Cable modem

Source: Wikipedia, the free encyclopedia.
ARRIS
Touchstone CM820B DOCSIS 3.0 cable modem

A cable modem is a type of

cable Internet, taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in the Americas, Asia, Australia, and Europe
.

History

MITRE Cablenet

Internet Experiment Note (IEN) 96[1] (1979) describes an early RF cable modem system. From pages 2 and 3 of IEN 96:

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.

Johnson Space Center
, but these are all standalone, local-only networks.

The system uses standard

branched like a tree
).
...

The BIUs contain

kbps
.

IEEE 802.3b (10BROAD36)

The

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.[4] 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

ARRIS Interactive.[7] Because of contractual agreements with Antec involving this joint venture, Nortel spun the LANCity group out into the ARRIS Interactive joint-venture. ARRIS continues to make cable modems and cable modem termination system (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, 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

Main article: 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 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

CDLP was a proprietary system manufactured by

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

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

DVB) and 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

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.

IETF

Although the

networks
.

DOCSIS

Main article: DOCSIS

In the late 1990s, a consortium of US

ITU
), developed a certification testing program for cable modem equipment, and has since drafted multiple extensions to the original specification.

While deployed

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 US's NTSC systems two main versions of DOCSIS exist, DOCSIS and EuroDOCSIS. The main differences are found in the width of RF-channels: 6 MHz for the US and 8 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,"[17] most cable operators only approve a very restricted list of cable modems on their network,[18][19][20][21] 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.

Multimedia over Coax Alliance

Main article: Multimedia over Coax Alliance

In 2004, the Multimedia over Coax Alliance (MoCA) was established to develop industry standard for the connected home, using the existing coaxial cabling. Initially developed for in-home networking with MoCA 1.0/1.1, the MoCA standards has continued to develop with MoCA 2.0/2.1 in 2010 and MoCa 2.5 in 2016.

In 2017, Multimedia over Coax Alliance introduced MoCA Access specification, based on the MoCA 2.5 standard, suitable for addressing broadband network access in-building using coaxial cabling.[22] MoCA Access extends MoCA 2.5 in-home networking to fit operators and ISPs that are installing fiber-to-the-basement/drop point (FTTB/FTTdp) and want to use the existing coax for connection to each apartment or house."

Multimedia terminal adapter

With the development of

voice over Internet Protocol (VoIP) telephony, analog telephone adapters
(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). Some high-speed Internet customers may use VoIP telephony by subscribing to a third-party service, such as Vonage, MagicJack+ and NetTALK.

Network architectural functions

In network topology, a cable modem is a

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 addressable network node, cable modems support functionality at other layers.

Layer 1 is implemented in the

TFTP
.

Some cable modems may incorporate a router and a DHCP server to provide the LAN with 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".[23] 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).[24] Types of flap include reinsertions, hits and misses, and power adjustments.[25]

Known vulnerabilities

In January 2020, a vulnerability affecting cable modems using

port which is open by default in the vulnerable models.[26][27]

See also

References

  1. MITRE
    Cablenet Project
  2. ^ "RF Micro Devices, Inc. Whitepaper Describing Historical CATV Components" (PDF). Piedmontscte.org. Retrieved 2016-08-03. Amplifiers are one of the common components used in CATV system
  3. ^ IEEE 802.3b-1985 (10BROAD36) Archived 2012-02-25 at the Wayback Machine - Supplement to 802.3: Broadband Medium Attachment Unit and Broadband Medium Specifications, Type 10BROAD36 (Section 11)
  4. ^ "IEEE SA - 802.7-1989 - Local Area Networks: IEEE Recommended Practice: Broadband Local Area Networks". Standards.ieee.org. 1990-03-09. Retrieved 2016-08-03.
  5. ^ staff, CNET News. "Bay Networks to acquire LANcity". CNET. Retrieved 2019-09-05.
  6. ^ Marshall, Jonathan; Writer, Chronicle Staff (1998-06-16). "Telecom Giants To Merge / Bay Networks bought by Nortel for $7.2 billion". SFGate. Retrieved 2019-09-05.
  7. ^ "Nortel ups stake in joint venture with Antec". CNET. Retrieved 2019-09-05.
  8. ^ Sallie Hofmeister (1996-08-23). "Americast Places $1-Billion Order for Set-Top Boxes". Los Angeles Times. Retrieved 2010-08-28.
  9. ISBN 978-0-8493-0859-8
    .
  10. ^ "WalkingDog.com". Archived from the original on 1996-12-26. Retrieved 2012-05-13.{{cite web}}: CS1 maint: bot: original URL status unknown (link) The IEEE 802.14 Working Group used WalkingDog.com as its web site.
  11. ^ a b DOCSIS RFI 1.0-I01 (March 26, 1997) Archived May 25, 2011, at the Wayback Machine (See section 6.2.3 for the DOCSIS ATM codepoint. See sections 6.1.2.3, 6.2.5.3, 6.4.7, 9, and 9.2.2 for DOCSIS 1.0 QoS mechanisms.)
  12. ^ "IEEE 802.14 WG Officers". Archived from the original on 1997-01-29. Retrieved 2012-05-13.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  13. ISBN 978-0-07-006417-1
    . Retrieved 7 April 2024.
  14. ^ "Ipcdn Status Pages". Tools.ietf.org. Retrieved 2016-08-03.
  15. ^ "Ipdvb Status Pages". Tools.ietf.org. Retrieved 2016-08-03.
  16. ^ DOCSIS RFI 1.1-I01 (March 11, 1999) (See section 8 and Appendix M.)
  17. ^ "DOCSIS Modem Interoperability and Certification Overview" (PDF). Stuff.mit.edu. Retrieved 2016-08-03.
  18. ^ "Cable". TekSavvy.com. Archived from the original on 2016-08-01. Retrieved 2016-08-03.
  19. ^ "Compatible Modems". vmedia.ca. Retrieved 2021-10-27.
  20. ^ "Unlimited Internet Plans Quebec | Cable, Fibre Optic | Acanac". Acanac.ca. Archived from the original on 2015-05-12. Retrieved 2016-08-03.
  21. ^ "Fast Unlimited Download High Speed Cable 75 Internet Plus Home Phone Bundle". www.worldline.ca. Retrieved 2018-04-23.
  22. ^ KMCreative. "MoCA Access™". www.mocalliance.org. Retrieved 2017-10-03.
  23. ^ "Flap List Troubleshooting for the Cisco CMTS" (PDF). Cisco. Retrieved 26 July 2016.
  24. ^ "Cable modem flapping.. - RCN | DSLReports Forums". Dslreports.com. Retrieved 2016-08-03.
  25. ^ "CMTS Troubleshooting and Network Management Features Configuration Guide". Cisco.com. 2016-01-27. Retrieved 2016-08-03.
  26. ^ "Hundreds of millions of cable modems are vulnerable to new Cable Haunt vulnerability". ZDNet.
  27. ^ Goodin, Dan (2020-01-13). "Exploit that gives remote access affects ~200 million cable modems". Ars Technica. Retrieved 2020-01-15.

Further reading

External links

Wikimedia Commons has media related to Cable modems.
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