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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
| reply to attsbcisgay
Re: Cable has so much potential
Unfortunately the speeds you read on Wikipedia are the maximum channel speeds; not those of your modems or connection.
The cable company can not simply ramp up the channel to the maximum possible speeds. It maximum bit rate depends on many technical factors in the design of the system and its physical characteristics of it and its environment. The maximum channel speed - that is shared by all users & upstream and downstream communications - is often fixed at a lower speed because its simply held back by the laws of physics. Your connection can just can not reach the maximum possible speed that the DOCSIS spec requires the CMTS to handle. To do so could require the cable company to rip out their entire cable plant, amplifiers, etc - and replace it. Its not happening. | |
MadMANN
Premium
join:2005-08-19
 ·Comcast
| said by whizkid3  : Your connection can just can not reach the maximum possible speed that the DOCSIS spec requires the CMTS to handle. To do so could require the cable company to rip out their entire cable plant, amplifiers, etc - and replace it. Not entirely true. There are equipment upgrades that can be done without "ripping" everything apart. Yes, some amps and headend equipment. As a matter of fact, many areas are upgrading to a higher capacity and installing the multiple CMTS reqired for DOCSIS 3.0. So, in fact, HFC systems can compete for a long time.
My opinion on the OPs point is that they are all being upgraded as more competition rises. For example, you will see cable companies competing with FiOS upgrading their systems before you will see another with no or only dish competition. In fact, the whole reason cable is where it is now is because of the dish. If not for them coming out and offering interactive guides and digital technology, the HFC system may not have been launched when it was. Same thing with FiOS. Verizon (Formerly Bell Atlantic) could and should have brought FTTH 13 years ago when they promised PA residents. They didn't, and now they are desperately trying to play catch up. But if not for the HFC system, who knows how long it would have taken them to even attempt to do what they are doing now. | |
whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
| 
DOCSIS 1.0 Mbps per MHz |
said by MadMANN :There are equipment upgrades that can be done without "ripping" everything apart. No doubt - good point. I think its in line with what I said; that the cable company can not simply flip a few switches... If they could, they would do so.
What is most important here, is that there are physical limitations on the data rate - constraints in the whole end-to-end system. There are two main ways that the data rate in a digital communications channel can be increased:
- increase the signal-to-noise ratio (SNR)
- increases in coding technology that allow more bits to be delivered per symbol
The first can be done by, for example, an increase of the power into the system; an improvement in the shielding of the cable itself; an improvement in the fiber portion of the system; installing RF amplifiers that generate a lower amount of noise; better cable modems; etc. All of which require (sometimes extensive) changes in hardware. The SNR has been the limiting factor in hybrid fiber-coax (HFC) systems. This is why that often improvements in data rate can not be made without ripping everything apart. (Sometimes they can, but not in every system.)
The second can be done with a coding improvement in the CMTS itself. By coding, I am referring to how the data is coded into transmittable symbols. However, very often while the CMTS could support more 'advanced' coding rates, higher SNRs in a particular HFC system are the limiting factor here as well. (i.e. the cable company using 256-QAM over 16-QAM. See attached chart. Note that the numbers in this chart are for DOCSIS 1.0 and are not the top end data rate, but Mbps per MHz of bandwidth. I don't have a chart comparing DOCSIS 3.0 modulation types.) Again, the SNR is the limiting factor. Often to make improvements on this end; again the cable company may have to rip everything apart. (Not always, but often.) Another point to note regarding coding improvements, is that some increase latency. This is often undesirable to gamers, for example.
Yes, its great that DOCSIS 3.0 is here, and can provide some faster data rates (speeds). However, simply switching to DOCSIS 3.0 doesn't guarantee the top-end speeds. Often very expensive and/or time consuming upgrades may be necessary. Cable companies are not going to make these changes without a business case and finacial incentive. (This often means competition from FIOS or raising your monthly fees.) | |
MadMANN
Premium
join:2005-08-19
·Comcast
| said by whizkid3 : the cable company can not simply flip a few switches... If they could, they would do so. What do ya mean? That's exactly what many people think techs do all day.  | |
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