DMS1
join:2005-04-06
Carrollton, TX
| reply to BosstonesOwn
Re: HD TV?
said by BosstonesOwn  :Are you serious ? How can fiber a digital medium carry analog signals ? It is turned into an analog signal at the ONT. Are you really serious about what you just said ? I am both really serious and right. Look at the second diagram that I posted here: »[ fiber tech] Pictures//info only today for some insight on the video system. An EDFA is an Erbium Doped Fiber Amplifier and is essentially an entirely optical analog amplifier and splitter. More details can be found here: »www.tlc.unipr.it/bononi/ricerca/edfa.html. The analog receiver function in the ONT is performed as part of the the optical to electrical interface which is called a triplexer. There is some background information here: »www.lightreading.com/document.as···int=true.
Finally, if you still don't believe that an optic fiber can carry an analog signal just picture what would happen if you took one of those fiber-optic table lamps and attached a dimmer to it. An analog signal over fiber is no more and no less than just a varying brightness. Of course, to carry an entire CATV-type signal the brightness has to change rather quickly - about 1.7 billion times a seconds in fact! |
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BosstonesOwn
join:2002-12-15
Everett, MA
clubs:
 ·Comcast
| optical IS DIGITAL no matter the brightness.
Everything on the fiber is a 0 or 1 not 0 to 1 hence it's digital. You really don't get basic digital prinicipals do you ?
--
"It's always funny until someone gets hurt......and then it's absolutely friggin' hysterical!" |
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DMS1
join:2005-04-06
Carrollton, TX
| No - you are wrong. If you are still not convinced then here is a link to the short-form data sheet for the triplexer used in the ONT610: »www.luminentoic.com/products/dat···S430.pdf. The video stage is just a series of amplifiers that take the photo diode output and increase it to a level where it can drive a length of coax. There is no D-to-A conversion anywhere in the path. |
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DMS1
join:2005-04-06
Carrollton, TX
| reply to BosstonesOwn
And in case you want even more convincing, look at this presentation: »www.ofcnfoec.org/materials/Piehl···erlay%22. It should be fairly clear from the diagrams exactly how it works as an entirely analog transmission system. |
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BosstonesOwn
join:2002-12-15
Everett, MA
clubs:
·Comcast
1 edit | said by DMS1 :And in case you want even more convincing, look at this presentation: » www.ofcnfoec.org/materials/Piehl···erlay%22. It should be fairly clear from the diagrams exactly how it works as an entirely analog transmission system. Dude what the hell are you smoking ? They use the same technology as cable. Each shade is a frequency ! That does not make it analog. It gets to be analog by the sensor which does the conversion.
Do you work in an office as an accountant or something ?
Actually why don't you yourself look at the How to choose slide ? RF based digital services ! Really learn the technology before you try and talk about said technology. |
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KenAF
join:2006-01-23
Arlington, VA | reply to Neyland
More on how FiOS is setup here:
»fioswatch.com/about-fios/ |
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new2fios
join:2006-07-20
Camillus, NY
| reply to Neyland
Hmm. This article »www.ofcnfoec.org/materials/Piehl···erlay%22 referenced by DMS1 does seem to imply that the 1550nm overlay is entirely analog but I am not convinced that this is true in FIOS. In this article referenced by Ken AF »fioswatch.com/about-fios/ it clearly states that the 850MHz ANALOG signal is actually encoded on the fiber as a DIGITAL 3.5Gbps signal on the 1550nm overlay, just a stream of ones and zeros. So the ONT definitely has a D/A converter in it to reproduce the RF. I think other authors are just trying to oversimplify things. There is just no way that the optical channel can have low enough distortion to carry 850MHz worth of RF in analog form. And please, everybody, don't flame people or make remarks about their intelligence or their professions. |
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jfoj
join:2005-05-06
Mclean, VA
| reply to Neyland
Do not know completely about FIOS, but just because there is fiber involved does not always mean everything is digital.
Used to work with the following gear that was totally analog RF distribution. The laser diode was directly modulated (AM) as I recall?
750+ MHz RF bandwidth input, 750+ MHz RF bandwidth output!
These things were not all that expensive in the big scheme either.
»www.foxcom.com/satlight/pdf/1303···Band.pdf
So it is totally feasible that FIOS can and does directly modulate the laser for a RF distribution of the video.
The thing about fiber RF is very little path loss (loss is mostly in the connectors, but they need to be angle polished "APC" type connectors), little to no amplification and if set up properly little to no intermod and distortion.
jfoj |
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DMS1
join:2005-04-06
Carrollton, TX
| reply to new2fios
The quoted article is unfortunately wrong, or at least confusing, in a couple of respects. Firstly, it talks about FiOS TV being all digital which it isn't. All the local and PEG channels (numbers less than 50) are available in both analog and digital form as can be tested by connecting a TV without using an STB. Secondly, I haven't got a clue where the 3.5Gbps figure comes from, but if the RF overlay was to be digitized, this rate would be nowhere near enough. The Nyquist theory states that a signal with an 850MHz bandwidth would need a sampling rate of 1700 million samples per second. With a total data rate of 3.5Gbps, this would equate to a resolution of only two bits per sample, which is woefully inadequate. The analog channels would be unwatchable with only four distinct brightness levels and QAM-256 digital would be impossible since this requires at least sixteen distinct levels. This latter point touches on another common source of confusion - the signal representing a 'digital TV channel' is most certainly not a digital (i.e binary) signal on a cable or fiber. Indeed, very few digital transmission mechanisms (including Ethernet and even simple RS232 serial) are truly on or off binary systems. |
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jfoj
join:2005-05-06
Mclean, VA
| reply to Neyland
And to clarify for anyone, RF is analog no matter which what you cut it. You may have digital modulation schemes, however, you are modulating an analog medium.
I would assume the FIOS TV is basically an RF CATV plant directly modulating a laser diode that is operating on a specific wavelength. Then the ONT just demodulates the optical path and converts it directly to RF which the STB's use.
The reason fiber is superior to coax is fiber is very low attenuation, very stable over temperature, has little to no attenuation slope and little group delay. The biggest problem with fiber is the type of connectors used and sloppy maintenance.
No need for 30-40 trunk amplifiers to get the signal from the head end to the STB with all kinds if level variations, attenuation tilt, distortion and inter-modulation products. Also very few CATV techs/engineers fully understand how to properly set up and maintain a cable plant with multiple amplifiers.
FIOS basically uses COTS CATV STB's that may CATV operators use. Not much magic here.
Now it appears the trick within the ONT is the STB return channel is demodulated from RF then converted to IP and the STB return path is IP based.
jfoj |
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DMS1
join:2005-04-06
Carrollton, TX
| said by jfoj :Now it appears the trick within the ONT is the STB return channel is demodulated from RF then converted to IP and the STB return path is IP based. Although the Motorola ONTs support this method, I don't believe Verizon use it, probably because as far as I know the Tellabs ONTs don't have an RF upstream ability. Instead, Verizon pass all upstream data from the STBs over IP directly (via MoCA through coax to the NIM/router and then Ethernet to the ONT). This may cause problems in the future when two-way cable cards become available since I suspect they will require an RF upstream path. However, since it is unlikely that these cable cards will support IPTV-based VOD anyway, it is probably a mute point. |
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jfoj
join:2005-05-06
Mclean, VA
| reply to Neyland
DMS1 you are probably correct on the return path.
I could not remember if this was addressed directly by the STB or the ONT?? but the STB obviously has MOCA in it.
I think the problem with Cable Card is most of the tuners out there are 1 way RX only, so everything I have heard about with a cable card does not support a return channel.
jfoj |
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DMS1
join:2005-04-06
Carrollton, TX
| reply to BosstonesOwn
Hopefully some of the other replies here have convinced you that I am not the rubbish-spouting idiot you seem to think I am. In case not, here is a link to an article about G.983.3 which is the standard used for FiOS TV: »www.bechteltelecoms.com/docs/btt···cle8.pdf. You will see it contains some in-depth analysis relating to the use of fiber for transmission of an analog RF overlay.
Finally, I would ask that in the future you do not make unnecessary, and unwarranted, comments about posters in these forums. Myself, along with most others who post here, do so because we believe that we are able to help and advise others. Making derogatory comments doesn't help anyone. By the way, for the record, I am not an accountant, but rather a professional electrical engineer with nearly twenty years experience designing advanced telcoms equipment. |
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DMS1
join:2005-04-06
Carrollton, TX
| reply to jfoj
said by jfoj :I think the problem with Cable Card is most of the tuners out there are 1 way RX only, so everything I have heard about with a cable card does not support a return channel. I don't believe two-way cable cards (i.e. CCs with a return path) are even fully defined yet, let alone deployed by anyone. However, I would be really surprised if the standard, when defined, increased complexity by adding MoCA. If I'm right, then this makes it totally incompatible with FiOSes VOD operation. |
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BosstonesOwn
join:2002-12-15
Everett, MA
clubs:
·Comcast
| reply to DMS1
said by DMS1 :Hopefully some of the other replies here have convinced you that I am not the rubbish-spouting idiot you seem to think I am. In case not, here is a link to an article about G.983.3 which is the standard used for FiOS TV: » www.bechteltelecoms.com/docs/btt···cle8.pdf. You will see it contains some in-depth analysis relating to the use of fiber for transmission of an analog RF overlay. Finally, I would ask that in the future you do not make unnecessary, and unwarranted, comments about posters in these forums. Myself, along with most others who post here, do so because we believe that we are able to help and advise others. Making derogatory comments doesn't help anyone. By the way, for the record, I am not an accountant, but rather a professional electrical engineer with nearly twenty years experience designing advanced telcoms equipment. Dude its an overlay ....... ON A DIGITAL MEDIUM It's digital then swapped to analog. Read the slides yourself and the specs. Digitial medium with an overlay in the spectrum.
The light wave can be analog by sweeping for all we care, but the medium is still digital. Hence the signals are not analog and are digital.
And why do you take offence to a question I asked ? Are office workers below you so you take offense to it ? Sounds like you have little man syndrome or something. Hell what ever you want to believe.
--
"It's always funny until someone gets hurt......and then it's absolutely friggin' hysterical!" |
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osakans
join:2003-08-27
Scarsdale, NY
| What's a "digital medium"? Not to put too fine a point on it, but a medium isn't by its nature analog or digital -- it's a description of a carrier of the information being transmitted, whether it's electromagnetic waves through space (in which case, there isn't a medium, but that's an issue of late 19th century physics we don't need to get into, do we  ), coaxial copper cable, twisted pair copper, optical glass fibers, film, magnetic tape or aluminum-coated disc. Media by their nature tend to be able to support both analog or digital signals -- some are better at one than the other, but most media I'm aware of can handle both. In particular, fiber optic cable can carry both.
"Analog" and "Digital" are interpretations we put on the signal carried on those media. "Digital" meaning that there's a threshholding process by which (following demodulation, etc.) signal one one side of a threshhold level is deemed to be a "1" and signal on the other side is deemed to be a "0." It's quite possible that a portion of the spectrum tranmitted through a medium to be interpreted as analog and a different portion to be interpreted as digital. My understanding is that's what's happening here. |
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Woof Woof
I Miss Brother Iz
join:2004-09-01
Keller, TX
| reply to BosstonesOwn
As DMS1 has stated, it is an analog signal on its own wavelength (lamba) of light. Just because it is carried over a fiber, does NOT mean it has to be digital.
This has been hashed and rehashed over a year ago when it first showed up in Keller. We have had a member buy an ONT on eBay, rip it apart, disect the RF section, including the chip part numbers, and even hunted down the mfg of the chip and looked over the tech notes for the chip. (And found a gaping flaw in the security of the local, unencrypted channels.)
The RF section of the ONT is dirt simple. It doesn't do any digital to analog RF, it simply takes the varying light level (AM) of that wavelenth, and converts it to an electrical RF signal at the F-Connector.
The data wavelength is digital, the return path is digital, the CATV part is not. The digital channels are then overlayed on top of this RF signal in QAM format, leaving the bottom 32 or so in analog format.
Cable companies have done the same thing for years... why reinvent the wheel when there is no need to?
Why argue the point? Because it is fun... especially in this medium where there is a right and wrong answer, and you have someone on the lure who is fighting the inevitable.
Exercise: Try to explain to us noobs how you can digitize a 1Ghz bandwidth analog signal, and cram it down a 622Mbit pipe. |
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DMS1
join:2005-04-06
Carrollton, TX | Thanks Woof Woof
It looks like "BostonesOwn" has gone away like they do. It must be that little-man syndrome. |
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