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'<!-- Deleted image removed: [[Image:Netgear cmd31t.png|thumb|right|150px|Netgear cable modem model CMD31T. One of the first DOCSIS 3.0 modems]] --> [[File:SBV6120E.jpg|thumb|right|[[Motorola]] SurfBoard SBV6120E EuroDOCSIS 3.0 cable modem]] {{refimprove|date=August 2010}} 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 (signal processing)|bandwidth]] of a HFC and RFoG network. They are commonly deployed in [[Australia]], [[Europe]], [[Asia]] and the [[Americas]]. ==History== ===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|Mbps]] broadband system to run up to 3600 [[Metre|meters]] over [[Cable_television|CATV]] [[Coaxial_cable|coax]] network cabling. The word [[Broadband|''broadband'']] as used in the original [[IEEE_802.3|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_signal|digital]] [[Baseband|''baseband'']] [[Square_wave|square-waveform]] [[Modulation|modulations]] (also known as [[Line_code|line coding]]), which begin near zero [[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|IEEE 802.3]]/[[Ethernet]] [[Baseband#Baseband_Ethernet|baseband]] standards such as [[10BASE5]] (1983), [[10BASE2]] (1985), [[Ethernet_over_twisted_pair|10BASET]] (1990), etc. ===IEEE 802.7=== The [[Institute_of_Electrical_and_Electronics_Engineers|IEEE]] [[IEEE_802|802 Committee]] also specified a [[Broadband|broadband]] [[Cable_television|CATV]] digital networking standard in 1989 with [[IEEE_802.7|802.7-1989]].<ref name="IEEE 802.7-1989 Standard">[http://standards.ieee.org/findstds/standard/802.7-1989.html IEEE 802.7-1989] - IEEE Local Area Networks: IEEE Recommended Practice: Broadband Local Area Networks</ref> However, like [[10BROAD36]], [[IEEE_802.7|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 highly asymmetrical communications would be sufficient to satisfy consumers connected remotely to an otherwise completely symmetric high-speed data communications network. This was important because it was very expensive to provide high speed in the upstream direction, while the [[CATV]] systems already had substantial broadband capacity in the downstream direction. 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 US. LANcity was sold to [[Bay Networks]] which 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 Corporation|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 USA and other countries, including [[GTE]]'s Americast service,<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> and used the [[Quadrature amplitude modulation]] technology as well as their own [[16VSB|16-level vestigial sideband modulation]] technique.<ref>{{cite book|title=Network Design: Principles and Applications|author=Gilbert Held|year=2000|pages=765|publisher=Auerbach Publications|url=http://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]] ([[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">[http://web.archive.org/web/19961226193928/http://walkingdog.com/ WalkingDog.com at Internet Archive] 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)] (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, 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">[http://web.archive.org/web/19970129161548/http://www.walkingdog.com/catv/officers.htm IEEE 802.14 WG Officers at Internet Archive]</ref> and his book, ''High-Speed Cable Modems'',<ref name="Azzam - High Speed Cable Modems">[http://en.wikipedia.org/wiki/Special:BookSources/978-0-07-006417-1 Albert A. Azzam, ''High-Speed Cable Modems''] [[International_Standard_Book_Number|ISBN]] [[Special:BookSources/978-0-07-006417-1|978-0-07-006417-1]]</ref> describes many of the proposals submitted to 802.14. ===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|DOCSIS RFI 1.0]] Issue-01 document discussed [[Quality_of_service|QoS]] extensions and mechanisms using [[Integrated_services|IntServ]] and [[Resource_Reservation_Protocol|RSVP]].<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)] (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, and 9.2.2 for DOCSIS 1.0 [[Quality_of_service|QoS]] mechanisms.)</ref> [[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)] (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|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. ==Cable modems and VoIP {{anchor|MTA}}== With the advent of [[Voice over Internet Protocol]] (VoIP) telephony, cable modems have been extended to provide telephone service. Some companies which offer cable TV service also offer VoIP phone, allowing customers who purchase cable TV to eliminate their [[plain old telephone service]] (POTS). Because many telephone companies do not offer [[naked DSL]] (DSL service without [[Plain old telephone service|POTS]] line service), [[VoIP]] use is higher amongst cable modem users.{{Citation needed|date=January 2009}} Any high-speed Internet service subscriber can use [[VoIP]] telephony by subscribing to a third-party service (e.g., [[Skype]]), the problem is that doing so, you need to turn on your computer to use the telephone, while cable modems have a port to connect the phone directly, without using a computer. However, there are also stand-alone VoiP systems available that connect directly to a broadband router (e.g., [[Vonage]] and [[MagicJack|MagicJack+]]). Many cable operators offer their own VoIP service, based on [[PacketCable]]. PacketCable allows [[multiple system operator]]s (MSOs) to offer both high-speed Internet and VoIP through the same cable [[transmission system]]. PacketCable service has a significant technical advantage over third-party providers in that voice packets are given guaranteed [[quality of service]] across their entire transmission path, so call quality can be assured. When using cable operator VoIP, a combined [[customer premises equipment]] device known as an ''embedded multimedia terminal adapter'' (E-MTA) will often be used. An E-MTA is a cable modem and a VoIP adapter (MTA, ''multimedia terminal adapter'') bundled into a single device. ==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 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 functionalities at other layers. Layer 1 is implemented in the [[Ethernet over twisted pair|Ethernet PHY]] on its LAN [[network interface|interface]], and a [[DOCSIS]] defined cable-specific [[PHY]] on its [[hybrid fibre-coaxial|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]], [[simple network management protocol|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". 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 incidents. 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>http://www.dslreports.com/forum/remark,2507788 Cable Modem Flapping</ref> Types of flap include: Reinsertions, Hits and Misses, and Power Adjustments.<ref>http://www.cisco.com/en/US/docs/ios/cable/configuration/guide/cmts_flaplst_trbsh.html Flap List Troubleshooting for the Cisco CMTS Routers</ref> ==See also== {{colbegin}} *[[Cable internet]] *[[Cable modem termination system]] *[[Cable telephone]] *[[DOCSIS]] *[[Hybrid fibre-coaxial]] *[[Internet access#Cable modem | Internet access with a Cable Modem]] *[[List of device bandwidths]] *[[Residential gateway]] *[[RFoG]] *[[Triple play (telecommunications)]] *[[HomePNA]] {{colend}} ==References== {{Reflist}} == 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}} [[Category:Digital cable]] [[Category:Cable television technology]] [[Category:Modems]] [[Category:Internet access]] [[af:Kabelmodem]] [[ar:مضمان قلسي]] [[bs:Kablovski modem]] [[de:Kabelmodem]] [[es:Cablemódem]] [[fr:Modem câble]] [[id:Modem kabel]] [[hu:Kábelmodem]] [[mk:Кабловски интернет]] [[ml:കേബിള്‍ മോഡം]] [[nl:Kabelmodem]] [[ja:ケーブルモデム]] [[no:Kabelmodem]] [[pl:Modem kablowy]] [[pt:Cable modem]] [[ru:Кабельный модем]] [[sr:Кабловски интернет]] [[fi:Kaapelimodeemi]] [[sv:Kabelmodem]] [[yi:קאבעל אינטערנעט]] [[zh:纜線數據機]]'