DOCSIS
Encyclopedia
Data Over Cable Service Interface Specification (DOCSIS) (often pronounced ˈdɒksɪs) is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV
(CATV) system. It is employed by many cable television operators to provide Internet access (see cable Internet
) over their existing hybrid fiber-coaxial (HFC) infrastructure.
and contributing companies including ARRIS
, BigBand Networks
, Broadcom
, Cisco
, Conexant
, Correlant, Harmonic
, Intel, Motorola
, Netgear
, Technicolor, Terayon
, and Texas Instruments
.
The first specification was version 1.0, issued in March 1997, with revision 1.1 (adding quality of service
(QoS) capabilities) following in April 1999. Because of increased demand for symmetric services such as IP telephony, DOCSIS was revised to enhance upstream transmission speeds; DOCSIS 2.0 was released in December 2001. Most recently, the specification was revised to significantly increase transmissions speeds (this time both upstream and downstream) and introduce support for Internet Protocol version 6 (IPv6). This version, DOCSIS 3.0, was released in August 2006. Cross-version compatibility has been maintained across all versions of DOCSIS, with the devices falling back to the highest supported version in common between both endpoints: cable modem
and cable modem termination system
(CMTS). For example, if one has a cable modem that only supports DOCSIS 1.0, and the system is running 2.0, the connection will be established at DOCSIS 1.0 speeds.
As of the end of 2011, the fastest deployments in North America are expected to be Shaw Cable's announced 250 Mbit/s download 15 Mbit/s upload, which will be implemented in phases, and Videotron
's 120 Mbit/s download / 20 Mbit/s upload service in Quebec City
, followed closely by existing 107 Mbit/s deployments in the USA. The U.S. Federal Communications Commission
(FCC) urged U.S. providers to make 100 Mbit/s a standard speed available to 100 million households before the end of the decade http://www.dailytech.com/FCC+US+Needs+Faster+Broadband+Standards+Aiming+for+100+Mbps/article17708.htm. Of wired technologies, only DOCSIS, FIOS
, E-line (advanced powerline networking with bandwidth equivalent to fiber) and Ethernet in the first mile
are likely to achieve this speed on large scale in that time frame.
In the UK, broadband provider Virgin Media
announced on 20 April 2011 an intention to start trials with download speeds of 1.5 Gbit/s and upload of 150 Mbit/s based on DOCSIS3.0.
standards which specify 6 MHz. The wider bandwidth in EuroDOCSIS architectures permits more bandwidth to be allocated to the downstream data path (toward the user). EuroDOCSIS certification testing is executed by Belgium company Excentis (formerly known as tComLabs), while DOCSIS certification testing is executed by CableLabs
. Typically, customer premises equipment
receives "certification", while CMTS
equipment receives "qualification".
Most cable systems in Japan and Colombia utilize the North American version of DOCSIS, while some employ a variant of DOCSIS that uses upstream channels that are based on a 9.216 MHz master clock (as opposed to 10.24 MHz used in DOCSIS/EuroDOCSIS) resulting in upstream channel widths that are a power-of-two division of 6 MHz (as opposed to 6.4 MHz in DOCSIS/EuroDOCSIS).
Note: While ITU-T Recommendation J.112 Annex B corresponds to DOCSIS/EuroDOCSIS 1.1, Annex A describes an earlier European cable modem system ("DVB EuroModem") based on ATM transmission standards. Annex C describes a variant of DOCSIS 1.1 that is designed to operate in Japanese cable systems. The ITU-T Recommendation J.122 main body corresponds to DOCSIS 2.0, J.122 Annex F corresponds to EuroDOCSIS 2.0, and J.122 Annex J describes the Japanese variant of DOCSIS 2.0 (analogous to Annex C of J.112).
(OSI) layers 1 and 2, the physical
and data link
layers.
Physical layer
:
Data link layer
:
Throughput: All of these features combined enable a total upstream throughput of 30.72 Mbit/s per 6.4 MHz channel, or 10.24 Mbit/s per 3.2 MHz channel. All three versions of the DOCSIS standard support a downstream throughput with 256-QAM of up to 42.88 Mbit/s per 6 MHz channel, or 55.62 Mbit/s per 8 MHz channel for EuroDOCSIS. (see table below)
Network layer
:
Common DOCSIS 3.0 speeds are listed in the table below.
Note that the number of channels a cable system can support is dependent on how the cable system is set up. For example, the amount of available bandwidth in each direction, the width of the channels selected in the upstream direction, and hardware constraints constrain the maximum amount of channels in each direction.
Note that the maximum upstream speed on all versions of DOCSIS depends on the version of DOCSIS used and the number of upstream channels used if DOCSIS 3.0 is used, but the upstream channel widths are independent of whether DOCSIS or EuroDOCSIS is used.
(CM) located at the customer premises, and a cable modem termination system
(CMTS) located at the CATV headend. Cable systems supporting on-demand programming use a hybrid fiber-coaxial system. Fiber optic lines bring digital signals to nodes
in the system where they are converted into RF channels and modem signals on coaxial trunk lines.
A typical CMTS is a device which hosts downstream and upstream ports (it is functionally similar to the DSLAM
used in DSL
systems). While downstream and upstream communications travel on a shared coax line in the customer premises, and connect to a single F connector
on the cable modem, it is typical for the CMTS to have separate F connectors for downstream and for upstream communication. This allows flexibility for the cable operator. Because of the noise in the return (upstream) path, an upstream port is usually connected to a single neighborhood (fiber node), whereas a downstream port is usually shared across a small number of neighborhoods. Thus, there are generally more upstream ports than downstream ports on a CMTS. A typical CMTS has 4 or 6 upstream ports per downstream port.
Before a cable company can deploy DOCSIS 1.1 or above, it must upgrade its Hybrid fiber-coaxial (HFC) network to support a return path for upstream traffic. Without a return path, the old DOCSIS 1.0 standard still allows use of data over cable system, by implementing the return path over regular phone lines, e.g. "plain old telephone service
" (POTS). If the HFC is already 'two-way' or "interactive", chances are high that DOCSIS 1.1 or higher can be implemented
The customer PC and associated peripherals are termed Customer-premises equipment
(CPE). The CPE are connected to the cable modem, which is in turn connected through the HFC network to the CMTS. The CMTS then routes traffic between the HFC and the Internet. Using the CMTS, the cable operator (or Multiple Service Operators - MSO) exercises full control over the cable modem's configuration; the CM configuration is changed to adjust for varying line conditions and customer service requirements.
DOCSIS 2.0 is also used over microwave frequencies (10 GHz) in Ireland by Digiweb
, using dedicated wireless links rather than HFC network. At each subscriber premises the ordinary CM is connected to an antenna box which converts to/from microwave frequencies and transmits/receives on 10 GHz. Each customer has a dedicated link but the transmitter mast must be in line of sight (most sites are hilltop).
layer security services in its Baseline Privacy Interface specifications. DOCSIS 1.0 utilized the initial Baseline Privacy Interface (BPI) specification. BPI was later improved with the release of the Baseline Privacy Interface Plus (BPI+) specification used by DOCSIS 1.1 & 2.0. Most recently, a number of enhancements to the Baseline Privacy Interface were added as part of DOCSIS 3.0, and the specification was renamed "Security" (SEC).
The intent of the BPI/SEC specifications is to describe MAC layer security services for DOCSIS CMTS to cable modem
communications. BPI/SEC security goals are twofold:
BPI/SEC is intended to prevent cable users from listening to each other. It does this by encrypting data flows between the CMTS and the cable modem. BPI & BPI+ utilize 56-bit DES
encryption, while SEC adds support for 128-bit AES
. All versions provide for periodic key refreshes (at a period configured by the network operator) in order to increase the level of protection.
The earlier BPI specification [ANSI/SCTE 22-2] had limited service protection because the underlying Key management
protocol did not authenticate cable modem. BPI+ strengthened the service protection feature by adding digital certificate based authentication
with a public key infrastructure
to its Key exchange
protocol.
Security in the DOCSIS network is vastly improved when only business critical communications are permitted, and end user communication to the network infrastructure is denied. Successful attacks often occur when the CMTS is configured for backwards compatibility with early pre-standard DOCSIS 1.1 modems which were "software upgradeable in the field," but did not include valid DOCSIS or EuroDOCSIS root certificates.
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
(CATV) system. It is employed by many cable television operators to provide Internet access (see 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...
) over their existing hybrid fiber-coaxial (HFC) infrastructure.
History
DOCSIS was developed by CableLabsCableLabs
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...
and contributing companies including 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...
, BigBand Networks
BigBand Networks
BigBand Networks is a multinational corporation headquartered in Redwood City, California, United States. BigBand manufactures and sells digital video and data processing platforms and solutions in areas ranging from digital video to CMTS.-Locations:BigBand has 2 major development centers...
, Broadcom
Broadcom
Broadcom Corporation is a fabless semiconductor company in the wireless and broadband communication business. The company is headquartered in Irvine, California, USA. Broadcom was founded by a professor-student pair Henry Samueli and Henry T. Nicholas III from the University of California, Los...
, Cisco
Cisco
Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...
, Conexant
Conexant
Conexant Systems, Inc. is an American semiconductor company, formerly the semiconductor division of Rockwell International. Currently it's privately owned by Golden Gate Capital, an equity firm headquartered in San Francisco.-History:...
, Correlant, Harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
, Intel, 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...
, Netgear
Netgear
Netgear is a U.S. manufacturer of computer networking equipment and other computer hardware....
, Technicolor, Terayon
Terayon
Terayon Communication Systems, Inc. was a company that vended equipment to broadband service providers for delivering broadband voice, video and data services to residential and business subscribers.-History:...
, and Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
.
The first specification was version 1.0, issued in March 1997, with revision 1.1 (adding 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...
(QoS) capabilities) following in April 1999. Because of increased demand for symmetric services such as IP telephony, DOCSIS was revised to enhance upstream transmission speeds; DOCSIS 2.0 was released in December 2001. Most recently, the specification was revised to significantly increase transmissions speeds (this time both upstream and downstream) and introduce support for Internet Protocol version 6 (IPv6). This version, DOCSIS 3.0, was released in August 2006. Cross-version compatibility has been maintained across all versions of DOCSIS, with the devices falling back to the highest supported version in common between both endpoints: cable modem
Cable modem
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...
and cable modem termination system
Cable modem termination system
A 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...
(CMTS). For example, if one has a cable modem that only supports DOCSIS 1.0, and the system is running 2.0, the connection will be established at DOCSIS 1.0 speeds.
As of the end of 2011, the fastest deployments in North America are expected to be Shaw Cable's announced 250 Mbit/s download 15 Mbit/s upload, which will be implemented in phases, and Videotron
Vidéotron
Vidéotron GP is a Canadian integrated telecommunications company active in cable television, interactive multimedia development, video on demand, cable telephony, wireless communication and Internet access services. Currently, the company primarily serves Quebec, as well as the francophone...
's 120 Mbit/s download / 20 Mbit/s upload service in Quebec City
Quebec City
Quebec , also Québec, Quebec City or Québec City is the capital of the Canadian province of Quebec and is located within the Capitale-Nationale region. It is the second most populous city in Quebec after Montreal, which is about to the southwest...
, followed closely by existing 107 Mbit/s deployments in the USA. The U.S. Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) urged U.S. providers to make 100 Mbit/s a standard speed available to 100 million households before the end of the decade http://www.dailytech.com/FCC+US+Needs+Faster+Broadband+Standards+Aiming+for+100+Mbps/article17708.htm. Of wired technologies, only DOCSIS, FIOS
Fíos
Fíos is one of 17 parishes in Parres, a municipality within the province and autonomous community of Asturias, in northern Spain....
, E-line (advanced powerline networking with bandwidth equivalent to fiber) and Ethernet in the first mile
Ethernet in the first mile
Ethernet in the first mile refers to using one of the Ethernet family of computer network protocols between a telecommunications company and a customer's premise. From the customer's point of view it is their "first" mile, although from the access networks' point of view it is known as the "last...
are likely to achieve this speed on large scale in that time frame.
In the UK, broadband provider Virgin Media
Virgin Media
Virgin Media Inc. is a company which provides fixed and mobile telephone, television and broadband internet services to businesses and consumers in the United Kingdom...
announced on 20 April 2011 an intention to start trials with download speeds of 1.5 Gbit/s and upload of 150 Mbit/s based on DOCSIS3.0.
Regional variants
As frequency allocation bandwidth plans differ between United States and European CATV systems, DOCSIS standards have been modified for use in Europe. These modifications were published under the name "EuroDOCSIS". The differences between the bandwidths exist because European cable TV conforms to PAL standards of 8 MHz bandwidth and North American cable TV conforms to ATSCATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
standards which specify 6 MHz. The wider bandwidth in EuroDOCSIS architectures permits more bandwidth to be allocated to the downstream data path (toward the user). EuroDOCSIS certification testing is executed by Belgium company Excentis (formerly known as tComLabs), while DOCSIS certification testing is executed by 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...
. Typically, customer premises equipment
Customer-premises equipment
Customer-premises equipment or customer-provided equipment is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel at the demarcation point...
receives "certification", while CMTS
Cable modem termination system
A 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...
equipment receives "qualification".
Most cable systems in Japan and Colombia utilize the North American version of DOCSIS, while some employ a variant of DOCSIS that uses upstream channels that are based on a 9.216 MHz master clock (as opposed to 10.24 MHz used in DOCSIS/EuroDOCSIS) resulting in upstream channel widths that are a power-of-two division of 6 MHz (as opposed to 6.4 MHz in DOCSIS/EuroDOCSIS).
International standards
The ITU Telecommunication Standardization Sector (ITU-T) has approved the various versions of DOCSIS as international standards. DOCSIS 1.0 was ratified as ITU-T Recommendation J.112 Annex B (1998), but it was superseded by DOCSIS 1.1 which was ratified as ITU-T Recommendation J.112 Annex B (2001). Subsequently, DOCSIS 2.0 was ratified as ITU-T Recommendation J.122. Most recently, DOCSIS 3.0 was ratified as ITU-T Recommendation J.222 (J.222.0, J.222.1, J.222.2, J.222.3).Note: While ITU-T Recommendation J.112 Annex B corresponds to DOCSIS/EuroDOCSIS 1.1, Annex A describes an earlier European cable modem system ("DVB EuroModem") based on ATM transmission standards. Annex C describes a variant of DOCSIS 1.1 that is designed to operate in Japanese cable systems. The ITU-T Recommendation J.122 main body corresponds to DOCSIS 2.0, J.122 Annex F corresponds to EuroDOCSIS 2.0, and J.122 Annex J describes the Japanese variant of DOCSIS 2.0 (analogous to Annex C of J.112).
Features
DOCSIS provides great variety in options available at Open Systems InterconnectionOSI 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...
(OSI) layers 1 and 2, the physical
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....
and data link
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
layers.
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....
:
- Channel width: All versions of DOCSIS utilize either 6 MHz channels (e.g. North America) or 8 MHz channels ("EuroDOCSIS") for downstream transmission. In the upstream, DOCSIS 1.0/1.1 specifies channel widths between 200 kHz and 3.2 MHz. DOCSIS 2.0 also specifies 6.4 MHz, but can use the earlier, narrower channel widths for backward compatibility.
- Modulation: All versions of DOCSIS specify that 64-level or 256-level QAMQuadrature amplitude modulationQuadrature 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...
(64-QAM or 256-QAM) be used for modulation of downstream data, utilizing the ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
J.83-AnnexB standard for 6 MHz channel operation, and the DVB-CDVB-CDVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable...
modulation standard for 8 MHz (EuroDOCSIS) operation. Upstream data uses QPSK or 16-level QAM (16-QAM) for DOCSIS 1.x, and it uses QPSK, 8-QAM, 16-QAM, 32-QAM, 64-QAM for DOCSIS 2.0 & 3.0. DOCSIS 2.0 & 3.0 also support 128-QAM with trellis coded modulationTrellis modulationIn telecommunication, trellis modulation is a modulation scheme which allows highly efficient transmission of information over band-limited channels such as telephone lines...
in S-CDMA mode (with an effective spectral efficiencySpectral efficiencySpectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system...
equivalent to that of 64-QAM).
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....
:
- DOCSIS employs a mixture of deterministic access methods for upstream transmissions, specifically TDMATime division multiple accessTime division multiple access is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This...
for DOCSIS 1.0/1.1 and both TDMATime division multiple accessTime division multiple access is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This...
and S-CDMA for DOCSIS 2.0 and 3.0, with a limited use of contention for bandwidth requests. In contrast to the pure contention-based MAC CSMA/CD employed in older EthernetEthernetEthernet 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....
systems (there is no contention in switched EthernetNetwork switchA network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
), DOCSIS systems experience few collisions. - For DOCSIS 1.1 and above the MAC layer also includes extensive quality-of-serviceQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) features that help to efficiently support applications that have specific traffic requirements such as low latency, e.g. voice over IPVoice over IPVoice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...
. - DOCSIS 3.0 features channel bondingChannel bondingChannel bonding is a computer networking arrangement in which two or more network interfaces on a host computer are combined for redundancy or increased throughput....
, which enables multiple downstream and upstream channels to be used together at the same time by a single subscriber.
Throughput: All of these features combined enable a total upstream throughput of 30.72 Mbit/s per 6.4 MHz channel, or 10.24 Mbit/s per 3.2 MHz channel. All three versions of the DOCSIS standard support a downstream throughput with 256-QAM of up to 42.88 Mbit/s per 6 MHz channel, or 55.62 Mbit/s per 8 MHz channel for EuroDOCSIS. (see table below)
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...
:
- DOCSIS modems are managed via an IPInternet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
address. - DOCSIS 3.0 adds management over IPv6IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
. - The 'DOCSIS 2.0 + IPv6' specification also allows support for IPv6 on DOCSIS 2.0 cable modems (via a firmware upgrade)
Speed tables
Maximum raw throughput including overhead (maximum usable throughput without overhead)| Version | |Upstream | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Channel configuration | |EuroDOCSIS throughput | |Upstream Throughput | |||||||||
| Minimum selectable number of channels | Minimum number of channels that hardware must be able to support | Selected number of channels | Maximum number of channels | Minimum selectable number of channels | Minimum number of channels that hardware must be able to support | Selected number of channels | Maximum number of channels | ||||
| 1.x | 1 | 1 | 1 | 1 | 42.88 (38) Mbit/s | 55.62 (50) Mbit/s | 1 | 1 | 1 | 1 | 10.24 (9) Mbit/s |
| 2.0 | 1 | 1 | 1 | 1 | 42.88 (38) Mbit/s | 55.62 (50) Mbit/s | 1 | 1 | 1 | 1 | 30.72 (27) Mbit/s |
| 3.0 | 1 | 4 | m | No maximum defined |
m × 42.88 (m × 38) Mbit/s | m × 55.62 (m × 50) Mbit/s | 1 | 4 | n | No maximum defined |
n × 30.72 (n × 27) Mbit/s |
Common DOCSIS 3.0 speeds are listed in the table below.
| Channel configuration | |Upstream throughput | |||
|---|---|---|---|---|
| Number of downstream channels | Number of upstream channels | DOCSIS | EuroDOCSIS | |
| 4 | 4 | 171.52 (152) Mbit/s | 222.48 (200) Mbit/s | 122.88 (108) Mbit/s |
| 8 | 4 | 343.04 (304) Mbit/s | 444.96 (400) Mbit/s | 122.88 (108) Mbit/s |
Note that the number of channels a cable system can support is dependent on how the cable system is set up. For example, the amount of available bandwidth in each direction, the width of the channels selected in the upstream direction, and hardware constraints constrain the maximum amount of channels in each direction.
Note that the maximum upstream speed on all versions of DOCSIS depends on the version of DOCSIS used and the number of upstream channels used if DOCSIS 3.0 is used, but the upstream channel widths are independent of whether DOCSIS or EuroDOCSIS is used.
Equipment
A DOCSIS architecture includes two primary components: a cable modemCable modem
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...
(CM) located at the customer premises, and a cable modem termination system
Cable modem termination system
A 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...
(CMTS) located at the CATV headend. Cable systems supporting on-demand programming use a hybrid fiber-coaxial system. Fiber optic lines bring digital signals to nodes
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
in the system where they are converted into RF channels and modem signals on coaxial trunk lines.
A typical CMTS is a device which hosts downstream and upstream ports (it is functionally similar to the DSLAM
Digital subscriber line access multiplexer
A digital subscriber line access multiplexer is a network device, located in the telephone exchanges of the telecommunications operators. It connects multiple customer digital subscriber line interfaces to a high-speed digital communications channel using multiplexing techniques...
used in DSL
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 ,...
systems). While downstream and upstream communications travel on a shared coax line in the customer premises, and connect to a single F connector
F connector
The F connector is a type of coaxial RF connector commonly used for "over the air" terrestrial television, cable television and universally for satellite television and cable modems, usually with RG-6/U cable or, in older installations, with RG-59/U cable. It was invented by Eric E...
on the cable modem, it is typical for the CMTS to have separate F connectors for downstream and for upstream communication. This allows flexibility for the cable operator. Because of the noise in the return (upstream) path, an upstream port is usually connected to a single neighborhood (fiber node), whereas a downstream port is usually shared across a small number of neighborhoods. Thus, there are generally more upstream ports than downstream ports on a CMTS. A typical CMTS has 4 or 6 upstream ports per downstream port.
Before a cable company can deploy DOCSIS 1.1 or above, it must upgrade its Hybrid fiber-coaxial (HFC) network to support a return path for upstream traffic. Without a return path, the old DOCSIS 1.0 standard still allows use of data over cable system, by implementing the return path over regular phone lines, e.g. "plain old telephone service
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....
" (POTS). If the HFC is already 'two-way' or "interactive", chances are high that DOCSIS 1.1 or higher can be implemented
The customer PC and associated peripherals are termed Customer-premises equipment
Customer-premises equipment
Customer-premises equipment or customer-provided equipment is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel at the demarcation point...
(CPE). The CPE are connected to the cable modem, which is in turn connected through the HFC network to the CMTS. The CMTS then routes traffic between the HFC and the Internet. Using the CMTS, the cable operator (or Multiple Service Operators - MSO) exercises full control over the cable modem's configuration; the CM configuration is changed to adjust for varying line conditions and customer service requirements.
DOCSIS 2.0 is also used over microwave frequencies (10 GHz) in Ireland by Digiweb
Digiweb
Digiweb is a telecommunications company in Ireland, supplying business and consumer broadband and web hosting.Digiweb is 100% Irish owned and run, and is headquartered in Dundalk, County Louth with its technical, installation and sales offices in Dublin....
, using dedicated wireless links rather than HFC network. At each subscriber premises the ordinary CM is connected to an antenna box which converts to/from microwave frequencies and transmits/receives on 10 GHz. Each customer has a dedicated link but the transmitter mast must be in line of sight (most sites are hilltop).
Security
DOCSIS includes MACMedia Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
layer security services in its Baseline Privacy Interface specifications. DOCSIS 1.0 utilized the initial Baseline Privacy Interface (BPI) specification. BPI was later improved with the release of the Baseline Privacy Interface Plus (BPI+) specification used by DOCSIS 1.1 & 2.0. Most recently, a number of enhancements to the Baseline Privacy Interface were added as part of DOCSIS 3.0, and the specification was renamed "Security" (SEC).
The intent of the BPI/SEC specifications is to describe MAC layer security services for DOCSIS CMTS to cable modem
Cable modem
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...
communications. BPI/SEC security goals are twofold:
- provide cable modem users with data privacy across the cable network
- provide cable service operators with service protection; i.e., prevent unauthorized users from gaining access to the network’s RF MAC services
BPI/SEC is intended to prevent cable users from listening to each other. It does this by encrypting data flows between the CMTS and the cable modem. BPI & BPI+ utilize 56-bit DES
Data Encryption Standard
The Data Encryption Standard is a block cipher that uses shared secret encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is...
encryption, while SEC adds support for 128-bit AES
Advanced Encryption Standard
Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...
. All versions provide for periodic key refreshes (at a period configured by the network operator) in order to increase the level of protection.
The earlier BPI specification [ANSI/SCTE 22-2] had limited service protection because the underlying Key management
Key management
Key management is the provisions made in a cryptography system design that are related to generation, exchange, storage, safeguarding, use, vetting, and replacement of keys. It includes cryptographic protocol design, key servers, user procedures, and other relevant protocols.Key management concerns...
protocol did not authenticate cable modem. BPI+ strengthened the service protection feature by adding digital certificate based authentication
Authentication
Authentication is the act of confirming the truth of an attribute of a datum or entity...
with a public key infrastructure
Public key infrastructure
Public Key Infrastructure is a set of hardware, software, people, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates. In cryptography, a PKI is an arrangement that binds public keys with respective user identities by means of a certificate...
to its Key exchange
Key exchange
Key exchange is any method in cryptography by which cryptographic keys are exchanged between users, allowing use of a cryptographic algorithm....
protocol.
Security in the DOCSIS network is vastly improved when only business critical communications are permitted, and end user communication to the network infrastructure is denied. Successful attacks often occur when the CMTS is configured for backwards compatibility with early pre-standard DOCSIS 1.1 modems which were "software upgradeable in the field," but did not include valid DOCSIS or EuroDOCSIS root certificates.
See also
- Data cableData cableA data cable is any media that allows baseband transmissions from a transmitter to a receiver.Examples Are:*Networking Media**Ethernet Cables **Token Ring Cables **Coaxial cable...
- DOCSIS Set-top GatewayDOCSIS Set-top GatewayDOCSIS Set-top Gateway is a specification describing how out of band data is delivered to a cable set-top box. Cable set-top boxes need a reliable source of out of band data for information such as program guides, channel lineups, and updated code images.- Features :DSG is an extension of the...
- Ethernet over coaxEthernet over coaxEthernet over Coax is a family of technologies that supports the transmission of Ethernet frames over coaxial cable.- History :The first Ethernet standard, known as 10BASE5 in the family of IEEE 802.3, specified baseband operation over coaxial cable...
- List of device bandwidths
- Multimedia over Coax AllianceMultimedia over Coax AllianceMultimedia over Coax Alliance is a trade group promoting a standard that uses coaxial cables to connect consumer electronics and home networking devices in homes. It allows both data communication and the transfer of audio and video streams....
External links
- DOCSIS 1.0 Interface Specification
- DOCSIS 1.1 Interface Specification
- DOCSIS 2.0 Interface Specification
- DOCSIS 3.0 Interface Specification
- Cisco documentation on Cable Technologies Technical information about cable TV and DOCSIS.