can you put two ADSL modems back to back without a DSLAM ?

Capt'n Midnight

Is there any way of doing this ?

Do you need a crossover of the phone wires ( I doubt it ) or do you need to put some voltage on the line like you do with some modems

I've a couple of DSL modems / routers and it would be nice to be able to send stuff to the WAN port to use the router function. I'm not trying to connect two houses, a meter would be enough.

One is the eircom netopia 2247 the other is a cayman 3300.

bushy...

I'd reckon they'd sit waiting for carrier tones , then theres the pppoe stuff to do .

Capt'n Midnight

But can you fake the carrier tones by injecting a DC voltage / AC signal ?

ressem

To start off with, I think that you'd have to replay most of if not the entire G.994.1 handshake.

http://www.kiwin.com/xdsl/body.html
the tutorial link there which also lists a sample transaction.

I would guess that the consumer level modems (ATU-R) would not be programmed to act as an ATU-C Central Office device. Their state machine just wouldn't include those steps, to save development costs.

They might be able to negotiate the ATM circuit between themselves once you get that far though.

http://www2.rad.com/networks/2005/adsl/xdsl_hs.htm
Deals in a more readable way with the handshake.

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Edit: I seem to remember something about the consumer devices being set to transmit and receive on the opposite frequencies to the equipment on the CO side, in which case it's a non runner without some specialised equipment.

Boston

Lack of a DSLAM is not your problem there. DSLAM primary fuction is to multiplex multiple DSL signals. Its at the network layer your problem lies. So you will need to impliment the pppoe protocol plus anything else required at the physical layer.

Sully

Boston; Isnt it pppoa?

Boston

Theres point to point protocol over ethernet and over ATM. Both are popular but from what I recall pppoe is what we use here, pppoa in the states.

Boston

Capt'n Midnight wrote:

But can you fake the carrier tones by injecting a DC voltage / AC signal ?

Information is transmitted by modulating a carrier signal. In the case of DMT adsl (there are two types) you have a load of orthogonal carrier signals (or tones), each individually modulated. No carrers not data transmission. You can't fake that, you need it to communicate. DC voltages have no relavence that i can think of.

ressem

Isn't pppoe overlaid on bridged ethernet overlaid again on ATM on your typical eircom DSL connection in Ireland?

If you got that far then you could just run a linux pppoe client and server at the respective ends, and use the modems in bridge mode, assuming they support it.

Boston

ressem wrote:

Isn't pppoe overlaid on bridged ethernet overlaid again on ATM on your typical eircom DSL connection in Ireland?

Read the other posts would you. Also you suggestion that pppoe is layered on top of pppoa doesn't make sense. pppoe and pppoa are modifications to ppp. You seem to be confusing pppoe with pppoeoa

anyway. Eircom ADSL was definitely originally pppoe.

If you got that far then you could just run a linux pppoe client and server at the respective ends, and use the modems in bridge mode, assuming they support it.

pppoe is merely a mechanism for establishing, authenticating, maintaining and terminating connections. It is in many ways the easy part. You can't establish a connection, if you've no physical means to send a signal.

ressem

You can't establish a connection, if you've no physical means to send a signal.

Yep, and if the Capt'n's trying to set up a test DSL setup, the question is how much of the physical, Data and network layers would have to be changed to get the setup working.

As far as I'm aware if you replaced the ATU-R chipset in a standard modem with a ATU-C chipset over a twisted pair cable to provide the physical layer 1 & part of data layer 2 (ATM + 802.3), then you have a working point to point communication channel over which you can talk using MAC frames.

Then you have the option of putting PPP on top.
Because we'd lack a PPPoE server on one of the modems, it would have to be on a server behind the modem.

So one modem could use the builtin PPPoE client, the other side would have to use an external PPPoE server like http://freshmeat.net/projects/rp-pppoe/.


Captn's problem is he hasn't got an ATU-C chipset in one of his modems. With an advanced signal generator the ATU-C handshake could be impersonated, and I was curious whether the 2 atu-R's could handle things between themselves after that. And having looked into it, I don't think so.

I'm not really sure what to make of

Also you suggestion that pppoe is layered on top of pppoa doesn't make sense

So, just so we're on the same hymn sheet.
http://www2.rad.com/networks/2005/adsl/pics/encaps.gif

I'm just saying that the PPP & RFC2516 need not be implemented on the modem hardware, nor is it difficult. It can just be software running on the device behind one or both modems, connected via ethernet.

Boston

Hmm, that hymn sheet is giving me some food for thought. In the PPPoE block the first 3 layers are what I would call pppoe while all five would be PPPoEoA, hmm, have to look at that one some more. Either way minor point, and we seem to agree he'ed need to insert some form of physical layer support to do what he wants to do.