Press release

Private customers / 18.01.2003

Internet file sharing without huge telephone bills


A firmware update for your MicroLink ADSL Modem Router is devolo AG’s reaction to the dynamic requirements of utilising online file-sharing clients. It ensures that the Router cuts the Internet connection once a data transfer is completed. The file is available as a free download here

Online file sharing with peer-to-peer clients is hugely popular. Less popular are the unexpectedly high telephone bills that many router owners receive at the end of the month. Especially those users who don’t have a DSL flatrate offering unlimited data-transfer volumes are wondering how these horrendous phone bills can arise. One possible cause is a feature of online peer-to-peer clients that, under certain circumstances, can prevent a SoHo router from automatically cutting the Internet connection after completing an upload or download.

“The reason that the failure of the normally reliable idle timers is that file-sharing programs send out unrequested data packets”, explains Werner Fehn, Product Manager at Aachen’s devolo AG. Even routers connected to the Internet and not being used for peer-to-peer file sharing can receive up to 40 data packets per minute. Fehn: “The resulting data traffic appears to prevent the idle timeouts from kicking in—for most the routers currently on the market.”

The devolo AG is now the first manufacturer to offer a firmware update for its MicroLink ADSL Modem Router that solves this problem. All new products from devolo will now be equipped with this feature. Modem Routers for the small and home office that have already been shipped can be easily updated with the help of this free download. It can be found under the address on the devolo homepage.

The technical problem in detail:

1. User “A” dials in to his provider and uses a file-sharing client. The IP address assigned to the user by the provider is now listed in the file-sharing network as a potential download source.

2. User “A” shuts down the Internet connection after completing a download, but the IP number remains listed in the file-sharing network. This is mainly due to the decentralised storage of this information, the complete update of which follows only after a number of hours.

3. The router of user “B” then connects to the same provider. It is coincidentally issued with the same IP number used by user “A” earlier.

4. The file-sharing clients of other users search for downloads and find this IP address, formerly used by user “A” but now in use by user “B”.

5. These programs then bombard the IP address—meaning “B”’s router—with requests, mostly as UDP packets.

6. The router responds to the UDP packets with “ICMP port unreachable”, to TCP packets with an RST, and to ping packets with an “ICMP echo reply”. The end result is a data flow over the router’s WAN connection, even though no request occurred from the LAN.

7. As the router detects traffic on the WAN interface, the idle timeout will not come into effect. The connection thus remains open for hours at a time, with logical consequences for the telephone bill.