I need for studing purposes to buy an adsl modem-router, but with linux
inside the modem. With open source of course. Is there exist on the market
such devices?

hi,

i think there many of them.
my very old dlink dsl-504t adsl modem/router was an embedded-linux - you can telnet into it, and provides you with the busy box.
you can execute some commands like iptables to non-permanent configuration, and others - but that was it, no other capability that you can play like those on regular pc-based linux since it was a stripped down linux and all config has to be configured from the web console (permanent).

HTH.

do you have source code for your modem?

My Netgear DG834 modem/router/firewall/ runs linux, and I recommend it.
Netgear publish the source code here: http://kb.netgear.com/app/answers/detail/a_id/2649

Also.. these are actual routers and really inexpensive.

http://www.omnima.co.uk/store/catalo...r-p-16140.html

These are £15.00 (in the UK - must be available internationally).

Theres a little connector on board and you can telnet into it via a serial port. It of course has ethernet connectors.

The OS is squidge and the source is available. It's Linux and very powerful for the size.

For the extra 'pennies', buy a couple of pre-configured bootable usb keys from the site (these is your boot disks - definitely get 2).
Get also the USB/serial cable with the connector for this board.