Electronics > Beginners
How can DOCSIS works on a single wire?
Electro Fan:
Yes, short answer is FDM (Frequency Division Multiplexing)
https://volpefirm.com/docsis101_rf-fundamentals/
Electro Fan:
Longer answer (QAM and OFDM) as you get to newer versions of DOCSIS such as 3.1:
https://en.m.wikipedia.org/wiki/DOCSIS
DOCSIS 3.1 : First released in October 2013, and updated several times since, the DOCSIS 3.1 suite of specifications support capacities of up to 10 Gbit/s downstream and 1 Gbit/s upstream using 4096 QAM. The new specs do away with 6 MHz and 8 MHz wide channel spacing and instead use narrower (20 kHz or 50 kHz wide) orthogonal frequency-division multiplexing (OFDM) subcarriers; these can be bonded inside a block spectrum that could end up being about 200 MHz wide.[6] DOCSIS 3.1 technology also includes some new energy management features that will help the cable industry reduce its energy usage, and the DOCSIS-PIE[7] algorithm to reduce bufferbloat.[8] In the United States, broadband provider Comcast announced in February 2016 that several cities within its footprint will have DOCSIS 3.1 availability before the end of the year.[9] At the end of 2016, Mediacom announced it would become the first major U.S. cable company to fully transition to the DOCSIS 3.1 platform.[10]
amyk:
Very short but not-entirely-correct analogy: imagine two people standing at the ends of a very long room shouting at each other.
mikerj:
--- Quote from: kuon on January 26, 2020, 03:33:02 am ---I do not understand how information can travel in two direction
--- End quote ---
You don't even need to use frequency division multiplexing to achieve this, have you ever used a telephone?
gf:
--- Quote from: mikerj on January 26, 2020, 10:02:43 pm ---
--- Quote from: kuon on January 26, 2020, 03:33:02 am ---I do not understand how information can travel in two direction
--- End quote ---
You don't even need to use frequency division multiplexing to achieve this, have you ever used a telephone?
--- End quote ---
Indeed, plain old analog telephones also use a similar circuit to split/combine incoming and outgoing signal, in order to support full-duplex telephony over a two-wire cable -> https://en.wikipedia.org/wiki/Telephone_hybrid, or more general https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers
EDIT: But I'm not sure whether this is relevant here - does DOCSIS really transmit downstream and upstream at the same time on the same frequencies?
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