What is DOCSIS and How Does It Work?

The Internet signals are transmitted via telephone, twisted pair, coaxial, and fiber-optic cables. The choice of medium depends on the existing network infrastructure and financial reasonability. Each option has its data transmission standard. DOCSIS is one of the standards. It states data transmission is carried out via deployed television (coaxial) cables. You can often see a digital value next to the DOCSIS standard. It stands for the version of the technical specification. Versions differ in network organization; for the user, the main difference is internet speed.

It is the era of the Gigabit Internet, but more than 90% of the US is currently connected to coaxial Internet, and only 25% have potential access to fiber-optic cable. So it looks like we’re still there. However, since the end of 2015, some of the existing cable connections have seen significant speed improvements (a few gigabits per second!) by simply replacing a few pieces of equipment – no new wiring is required. This standard, DOCSIS 3.1, has been in place since 2013, but with the increasing number of ISPs updating their equipment, it is possible that in a few years, most users will not have to wait until the actual fiber reaches the speed of the fiber.

Recently, CableLabs has provided technical documentation for the DOCSIS 4.0 standard. Let’s take a look at this technology in our article, too-

What is DOCSIS technology

What is DOCSIS?

DOCSIS stands for Data Over Cable Service Interface Specifications. It is an international telecommunications standard for high-speed data transfer over coaxial cables. In 1998, an ITU working group in Geneva endorsed the fundamental standard J.112, which defines data transmission methods over cable television networks. Based on ITU standards J.112 and J.83, a single international standard known as Data Over Cable Service Interface Specification (DOCSIS) was developed by a consortium of CableLabs in collaboration with a wide range of equipment manufacturers.

This standard transmits high-bandwidth data over a cable television network at a maximum speed of 42 Mbit/s. (with a 6 MHz bandwidth and 256 QAM multi-position amplitude modulation) and data acquisition from the subscriber at a rate of up to 10.24 Mbit/s. It is intended to replace the previously dominant solutions based on proprietary data transfer protocols and modulation methods, which are incompatible. It should guarantee the compatibility of equipment from different manufacturers.

ITU documents also contain three applications that consider the specific features of the US, European, and Japanese CATV services markets and the standards used in these regions (NTSC, PAL, SECAM).

How Does DOCSIS Work?

The standard of the client’s connection to the network via coaxial cable systems uses a downstream channel, i.e., carried out from top to bottom.

A standard cable TV channel (Internet and multimedia services) is used for data transmission. A cable modem is connected to the user’s computer via a USB port or a network card, which, like a TV, connects to the cable TV network. After connection, the cable modem determines the channel through which data can be transmitted, connects to the CMTS (Cable Modem Termination System) installed at the KTV Operator, which has an Internet connection, receives an IP address, and allows the user to access the Internet or other services offered by the operator. Finally, the cable modem receives a digital stream of information transmitted via the cable TV network and sends it to the computer via a USB or standard Ethernet network interface.

This scheme implies the internet distribution through the main modem, CMTS, to all connected users simultaneously.

Is DOCSIS Technology Useful?

DOCSIS has been used since 1998. It was released in 1997. The task of the standard is to unify the requirements for data transmission over coaxial lines and guarantee the compatibility of equipment supplied by different manufacturers.

The technology was promising at its introduction. It allowed us to carry out the Internet through existing networks and thus reduce expenses for creating new infrastructure. For cable internet operators, this meant the possibility of expanding the list of services provided and, for users, inexpensive Internet with relatively high speed.

Now, connection via DOCSIS is inferior in speed to other network connection options, such as FTTB, PON, and HCNA.

Hereunder, we’ve covered everything you need to know about DOCSIS.

Different DOCSIS Versions

DOCSIS is divided by type of specification. The division is carried out in the order of updates with additional functions:

  • DOCSIS 1.0
  • DOCSIS 1.1
  • DOCSIS 2.0
  • DOCSIS 3.0
  • DOCSIS 3.1
  • DOCSIS 3.1 FD
  • DOCSIS 4.0

The differences between the types are determined by the quality of service (QoS) criteria, flow capacity, modulation, and noise immunity. EuroDOCSIS – an adaptation of the standard to the European frequency grid.


Improves DOCSIS 3.1 to use the full range of cable (from 0 MHz to ~1.2 GHz) simultaneously in both directions. The standard provides multi-gigabit symmetrical services while remaining backward compatible with DOCSIS 3.1. CableLabs released the full specification in October 2017. Initially introduced as DOCSIS 3.1 Full Duplex, the new standard was renamed DOCSIS 4.0.

DOCSIS 4.0 standard technical documentation includes full-duplex and extended-spectrum modes. This technology allows data transmission speeds of up to 10 Gbit/s in the downstream channel, doubling the maximum download speed compared to DOCSIS 3.1 technology.

The upstream data rate is increased to 6 Gbit/s, four times the maximum upstream speed of DOCSIS 3.1.

All cable network operators have to respond to the ever-increasing demands of their customers, which is especially important in the growth of telecommuting and education sectors and online health services. All of these areas will benefit from the introduction of DOCSIS 4.0 technology, which will bring improvements in broadband quality, commented Doug Jones, senior developer of the DOCSIS 4.0 architecture. The DOCSIS 4.0 technical documentation development, part of the 10G Platform, began in August 2016. The spectrum expansion was completed in September last year.

In addition to the increase in data transmission rate, the DOCSIS 4.0 technical documentation shows the reduction of the delay time, which was first included in the DOCSIS 3.1 standard. According to internet statistics, reducing the delay time will open up additional opportunities for users of applications such as online games and multimedia.

Have you upgraded your modem yet? No. You should consider upgrading your DOCSIS 2.0 modem to a DOCSIS 3.0 modem or DOCSIS 3.1 modem to a new modem for high-bandwidth downstream and upstream channels. You’ll get the fastest downstream speed.


First introduced in October 2013, the DOCSIS 3.1 specification regulates the forward channel rate of 10 Gbps or more and the return channel rate of 1 Gbps, using a 4096 QAM modulation scheme. It made the implementation of GigabitEthernet services possible in existing HFC networks. Instead of the channels’ 6 MHz and 8 MHz frequency division, carrier widths from 20 kHz to 50 kHz with OFDM multiplexing are used. They can be stacked in a spectrum up to 200 MHz wide. DOCSIS 3.1 also regulates energy management tools to reduce the power consumption of the cable television industry.

The new amendment to DOCSIS 3.1 made the forward and reverse channel rates equal (full-duplex). It also increased the return rate to ten gigabits per second thanks to sharing the cable frequency range (from zero MHz to 1.2 GHz) for sending and receiving data. This allows time slots to be optimized.

Version 3.1 specifies a forward channel rate of up to 5 Gbit/s and a reverse channel rate of up to 1 Gbit/s, which significantly exceed previous specifications. The standard also provides for reducing power consumption using power management tools, making the coax cable industry more economical.


The asymmetry of the channel existed in the subsequent years with the release of updates. Only in the latest version of the specification could equalize the flow rates.

Issued in August 2006, ratified as an international standard ITU-T J.222 (2007).

Starting with DOCSIS 3.0, the data transmission rate was increased to 1.2 Gbit/s in the forward channel and 200 Mbit/s in the reverse direction.

DOCSIS 3.0 allows you to combine multiple channels (Channel bonding) on a cable modem, increasing access speed. It combines up to 16 forward and 8 reverse channels. Before DOCSIS 3.0, the bandwidth per user in a downstream channel was approximately 25 Mbit/s (download speed); in an upstream channel, it was no more than 10 Mbit/s (upload speed). This is due to the impossibility of allocating all the time slots for one subscriber device.

Also, DOCSIS 3.0 supported multicast, AES encryption, and others.

DOCSIS 1.0 & 2.0

The first DOCSIS network implied data transmission at a speed of no more than 42 Mbit/s and in the opposite direction up to 10 Mbit/s.

The Difference between DOCSIS 4.0, 3.0, 2.0 & 1.0

DOCSIS version Production date Maximum downstream capacity Maximum upstream capacity
1.0 1997 40 Mbps 10 Mbps
1.1 2001
2.0 2002 30 Mbps
3.0 2006 1.2 Gbps 200 Mbps
3.1 2013 5 Gbps 1-2 Gbps
4.0 2017 10 Gbps 6 Gbps

How is the Speed Divided Between Users?

DOCSIS is not a personal, dedicated line. Instead, it is divided between all users currently exchanging data, so the value for a particular user varies widely.

DOCSIS 2.0 standard differs from 3.0 technology in speed and the possibility of combining channels. The third version allowed uniting channels on a cable modem for the first time. With the help of this function, it is possible to obtain higher speed values.

What is DOCSIS 4.0?

This latest DOCSIS standard provides quite a high speed, and if you look ahead, with the introduction of another correction, you can receive and send data equally fast. The technology will compete with fiber. However, deploying new coaxial networks is expensive, and the speed for the user with other types of connections is higher.

On the other hand, in sparsely populated areas with private households, it will be even more expensive to deploy fiber. If you have coax cables, it is much cheaper to connect users to the Internet through them. Even version 3.0 can compete with fiber-optic networks, and 4.0 is far superior in the future. Learn why is my fiber-optic Internet slow.

The Equipment of DOCSIS

There are many options for equipment that fits this type of connection. The choice depends on the manufacturer, additional features, and a suitable price category. The offers include two-in-one devices: cable modem and WiFi.

One of the most popular manufacturers of such equipment is Netgear. In particular, they supply a WiFi router for the DOCSIS model N450, which provides quick access to the network. However, other manufacturers are not inferior in quality. So, when choosing equipment, consult with your operator.

Summary of DOCSIS

  • It’s a technology that connects to the Internet through television cables.
  • It simplifies access to the network for users in private households, where it is expensive to install fiber optics.
  • Internet speed via DOCSIS is superior to fiber-optic networks.
  • Most versions of the standard specifications provide asymmetric data transmission speeds.
  • Speeds up to 10 gigabits per second in the direct channel, depending on the version.
  • It divides the bandwidth between all subscribers exchanging data.

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