Cell multiplexing device for synchronous digital interface and method thereof

A cell multiplexing device for mapping asynchronous fixed-length cells onto an existing synchronous digital interface, comprising:

• a plurality of line interface controlling means for terminating lines of a plurality of synchronous digital interfaces;
• bandwidth controlling means for generating a timing signal which specifies respective timing of a plurality of time slot groups in order to divide a plurality of time slots structuring each of said plurality of synchronous digital interfaces into the plurality of time slot groups in each of said plurality of synchronous digital interfaces;
• a plurality of cell mapping controlling means for respectively identifying a single predetermined time slot group among said plurality of time slot groups in a single predetermined synchronous digital interface among said plurality of synchronous digital interfaces based on the timing signal, and mapping a data stream of asynchronous fixed-length cells, which belongs to a single predetermined communication device interface among a plurality of communication device interfaces, onto the identified single time slot group;
• and
• means for switching said single predetermined synchronous digital interface and said single predetermined time slot group to another extra synchronous digital interface and another extra time slot group.