Data Bandwidth in Cable Networks

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Data Bandwidth in Cable networks.

The downstream data rate as specified by the DOCSIS standard is by default on the down stream at 64 QAM in North American DOCSIS 27 Mb and at 256 QAM 39 Mb.

Because of larger RF band width (8 Mb) this increases in Euro DOCSIS at 64 QAM to 38 Mb and at 256 QAM to 52/56 Mb.

The change between the 2 QAM modulation rates is purely by configuration (no hardware change).

The change from American DOCSIS to the European standard, however, is not possible. The lower modulation is more secure in the delivery.

For normal Internet and data use, a CMTS unit with the above data rate is sufficient for about 300 homes. By adding 1 or more CMTS units, the band width multiplies proportionally.

A common misconception is that fiber is the answer to true VOD (Video On Demand)in MPEG 2 or MPEG 4 compression technology. The reality is, however, fiber of any kind will not have enough band width for true VOD in anyone of the housing estates. The only way to overcome this is by video streaming (analogue or digital) with conditional access (first choice) and/or dumping the movie onto a local storage ( last choice).

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