Abstract: ISDN can supplied a point-to-point digital connection that can be used to carry multi-traffic including both audio and non-audio signals and perform many operations such as dialing to access the Internet,and video phone especially.In this paper,the special driver model for a video phone ISDN card,which hardware was designed for multiplexed multifunction,to access the Internet is developed.The related ISDN network communication protocols are discussed in detail and the principle of the ISDN multimedia terminal card accessing the Internet under the scheme of MS-Windows RAS(remote access system) is analyzed.In the structure of RAS,the call control in the line is managed by TAPI(Telephone API),and the data transport is achieved by transport drivers.NIC(Network interface card) drivers must complete four functions:to complete the protocols Q.931 and Q.921 in ISDN D channel and control the communication in physical channels;to receive or send data in B channel;to function the interface with TAPI and the management of link layer;to act as the interface with transport drivers by WAN function library and NDIS function library.A miniport driver based on NDIS(network driver interface specification) for the ISDN multimedia card,which enables the card to function as an ISDN modem and a multimedia terminal simultaneously,is developed and the design guide and implementation details are reported.