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data over cable service interface specification (DOCSIS)

The Data Over CableServiceInterface Specification (DOCSIS) is the potential CATV standard of the USA, which is supported by all well-known US cable modem manufacturers. In 1997, the first version of DOCSIS was published by CableLab, in which basic functionalities for quality of service

(QoS) were already implemented. As early as 1999, the enhanced version of DOCSIS V1.1 was released, which specifically considered enhancements for the transmission of Internet telephony and for other time-critical services, e.g. standardized IP multicast

, upstream fragmentation via thehead-end station and full QoS features including Available Bit Rate (ABR), Variable Bit

Rate(VBR) and Constant Bit

Rate(CBR). In addition, privacy is protected with digital signatures through a public key process

. Each user can be authenticated and only receives the data assigned to him.In the DOCSIS 2.0 version, a transmission channel is permanently assigned to

the subscriber. This means that the bandwidth is not scalable or expandable. A single channel has a data rate of approximately 50 Mbps. In practical use, one or two subscribers making downloads

at high data rates can restrict the data rate of other subscribers

DOCSIS protocol layers in relation to the OSI layer model

DOCSIS protocol layers in relation to the OSI layer model

Version 3.0 of DOCSIS

In the more recent DOCSIS 3.0 version, channel bundling is supported, as are IPv6, quality of service (QoS), Internet television (IPTV) and IP multicast. The channel bundling works dynamically and distributes the data to the available channels. In this version, a total of 16 channels are available for downstream, or even more if necessary, to which the data can be distributed. This should not cause any bottlenecks, as the data rate of 400 Mbit/s is distributed among the subscribers for 8 channels and 800 Mbit/s for 16 channels. For the upstream, the DOCSIS standard provides for three 7 MHz wide channels, namely in the lower VHF range on TV channels 2, 3 and 4 in the frequency range between 47 MHz and 68 MHz. The data rate can be 100 Mbit/s and higher. The 16 channels for downstream are in the mid UHF range

between 630 MHz and 862 MHz.Since the specifications of European cable distribution networks differ from those of the U.S., specifications for European cable networks were presented in 1998, the EuroDOCSIS

.In the U.S. DOCSIS, which is standardized by the International Telecommunication Union (ITU) under Recommendation J.112, the forward channel

has a bandwidth of 6 MHz, and thereturn channel

is inthe frequency range between 5 MHz and 42 MHz and has selectable bandwidths. All changes of EuroDOCSIS compared to the American version refer exclusively

to thephysical layer of the OSI reference model

, all other layers, especially the MAC layer, remain unchanged

Version 3.1 of DOCSIS DOC

SIS 3.1 has a completely new physical layer for the data transmission system over HFC networks, based on Orthogonal Frequency Division Multiplex (OFDM), forming a global standard. Full coexistence with DOCSIS signals from previous variants ensures backward compatibility, including with EuroDOCSIS variants.

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Englisch: data over cable service interface specification - DOCSIS
Updated at: 15.12.2015
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