Talk:Cable modem

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modulation and demodulation is required, this is wrong... I'm not sure what to replace it with, though. The reason a modem isn't considered a modem, I believe, is that it does much more than a regular phone modem. (Acts as a router, bridge, etc) someone please expand. - Booyabazooka

It's also awfully chatty, but I don't know enough to fix it, nor is it marked up correctly. (I'm glad I'm not working on wikipedia at 56k though!)Ortolan88

This page is lacking a detailed description of the cable modem architecture (or I might have missed it somewhere in Wiki). The DSL article is a good example of what we can have. --claus

cable router, instead of modem.

Disadvantage 2? - commercial practice rather than technology[edit]

Disadvantage '2' seems to be a matter of the structure and practices of the industry in the US rather than any disadvantage with the technology itself. Outside the US, for example in the UK, this practice of 'bundled pricing' exists with providers of DSL+Satellite TV (BSkyB) and now IPTV services (BT) as well as with cable. Generally, prices in the UK for standalone access on cable are as good as for standalone DSL.

Perhaps a compromise is to say something like "In some areas, cable companies' monopoly over their own infrastructure reduces the competitiveness of the medium when compared to unbundled DSL services, particularly if the customer only wishes to buy internet access."

Though IMO this is still a matter of commercial practice in specific areas rather than technology and it's relevance here at all is debatable. 01:22, 8 January 2007 (UTC)


I think the cable modem is in reality still a modem, in the literal sense of the word: MOdulator, DEModulator. It modulates the date it receives (from USB, ethernet, etc) into the analog signal used to transmit across the line. This is what I knew from 2002, and it might have changed to digital since I last looked.

"This network ran parallel to the newer DOCSIS system for a number of years, in 2004 the CDLP network was switched off and now is exclusively DOCSIS."

This also looks like a runon. Anyone want to fix it?

I went ahead and modified it. I removed the cable-modems-are-not-modems paragraph and wrote a small "cable modems in the osi layer" section. --Octavio.


How fast are people getting cable modem in the US? Here in Honduras I only get 128K maximum and I wondered if it was a limitation of Honduras or cable modems, as at that speed VoIP is fine computer to computer but not good for callas to other telephones, SqueakBox 21:53, 10 December 2005 (UTC)

I get around 8.5 Mbit/s down and about 1.2 Mbit/s up, although I'm in Sweden, not in the US. Init 15:23, 17 January 2006 (UTC)

I live in New Zealand and am on a 10mbit/2mbit plan. I typicaly get at most 9.1mbit down and ~2mbit up. I usually only hit 2mbit uploading when uploading to my places, such as when using bittorrent. Mirddes 08:08, 8 October 2006 (UTC)

NTL cable in the UK are said to be trialling 50Mb services; currently 10Mb is the fastest they offer. 01:22, 8 January 2007 (UTC)

I have Comcast in GA (USA), and have a plan with 8Mbps down and 768Kbps up, and with Comcast Speedboost which lets me actually connect as high as 12Mbps(advertised), I've actually downloaded at 14Mbps for about 10 minutes straight using bittorrent... —Preceding unsigned comment added by (talk) 20:01, 23 September 2007 (UTC)

Working in different locations[edit]

Will a cable modem work with any cable line? They installed a seperate line for my modem, but that may be so it doesn't tie up the TV's.

Can cable internet and satellite TV coexist?[edit]

Out of curiosity i was wondering if someone who has satellite TV could also get cable internet or would it be impossible because of the seperate signals? thx-AERODARt

i just had cable internet installed yesterday, through comcast. i also have satellite tv service through dish network, and i haven't experienced a problem yet. they actually both work pretty well; i'm never going back to dsl. :) 11:30, 29 June 2007 (UTC)

Answers to some of the above questions[edit]

Regarding the question about whether 128 kbps speed being achieved from the cable modem is a result of the cable modem, no, cable modems have a maximum bandwidth of single digit and possibly upto double-digit mbps (as mentioned in the article too). The 128 kbps maximum bandwidth you are getting would be controlled from the ISP end (sucks doesn't it)

Regarding the question whether a cable modem will work with any cable line, no, it requires a coaxial cable (one used to provide cable TV) of a greater thickness than a mere cable TV line. Also it needs proper insulation from electromagnetic interference. Of course cable TV can be provided over the same cable too but then it can also be provided over a cheaper, less stringent and of course less thicker cable.

Regarding the question about cable internet being possible through satellite TV, cable internet is just a method of mixing the TV signals and the internet signals over cable TV cables and transmitting it to user-premises. You'd need a way to get the internet signals from the satellite here which is another technology called satellite internet.

-- 18:54, 17 June 2006 (UTC)

Section: Cable Modems and VoIP[edit]

This section includes a reference to a disambiguation page. As someone who knows nothing about this technology (other than, how to turn it back on when my kids turn it off ;) ) I don't know which link I should follow when I hit the page MSO. Could someone who knows this stuff please point this link directly to the intended destination? Thanks Garrie 11:52, 8 December 2006 (UTC)

Fixed. -- 07:37, 23 February 2007 (UTC)

I removed the entire 'comparison' section. They why should be obvious. This article is about Cable Modem/Internet. It is not about DSL, nor is about comparing each technology.

Splitting into Cable modem and Cable internet[edit]

It seems like the physical piece of hardware known as the cable modem should be described in this article and cable internet service should be described in a Cable internet article. It's odd that the Cable modem article serves as the main article for cable internet Dav2008 14:20, 22 August 2007 (UTC)

Agree. Eric Wester 21:33, 27 August 2007 (UTC)
Far as I see, the cable internet section hasn't been written yet, and this article is short, so there's nothing yet to split off that will make much more than a stub of a new article. Perhaps either that section should be written in this article and split off when it's ready to fly on its own, or the separate article should be started with plenty of new material and any scraps from this article that may be useful. Jim.henderson 03:17, 12 September 2007 (UTC)
For that matter, the DOCSIS page contains a lot of material that isn't DOCSIS related (such as an endlessly updated list of who is selling what where and for how much), but would fit better on a cable internet article.-- 05:30, 9 October 2007 (UTC)
Ah, so the information is already present, but the articles are not linked by categories, See alsos, or inline links. This one, for example, has two cats for the digital side of things but none for the CATV side, while DOCSIS is linked to articles about its components but not to ones about how it fits into other systems. And several of these articles slop over natural boundaries into each others' territory. So, what's needed is not so much another article, and especially not a split of this article, but better connections and more precise distribution of information among existing articles. If there's a need for splitting an article, it's to make a list article for the various national DOCSIS implementations. As it happens, it's all a bit outside my technical expertise (telephone worker) but needs attention from an insider. Jim.henderson 16:31, 9 October 2007 (UTC)
I support the proposal to split (but please be sure to cross-link); as I almost always support article splits but oppose article mergers; splitting allows knowledge to be found (searched & discovered) more effectively and categorized most concisely (even if there is much redundancy), and most completely. Inclusion over deletionism! Shanoman 17:31, 17 October 2007 (UTC)
Split what? Where's the section in the present article that belongs in the proposed new article. Perhaps you mean split some other article? Jim.henderson 21:07, 17 October 2007 (UTC)
Split out the "cable internet access" to the "cable internet" article and merge in the transfer rates section from DOCSIS. I went ahead and did it, mainly to fix the DOCSIS article. —Preceding unsigned comment added by (talk) 22:41, 2 December 2007 (UTC)
I've changed the Cable Internet redirect to Cable internet rather than this page, and added inter-wiki links from this page to the other. Additionally, I updated and cleaned up the introduction to the other article somewhat. (I also changed a peculiar capitalisation issue in that article.) Dan Villiom Podlaski Christiansen (talk) 19:25, 26 April 2008 (UTC)

Needs a mention of Sigma and TCNiSO[edit]

They conquer articles that aren't NPOV, but this article is very pro-cableco POV. --TIB (talk) 18:54, 10 June 2008 (UTC)

Please clarify the bias. Far as I see, the article says how cable modems work and their history. Yes, some people modify them. So what? Jim.henderson (talk) 18:10, 18 July 2008 (UTC)

Not an NPOV issue. Simply a lack of information - feel free to add it. Apteva (talk) 16:48, 27 September 2008 (UTC)

Cable modem[edit]

NOTE: copied from User talk:Jesse Viviano on 22 Sep 2009

Re your edits and summaries here, are you saying a cable modem has a modem separate from the digital part to hook to a TV or the modem part also interacts with a computer? I know they carry the signals separately: TV, Internet, and phone (in that order inside to outside of the coax line). And I thought these were digital signals. Can you elaborate more? Tks. Post here is fine. RlevseTalk 22:39, 22 September 2009 (UTC)

The thing about "digital cable" that shows that it really is a hybrid system like most long-haul cable systems using metal wires is that pure digital signals monopolize metal cables and can carry very little data compared to what an analog signal on a metal cable can carry. Therefore, to reduce the bandwidth consumed and increase throughput, the digital message is transformed into an analog message at the right frequency and then sent. (I am using the correct meaning of bandwidth: the amount of frequencies taken up by a signal. Throughput is the term used for the speed of a digital message going through a channel, not bandwidth.) The receiver reverses the process and attempts to recover the digital message. The tricks that could be used to make this scheme succeed are the following: make each analog signal distinct enough from each other so that picking them apart is possible, adding enough redundancy to the message either in the digital domain (traditional forward error correction) or the analog domain (like in advanced methods of forward error correction like turbo codes) to make it possible to correct errors, and adding checksums to the message to allow the receiver to reject or discard messages that are so mangled in the transmission that they are too hopelessly corrupted to be fixed. The modem part only interacts with the coax in the cable system, and does not interact with the computer or Ethernet network attached to the cable modem. Therefore, the "digital cable" signals you are getting really have been transformed into analog in such a way that recovery of the digital data is almost guaranteed as long as there is no SNAFUs on the path from the cable head end to your cable modem.
This creates a lot of benefits. First, this allows legacy analog sets to continue receiving analog TV because the digital signals do not interfere with the ananlog TV. Second, the cable head end can create lots of physical digital channels to partition the cable system so that receivers only have to sort through a tiny portion of data being offered by locking onto the correct frequencies and ignoring the rest. This allows a digital cable set-top box to easily ignore the phone or Internet traffic by tuning it out. A cable modem can ignore the digital TV stuff by tuning it out. Third, if a physical digital channel gets maxed out, the cable company can add another physical digital channel to fix the situation as long as there is room on the cable for another physical digital channel. Fourth, this boosts throughput because analog signals can carry much more data than digital signals. However, analog is much more difficult to work with than digital, and that is why our computers are digital. Since Ethernet cables must carry digital data, they must be made much more carefully than an analog cable, driving up their prices drastically. Coax cables for cable TV cost little, but Ethernet cables can cost more because of tighter tolerances, which require more precise and expensive machinery to manufacture.
In short, in order to reduce bandwidth, boost throughput, partition the cable spectrum, and possibly remain compatible with legacy cable TV sets if the cable operator decides that doing so costs less than the cost of cable theft (which requires eliminating all legacy analog television signals on its plant to eliminate and forces the cable company to offer free rent on at least one cable set top box per customer to convert the digital cable to analog for older TVs), cable is by necessity mainly an analog system that makes it relatively easy to recover the desired digital data encoded within it while ignoring the irrelevant digital data.
As for where TV, Internet, and phone are placed in the cable; they are mixed together. They are not layered like you suggest. The beauty of an analog system where everything is on different frequencies is that the signals are designed to be tuned out by equipment that does not need them. Therefore, the legacy TV set could tune to a legacy analog signal. The digital set top box can tune to another channel and recover the digital HDTV signal and send it over to the MPEG-2/H.264 decompressor, which turns the compressed video into a displayable image. The digital phone and Internet traffic are necessarily mixed together in the same channel because cable modems sometimes do double duty for phone and Internet service, so they use one modem (which is the expensive hardware part) and split the phone and Internet data after they have been turned back into digital by software running on the CPU, which is cheap compared to having a second modem for both, as far as I know.
By the way, the only ways to mix multiple digital signals are as follows:
  • Transform them into analog signals using different carrier frequencies on metal cables or radio waves.
  • Increase the throughput and add overhead to the signals to allow them to be separated out after they have been mixed together.
  • Place them on fiber optic lines and use different colored lasers for each signal. Using color filters, the signals can be separated.
Cable uses a mix of the first two methods. Jesse Viviano (talk) 06:32, 23 September 2009 (UTC)
One other thing I forgot to mention is that even satellite is basically a hybrid system like cable. If satellite TV used digital signals only, the resulting signal would be too slow for TV purposes. Jesse Viviano (talk) 14:02, 23 September 2009 (UTC)
Quite interesting and by far the best explanation I've ever read. As for the separation of the 3 signals, that's what my local cable company has always told me. Could you perhaps distill this into the article? You've already made it better and I think throwing in some of this would help even more. I'm copying this to the article talk page too. RlevseTalk 15:19, 23 September 2009 (UTC)


Appearantly, cable modems are often very insecure, and I heard that some other broadband access methods (xDSL) are much more secure since they have a point to point connection rather than a a connection made in series. See also this post of a guy that managed to hack his cable modem and was able to eavesdrop the entire network (all users). Perhaps worthy to mention in article. — Preceding undated comment added 14:09, 18 October 2014 (UTC)

A forum post is not a reliable secondary source. We would need those before proceeding to add assertions to the article, especially contentious ones such as these. Elizium23 (talk) 17:51, 18 October 2014 (UTC)

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