linux as an xDSL router?

[fuzzbot]

Does any one know of a card that would allow me to plug my ADSL "phone" line into my box and use linux as a router/firewall (I have a nice little 486/66 all tuned and ready) instead of buying a seperate (expensive) translator/router?
Thanks
-C-

[ds801]

You need a DSL modem to receive the DSL signal, and sine there aren't any Linux drivers for any of the internal DSL modems, the best you could hope for is your DSL 'phone' wire, connected to an external modem, to the 486 box (nic1),from the 486 box (nic2), to a hub, to your network.

[fuzzbot]

Thanks ds801.
All xDSL "modems" (that I have been able to find) external or internal also function as routers/translators. And are expensive. I want a simple card that will convert the xDSL signal and allow the OS to do routing, firewalling, translating, etc. I currently have a Cisco 675 set up very much like what you describe but would like to set the extra box up to do it all on the second DSL we need to add this summer.
-C-


[This message has been edited by fuzzbot (edited 05 June 2000).]

[Sweede]

you'll also have to make sure that the DSL router (THERE IS NO SUCH THING AS A DSL MODEM, sorry pet peeve), is compatiable to your ISP/providers equipment.

why not just use the equipment that your ISP gives you. after all.. thats what its for.
pop a network card in your computer and its all set.

[This message has been edited by Sweede (edited 05 June 2000).]

[Craig McPherson]

Originally posted by Sweede:
THERE IS NO SUCH THING AS A DSL MODEM, sorry pet peeve

You are my new favorite person.

Back on-topic: I'm not an expert on all the networking hardware available out there, but I doubt you'll find anything with a DSL transceiver that's cheaper than a good old external DSL router, especially since most DSL providers are giving the away for free with service now. Of course, there are the cool ones from Cisco, but there are also cheaper varieties: they're generally from no-name companies, look roughly like an exernal analog modem, and are actually sold as "DSL Modems" (ugggggg) rather than "DSL Routers". Heck, having the correct word "router" in the name of the product seems to double the price of it http://www.linuxnewbie.org/ubb/frown.gif! That's just my observation, your results may vary.

Now you've gotten me curious about the availability of cheap internal devices with DSL transceivers... I'll let you know if I find out that such an animal exists.

[fuzzbot]

Thanks all. My DSL provider *gives* nothing away. In Tucson you buy the line from the telco and purchase your bandwidth seperately. None of the twelve ISP's currently offering service in my area *give* anything away. There isn't much competition down here yet. The kit US West (telco) sells is around $250. We did better than that sourcing our own router/cards/etc but if I could get away spending about what I would for a fastether card.....

The translator/tranceiver chips have to exist, every router sold has one in it! Has anyone thought to put one on a PCI card tho. Aye, that's the rub.

Should I get lucky, I'll em you Craig and vice/vers?

-C-

ps- "Routers" are scary networking geek devices. "Modems" are nice friendly harmless things everyone is used to. Be careful, you'll scare joe comsumer!


[This message has been edited by fuzzbot (edited 05 June 2000).]

[ds801]

DSL MODEM! DSL MODEM! DSL MODEM!

O.K., first of all, Bell Atlantic is selling DSL "Modems" for $99, and this hardware purchase is separate from their DSL service (PCI, USB, Ethernet are all the same price). So, that's not too expensive.

Secondly, if you know how to turn these "dumb" devices into "intelligent" ROUTERS (as in the router has a 'routing table' that is configurable, and can make decisions about what port/network segment a data packet should be sent out on) then PLEASE TELL US!!! It would save all of us the trouble of buying Hubs and using programs like Wingate or AllAboard.

Technically, I guess these basic DSL devices are not MODulators/DEModulators, but in a broader sence, they are modems in that they receive the many DSL channels, assemble the data back into a single package, and pass it on to the Computer/USB port/NIC that the DSL device is attached to.

My only point, in my original post, was that so many people have either PCI or USB DSL modems, and they can't use them with Linux because there aren't any Linux drivers for them. An getting back to your search for a card that you can plug into your linux box, what's the real difference between an internal DSL "translator", and an external ethernet modem attached to a NIC in the Linux box?



[This message has been edited by ds801 (edited 05 June 2000).]

[Sweede]

Originally posted by ds801:

Technically, I guess these basic DSL devices are not MODulators/DEModulators, but in a broader sence, they are modems in that they receive the many DSL channels, assemble the data back into a single package, and pass it on to the Computer/USB port/NIC that the DSL device is attached to.

[This message has been edited by ds801 (edited 05 June 2000).]

That still wouldnt come close to being a modem, the proper term would be CSU/DSU.
the essence of the word, MODEM, can only apply to analog transmission.

But i understand why they are labeled modems.
Companies dont want to have to explain to everyone what a CSU/DSU is/does, they can just call them a modem.

[kernelpanic]

THERE IS NO SUCH THING AS A DSL MODEM

Yea there is I own one. http://www.alcatel.com/telecom/asd/keytech/adsl/adsl/modem/mod.htm

[Sweede]

do you really want me to explain why there cannot be a device such as a Digital Subsciber Line MODulator/DEModulator ?

they are labeled a "Modem" for marketing reasons.

[This message has been edited by Sweede (edited 06 June 2000).]

[Craig McPherson]

"Modem" implies ANALOG. Yeah man. I gotta get one of those analog communication devices for my Digital Subscriber Line.

[fuzzbot]

Well, kernelpanic and ds801 are right. That device, according to the ITU Networking Technologies Center (http://www.itu.int/plweb-cgi/fastweb?getdoc+view1+www+5832+10++alcatel%20modem) writeup kp has linked to mod/dems like our analog friends. Now, if I could just find out who's selling them so I can ask a few pointed questions. What kind of idiot builds (see kp's link) a sell sell page like that and then does not tell you where to buy the damn thing and how much they think their retailers should screw you out of.

ds801-My scheme still involves a hub. But correct me if I am wrong, can't a linux box be used as a router? Isn't that the point of the LRP (http://www.linuxrouter.org) and projects like it? I don't want to make the dumb device smart, I want a dumb device to put in the smart one I already have instead of buying another (expensive) smart one. To answer your last q: I'd rather buy one card than a card and modem.

Well I emed alcatel about their card and will hopefully know something in a couple of days. Meantime, if no drivers exist, I guess I'll have to move Linux Drivers up in the book que and start bugging the folks on the programming board. Heh.

-C-

[Craig McPherson]

People at my workplace know not to refer to that little thing with the blinking lights as a "modem", because they know that if they do, they'll never be getting on MY network again, and strange things might very well happen to their accounts and to the stuff in their home direcories. You've just got to TRAIN people. They'll learn, if you teach them. I know of very few people other than complete computer newbies who don't know that there's no such thing as a Cable/DSL modem. People who do say such a thing are often either complete computer illiterates, or severely undereducated. That's not an insult, that's a fact: IRL I've never encountered an INTELLIGENT, educated person who believed there was such a thing as a DSL modem. You're pulling that 99% out of your butt. At most, it's 20%, and most of those are trainable.

Calling a watch a Rolex doesn't make it a Rolex. Would you argue that that guy on the streetcorner selling "Rolexes" for five bucks is REALLY selling Rolexes? My gosh.

And Hamburger isn't misnamed. It's not of English origins, it's German. And it's not named after any kind of meat, it's named after the city of Hamburg, Germany. Many German cities have signature foods named after them: Hamburg -> Hamburger, Frankfurt -> Frankfurter, Berlin -> Berliner (a kind of doughnut).

Any other objections?

[cactoss]

so what do you call them?

[kernelpanic]

Ok I agree that there is no such thing as a DSL "modem" technically. But, you should not be suprised if somone calls it a DSL "modem" because *almost* every company that makes DSL routers call them "modems". Now if you will excuse me I am going to go download X 4.0 on my External ADSL router connected to my Asymmetric Digital Subscriber Line http://www.linuxnewbie.org/ubb/wink.gif

[This message has been edited by kernelpanic (edited 06 June 2000).]

[Sweede]

they are routers or DSU/CSU's (CSU/DSU i always get them mixed up).

Digital-analog transmission

"In its simpliest form, a modem senses the [digital] signal from the data terminal equipment(the computer?). when it senses a 0 bit, it sends an analog signel with certian attributes (amplitude, frequency, phase). When it senses a 1 bit, it sends a diferent signal, with at least one of the attributes changes."

notice the keyword analog. another thing about a modem, is they change the digital signals to fit in a specific freuquency bandwidth 300hz-3300hz.


Digital transmission does not have frequency bandwidth limits like that. instead it pulses the 1's and 0's (on/off), at various levels of amplitude but in a square wave of only ON/OFF , sine waves vary from +5 volts to - 5 volts, Square wavs are just on and off.

in essence, morse code was one of the first forms of digital transmissions, and more code over the radio waves was the first digital-analog "modem" so to speak.

while im tired and want to leave, perhaps someone else, (Craig ?) can elaborate

[helpmyipsisbroken]

what ?? u mean adsl do not stand for "analog digittl subscirber line"??????

[fuzzbot]

HEY GUYS-GO HERE (http://www.itu.int/plweb-cgi/fastweb?getdoc+view1+www+5832+10++alcatel%20modem) I'll leave it to you to research Discrete Multi-Tone Modulation. If it mod/demods, like the device described in that article, it is a modem. Heh.
-C-


[This message has been edited by fuzzbot (edited 06 June 2000).]

[Craig McPherson]

la la la la i can't hear you

[kernelpanic]

Originally posted by helpmyipsisbroken:
what ?? u mean adsl do not stand for "analog digittl subscirber line"??????

No. ASDL stands for Asymmetric Digital Subscriber Line

[Lorithar]

*sighs*

I don't wanna get tooooo deep here.
All those telco's offering *dsl are providing MODEMS.
The mo/dem function is just that. There is no ROUTING capability in the damn thing. It is NOT a CSU/DSU -- although there are CSU/DSU's which will provide the same capability (direct to ethernet conversion from DMT transmission) most CSU/DSU units are much more capable than the standard DSL modem.
There are TWO wires carrying an ANALOG signal from the modem to the CO. There it plugs into another modem for conversion to the digital signal (typically ethernet, possibly frame relay, god KNOWs what different telcos are doing) that will be pumped out to the internet.
UNLIKE cable modems, which do a similar conversion, although it is digital to digital, there is still modulation/demodulation involved, as the signals are carried on vastly different media.
Nor are cable modems routers, they provide NO routing.

Sorry folks ... they's still modems in the real world.

[Sweede]

Originally posted by Lorithar:
*sighs*

I don't wanna get tooooo deep here.
All those telco's offering *dsl are providing MODEMS.

i'll go in pretty deep here.
they are not modems.
they do not modulate a digital signal to analog form, nor do they demodulate a analog signal to digital form.
[b]
The mo/dem function is just that. There is no ROUTING capability in the damn thing.

Granted, it might not be a router. but if my SDSL Network Box has its own IP that is a gateway address. it is a router.

ALL Digital Subscriber Line technology, except ISDN, use a router as its juction between the telco equipment and your network card (YES, ISDN is a form of Digital Subscriber Line [DSL] )

It is NOT a CSU/DSU -- although there are CSU/DSU's which will provide the same capability (direct to ethernet conversion from DMT transmission) most CSU/DSU units are much more capable than the standard DSL modem.

"in practice, an interface unit, called a digital transmitter reciever, sometimes called a data service unit/channel service unit (DSU/CSU), is required. The digital transmitter ensures that the digital data that enteres the communication line is properly shaped into square wave pulses that are precisely timed. sometimes it needs to convert the digital pulses coming from the DTE [your telco equip] to a form that suitiable for the line. the digital transmitter also proviced the physical and electrical interface between the DTE and the line. the primary purpose of the CSU portion of the unit is to provide cirtucty to protect the carrier's network from excessive voltage coming from the customers transmission equipment. the transmitter may also provide diagnostic and testing facilities. Sine they do not perform digital-to-analog or analog-to-digital conversio, however, digital transmitter/receivers are much simpler than traditional modems"



There are TWO wires carrying an ANALOG signal from the modem to the CO. There it plugs into another modem for conversion to the digital signal (typically ethernet, possibly frame relay, god KNOWs what different telcos are doing) that will be pumped out to the internet.

That correctly explains the MODEM (as in 56k modems) connection. let me explain the a bit more.
Lets start at the customers house.
They want to get onto the internet, since their area doesnt provide Digital Subscriber Line services, they must use a regular modem.
So they went out and bought a fancy US Robotics 56k modem, How 56k works is irrelevent. the main thing is that the must take 010100101010101010 and convert it into a sine wave suitable for transmitting over the POTS system (or the local loop to be more precise. which is the physical line between your switching station and your home). so now this modem does it's duty and you got a sine wave going out to your switching station.

The equipment at the switching station needs to change the analog signal back to digital, because thanks to AT&T and the guy that created Unix, the old mechanical switches werent needed anymore. but now they must do things in 0100101001010101010 again.

and thats a modem,
home - local loop - switching station
digital - analog - digital

Digital Subscriber Line services include everything from ISDN to DS3/T3 lines
ISDN, xDSL all operate on a single pair of twisted wires (2 wires).
T-1 and T-3 are on 2 pair. lets work with the single pair, xDSL, ISDN.

now since your computer doesnt exaclty talk the 'Digital Line' Language, it needs a DSU/CSU to convert it from pure binary ( 0101001010010101) to a square wave that is sutiable for transmission over copper (or fiber optic, but thats more than i want to talk about).
So now your new DSU/CSU has formated your digital data into a neatly shapped square wave and pumps it out over your local loop. problem is your local loop is all noisy with bridges, splices, traps, and filters. When they telco tells you that it'll be installed in 5 days, its not because they are lazy. they have A LOT of work to do removing all the filters, bridges, etc, all so you can download MP3's and pr0n faster. but the work doesnt stop there.

At the switching station, they have Network cards (or, in actuality, modems) that convert analog from the Local Loop into a digital format for Unix to have it nasty way with. well that just wont work. so they remove the modem and replace it with another DSU/CSU. So now you have

Computer <-> DSU/CSU <-Local Loop-> DSU/CSU <-> Switching Station <-Internet-> Favorite pr0n site

Now, because a GREAT deal of modern telephones have built in Analog to Digital converts, they actually transmit from the base, a semi digital signal that can share the line with ADSL and not interfere with calls or billing issues. (this is also why ADSL has adopted the term "MODEM" and why ADSL is actually infeorior and less efficient than other forms of digital subscriber lines/digital circuits, but it is one of the fastest forms, it has the longest range at 23,000 feet, and it doesnt need dedicated wiring). HDSL, VDSL, SDSL, IDSL all require their own circuit that is purely digital.
( my DSL router http://www.lucent.com/ins/products/multidsl/dslpipehst.html )

i dont think i forgot anything there.


UNLIKE cable modems, which do a similar conversion, although it is digital to digital, there is still modulation/demodulation involved, as the signals are carried on vastly different media.

Cable modems are in fact modems. they convert the digital signal from your computers NIC card to an analog signal at the upper bands of the UHF spectrum. (cant remember the exact frequencys, been a while since my HAM radio tests). The coaxial cable used in television transmission is in analog form (or digital cable wouldnt be a big hit. or was it?)


Nor are cable modems routers, they provide NO routing.


The only thing Craig, I, or any other network engineer, Consultant, Technition would agree with you on this post (and the fact that i cannot spell anything).

Sorry folks ... they's still modems in the real world.


if none of the above convinced you that DSL is PURE digital, NO analog equipment, therefore making it a DSU/CSU and not a modem. Take out a ocilliscope, hook it up to the ring and tip of your SDSL line and tell me what it looks like.

I'll give you a hint.........

_ __ ___ __ _ __
__| |_| |_| |_| |_| |_| |__
00110011100111100111001100111000

[Sweede]

This will Explain the difference between ADSL using the term "modem" and All forms of digital transmission.

ADSL - Asymmetric or Asynchronous Digital Subscriber Line.
Async (for short), is a transmission technigue in which each character sent on a com line is preceded by an extra bit called a start bit and followed by 1 or more extra bits called stop bits. Sometimes called start/stop transmission.

When async transmission is used, characters do not have to follow each other along in a precisly timed sequence. to visualize this, think of an amature typing.. its eratic, slowing and speeding up in bursts..

Async transmission is relatively simple and inexpensive to implement. a penalty in terms of transmission effinceny is paid, because at least 2 extra bits are needed to each character transmitted.

CODE Number of bits Start/stop bits total bits transmission efficiency

Baudot 5 2 7 5/7 or 71%
ASCII 7 2 9 7/9 or 77.7%
EBCDIC 8 2 10 9/10 or 80%

When ascii code is sent with a parity bit, its transmission effciency is 8/10, or 80%.

All other forms of Digital Transmission.
SDSL, HDSL, VDSL, IDSN, IDSL, T-1,2,3,4 DS0,1,3 and Fiber circuits use Synchronous Transmission. (Sync for short) (Symmetrical for SDSL)

When Sync transmission is used, bit synchronization is maintained by a clock circuitry in the transmitter and in the reciever [the DSU/CSU's] The timing generated by the transmitter's clock is selnt along with the data so that the reviever can keep its clock synch'd up throughout a long transmission.

With Sync transmission, data characters usually are sent in large groups called blocks. the blocks contain the special sync bits in the begining and sometimes the middle of the blocks.
a comparison of Async efficiency and Sync efficiency.

Async.
250 Characters X (7 data + 2 start/stop bits per chacacter) = 2,250 bits

Sync.
(250 Characters + 4 Sync Characters) X 7 bits/char = 1778 bits

in this, Sync transmission is 21% more efficient than Async transmission

Sync transmission REQUIRES a DSU/CSU for the timing.

Async transmission does not use a DSU/CSU for timing, as there is no timing with Async.


[This message has been edited by Sweede (edited 07 June 2000).]

[liz]

I am with a communication equipment manufacturer. You would be able to see Linux-based router towards end of 2001.

What would you like to see as the capabilities? For example, how many ports? What type? 10/100/1000? What routing protocol? RIP v2?

[Chase]

I can get you another Cisco 675 factory sealed for $125 http://www.linuxnewbie.org/ubb/smile.gif

[Nandy]

Hmmm, well, i am one of the new guys here. Well, i work for the telco. Ok, don't yell!!! Well, Modem, last time i check, and if i am not recalling wrong from college, is an abreviation of modulation,demodulation. Do you agree? If not stop reading, nothing will do sense if you dont agree this point...

You can modulate analog and digital signals, we do that all the time in the comunication industry. You have a carrier, and you put the info in the carrier by modulating it's carrier to the tune of your signal. Being digital pulses or analog. The process are different for digital and analog, being analog the one with the extra step converting the analog to digital(sampling) to then go in the carrier...

So your dsl router or modem(however you want to call it) modulates the carrier between it and the mux in the central office by pulses(was that pulse code modulation the right technical name, hmmmm, can't really remember). The atm mux in the central office will create the atm envelope with your signal and others comming from the hub and will be routed to your isp.

Do there is modulation upstream and demodulation downstream?(MO-DEM) YES... But it is digital... The modulation happen when your xdsl eqpt modulates the signal between itself and the hub and the demodulation happen when the info is comming back to the pc...

Also, there is frequency and amplitude on digital, If not how the heck will you send the signal? How will the system knows 1 from 0? All signals have amplitude and frequency, from sounds, to light, vibration....There we go again, you have a carrier, which is a digital signal with an specific frequency,(for a t1 is, hold on, let me see if i remember... is little bit more than 1.5 mhz, you will need 1536 khz for the 24 ds0's and a little more for overhead info) and it has an specific amplitude(the amplitud is more realy depending on the manufacturer of the mux, alcatel, att, Northens,more of less all are the same but the tolerance might be different). By the way, in fiber optics comunication there is not realy a light going on and off, it is really a spectrum variation to determinate 1's and 0's. Nobody truns the laser on and off...

Well i would love to explain in more details, but i just had one extra hour on my hands. Daylight savings!!!! God!!! Can't get used to this!! You can figure it out why i am saying this....

Off to work,

Fernando Quinones
(soon to be ATM BROADBAND ADSL SPECIALIST NETWORK MANAGER)
Bellsouth Network Reliability Center

PS-Scary aint it!!!! Sorry about the spell and gramar, im in a little hurry...