Cable modem
Encyclopedia
A cable modem is a type of network bridge and modem
that provides bi-directional data communication via radio frequency
channels on a 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 of a HFC and RFoG network. They are commonly deployed in Australia
, Europe
, Asia
and Americas
.
(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.
which was then acquired by Nortel
, which eventually spun the cable modem business off as ARRIS
. ARRIS
continues to make cable modems and CMTS equipment compliant with the DOCSIS
standard.
technology was used by several cable television systems in the USA and other countries, including GTE
's Americast service, and used the Quadrature amplitude modulation
technology as well as their own 16-level vestigial sideband modulation
technique.
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 customer premises equipment (CPE) was capable of both PSTN (telephone network) and 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
.
committee formed a subcommittee (802.14) to develop a standard for cable modem systems. While significant progress was made, the group was disbanded when North American multi system operator
s instead backed the then-fledgling DOCSIS
specification.
from the Motorola
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. 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 MHz for the USA and 8 MHz for Europe. A third variant of DOCSIS was developed in Japan
and has seen limited deployment in that country.
(POTS). Because many telephone companies do not offer naked DSL
(DSL service without POTS
line service), VoIP use is higher amongst cable modem users. 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
,).
Many cable operators offer their own VoIP service, based on PacketCable
. PacketCable allows multiple system operators (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.
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 PHY
on its LAN interface
, and a DOCSIS
defined cable-specific 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 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 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 DHCP
, SNMP
, and 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.
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
that provides bi-directional data communication via radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
channels on a HFC
Hybrid fibre-coaxial
Hybrid fiber-coaxial is a telecommunications industry term for a broadband network which combines optical fibre and coaxial cable. It was commonly employed globally by cable television operators since the early 1990s.-Description:...
and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access
Broadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
in the form of cable Internet
Cable internet
In telecommunications, cable Internet access, often shortened to cable Internet or simply cable, is a form of broadband Internet access that uses the cable television infrastructure. Like digital subscriber line and fiber to the premises services, cable Internet access provides network edge...
, taking advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
.
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 networkPublic switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
(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 NetworksBay Networks
Bay Networks was a network hardware vendor formed through the merger of Santa Clara, California based SynOptics Communications and Billerica, Massachusetts based Wellfleet Communications on July 6, 1994...
which was then acquired by Nortel
Nortel
Nortel Networks Corporation, formerly known as Northern Telecom Limited and sometimes known simply as Nortel, was a multinational telecommunications equipment manufacturer headquartered in Mississauga, Ontario, Canada...
, which eventually spun the cable modem business off as ARRIS
ARRIS
ARRIS Group Inc. is a telecommunications equipment manufacturing company which provides cable operators with high-speed data, video and telephony systems for homes and businesses...
. ARRIS
ARRIS
ARRIS Group Inc. is a telecommunications equipment manufacturing company which provides cable operators with high-speed data, video and telephony systems for homes and businesses...
continues to make cable modems and CMTS equipment compliant with the DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
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 ModemZenith Cable Modem
Zenith Cable Modem is one of the first proprietary cable modems deployed at limited scale. There were 2 basic models, one operating at 500 kbit/s, the other at 4 Mbit/s using BPSK and about a 25% alpha.-History:...
technology was used by several cable television systems in the USA and other countries, including GTE
GTE
GTE Corporation, formerly General Telephone & Electronics Corporation was the largest independent telephone company in the United States during the days of the Bell System....
's Americast service, and used the Quadrature amplitude modulation
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
technology as well as their own 16-level vestigial sideband modulation
16VSB
16VSB is an abbreviation for 16-level vestigial sideband modulation, capable of transmitting four bits at a time.-How it works:Other slower but more rugged forms of VSB include 2VSB, 4VSB, and 8VSB...
technique.
Com21
Com21Com21
Com21 was an early pioneer in developing cable modem networks in the era before the standard DOCSIS was introduced for Internet access via cable television networks. The company filed for bankruptcy in 2003.-The company:...
was another early pioneer in cable modems, and quite successful until proprietary systems were made obsolete by the DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
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
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
(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 MotorolaMotorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
. CDLP customer premises equipment (CPE) was capable of both PSTN (telephone network) and radio frequency (cable network)
Cable network
A cable channel is a television channel available via cable television. Such channels are usually also available via satellite television, including direct broadcast satellite providers such as DirecTV, Dish Network and BSkyB...
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
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
(DSL) service. The standard is in little use now while new providers use, and existing providers having changed to the DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
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
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n ISP BigPond
BigPond
BigPond is an Australian Internet service provider and is a product of Telstra. BigPond is Australia's largest ISP and based in Melbourne.- Internet :...
employed this system when it started cable modem tests in 1996. For a number of years cable Internet access was only available in Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
, Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...
and Brisbane
Brisbane
Brisbane is the capital and most populous city in the Australian state of Queensland and the third most populous city in Australia. Brisbane's metropolitan area has a population of over 2 million, and the South East Queensland urban conurbation, centred around Brisbane, encompasses a population of...
via CDLP. This network ran parallel to the newer DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
system for several years. In 2004, the CDLP network was terminated and replaced by DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
.
CDLP has been also rolled out at the French cable operator Numericable
Numericable
Numericable is a British-American-Luxembourgian owned cable television operator operating in France, Belgium and Luxembourg, currently proposing standard quadruple-play services .- History :...
before upgrading its IP broadband network using DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
.
IEEE 802.14
In the mid-1990s the IEEE 802IEEE 802
IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...
committee formed a subcommittee (802.14) to develop a standard for cable modem systems. While significant progress was made, the group was disbanded when North American multi system operator
Multi system operator
A Multiple System Operator or Multi System Operator is an operator of multiple cable television systems. A cable system in the United States, by Federal Communications Commission definition, is a facility serving a single community or a distinct governmental entity, each with its own franchise...
s instead backed the then-fledgling DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
specification.
DOCSIS
In the late 1990s, a consortium of US 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 layerPhysical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
from the Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
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
CableLabs
Founded in 1988 by cable television operating companies, Cable Television Laboratories, Inc. is a not-for-profit research and development consortium that has cable operators as its members. System operators from around the world are eligible to be members. Members dues are based on revenue...
which maintained the specification, promoted it in various standards organizations (notably SCTE
SCTE
The Society of Cable Telecommunications Engineers or SCTE is a non-profit professional association for the advancement of technology related to cable telecommunications engineering. Founded in 1969, SCTE has a current membership of over 12,000 individuals.- Publications :SCTE offers several...
and ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
), developed a certification testing program for cable modem equipment, and has since drafted multiple extensions to the original specification. Virtually all cable modems operating in the field today are compliant with one of the DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
versions. Because of the differences in the European PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and USA's NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
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 USA and 8 MHz for Europe. A third variant of DOCSIS was developed in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and has seen limited deployment in that country.
Cable modems and VoIP
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 servicePlain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
(POTS). Because many telephone companies do not offer naked DSL
Naked DSL
A naked DSL is a digital subscriber line without a PSTN service — or the associated dial tone...
(DSL service without POTS
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
line service), VoIP use is higher amongst cable modem users. Any high-speed Internet service subscriber can use VoIP telephony by subscribing to a third-party service (e.g., Skype
Skype
Skype is a software application that allows users to make voice and video calls and chat over the Internet. Calls to other users within the Skype service are free, while calls to both traditional landline telephones and mobile phones can be made for a fee using a debit-based user account system...
), 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
Vonage
Vonage is a publicly held commercial voice over IP network and SIP company that provides telephone service via a broadband connection. The company's name is a play on their motto "Voice-Over-Net-AGE"....
,).
Many cable operators offer their own VoIP service, based on PacketCable
PacketCable
PacketCable is an industry consortium founded by CableLabs with the goal of defining standards for the cable television modem access industry....
. PacketCable allows multiple system operators (MSOs) to offer both high-speed Internet and VoIP through the same cable transmission system
Transmission system
In telecommunications a transmission system is a system that transmits a signal from one place to another. The signal can be an electrical, optical or radio signal....
. PacketCable service has a significant technical advantage over third-party providers in that voice packets are given guaranteed quality of service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
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 802.1DIEEE 802.1D
802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree and others. It is standardized by the IEEE 802.1 working group. It includes details specific to linking many of the other 802 projects including the widely deployed 802.3 , 802.11 and 802.16 standards.VLANs are not...
for Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
networking (with some modifications). The cable modem bridges Ethernet frames between a customer LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
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
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
of network design, a cable modem is both Physical Layer
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
(Layer 1) device and a Data Link Layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
(Layer 2) forwarder. As an IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
able network node, cable modems support functionalities at other layers.
Layer 1 is implemented in the Ethernet PHY
Ethernet over twisted pair
Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Other Ethernet cable standards employ coaxial cable or optical fiber. Early versions developed in the 1980s included StarLAN followed by 10BASE-T. By the 1990s, fast, inexpensive...
on its LAN interface
Network interface
Network interface may refer to:* Network interface controller, the device a computer uses to connect to a computer network* Network interface device, a demarcation point for a telephone network...
, and a DOCSIS
DOCSIS
Data Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
defined cable-specific PHY
PHY
PHY is an abbreviation for the physical layer of the OSI model.An instantiation of PHY connects a link layer device to a physical medium such as an optical fiber or copper cable. A PHY device typically includes a Physical Coding Sublayer and a Physical Medium Dependent layer. The PCS encodes and...
on its HFC
Hybrid fibre-coaxial
Hybrid fiber-coaxial is a telecommunications industry term for a broadband network which combines optical fibre and coaxial cable. It was commonly employed globally by cable television operators since the early 1990s.-Description:...
cable interface. The term cable modem refers to this cable-specific PHY. The Network Layer
Network Layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
(Layer 3) is implemented as an IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
host in that it has its own IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
used by the network operator to maintain the device. In the Transport Layer
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
(Layer 4) the cable modem supports UDP
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
in association with its own IP address, and it supports filtering based on TCP and UDP port
TCP and UDP port
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication...
numbers to, for example, block forwarding of NetBIOS
NetBIOS
NetBIOS is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, NetBIOS is not a networking protocol...
traffic out of the customer's LAN. In the Application Layer
Application layer
The Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....
(Layer 7), the cable modem supports certain protocols that are used for management and maintenance, notably DHCP
Dynamic Host Configuration Protocol
The Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...
, SNMP
Simple Network Management Protocol
Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
, and TFTP
Trivial File Transfer Protocol
Trivial File Transfer Protocol is a file transfer protocol known for its simplicity. It is generally used forautomated transfer of configuration or boot files between machines in a local environment....
.
Some cable modems may incorporate a router and a DHCP server to provide the LAN with IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
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
Residential gateway
A residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
. So, the cable modem function will have its own IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
and MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
as will the router.
See also
- Cable internetCable internetIn telecommunications, cable Internet access, often shortened to cable Internet or simply cable, is a form of broadband Internet access that uses the cable television infrastructure. Like digital subscriber line and fiber to the premises services, cable Internet access provides network edge...
- Cable modem termination systemCable modem termination systemA cable modem termination system or CMTS is a piece of equipment typically located in a cable company's headend or hubsite, and used to provide high speed data services, such as cable Internet or voice over Internet Protocol, to cable subscribers...
- Cable telephone
- DOCSISDOCSISData Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
- Hybrid fibre-coaxialHybrid fibre-coaxialHybrid fiber-coaxial is a telecommunications industry term for a broadband network which combines optical fibre and coaxial cable. It was commonly employed globally by cable television operators since the early 1990s.-Description:...
- List of device bandwidths
- Residential gatewayResidential gatewayA residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
- RFoG
- Triple play (telecommunications)Triple play (telecommunications)In telecommunications, triple play service is a marketing term for the provisioning of two bandwidth-intensive services, high-speed Internet access and television, and a less bandwidth-demanding service, telephone, over a single broadband connection. Triple play focuses on a combined business...
- HomePNAHomePNAThe HomePNA Alliance is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and telephone wiring within homes.-Overview:HomePNA does not manufacture products, although its members do...