an atm cell with cntl information and crc as well as pad information if necessary appended to the datagram to form the payload of the atm cell thereafter the payload generator 350 outputs the payload into a main selector element 365 through a payload communication line 366 the header of the atm cell is stored in a header generator 370 the header generator 370 is local memory maintained by system software this local memory is separated into a number of entries according to a 34 table 34 format wherein one of the entries is selected by the channel number transmitted through a communication line 306 upon the response the header generator 370 outputs the header stored in the selected entry through communication line 368 and into the main selector element 365 the header and payload are combined by the selector element 365 under control by the payload generator 350 via control line 367 to produce the atm cell referring to fig5 the scheduler 310 is used for generating an event or a sequence of events to initiate the generation of a corresponding one or sequence of atm cells the scheduler 310 comprises at least one scheduler element but preferably a plurality of scheduler elements 311a 311m 34 m 34 being arbitrary as illustrated each capable of generating a single or a sequence of events in order to prompt the generation of atm cell s each of the.