value is set higher than the upper limit value for the u201c empty u201d case considering the ease of implementation it is desirable that the upper limit value here be set equal to an integral multiple of the bandwidth set value similarly the upper limit value for the u201c empty u201d case may be set for example equal to twice the bandwidth set value provided that it is set lower than the upper limit value for the u201c not empty u201d case when the surplus bandwidth mode is permitted situations such as described with reference to fig4 can occur in overlapping fashion therefore the upper limit value for the u201c not empty u201d case must be set higher than when only the bandwidth management mode is performed if the upper limit value for the u201c not empty u201d case when the surplus bandwidth mode is permitted is to be estimated on the safest side this should be done by assuming the case where as shown in fig8 the longest packet is output in the surplus bandwidth mode immediately before the update time followed by the output of the longest packet from other than the attention queue 0 in the bandwidth management mode if a packet destined for 0 arrives during this period the packet cannot be output but the number of times that the update time is expected to arrive during this period should be.