Can cable and DSL modems do data compressions?

[Ant]

Hello.

I know dial-up modems can compressed datas if not already. Can cable
modems do the same too?

Thank you in advance. :)
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[Andrew Rossmann]

In article <kZGdnaCg2cIi55jP...@earthlink.com>,
ANT...@zimage.com says...

>
> Hello.
>
> I know dial-up modems can compressed datas if not already. Can cable
> modems do the same too?
>
> Thank you in advance. :)

I don't believe modems do any form of in-line compression. They just
pass the data on. Any compression is typically done by the computers at
either end, depending on the protocols used.

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[David H. Lipman]

From: "Ant" <ANT...@zimage.com>

> Hello.
>
> I know dial-up modems can compressed datas if not already. Can cable
> modems do the same too?
>
> Thank you in advance. :)

Both DSL and Cable use Quadrature Amplitude Mdulation (QAM)
http://en.wikipedia.org/wiki/Qam


http://club.myce.com/f181/overview-qam-hd-signal-compression-mpeg2-242503/

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[Ant]

> > I know dial-up modems can compressed datas if not already. Can cable
> > modems do the same too?
> >
> > Thank you in advance. :)

> Both DSL and Cable use Quadrature Amplitude Mdulation (QAM)
> http://en.wikipedia.org/wiki/Qam

> http://club.myce.com/f181/overview-qam-hd-signal-compression-mpeg2-242503/

Um, isn't that for video/TV stuff?

[David H. Lipman]

From: "Ant" <ANT...@zimage.com>

>>> I know dial-up modems can compressed datas if not already. Can cable
>>> modems do the same too?
>>>
>>> Thank you in advance. :)
>
>> Both DSL and Cable use Quadrature Amplitude Mdulation (QAM)
>> http://en.wikipedia.org/wiki/Qam
>
>> http://club.myce.com/f181/overview-qam-hd-signal-compression-mpeg2-242503/
>
> Um, isn't that for video/TV stuff?

I'll help you understand the technology. TV is now digital.

[Ant]

> >>> I know dial-up modems can compressed datas if not already. Can cable
> >>> modems do the same too?
> >

> >> Both DSL and Cable use Quadrature Amplitude Mdulation (QAM)
> >> http://en.wikipedia.org/wiki/Qam
> >
> >> http://club.myce.com/f181/overview-qam-hd-signal-compression-mpeg2-242503/
> >
> > Um, isn't that for video/TV stuff?

> I'll help you understand the technology. TV is now digital.

I wasn't talking about video/TVs stuff. I was talking about Internet.
Dial-up modems didn't do TV/video stuff.
--
Quote of the Week: "Look not to the windmill's turning while the ant still burrows." --unknown

[David H. Lipman]

From: "Ant" <ANT...@zimage.com>

>>>>> I know dial-up modems can compressed datas if not already. Can cable
>>>>> modems do the same too?
>>>
>>>> Both DSL and Cable use Quadrature Amplitude Mdulation (QAM)
>>>> http://en.wikipedia.org/wiki/Qam
>>>
>>>> http://club.myce.com/f181/overview-qam-hd-signal-compression-mpeg2-242503/
>>>
>>> Um, isn't that for video/TV stuff?
>
>> I'll help you understand the technology. TV is now digital.
>
> I wasn't talking about video/TVs stuff. I was talking about Internet.
> Dial-up modems didn't do TV/video stuff.

It uses the same technology.

VDSL and DOCSIS QAM.

You have to look at the question from the POV of the OSI model.

[Ant]

> Cable modems aren't modems, so you can't compare dial-up modems to what
> the cableco puts in the middle between your coax and your ethernet.

Interesting. Why did they call it modems then? What about DSL?

[Retired]

On 8/13/13 5:14 AM, Elmo P. Shagnasty wrote:
> In article <GLSdnfEcJenRHJTP...@earthlink.com>,

> ANT...@zimage.com (Ant) wrote:
>
>>> Cable modems aren't modems, so you can't compare dial-up modems to what
>>> the cableco puts in the middle between your coax and your ethernet.
>>
>> Interesting. Why did they call it modems then? What about DSL?
>

> You don't know much about human nature, do you. People were used to
> getting online with modems--so when the cable company came by and said
> "we can do it too," they called their thingy a "modem" as well so as to
> give people a familiar point for conversation.
>
> DSL, same thing.
>
> In other words, they took the term that is short for
> "modulate/demodulate" and simply applied it to something else that does
> not modulate and demodulate, all for the sake of convenience. Now
> "modem" is a general term that defines that thing that provides you paid
> broadband, and no longer means "modulate/demodulate".
>
> And since there's no modulation/demodulation, there's no compression to
> be offered.
>

Sorry, wrong.

Cable modems are very much mod/demod devices. Read this from

http://www.vicomsoft.com/learning-center/cable-modems-part-2/

14. What Is A QPSK And QAM?

Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude
Modulation (QAM) are two different forms of modulation techniques used
with cable modem technology.

Quadrature Phase Shift Keying (QPSK) is easy to implement and fairly
resistant to noise. It is used primarily for sending data from the
cable subscriber upstream to the Head-End, but sometimes it can also
be used to send data downstream.

Quadrature Amplitude Modulation (QAM) is primarily used for sending
data downstream. QAM is very efficient, but QAM's susceptibility to
interfering signals makes it ill-suited to noisy upstream
transmissions from the subscriber to the Head-End. There are three
variations, 16QAM, 64QAM and 256QAM. A single downstream 6 MHz channel
may support up to 27 Mbps of data throughput from the Head-End using
64QAM while speeds can be boosted to 36 Mbps using 256QAM. A single
6MHz upstream channel may support between 500Kbps to 10Mbps of data
throughput from cable subscribers homes using 16QAM or QPSK depending
on the amount of frequency spectrum allocated for the
service.



BTW, so are DSL modems. See

http://www.vicomsoft.com/learning-center/dsl-part-2/#3

In implementing ADSL, line coding techniques were an important issue.
There are two flavours, Discrete Multitone Modulation (DMT) and
Carrierless Amplitude Phase Modulation (CAP). The conclusion is that
although CAP is widespread, more and more products are issued with DMT.

Both Cable and DSL modems had to be designed to operate over wire
cable plants that were built to expect to carry analog signals. Cable
TV originally carried RF analog TV channels on coax. Telco local loops
carried analog voice on twisted pair.

Also, analog modulated signals carry farther over wire than raw
digital data such as TTL, RS-232, Ethernet, USB, etc.

Also, modulation schemes and data compression schemes are not mutually
exclusive. You can do one without the other if necessary for the
application.

There are 2 main reasons compression is not done in Cable or DSL modems
1. A high percentage of TCP/IP data packets are already compressed via
such as JPEG, MPEG and other schemes. So further attempts at
compression yield no advantage.
2. The data rates are so high already, the added processing needed to
perform compression algorithms in the modem would only serve to delay
data throughput.

[Jeff Jonas]

> I know dial-up modems can compressed datas if not already.
> Can cable modems do the same too?

Later "smart" modems added compression,
thus the false advertising for 4x the actual speed
(they always assumed a 4:1 compression, which was unrealistic)
See:
http://en.wikipedia.org/wiki/Microcom_Networking_Protocol
MNP 5, introducing on-the-fly data compression in the modem.

There have been great replies about cable & DSL modulation schemes.
For compression, it's up to the applications such as ssh
(which allows compression regardless of the link).

[ps56k]

hmmm - so tell me - how do they present a "carrier" for any type of wire -
be it telco DSL or coax cableTV ????
just because you have a digital 1 or a digital 0 - it still needs to travel
in the "analog world" via some kind of analog carrier,
which is of course - MODULATION -
oh yeah -
digital TV - now how is that transmitted via over the air waves ?
digital cellphones - what "freq" was that transmitter ?

[Retired]

Re Digital TV, see page 23 Section 5.4 for info on the 8-VSB
Modulation Method carrier used by US terrestrial TV systems

http://www.atsc.org/cms/standards/a53/a_53-Part-2-2011.pdf

Re cell phone frequencies, it varies by country and "G-type" ( 3G, 4g,
etc)

see here for a listing

http://www.gsmarena.com/network-bands.php3?sCountry=UNITED+STATES

[ps56k]

"Retired" <Ret...@home.com> wrote in message
news:puKdnfwvI6xaT73P...@giganews.com...

sorry - was being tongue in cheek sarcastic -

people tend to forget that ANY digital representation MUST have an analog
equiv to be transported in the real world,
and this usually involves some form of modulation of a carrier.