The invention relates to a method for managing data transmissions via an internet network between calling and called subscribers and also an associated smart card. The printing apparatus restricts reprinting based on history information of a job using data obtained from a file server on a network. Further, embedded conductive layers are formed in an insulating layer so that large contact areas are obtained between the embedded conductive layers and the source and drain electrodes; thus, the contact resistance of the transistor can be reduced.