all of the information identified in fig2 b showing the internal cell format of a cell 220 according to the first embodiment of the invention except for the vci cell discard threshold information 227 as a result as shown in fig1 b the fifo buffer 2107 is modified as compared with the fifo buffer 107 shown in fig3 in that no counter for each vci 308 and correspondingly no counter control circuit 306 are provided accordingly the fifo buffer 2107 merely counts the length of the buffers 301 and 302 and provides an output signal 156 that is transmitted to fifo congestion state judgment circuit 106 fig1 c shows the input line interface unit lifi 2102 according to this embodiment of the invention which does not have a vci congestion state judgment circuit as does the lifi 102 of fig4 the fifo level measurement circuit 430 receives the fifo congestion state judgment circuit output 106 through input signal line 152 and registers the value in register 432 then the registered fifo subclass congestion state held in register 432 is compared with the traffic subclass information 225 of cell 2220 to make a packet discard judgment fig1 d discloses the decision made in step 712 u2032 that either provides a cell discard instruction that is given to the cell buffer when the subclass congestion state exceeds the traffic subclass step 714 or ensures that no cell discard instruction is given to the cell buffer and no packet discarding state is activated.