/19970129161548/http://www.walkingdog.com/catv/officers.htm |archivedate=1997-01-29 |df= }}</ref> and his book, ''High-Speed Cable Modems'',<ref name="Azzam - High Speed Cable Modems">Albert A. Azzam, ''High-Speed Cable Modems'' {{ISBN|978-0-07-006417-1}}</ref> describes many of the proposals submitted to 802.14. ===IETF=== Although the [[Internet Engineering Task Force]] (IETF) generally does not generate complete cable modem standards, the IETF chartered [[Working group|Working Groups]] ([[Working group|WGs]]) that produced various standards related to cable modem technologies (including 802.14, DOCSIS, [[PacketCable]], and others). In particular, the IETF WGs on IP over Cable Data Network (IPCDN)<ref name="IETF IPCDN WG">{{cite web|url=http://tools.ietf.org/wg/ipcdn/ |title=Ipcdn Status Pages |website=Tools.ietf.org |date= |accessdate=2016-08-03}}</ref> and IP over [[Digital Video Broadcasting]] (DVB)<ref name="IETF IPDVB WG">{{cite web|url=http://tools.ietf.org/wg/ipdvb/ |title=Ipdvb Status Pages |website=Tools.ietf.org |date= |accessdate=2016-08-03}}</ref> produced some standards applicable to cable modem systems, primarily in the areas of [[Simple Network Management Protocol]] (SNMP) [[Management information base|Management Information Bases]] ([[Management information base|MIBs]]) for cable modems and other networking equipment that operates over CATV [[Television network|networks]]. ===DOCSIS=== {{main|DOCSIS}} In the late 1990s, a consortium of US [[Multiple system operator|cable operators]], known as "MCNS" formed to quickly develop an open and interoperable cable modem specification. The group essentially combined technologies from the two dominant proprietary systems at the time, taking the [[physical layer]] from the [[Motorola]] [[Cable Modem#CDLP|CDLP]] system and the [[MAC layer]] from the LANcity system. When the initial specification had been drafted, the MCNS consortium handed over control of it to [[CableLabs]] which maintained the specification, promoted it in various standards organizations (notably [[SCTE]] and [[ITU]]), developed a certification testing program for cable modem equipment, and has since drafted multiple extensions to the original specification. While deployed [[DOCSIS|DOCSIS RFI 1.0]] equipment generally only supports [[Best-effort|best efforts service]], the DOCSIS RFI 1.0 Interim-01 document discussed [[Quality of service|QoS]] extensions and mechanisms using [[Integrated services|IntServ]], [[Resource Reservation Protocol|RSVP]], [[Real-time Transport Protocol|RTP]], and Synchronous Transfer Mode (STM) [[telephony]] (as opposed to [[Asynchronous Transfer Mode|ATM]]).<ref name="DOCSIS RFI 1.0-I01"/> [[DOCSIS|DOCSIS RFI 1.1]]<ref name="DOCSIS RFI 1.1-I01">[http://www.cablelabs.com/specifications/SP-RFIv1.1-I01-990311.pdf DOCSIS RFI 1.1-I01 (March 11, 1999)]{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }} (See section 8 and Appendix M.)</ref> later added more robust and standardized [[Quality of service|QoS]] mechanisms to DOCSIS. [[DOCSIS|DOCSIS 2.0]] added support for [[Synchronous Code Division Multiple Access|S-CDMA]] [[PHY (chip)|PHY]], while DOCSIS 3.0 added [[Internet Protocol version 6|IPv6]] support and [[channel bonding]] to allow a single cable modem to use concurrently more than one upstream channel and more than one downstream channel in parallel. Virtually all cable modems operating in the field today are compliant with one of the DOCSIS versions. Because of the differences in the European [[PAL]] and USA's [[NTSC]] systems two main versions of DOCSIS exist, DOCSIS and EuroDOCSIS. The main differences are found in the width of RF-channels: 6&nbsp;MHz for the USA and 8&nbsp;MHz for Europe. A third variant of DOCSIS was developed in [[Japan]] and has seen limited deployment in that country. Although interoperability was the whole point of the DOCSIS project,<ref>{{cite web|url=http://stuff.mit.edu/afs/sipb.mit.edu/contrib/doc/DOCSIS/overview/certification/Certification_Overview.pdf |format=PDF |title=DOCSIS Modem Interoperability and Certification Overview |website=Stuff.mit.edu |accessdate=2016-08-03}}</ref> most cable operators only approve a very restricted list of cable modems on their network,<ref>{{cite web|url=http://teksavvy.com/en/residential/internet/cable |title=Cable |website=TekSavvy.com |date= |accessdate=2016-08-03}}</ref><ref>{{cite web |url=http://www.vmedia.ca/internet/cable-modem-list.aspx |title=Archived copy |accessdate=2013-06-17 |deadurl=yes |archiveurl=https://web.archive.org/web/20130730082310/http://www.vmedia.ca/internet/cable-modem-list.aspx |archivedate=2013-07-30 |df= }}</ref><ref>{{cite web|url=http://www.acanac.ca/Approved_Modems_Ontario.html |title=Unlimited Internet Plans Quebec &#124; Cable, Fibre Optic &#124; Acanac |website=Acanac.ca |date= |accessdate=2016-08-03}}</ref> identifying the 'allowed' modems by their brand, models, sometimes firmware version and occasionally going as far as imposing a hardware version of the modem, instead of simply allowing a supported DOCSIS version as it should. From this point of view, the DOCSIS standard has failed to provide the promised practical interoperability for the end user. ==Multimedia terminal adapter{{anchor|MTA}}== With the development of [[voice over Internet Protocol]] (VoIP) telephony, [[analog telephone adapter]]s (ATA) have been incorporated into many cable modems for providing telephone service. An embedded ATA is known as an ''embedded multimedia terminal adapter'' (E-MTA). Many cable TV service providers also offer VoIP-based telephone service via the cable infrastructure ([[PacketCable]]). High-speed Internet access service subscriber may use VoIP telephony by subscribing to a third-party service, such as [[Vonage]], [[MagicJack|MagicJack+]] and [[NetTALK]]. ==Network architectural functions== In network topology, a cable modem is a [[network bridge]] that conforms to [[IEEE 802.1D]] for [[Ethernet]] networking (with some modifications). The cable modem bridges Ethernet frames between a customer [[LAN]] and the coax network. Technically, it is a modem because it must modulate data to transmit it over the cable network, and it must demodulate data from the cable network to receive it. With respect to the [[OSI model]] of [[network planning and design|network design]], a cable modem is both [[Physical Layer]] (Layer 1) device and a [[Data Link Layer]] (Layer 2) forwarder. As an [[IP address]]able network node, cable modems support functionality at other layers. Layer 1 is implemented in the [[Ethernet over twisted pair|Ethernet PHY]] on its LAN [[Network interface controller|interface]], and a DOCSIS defined cable-specific [[PHY (chip)|PHY]] on its HFC cable interface. The term ''cable modem'' refers to this cable-specific PHY. The [[Network Layer]] (Layer 3) is implemented as an [[Internet protocol|IP]] host in that it has its own [[IP address]] used by the network operator to maintain the device. In the [[Transport Layer]] (Layer 4) the cable modem supports [[user datagram protocol|UDP]] in association with its own IP address, and it supports filtering based on [[TCP and UDP port]] numbers to, for example, block forwarding of [[NetBIOS]] traffic out of the customer's LAN. In the [[Application Layer]] (Layer 7), the cable modem supports certain protocols that are used for management and maintenance, notably [[Dynamic Host Configuration Protocol]] (DHCP), [[SNMP]], and [[trivial file transfer protocol|TFTP]]. Some cable modems may incorporate a [[Router (computing)|router]] and a DHCP server to provide the LAN with [[Internet Protocol|IP]] network addressing. From a data forwarding and network topology perspective, this router functionality is typically kept distinct from the cable modem functionality (at least logically) even though the two may share a single enclosure and appear as one unit, sometimes called a [[residential gateway]]. So, the cable modem function will have its own [[IP address]] and [[MAC address]] as will the router. ==Cable modem flap== Cable modems can have a problem known in industry jargon as "flap" or "flapping".<ref>{{cite web|url=http://www.cisco.com/c/en/us/td/docs/cable/cmts/feature/guide/cmtsfg/ufg_flap.pdf|title=Flap List Troubleshooting for the Cisco CMTS|last=|first=|date=|website=|publisher=Cisco|access-date=26 July 2016}}</ref> A modem flap is when the connection by the modem to the head-end has been dropped (gone offline) and then comes back online. The time offline or rate of flap is not typically recorded, only the incidence. 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. If there are usability problems due to flap the typical cause is a defective modem or very high amounts of traffic on the service provider's network (upstream utilization too high).<ref>{{cite web|url=http://www.dslreports.com/forum/remark,2507788 |title=Cable modem flapping.. - RCN &#124; DSLReports Forums |website=Dslreports.com |date= |accessdate=2016-08-03}}</ref> Types of flap include reinsertions, hits and misses, and power adjustments.<ref>{{cite web|url=http://www.cisco.com/en/US/docs/ios/cable/configuration/guide/cmts_flaplst_trbsh.html |title=CMTS Troubleshooting and Network Management Features Configuration Guide |website=Cisco.com |date=2016-01-27 |accessdate=2016-08-03}}</ref> ==See also== {{colbegin}} *[[Cable modem termination system]] *[[Cable telephone]] *[[Internet access#Cable Internet access|Internet access with a cable modem]] *[[List of device bandwidths]] *[[Triple play (telecommunications)]] *[[HomePNA]] {{colend}} ==References== {{Reflist|30em}} == Further reading == * {{cite web|title=How Cable Modems Work|author=Curt Franklin|url=http://computer.howstuffworks.com/cable-modem.htm/printable|publisher=''[[HowStuffWorks]]''|accessdate=2010-08-28}} * {{cite web|title=How It Works: Cable Modems|url=http://www.pcworld.com/article/14281-2/how_it_works_cable_modems.html|author=Andrew Brandt|publisher=''[[PC World (magazine)|PC World]]''|year=1999|accessdate=2010-08-28}} ==External links== {{Commons category|Cable modems}} * {{dmoz|Computers/Data_Communications/Cable_Modem/}} {{Internet Access}} {{IEEE standards}} {{Telecommunications}} [[Category:Digital cable]] [[Category:Cable television technology]] [[Category:Modems]] [[Category:Internet access]]'