In an Multi-Protocol Label Switching (MPLS) network domain, Asynchronous Transfer Mode--Label Switch Routers (ATM-LSRs) are considered the best candidate for providing the highest forwarding capability. ATM-LSRs implement a VC-merging scheme that allows many IP routes to be mapped into the same VPI/VCI label, hence supporting scalability. The VC-merging requires reassembly buffers to reconstruct an original packet from its segmented but interleaved AAL-5 cells. In this paper, we analyze the performance of an ATM-LSR with partial VC-merging capability and investigate the impact of VC-merging on the requirement of the reassembly and output buffer. The numerical computation complexity of the mathematical analysis can be reduced from O(M4) to O(M2), where M is the total number of ON-OFF sources. We also propose a closed-form equation, which approximates the distribution of the output buffer with satisfactory accuracy. Numerical results show that when incoming cells are severely interleaved, the VC-merging needs the reassembly buffer size to be of the same order as the output buffer size, which cannot be ignored.

LSR (Label Switching Router)s in MPLS (Multiprotocol Label Switching) networks map arriving IP flows into some labels on Layer 2 switching fabric and establish LSP (Label Switching Path)s. By using LSPs, LSRs not only transmit IP datagrams fast by cut-through mechanism, but also solve traffic engineering issue to optimize the delay of some IP datagram flows. So far, we have analyzed the performance of LSR focusing only on the maximum number of LSPs which can be set on Layer 2. In this paper, we will also consider the bandwidth allocated to each LSP and analyze the IP datagram transmission delay and the cut-through rate of LSR. We suppose the label mapping method as the data-driven scheme in the analytical model, so that the physical bandwidth of LSR is shared by both the default LSP for hop-by-hop transmission and the cut-through LSPs. Thus, we will investigate the impact of the bandwidth allocation among these LSPs on the performance.