Apparatus is dedicated to switching data packet frames of different types coming from at least two transport networks that use different transport protocol layers. Said apparatus includes a switching module and at least two access cards, each of which is connected to a respective one of said networks and to said switching module, each access card including processing means that, when they receive a frame coming from a source network to which they are connected and for a destination network, have the tasks of removing from said frame the transport protocol layers that it contains, and then of adding an internal header to the payload data of at least one packet of said frame, prior to transmitting it to said switching module, said internal header comprising at least: a channel identifier field containing a value representative of a channel assigned to the connection used by said frame on being set up; a length field containing a value representative of the number of bytes contained in the packet in question; and a type field containing values representative of characteristics of the payload data of the packet in question.