DSL modem

Unanswered Question
Jul 10th, 2007

Hi there! I have a question that I hope someone is kind enough to help me with:

If there is a DSL modem at the home that connects via the local loop to the DSLAM, and that in turn, is connected to an ISP router. Will the router need to have a modem attached to it? Or does the DSLAM convert the analog data into digital before forwarding it onto the ISP router?

I ask this question because no where in my material have I found a suitable answer. Thank you all in advance for your help.

Kind regards,


I have this problem too.
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Paolo Bevilacqua Tue, 07/10/2007 - 13:03


No the ISP router does not need a modem. The DLAM have either an ATM interface (older models) or gigabit ethernet interface (current models).

In both cases is a purely digital interface.

Hope this helps, please rate post if it does!

ashraf_can2 Tue, 07/10/2007 - 16:44

Hi there! Thank you very much for your reply. I much appreciate it!

Sir, am I then wrong in thinking that the DSL modem (at home/office) converts digital signals to analog electrical signals?

If the DSLAM has a purely digital interface then I would suppose the DSL modem does not convert from digital to analog?

Thank you in advance for your help.

Paolo Bevilacqua Wed, 07/11/2007 - 04:01


the DLAM has a digital interface toward the ISP router. Toward the users, has multiple interfaces that work in the analog domain. So it does the conversion that you mentioned.

ashraf_can2 Wed, 07/11/2007 - 20:45

Thank you very much for your reply. It's most kind of you to help in such a way!

I do, however, have one more question. I hope you don't mind me asking:

Assuming I have a DSL router at home which connects to the DSLAM at the Telco CO. The DSL router, if I'm right in thinking, will send digital signals to the DSLAM. If the DSLAM is acting like a modem and converting analog to digital, then would it not do a conversion in this instant (when receiving digital signals from the DSL router based at home)?

Paolo Bevilacqua Thu, 07/12/2007 - 00:38


ADSL, like many other things, works by sending digital signal in the analog domain of the frequencies allow on a copper loop.

So we tend to say that the signal on DSL line is "analog", as opposed to ethernet for example that is "digital" because the much more simplified coding used.

Hence both the home DSL modem and the DSLAM at the C.O. are doing analog to digital conversion in real time.

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