DOCSIS
Data Over Cable Service Interface Specification ( DOCSIS ) is a technology developed by CableLabs around 1997 specification for interfaces of cable modems and associated peripherals, ratified (ITU- T Recommendation J.112 ) by the ITU in March 1998. DOCSIS is a standard that defines the requirements for data transmission in a broadband cable network. The main scope of DOCSIS is the rapid transmission of data over existing cable TV networks.
The successor DOCSIS 2.0 specification was introduced in 2002 against the backdrop of increased demand of symmetric, real-time data requiring services such as IP telephony.
DOCSIS achieved in the receive direction (English " downstream") and a usable data transfer rate of about 38 Mbit / s ( EuroDOCSIS: 50 Mbit / s) per channel in the frequency range from 50 MHz to about 862 MHz, and in the transmit direction (English " upstream" ), a usable data transfer rate of about 27 Mbit / s per channel in the frequency range 5-65 MHz. With DOCSIS 3.0, by bundling four channels at speeds of up to 160 Mbit / s ( EuroDOCSIS: 200 Mbit / s) in the receive direction and up to 108 Mbit / s can be achieved in the transmit direction. A grouping of eight channels is also possible with correspondingly doubled the maximum data rates.
DOCSIS is often mistakenly equated with DSL. While you can reach with DOCSIS similar bandwidth as with DSL, DOCSIS, however, is based on a slightly different technology.
Especially in France, Austria, Switzerland and the USA as well as in urban areas of other industrialized countries working with the DOCSIS cable modems are widely used. In Germany the number of DOCSIS providers due to the historically complicated division of the lattice planes of the cable networks is still relatively limited and the bandwidth offered irritate not yet made the full capacity of DOCSIS. However, the availability and acceptance of the DOCSIS Offers is currently growing rapidly in Germany.
EuroDOCSIS
Because of the different television systems, the frequencies in the U.S. and European cable networks are distributed differently. While the European PAL system calls bandwidths of 8 MHz, the U.S. NTSC satisfies a bandwidth of 6 MHz.
For this reason, the DOCSIS specifications for the European market were adjusted and operate under the name EuroDOCSIS.
Due to the greater frequency bands allows EuroDOCSIS a greater data rate downstream.
DOCSIS in the OSI reference model
DOCSIS is located in the OSI layers 1 and 2 and thus provides the platform for the transfer and backup of data.
At the physical level DOCSIS 1.0 provides transmission bandwidth of 200 kHz to 3.2 MHz, DOCSIS 2.0 up to 6.4 MHz. DOCSIS 2.0 is fully backward compatible with DOCSIS 1.0. The data to be transmitted to the quadrature amplitude modulation is modulated (64- QAM or 256 -QAM for the downstream, and 16- QAM and QPSK for the upstream, DOCSIS 2.0 provides also 32- QAM, 64- QAM and 128 -QAM for the upstream before ).
Layer 2 DOCSIS utilizes a combination of time division multiplexing and code division multiplexing.
Technology
The DOCSIS architecture consists of two main components: a cable modem on the customer side and a cable modem termination system ( CMTS ) at the cable headend of the provider.
, The CMTS comprises a plurality of downstream and upstream modulators, each of which forms a port and establish the connection to the cable modem, similar to a DSLAM in a DSL network. Since the upstream and downstream are each located in different frequency ranges, always two physical ports are needed for an existing duplex connection. A WAN interface manages the connection between the CMTS and the IP backbone.
The subscriber terminals (Customer Premises Equipment) such as computers or telephones are connected so via Ethernet, USB or ATA with the cable modem and the CMTS continues over the IP backbone.
About implemented by DOCSIS Media Access Control (MAC), the cable operator can configure the cable modem, regulate the transmission bandwidths and enable or disable certain services. Since potentially to each attached device (and thus also to other cable modems) is transmitted in a broadband cable network broadcast information, is also among themselves ensured by MAC encryption, the privacy of our clients.