AAL2/AAL5 CONVERTING APPARATUS AND A METHOD THEREOF, PARTICULARLY FOR PERFORMING INTERCONVERSION BY IMPLEMENTING AN AAL2 SSTED FUNCTION WITHOUT CREATING AN AAL2 SSTED-SDU

PURPOSE: An AAL(ATM Adaptation Layer)2/AAL5 converting apparatus and a method thereof, particularly for performing interconversion by implementing an AAL2 SSTED(Service Specific Transmission Error Detection) function without creating an AAL2 SSTED-SDU(Service Data Unit), are provided to reduce required memory resources to maximum 128 bytes and reduce transmission delay time by minimizing the amount of data stored during interconversion. CONSTITUTION: An AAL2 CPS receiver(71) extracts an AAL2 CPS packet from an AAL2 ATM cell received from a lower ATM layer and transfers it together with an AAL2 CPS packet UUI. An AAL5 CPCS(Common Part Convergence Sublayer) and SAR(Segmentation And Reassembly) transmitter(72) checks whether an AAL2 CPS packet is the final part of an AAL2 SSSAR(Service Specific Segmentation And Reassembly) and whether it can be one ATM-SDU, calculates a length of an AAL2 SSTED and a CRC(Cyclic Redundancy Check) with respect to the AAL2 CPS packet and stores them in the second memory(72-1), and creates the AAL2 CPS packet as an ATM-SDU and transmits it to the other party. When an AAL5 cell is received, an AAL5 CPCS and SAR receiver(73) separates user data and checks whether the AAL5 cell is the final cell. If the AAL5 cell is the final cell, the AAL5 CPCS and SAR receiver(73) calculates a length and a CRC of an AAL2 SSTED and transfers them together with user data. If the AAL5 cell is not the final cell, the AAL5 CPCS and SAR receiver(73) temporarily stores the AAL5 cell in the third memory unit(73-1), calculates a length and a CRC of an AAL2 SSTED by adding the final cell with the data stored in the third memory unit(73-1), and transfers them together with user data. An AAL2 CPS transmitter(74) creates data received from the AAL5 CPCS and SAR transmitter(72) to an AAL2 CPS packet, completes it as an ATM cell, and transmits it to an ATM layer.