What is DOCSIS & How Does It Work?

Data Over Cable Service Interface Specification (DOCSIS) is a standard for cable transmission of Internet Protocol (IP) data services. DOCSIS is an internationally accepted telecom standard that allows broadband data transfer using cable systems originally used to transmit cable television signals (CATVS).
What is DOCSIS & How Does It Work

DOCSIS enables bidirectional communications by use of an upstream and downstream channel. The communication occurs between a Cable Modem (CM) and a Cable ModeYm Termination System (CMTS).

There are many different versions of the standard because of regional differences in cable bandwidth. The American DOCSIS standard uses 6 Mhz channels, while the European EuroDOCSIS standard works with 8 MHz channel bandwidths. 

How Does DOCSIS Work?

A cable television channel is used to transmit multimedia and internet services. The user’s computer is connected —via a network card or USB port— to the cable TV network with a cable modem. 

Once it’s connected, the modem controls the channels that transmit data and links to the CMTS, which is connected to the internet. It is given an IP address and lets the user access the services offered. [1]

A digital stream of information is transferred through the TV network to the modem. The modem sends the information to the computer through an Ethernet interface or a USB interface. 

History of DOCSIS

Keep reading to learn the specifications and improvements of each DOCSIS specification over the years, starting from March 1997. 


The premier generation of DOCSIS —DOCSIS 1.0— began in March 1997 and was created to implement Internet access-related services. D1.0 supported bandwidth of about 10 Mbps in the upstream channel and around 40 Mbps in the downstream channel.

In April 1999, it was improved to version D1.1, keeping the same bandwidth rates but becoming a basis for implementing VoIP services with cable subscribers. D1.1, with the aid of Quality of Service (QoS) elements, started to attain the DES 56 transmission security requirements. Some of these requirements are transmission encryption and the implementation of filters. 


By January 2002, a more improved version of DOCSIS was released —DOCSIS 2.0. The D2.0 provided more symmetrical upstream and downstream transport bandwidth to solve the consumers’ issue with network bandwidth. 

DOCSIS 2.0 achieved maximum speeds of 30 Mbps upstream and 40 Mbps downstream, which became possible by utilizing more efficient modulation schemes and widening the band available for uploading —or the upstream channel. 


The DOCSIS 3.0 was launched in 2006 as a solution to the issue of increasing speed. The D3.0 provided the opportunity of integrating IP multicast, AES encryption, channel bonding —combining upstream and downstream channels— and IPv6 functionality. 

DOCSIS 3.0 can connect eight or 6MHz channels downstream and achieve speeds up to 440 Mbps (EuroDOCSIS) and 340 Mbps (DOCSIS). Upstream, the D3.0 can reach speeds of up to 120 Mbps., The D3.0 has been the basis of operations in HFC network technology since it was introduced.

The execution of DOCSIS and its modifications over the years have catalyzed HFC technology development, which plays a huge part in the telecom industry. 

The Hybrid Fiber Coax (HFC) network arrangement consists of cables linked to an optical node. The node helps in electrical to optical conversion and is linked with a central location —Cable Modem Termination System (CMTS)— with a fiber. Optical nodes usually supply power to an amplifier that’s connected to the coaxial cables. The CMTS is a hub for modems linked with a distributed HFC network.  


In 2013, the DOCSIS 3.1 was released, and it enabled the application of GigabitEthernet services in HFC networks and response to the issue of fiber-access networks. 

D3.1 implements a new physical layer generation (PHY) that combines the Orthogonal Frequency Division Multiplexing (OFDM) and Forward Error Correction (FEC) operations. The integration of OFDM and FEC mechanisms amplifies efficiency by 66% in the upstream direction and 50% in the downstream direction. This is due to the enhanced modulation from 1024QAM to 4096QAM. 

DOCSIS 3.1 also supports a bandwidth of 10 Gbps downstream and 1 or 2 Gbps upstream. The 6 or 8 MHz bandwidths are replaced by narrower OFDM subcarriers which are 25 kHz or 50 kHz wide. These subcarriers combined to make a spectrum that can be up to 200 MHz wide. 


As we said earlier, there are two different DOCSIS standards for Europe and the US. The various standards were developed because of the notable contrasts between the American and European systems. 

The European Cable Television complies with the SECAM (Séquentiel couleur à mémoire) or Phase Alternating Line (PAL) system. On the other hand, the US uses the analog National Television System Committee (NTSC) color system.  [2]

They also utilize different RF (radio frequency) channels — 8 MHz in Europe and 6 MHz in the US. The difference in RF channels leads to subsequent differences in channel bandwidth, with the 8 MHz in EuroDOCSIS allowing the downstream channel to be assigned with more bandwidth. 

How To Manage DOCSIS Devices

Coax Cable

Over the years, DOCSIS has established itself as a quite popular and efficient standard internationally. Despite this, the vast amounts of subscriber devices and cable modems in the industry still pose a serious issue to ISPs (Internet Service Providers). 

A rough estimate shows that about 5000 to 9000 CPE models that support different versions of DOCSIS come from a few manufacturers in the industry. As a result, attempting to manage so many devices —which are usually incompatible— without an efficient solution is a big issue for small-scale and large-scale enterprises. 

AVSystem is a management software provider that can solve the issue of handling DOCSIS mechanisms and successfully integrating them with other technologies.

Unified Management Platform —AVSystem’s solution— provides full support for D3.1, D2.0, D1.1, and D1.0 and security extensions. It even offers an adaptable procedure for the auto-discovery of newer CPEs. 

Already available DOCSIS-enabled devices are monitored with a management protocol that allows further operations like reboots and firmware upgrades. 

What’s Next For DOCSIS?

Contrary to the rumors that have run rampant for over twenty years, DOCSIS is not in danger of becoming obsolete. In fact, CableLabs just informed the public that they have completed the DOCSIS 4.0 specification. D4.0 can now potentially support speeds up to 10 Gbps and allow speeds of 6 Gbps in the upstream direction. 

Fundamentally, DOCSIS 4.0 is quite similar to the available fiber-optic solutions. This means that DOCSIS 4.0 is a way of making sure the HFC network and the cable industry as a whole don’t become obsolete due to technological advancement. [3]

Data Over Cable Service Interface Specification doesn’t seem to be lagging technologically. The DOCSIS technology appears to be making technological leaps and bounds. 

Bottom Line

DOCSIS is a technological innovation that allows users to connect to the internet with TV cables. It makes accessing the internet a lot simpler for households, and it’s not as expensive as fiber-optics. The bandwidth in DOCSIS is shared among all the internet users. 

All in all, DOCSIS is an excellent method of accessing the internet, and it makes use of standard equipment like cable television channels.

If you want to learn more about DOCSIS check out DOCSIS 3.0 vs 3.1 – Which is best?

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