From: "Ashwin Mansinghka" <[EMAIL PROTECTED]>> > 1. cable tv is still co-axial .. not digital
Co-axial is just a cable type......Cable does not determine if it is digital or analog.
right ! .. its the signal passed over the medium .. adding : as of now, cable tv operators haven't gone 'digital' since the signals don't come in 0's and 1's .. like in hdtv signals
Correct, the signals are analog following the PAL (European) or NTSC (American) standards.
If> > 2. there is no digital speed on the co-axial for tv
Well there is, which is nearly 30 to 40 Mbps in shared mode, per channel.we combine more channels more speed.
i guess what this means is that rpg, siticable, etc use fibre optic cables
to
transmit tv data AFTER digitising it .. and that needs 30/40Mbps .. from
what
i see in my area's CVO's place, there is a h/w which converts the optic feed
into signals which are then sent over the coax cable as a non-digital feed.
i am SURE that my tv's tuner is NOT digital but just a tuner .. aka the radio tuner
i recall nn banerjee (gm, development, bsnl, assam now) telling me that to
send
video over a medium, a 4.5 to 5 Mbps capacity is sufficient .. strangely the
bandwidth
needs are miniscule to what fibre optic can carry !
Hmmmmm............. maybe my comments were confusing. Let me attempt to provide clarity. The data is digital at origin, travels as digital through satellite uplink and downlink and gets to the decoder and gets decoded and is still digital and gets carried over the Fiber in digital format emerges as digital at local cablewallah and then gets converted to analog signal and travels over the local cable network as analog and reaches the TV as analog. Now let's talk about this analog channel, what is the bare analog channel capacity....... too little of use. What is the digital capacity of this analog channel ........ yes quite useful, very high. Fine, now I have Internet data i.e. digital data to be transmitted over this analog path, what do I do ?
> > 3. the analogue signal is the carrier
The signal carrier is RF
hmm .. so not 0's and 1's .. this would naturally mean issues like freq. modulation and amplitude modulation would be the issues.. as different from 'bit' manipulation
flowing along ("not through" the medium, like in case of electronic signal)
oops .. gaps in my understanding .. 'along' and 'through' ? .. i always understood that the mild milli/pico-watt currents gave RF type waves .. and that electrons were the particles that did this .. NOT by 'flowing' .. BUT by making electrons of adjoining atoms of copper shift to adjoining atoms of copper .. but i would really like to know the reality (it's now 35 years since i stood 19th in HigherSecondary from science :-( so things are better understood now, perhaps)
As an analogy, electronics and movement of electrons is like taking a tube (conductor) and filling up the tube with the balls (electrons) to its full capcity and then pushing an extra electron from one end (potential difference) and out pops the electron oops... the ball at the other end (circuit). The result is some work done (power applied) and time taken (resistance). Electrical Engineers will kill me due to this oversimplified analogy.
RF is like a stream of water flowing and losing its energy along the path of the flow due to obstruction and roughness in the path (conductor).
If RF was like moving of electrons, how can it travel from antenna to antenna - one oversimplified guess would be the possible conduction in the atmosphere.....now how about the antennas on the spaceship and moons and the free space (vaccum), RF still moves, light still travels without the conductor. So the next question arises why do we need co-axial .. forget co-axial why any cable for that matter. The cable is nothing but a guide path like a pre-dug out channel for a irrigation canal. The digging for the canal is to provide a guide path for the water to flow to the destination. Now movement along the path will suffer due to the qualities of the path in question, how smooth it is, how tight are the bends etc. etc.
the co-axial cable which acts as the RF feeder.
would this mean that the wave propogation (radio freq) through/along the medium does the work of transferring the 'signal' ?
Wave propagation to be more precise "electromagnetic wave" propagation (sound waves are mechanical waves and propagation in that case is little different) "along" the medium in case of cables (RF feeders / waveguides to be more precise) and "across" the medium in case of air and free space provides the way for spread of signal from the origin. "Transfer" of RF signal is incorrect, as there is no direct or indirect creation of potential difference at either ends to induce such a "transfer" from one point to another. There is RF generation, using oscillator electronics and it "radiates" in all possible directions depending on the radiating element type i.e "antenna".
Now, how and why does another antenna a little or far away gets this RF energy although having no direct or indirect physical contact (remember vaccum) ?
I invite someone to answer this query ? (just as a clue - this is a problem of perception).
Therefore, we measure the signal in dB i.e. SNR - Signal to Noise Ratio.Thesignal type is analog definitely as long as it is on the co-axial cable.
hmm .. so it is not in 0's and 1's .. it is non-digital .. an addition here .. 'signal' or 'freq' by freq/amlitude modulation/demodulation does not compulsorily mean that it has to be electron based .. it can be thru short waves/medium waves/microwaves ('disturbances in the radio freq spectrum' which one tunes into) .. and can also be thru photons .. as in laser based optic fibres .. or even sound based .. like in the earlier 'modems' on which the telephone hand set had to be placed .. SNR would apply to all these scenarios.
Well SNR is a universal principal. The impact can be felt by the sentence below.
Imagine a world without "Noise" i.e. "unwanted Signals" intefering with "desired and required signals". All the electrical / electronics, acoustics, mechanical (in some special fields), biomedical (scan machines etc.), radio physics, astronomy, communications etc. etc. engineers and professors and students in the respective fields of today of this world will suddenly loose their jobs and reasons to exist.
RF is pure energy (electromagnetical in nature) and may be indicatively understood as analog in nature (i.e. in case, if someone insists on strictly defining it between either "analog" or "digital").
> > 4. there are 99+ channels on ONE co-axial
Well yes, there are all those channels on ONE feeder.
and many frequencies .. for the many 'channels' .. and all in non-digital
mode too ..
DTH works on similar basis .. only that the medium is radio freq signal
direct
from the satellite in the sky to the dish antenna at consumer's premises ..
similar
to V-Sat dish antennas .. ONE feeder .. many many channels
Again true, the no. of frequencies on the same feeder depends on the radiating element - the specified cans used in cantenna is again for the same reason. So is the reason for the antennas of TV Tower or All India Radio Antennas and the wires strung across poles etc.
frequencies> 5. frequencies of the channels are different
Very true, each channel occupies 6 Mhz bandwidth with the centerranging from 50 Mhz to 864 Mhz.
there .. so its not 4.5 or 5 Mbps .. but 6Mbps .. we do know that the
'hertz' in
the MegaHertz means cycles .. and i guess we also know that with the
enormous
progress in h/w .. each cycle CAN be made to carry more than a single bit ..
by
cutting up the + and - parts of the cycle into yet further segments (prior
half of +
part of the cycle to represent a bit and the latter half of a + part of the
cyle to
represent yet another bit)
True, you just conveyed the idea of modulation in oversimplified terms. Congrats, we are coming in sync. Engineers will however hate this oversimplification of their thoughtful and well researched work of ages :) Hope engineers, and the would be engineers do not get offended. Professors and teachers would love this discussion for sure.
Local cable tv provider can certify this for you.
oops .. these guys don't know how things work .. ketan may .. he is helping
on cable operator to give broadband (read shared rj45 wan) from beck bagan
to golf green as of now .. but even ketan can't authoritatively tell ..
for authoritative measurements, our list's geniuses are capable .. so is
tapan sengupta who joined us at the last meeting .. he even has the h/w and
s/w
to do such measurments .. and he did talk to me about signal types/levels
yesterday too
.. we are trying to put in a wi-fi wan .. hot spots .. in udita .. with
bsnl's broadband
connection being used by nodes to access internet (legal issues ARE
involved) .. at
the ilug-cal's recent meeting location : UDITA
Local cable wallahs even those who hang the cables know a lot about poor and good signal and the bends and joints etc. (in rustic terms) affecting the RF path. They will basically explain the behaviour of RF as observed by them. Ofcourse, if we ask them about modulation schemes and encoding they may refuse to talk to us in future. RJ45 WAN is very popular in congested cities in a country like India (I have seen large networks in Mumbai about 3 years back), where one can tap small amounts of electricity along the way using the inexpensive POE (Power over Ethernet) jacks. Basically using the spare pairs in the CAT-5 cable to feed power.
Hope in the next meeting both Tapan and Ketan can share more time and information with us.
PAL> > 6. a 'tuner' is used to get the channel of one's choice
Very true again.
> > 7. there is audio AND 'video' data
There is no data in strict sense as long as it is ANALOG that is regulartype TV signals. When the contents of a given channel are MODULATED at thecarries
HeadEnd i.e at Cable providers premises, then the particular channelDIGITAL DATA and is obtained at the customer's premises upon DEMODULATION,
this is simple to understand .. i believe the Mod/DeMod is tuning into the channel .. there are other things involved as well .. Mux-ing/DeMux-ing and also the Compression/DeCompression (digital only ?)
yes we are talking of Cable Modem.
.. ah ! .. music to our ears .. when ? how ? .. go on .. any installations up and running commercially yet ?
as of now, the cable tv operators are offering WAN thru RJ45 .. the CableModems are too costly to buy/install and the provider end equipment and s/w are costly too
we have been talking to RPG and others and they just seem to be blissfully ignorant of such things
breifly .. this would need a splitter .. at our end .. which sends the tv signals to the tv and the digital signals to the pc .. this CableModem is different from the DSL .. err .. ADSL based broadband implementations of bsnl .. then how in the world will bsnl provide video-on-demand thru THEIR broadband ? .. 'digital' video specifically
Aha.... now I see. That is over simplified. No, tuning into a particular frequency is not demodulation. As an analogy "Tuning" can be better understood as using a hearing aid to catch the sound by the ear (this relates to the so far unanswered query i.e. perception problem as above) and then the sound which one hears can be some words, sentences, song, music etc. First of all to realize that the sounds are not sounds but some words, sentences etc. and then the ability to comprehend the information conveyed from such sound, words , song etc. can be understood as demodulation. Understanding the Language may be termed as can be "decoding". These are again to be considered as analogy only. MODULATION / DEMODULATION, ENCODING/DECODING, COMPRESSION/UNCOMPRESSION, ERROR-CHECKING, ERROR-CORRECTION etc. are all HIGHER LEVEL functions which are to be carried out by some already present intelligence i.e through some computations as in computers with logic, memeory etc. or as by brain in humans."TUNING" is much lower level function. It is like, are we getting desired "voltage" ?can be measured and changed, similarly are we able to perceive the desired frequency and then tune to a particular frequency / channel i.e. adjust the perception / reception level.
The day Indian society (especially the middle class and lower middle class, i.e. mass consumers) can easily afford to pay (rather throw away) about Rs.5000/- per month for TV viewing, High Speed Internet etc. then why RPG, even the local cable wallah will know about all this technology overnight (educated by all those foreign techies trying to sell their cheap prototypes for testing in Indian markets). Again I am saying, what we are discussing here is already a reality in India and by Indians for Indians, pliot projects (commercially oriented) are already underway in a few cities, none of which are in eastern part of India though.
This will sound offending to a few - Such pilot projects can be carried out (with economic viability) only in such places where consumers are aware and can afford, on both these counts even the Megacity of the east i.e. our own Calcutta falls below the standards.
Digital Video on ADSL or Cable can only be offered when the receiver units can receive such digital video i.e. a PC Desktop or a DIGITAL TV. So we again come back to consumers and their ability to spend. How many of us will actually buy the DIGITAL TV or a Costly PC Desktop with VGA Accelerator card at a prohibitive cost of Rs.70,000/- or plus to enjoy the service even if the service is offered for free.
Someone may, very insignificantly say, let the services be launched, the markets will do it and the costs will go down for the PCs or DigiTVs.
OK, for such an argument I inform and then ask :
BSNL offers free SMS from landline phones. Such phones are available in the market at Rs.1500/- approx. how many of us have bought it ? Even if one sends 10 SMS per day you recover the whole cost in how many months (taking the present tariff of SMS on mobile) ? Everyone is happy to send 20 SMS on mobiles sitting on the desk / bedroom and even where a landline is already present and pay Rs.20/- for the same with no problems.
Calcutta Telephones is the first to offer this service, that too free. What is the Calcutta society doing about it ?
Do not ask others, ask yourself. When I ask myself - I say I have not bought a phone with SMS as the department gives an instrument which is free and therefore I am not paying for my own instrument, the next day I go buy a cordless worth Rs.3000/- but not an SMS phone.
Basically, I am trying to highlight the awarness level of this part of the country as consumers and their behaviour which prevents any Tech oriented project to be tried in the city at all. The guys in a Bangalore based Indian company did a fantastic job with ADSL, pilot project carried out at one of the prestigious Housing Complex of Calcutta which had highly learned and rich dwellers about 3 years back. The choice of site was made with some objectives, one of them was, that learned people will provide a good and informative and analysed feedback. About 32 users enjoyed high speed internet at that time, free of cost and the project was termed as failure. After a year or so a foreign company with its unreliable products, not meant for Indian conditions provides the largest ISP of India, the hardware to roll out the Broadband. Think again, if the Indian project was made successful, the service rates would have been lower as the hardware would be cheaper and more reliable being designed for Indian conditions.
Is there anyone here, willing to change all this ?
> > 8. pic res is 352 x 288 pixels (ugh !)
That is regular TV, not digital data. 30 Mbps can carry a lot.
are we talking about hdtv here .. or digital/digitised high-res but 'regular' tv channel signals ?
We are talking about encoding and compression standards which allows us to pack digital data for video.
TV> 9. tv delivers (so do webcams, even digital ones .. where the pic IS > digitally recorded and can be played back in DVD format too)
Well we are not talking about TV anymore, when we want Internet on Cablenetwork we talk about digital data packets inside the shell of analog signal, quite like our regular DIAL-UP modem.
OK .. so we come to the main, core issue .. and let's work on this
Some one from computer science, preferably students learning new avenues in technology should elaborate on this. Why a student ? Because that is what the business of a student is. To find more and share more to learn more. Let a student wanting to try unconventional methods of learning (i.e. not only reading books by heart for exams, but reading and experimenting beyond the realms of the books written by great writers) come forward and put in his energies here. Is anyone even willing ? Forget about being capable. Man is born, as incapable as, any other animal on the planet.
> 10. non-digital in NOT analogue .. its just non-digital .. likenegatives> of > photos, older audio casettes/wax/vinyl records, video .. err .. movie > films, > video casettes, etc .. even human sound is not 'analogue' .. > electronically > that is ! .. it just NOT digital
Well this is again true. But we should remember about MOULATION-DEMODULATION.
and muxing and compression too ?
Compression yes. No "MUXING" at present. 30 to 40 Mbps over a single channel in a shared medium is more than enough for the present moment.
Now, I want some one to talk about possible Modulation methods (standards)
and Encoding methods (standards) which can provide us this data rate.
Just to provide a clue, we are talking about QAM and MPEG together.
Maybe one of our very learned friends here from a reputed institute will tell us about Error Correction applied in this case ;)
yep .. this will be a great help and a very fruitful discussion !
all geniuses, please contribute and let's work together .. but NOT against each other .. the issue needs to be addressed .. the level of knowledge of the participants in this discussion is NOT to be targetted please ! inputs are going to help .. criticism, comments, shooting-down won't help !
Even this discussion can have errors. Let some one shoot down those errors i.e. Error-Checking. ;)
However (on a serious note), Error-Correction is important. A little more important than Error-Checking, which alone cannot correct the errors. To correct the errors, one has to be involved and has to contribute....... Let us have more contributions in whatever ways.................
Finally, are we dreaming ?
NO, you can take my word for the same.
quoting from a recent email : those who dream with eyes open .. have the power to make their dreams happen too !
no, we are NOT dreaming ! we are working, discussing, co-operating, collaborating, IMPLEMENTING and wanting to be the early birds !
Jigyasa, Jaagriti aur Athak Parishram hi, Karm aur Karm ki Sadhna ke Pratibimb hai
Too much of philosophy, take a cup of coffee / tea, can of pepsi, tumbler of buttermilk and wash it down for the time being.
We will discuss it as TOT (Toooo Out of Topic) sometime when situations permit :)
good luck .. and thank you for this very relevant tech topic co-ordinating ashwin !
A humble thank you PK.
with Regards, ASHWIN
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