What is DOCSIS?

Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that adds high-bandwidth data transfer capability to an existing cable television (CATV) system. Many cable television operators use it to provide cable Internet access over their existing hybrid fiber-coaxial (HFC) cables with the addition of an Internet cable modem.

DOCSIS was the stepping stone that enabled coaxial cable technology to stay relevant even with the introduction of faster forms of data transfer mediums like optical fiber, wireless etc. It enables fast Internet access while avoiding the challenging and costly task of replacing the whole well-established physical network infrastructure of coaxial cables. Along with the rapidly evolving data transfer technology, DOCSIS also has gone through a lot of improvements and modifications since its inception back in 1997. There have been a number of DOCSIS versions since the inception of the standard.

DOCSIS 1.0/1.1

DOCSIS 1.0 specification was introduced in March 1997 and implemented typical services related to Internet access including proprietary cable modem functions. It uses frequencies ranging from 91 to 857 MHz for downstream and 5 to 42 MHz for upstream. D1.0 could provide a bandwidth of up to 40 Mbps in the downstream channel and about 10 Mbps in the upstream channel. It was upgraded to version 1.1 in April 1999, implementing VoIP services for cable TV subscribers, extended security requirements for DES 56 data transmission which included the use of filtration and transmission encryption and other improvements in QoS (Quality of Service).

DOCSIS 2.0

DOCSIS 2.0 was launched in January 2002 and provided more symmetrical transport bandwidth (downstream and upstream) as a response to manufacturers’ increased demand for network bandwidth. It used frequencies ranging from 50 to 864 MHz for downstream and 5 to 42 MHz for upstream. D2.0 provided maximum speeds of up to 40 Mbps download and up to 30 Mbps upload. This was made possible by using a wider band with a channel spacing of 6.4 MHz in the upstream direction (compared to 3.2 MHz in D1.0/1.1) and by implementing more effective modulation schemes.

DOCSIS 3.0

DOCSIS 3.0 specification was introduced in 2006 and provided the possibility of combining downstream and upstream channels (channel bonding), IP multicast, IPv6 functionality, and AES encryption. It used frequencies ranging from 108 MHz to 1 GHz for downstream and 5 MHz to 85 MHz for upstream. DOCSIS 3.0 standards were also later modified for use in Europe and are called EuroDOCSIS. It was capable of connecting 6 (North American Cable TV) or 8 MHz (European Cable TV) channels in the downstream direction, achieving speeds of up to 1 Gbps. In the upstream it is able to achieve speeds of about 200 Mbps. DOCSIS 3.0 also established the basic technology for HFC (Hybrid Fiber-Coax) networks and introduced support for IPv6.

DOCSIS 3.1

D3.0 was upgraded to DOCSIS 3.1 in 2013 allowing the implementation of Gigabit-Ethernet services in existing HFC networks in response to fiber access networks. It introduced a new generation of the physical layer (PHY), which integrates the OFDM (Orthogonal Frequency Division Multiplexing) and FEC (Forward Error Correction) mechanisms. This combination increased efficiency by 50% in the downstream direction and 66% in the upstream direction via the use of improved modulation schemes from 1024QAM to a maximum of 4096QAM. It used frequencies ranging from 258 MHz to 1794 MHz for downstream and up to 204 MHz for upstream. D3.1 also used the available channel bandwidth in other ways. The 6 or 8 MHz channel widths featured in previous versions were replaced by narrower (25 kHz or 50 kHz wide) OFDM subcarriers, which combined to form a block spectrum as wide as 200 MHz. As a result, version 3.1 supported bandwidths of 1 or 2 Gbit/s upstream and up to 10 Gbit/s downstream. DOCSIS 3.1 technology also included power-management features that enabled the cable industry to reduce its energy usage and the DOCSIS-PIE algorithm to reduce problems like high latency & jitter.

DOCSIS 4.0

DOCSIS 4.0 is the latest version of DOCSIS released in October 2017 and uses the full spectrum of the cable plant (0 MHz to ~1.8 GHz) at the same time in both upstream and downstream directions. This data transmission technique is called frequency division duplex (FDD) and enables multi-gigabit symmetrical (upstream/downstream) services while retaining backward compatibility with DOCSIS 3.1. D4.0 uses frequencies ranging from 108 to 1794 MHz for downstream and 5 to 684 MHz for upstream. It delivers data rates of up to 10 Gbps in downstream and up to 6 Gbps in upstream.