Abstract: An analytical comparison of switching delays of AAL3/4 and AAL5 in VC merging for MPLS is presented. Based on the switching model with output buffers, an explicit expression of mean switching delay is given, and the relation between the merging factor(the proportion of the cells involved in VC merging) and the mean switching delay is discussed. Finally the result is verified by simulation using MATLAB. The analysis result indicates that, in VC merging, without the waiting requirement of gathering all cells belongings to a packet due to possession of MID field in the PDU format, the cells of AAL3/4 have a smaller mean dealy and the lower buffer demand than those of AAL5.

Key words: switching delay, AAL5, AAL3/4, VC merging