How Does Adsl Work?

[markg]

I used to use a modem. So a cable goes from my PC to the telephone socket in the wall.

Now i am using adsl. A lovely chunky cable, thick and workmanlike, goes from the fat socket in my pc to my router, then it goes down the normal, weedy, standard telephone cable to the phone socket in the wall.

How does this work then?

I'm wondering, if the cables are essentially the same, why cant you just get a faster standard modem in your computer? Say 1Gig, and run that down the same weedy phone cable?

Just wondering really how its done.

i could understand it if the whole jolly lot ran off a chunky cable to internet land, but not all of it does, some/most/all of it is run down the same standard weedy cable.

[briley]

One point is that the cable from your router to the computer has 8 cores, one pair to the router, one pair from the route and a spare set (incase they break? - actually they can carry telephone, other networks etc)

The telephone cable is one pair.

Add to that the telephone cable can carry, currently but not in Thailand, a max of about 32 Meg bits per second, and the other cable 1000 Meb bits per second,

But there are many other things to consider!

[cdnvic]

It's not that the cable makes such a difference, it's how the modem processes data that makes adsl work. You can run regular telephone cable and still get dsl, although at a degraded performance, but if you have the thicker cable (known as 'Cat 5') from the wall to the modem, and along your whole network, it will get you better speeds.

Further reading:

http://computer.howstuffworks.com/modem3.htm

[markg]

It's not that the cable makes such a difference, it's how the modem processes data that makes adsl work. You can run regular telephone cable and still get dsl, although at a degraded performance, but if you have the thicker cable (known as 'Cat 5') from the wall to the modem, and along your whole network, it will get you better speeds.

Further reading:

http://computer.howstuffworks.com/modem3.htm

Thanks for the link vic i ll read it later.

This is the whole point i dont understand though. The point i m making is that the whole network doesnt have the thicker cable. There is a weak link in the chain. From the router to my phone socket is the standard 2 core phone cable. And i dont know what happens after my wall socket as that is the phone company's business.............you see what i m saying. I m running adsl and there is a 2 core cable in the link and it still works fine, so what is the point of the thick cable?

Also, why did modem technology stop at 56k. If its the modem/router making us have adsl then why arent they built into laptops and desktops now?

Edited February 17, 2007 by markg

[markg]

Add to that the telephone cable can carry, currently but not in Thailand, a max of about 32 Meg bits per second, and the other cable 1000 Meb bits per second,

Presumably then, if you have so much as 1 inch of 2 core cable in your cabling link to internet land, that would max out your system at 32mbs. And from where i m sitting, i have 3 metres of 2 core from the router to the phone socket. In fact, there isnt a socket in the router that would let me have the thicker cable anyway.

[lomatopo]

It's not that the cable makes such a difference, it's how the modem processes data that makes adsl work. You can run regular telephone cable and still get dsl, although at a degraded performance, but if you have the thicker cable (known as 'Cat 5') from the wall to the modem, and along your whole network, it will get you better speeds.

Further reading:

http://computer.howstuffworks.com/modem3.htm

Thanks for the link vic i ll read it later.

This is the whole point i dont understand though. The point i m making is that the whole network doesnt have the thicker cable. There is a weak link in the chain. From the router to my phone socket is the standard 2 core phone cable. And i dont know what happens after my wall socket as that is the phone company's business.............you see what i m saying. I m running adsl and there is a 2 core cable in the link and it still works fine, so what is the point of the thick cable?

Also, why did modem technology stop at 56k. If its the modem/router making us have adsl then why arent they built into laptops and desktops now?

You are running two distinct and different standards-based communications protocols on these two connections. These protocols were developed independent of each other, and to address specific requirements. Each communication protocol is made up of up to seven independent 'pieces'. Two of these pieces describe the physical and electrical interfaces used by the protocol. In this case the phical and electrical specifications for xDSL and Ethernet are different, hence the different wires/connectors.

You could integrate a DSL modem into a notebook or onto a MB/PC/PCI card. There are several, including USB, styles and models currently available. The main reason you don't see DSL modems integrated into notebooks is that there are many different 'flavors' of DSL, although certainly more or less standardized around G.992 today, and there can be some interoperability issues. Terminating a single DSL line on a single notebook though really reduces your flexibilty to share that broadband connection. The general application is to present DSL into a home or small business, terminate that at a DSL modem, which handles the interface between DSL and Ethernet. This allows maximum flexibilty.

Your DSL connection is the short straw in your home network. Ethernet can run at 1/10/100/1,000 Mbps, while your DSL connection runs at 0.5 to a max. 6.4 Mbps.

There are other forms of digital data communications that utilize the telephone company's physical wiring plant of copper (skinny) wire(s) to deliver up to 45 Mbps (DS3).

Traditional (frequency/phase/amplitude modulation) modem technology stopped at 56 Kbps because that is the inherent physical/electrical limit of the voice network. In the simplest of terms, a single voice telephone call uses a single 56 Kbps channel, so that's all there is. There is ISDN which can deliver up 128 Kbps in a similar application but that is a form of digital communications, and there are other methods to combine and bond multiple voice channels but that's maybe another topic.

[markg]

You've lost me here a bit Lamatopo.

Here's an analogy for thick people like me.

You have a fire hydrant (your PC) and you attach a 4 inch diameter fire hose to it. (MY yellow, chunky ADSL wire) Water passes through at an impressive rate. Fires are put out quickly.

You then attach a valve (the router) and from the valve, you run a standard half inch garden hose (the skinny phone cable) then after some distance, you stick a 4 inch fire hose on the end of the garden hose. The rate of flow will only be the maximum flow that the garden hose can take. The fact you stick a 4 inch fire hose on either end doesnt matter. Fires dont get put out and everyone is frustrated.

So, if one part of my ADSL network has the piddly little telephone wire in it, then surely all the rest of the chunky cables are redundant?

Or look at it another way, if the piddly little cable is good enough for a link in my ADSL network, then why isnt the whole network made of the same stuff.

I dunno. I m confused. I cant make logical sense of it and i regret asking the question now !

[cdnvic]

Imagine a small hose carrying water, another carrying foaming agent, and the two mix and become huge in volume, needing a much larger tube to hold the resulting product.

This is really getting abstract.

[lomatopo]

I dunno. I m confused. I cant make logical sense of it and i regret asking the question now !

Equating the diameter of the cable assembly with bandwidth capacity is a flawed analogy, as is the hose analogy as you've neglected to account for pressure and its affects on volume flow.

The DSL ("skinny", "tweedy") physical (connecter, number of wires, construction of wire into cable) and electrical characteristics are part of a standards-based (ITU-T) specification designed to support digital data communications over the installed base of telephone copper wire running between your home and the local entral office which houses telephone switching equipment

The Ethernet cable ("chunky") is part of an IEEE standard (802.3) initally invented to support data communications between computers in order to exchange data. These computers were physically next to each other, hence the term Local Area Network (LAN).

DSL and Ethernet are vastly different so have different requirements, and were designed to maximize the capabilities of the technology, hence required cables have different physical appearances.

[Sunny Valentine]

Here is a very basic (and quite inaccurate in some detail which is of no concern to you right now, but of big concern to technicians ...):

The Modem connects with the Internet through a series of audio signals. Ever heard the speaker of the modem when it connects? These hisses and whistles are basically the data, transformed into sound.

Phone lines have a frequency range, which permits data to be transferred not faster than the 56k we know from Modems.

DSL now uses other frequency areas of the phone line, leaving the audio frequencies out, so you can still make phone calls on the same line you use for DSL. These frequencies can carry a lot more data than the limited set of frequencies used for voice, therefore the higher speed.

The thickness of the cables have no (or very little) influence on the data speed. The CAT 5 network cable is just a different cable standard used, similar to different other cable standards used in the world of computers, like USB, Serial, Parallel, Fire wire and so on. All these standards have some advantages in special fields, hence they are used where their advantages over weigh their other shortcomings.

Hope that helps first!

Sunny

[monty]

I think most replies are missing the question of the original poster

His question was (if I understand correctly!) that if on his old dial-up, he could just plug the phoneline straight into his PC, then why with his ADSL he has to put the same phoneline first into an ADSL modem and then from there to his PC using a complete different cable.

He wonders why he just can't upgrade his old dial up modem in his pc, to an internal fast ADSL modem so that he still can plug the phoneline straight into his PC!!!

Actually it's perfectly possible with a PCI ADSL modem (just like the PCI 56k modem he has probably built in)

http://www.ciao.de/Trust_Speedlink_215A_AD..._Modem__1840460

My guess why this never became popular lies in the simple reason that with the fast ADSL speeds, it became practical to share this fast internet access over several PC's.

So the most popular ADSL modem device ended up being an ADSL router, the device he probably uses now.

Without much technical knowledge almost anybody can hook up several PC's to that same ADSL router, and without having to install any software on any of those PC's thy all have instant internet access!

And hooking up several PC's together has been done for ages with that

lovely chunky cable, thick and workmanlike

the original poster so colorfully describes

[astral]

I had problems in my house as the electrician had skimped on the telephone cables.

A thicker telephone cable from the box on the outside of my house to the socket in the computer room

did improve the connection, but that was on dial up.

With ADSL it is all the same.

An ordinary modem cable will suffice from socket to modem,

from the modem on it is a LAN cable, quite a bit thicker and with a dedicated purpose.

No substitutes allowed. It usually comes with the modem.

[Simmo]

[

Also, why did modem technology stop at 56k.

One of the fundamentals of information theory.

http://en.wikipedia.org/wiki/Shannon-Hartley_theorem

They had to do some neat tricks to go from 33.6 to 56k.

[monty]

Aaaaah

Completely clear now Simmo :D

[markg]

Here is a very basic (and quite inaccurate in some detail which is of no concern to you right now, but of big concern to technicians ...):

The Modem connects with the Internet through a series of audio signals. Ever heard the speaker of the modem when it connects? These hisses and whistles are basically the data, transformed into sound.

Phone lines have a frequency range, which permits data to be transferred not faster than the 56k we know from Modems.

DSL now uses other frequency areas of the phone line, leaving the audio frequencies out, so you can still make phone calls on the same line you use for DSL. These frequencies can carry a lot more data than the limited set of frequencies used for voice, therefore the higher speed.

The thickness of the cables have no (or very little) influence on the data speed. The CAT 5 network cable is just a different cable standard used, similar to different other cable standards used in the world of computers, like USB, Serial, Parallel, Fire wire and so on. All these standards have some advantages in special fields, hence they are used where their advantages over weigh their other shortcomings.

Hope that helps first!

Sunny

Thanks sunny. I kinda get it now.

[autonomous_unit]

The plain old telephone system was designed to carry human voice from end to end, and a single copper pair of wire was more than sufficient for that purpose in a city or small region. Periodically, the analog signal would go through switches and amplifiers to get over long distances, and if you recall any very old long distance calls, there was a noticeable increase in background noises as the analog signal jumped its way across the phone network. Over time, the telecoms began deploying digital systems that converted the human voice to digital data, sent the data over a long distance, and then converted it back to analog. All of these analog and digital systems were designed with an assumption of carrying a defined frequency range that is sufficient to carry the human voice, but insufficient for, say, hi-fidelity music reproduction. They have the advantage that a "perfect" amplifier can be built cheaply to send the signal over long distances without degradation.

Old fashioned modems were designed, perversely, to convert digital data into sounds that could be carried over these voice channels. They suffered from the need to work within the narrow confines of the whole end to end "voice path".

Systems like ISDN and ADSL bring "digital" to the last-mile from the customer premises to the telecom network. This means that the copper wire is now carrying a signal designed to go directly from the customer to the telecom and fully utilize that copper, as opposed to sending just one meager voice conversation in analog, while ignoring most of the signalling capacity of the wire. This is, for example, how you can have ADSL and voice on the same copper. The ADSL signal occupies a wide range of high frequencies outside the range of the narrow band voice signal, and the ADSL "splitter" is just a filter to separate the signals based on their frequencies.

At the same time, systems like ethernet were developed to carry much higher data rates over short distances. The high speed rates that ADSL is just starting to achieve with elaborate, modern signal processing hardware have been available over ethernet since the 1980s, using much simpler electronics! And when you talk about a CAT6 cable and gigabit ethernet, you are talking about a digital signal spread across four pairs of copper with symmetric capacity in both directions, i.e. 2 Gb/s of information is flowing through the cable at peak usage. The best ADSL standards right now are only approaching 100 Mb/s, or roughly 1/20 of the information capacity. However, the ADSL can go over much worse cables and much longer distances.

As for the original question, more ADSL modems are appearing with an ethernet interface to the computer because of simple engineering costs and versatility. Ethernet has become the defacto standard networking interface for PCs, meaning one modem can be designed and sold that will connect to any PC. It also gives you ease of installation for users who can manage a plug or two but probably not a screwdriver. Recall, modems used to be external devices that connected to a serial port...