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I'm new to Raspberry Pi and I asked myself: Can I use my new RasPi 3 to replace my home DSL modem?

I read a lot about setting up RasPis as WiFi access points or routers, but always connected to an already existing modem. Nobody seems to even consider the possibility of replacing this modem.

I thought of using the ethernet jack of the RasPi as WAN port and its WiFi antenna for LAN. Is there any distribution/software I could do this with? Or is it impossible hardware-wise?

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Nobody seems to even consider the possibility of replacing this modem.

Probably because ISP provided routers/modems use either coax cable or (in the case of DSL) telephone line inputs, so you are now having to add some hardware and corresponding difficulty for dubious gain; it might be worthwhile for educational or prototyping purposes but it is unlikely to be of practical value.

Further, most ISPs, particularly the large ones, aren't going to support you on this. They may not forbid it, but they very likely employ proprietary software in those devices that will make replacing them somewhere along a spectrum of difficult that ends with impossible. This may be a bit easier with smaller ISPs that use something closer to a stock router or modem you could buy yourself (but don't count on it).

If what you have already is something you bought yourself, then the last paragraph doesn't really apply, but I think now-a-days that is on the unusual side, which is why people who want to use their own routers attach them to the ISP provided one rather than trying to replace them. That is drop dead simple because it is just another network device and your ISP isn't going to care how many subnets or access points you want to deploy, they're just going to enforce whatever bandwidth usage limits apply under your contract.

However, the pi is not a good choice for this in any case unless you live alone and don't care much about connection speed. It is a low network throughput device; the ethernet and USB ports are all on one bus with a maximum throughput of at best, in theory, 280 Mbps (I've seen them hit ~30 MB/s writing to a USB drive, so the peak reality is close to this). If you are providing uplink access via such a device, that means the maximum volume is half that, since it must come in and go out the same bus, i.e., 140 Mbps. That's the equivalent of one normal wifi connection.

Also note the actual ethernet jack is only 100 Mbps.

The Pi 3's onboard wifi doesn't really save you from this (except in the sense that it may make the theoretical limit just mentioned more reachable), because it is limited to the speed of one such connection, 150 Mbps.

In other words, can you do this? Perhaps. Is it worthwhile for most people? Absolutely not, which is why you have not found much material related to it.

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    ADSL is pretty complicated. I'd guess all the hard stuff is done in custom chips (binning, FEC (Forward Error Correction), etc). I don't think a Pi would be able to cope. – joan Aug 14 '16 at 20:40
  • I believe there's quite a gnarly mash-up of multiplexing techniques used too (FDM, TDM, ...) so in the end the "additional hardware required" might essential mean "a physically hacked DSL modem". – goldilocks Aug 14 '16 at 20:58
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    The modem can definitely not be replaced directly by the Pi. What one can do though, is buy a cheap bridge-only modem that connects to the telco, then on the Pi, have it do all routing, NAT and other router-type functionality including the PPPoE communication (if that's what's in use, vast majority of the time it is) through the bridge modem. A Pi just doesn't have the physical properties, nor the signalling/communications properties to communicate on an *DSL telco network directly – stevieb Sep 16 '16 at 12:41
  • That goes for any type of communication protocol that isn't Ethernet directly; DOCSIS (cable), *DSL, ISDN, etc. – stevieb Sep 16 '16 at 12:44
  • Can you introduce a module for telephone line? I mean something like SIM 900 module (GSM signal to digital data converter in brief). – SuB Dec 5 '17 at 15:58
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You can do it with OpenWRT.

https://wiki.openwrt.org/toh/raspberry_pi_foundation/raspberry_pi

Then add a USB ADSL Modem

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The question has already a great age but has been pumped by Community.

Some months ago I stumbled again about a Linux distribution that i used a decade ago. This project offers a rpi packages. Unfortunately it is still in development and not feature complete.

Here are is a tutorial (translated to English w/ Google). As others here mentioned, a PRi as DSL cant replace a dedicated hardware - it works more as PoC.

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