Стандарт DOCSIS для передачи данных по кабельному телевидению

Standard for computer networking over a cable television system

Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high bandwidth data transfer to an existing cable television (CATV) system. It is used by many cable television operators to provide cable Internet access over their existing hybrid fiber coaxial (HFC) infrastructure. DOCSIS was originally developed by CableLabs and contributing companies, including Arris, BigBand Networks, Broadcom, Cisco, Comcast, Conexant, Correlant, Cox, Harmonic, Intel, Motorola, Netgear, Terayon, Time Warner Cable, and Texas Instruments.

DOCSIS employs a mixture of deterministic access methods for upstream transmissions, specifically time division multiple access (TDMA) for DOCSIS 1.0/1.1 and both TDMA and S CDMA for DOCSIS 2.0 and 3.0, with a limited use of contention for bandwidth reservation requests. In TDMA, a cable modem requests a time to transmit and the CMTS grants it an available time slot. For DOCSIS 1.1 and above, the data layer also includes extensive quality of service (QoS) features that help to efficiently support applications that have specific traffic requirements such as low latency, e. g. voice over IP. DOCSIS 3.0 features channel bonding, which enables multiple downstream and upstream channels to be used together at the same time by a single subscriber.

The first three versions of the DOCSIS standard support a downstream throughput with 256 QAM of up to 42.88 Mbit/s per 6 MHz channel (approximately 38 Mbit/s after overhead), or 55.62 Mbit/s per 8 MHz channel for EuroDOCSIS (approximately 50 Mbit/s after overhead). The upstream throughput possible is 30.72 Mbit/s per 6.4 MHz channel (approximately 27 Mbit/s after overhead), or 10.24 Mbit/s per 3.2 MHz channel (approximately 9 Mbit/s after overhead). DOCSIS 3.1 supports a downstream throughput with 4096 QAM and 25 kHz subcarrier spacing of up to 1.89 Gbit/s per 192 MHz OFDM channel. The upstream throughput possible is 0.94 Gbit/s per 96 MHz OFDMA channel.

DOCSIS modems are managed via an Internet Protocol (IP) address. The 'DOCSIS 2.0 + IPv6' specification allowed support for IPv6 on DOCSIS 2.0 modems via a firmware upgrade. DOCSIS 3.0 added management over IPv6. In recent years, cable operators have begun to increase the amount of bandwidth dedicated to the upstream. The two most popular options for this include a "mid split" or "high split". A mid split increases the upstream frequency range to 5–85 MHz, supporting a total shared upstream capacity of ~450 Mbit/s (assuming 4 SC QAM + OFDMA channels). A high split increases the upstream frequency range to 5–204 MHz, supporting a total shared upstream capacity of ~1.5 Gbit/s (assuming 4 SC QAM + OFDMA channels).

A DOCSIS architecture includes two primary components: a cable modem located at the customer premises, and a cable modem termination system (CMTS) located at the CATV headend. 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 provisioning systems and through the CMTS, the cable operator exercises control over the cable modem's configuration.

DOCSIS 1.0 specifications
DOCSIS 1.1 specifications
DOCSIS 2.0 specifications
DOCSIS 3.0 specifications
DOCSIS 3.1 specifications
DOCSIS 4.0 specifications