This attribute describes the type of the designated port. Exteral port is a port with a physical connector. Internal port might be of two types, one is a composite port which collects data of a few external ports into a common bandwidth (usually routed trough DS1 link); the other type is internal ports which get only part of external port data (usually a few DS0's). In the Kilomux-2100, the internal(3) value is used for composite channels or sub-channels of an ISDN Ch.