This enables support for two kinds of ISDN-cards made by a German company called ICN. 2B is the standard version for a single ISDN line with two B-channels, 4B supports two ISDN lines. For running this card, additional firmware is necessary, which has to be downloaded into the card using a utility which is distributed separately. See <file:Documentation/isdn/README> and <file:Documentation/isdn/README.icn> for more information.