Internet-Protokoll-Schichtprozessor

An internet protocol (IP) layer processor has an IP header processing section for checking a defect in an IP header of a first ATM cell of an AAL5 frame, and a SAR (segregation and reassemblage) section for transferring the AAL5 frame in the form of separate ATM cells if the check by the IP header processing section indicates a normal IP header, without using a CPU. SAR notifies a defect in the IP header to CPU without transmission of the AAL5 frame if the check indicates the defect in the IP header. The IP layer processor achieves a higher processing due to the direct transfer by the SAR without using processing by a software.