Parallel Packet Switch without Segmentation-and-Reassembly

Abstract

The ever increasing demand for more bandwidth at core routers has been a challenge for switch design. To address the challenge, parallel packet switches (PPSs) combine multiple parallel switching fabrics and provide huge aggregate bandwidth. However, most existing PPSs handle only fixed length packets, also called cells, mainly because traditional switching fabrics can process only cells. Since packets in the Internet are of variable length, existing PPSs need segmentation-and-reassembly (SAR) to process such packets, which will introduce padding bits and waste precious bandwidth. In this paper, we propose a PPS to directly handle variable-length packets without SAR. First, we present a simplified $1 \times 1$ variable-length PPS. We design the packet distribution and collection algorithms, and show that input and output conversion buffers are bounded by $2L$, where $L$ is the maximum packet length. Next, we present a general $N \times N$ variable-length PPS, and propose the packet scheduling algorithms. We then prove our main result that such a PPS can emulate a first-in-first-out (FIFO) output queued (OQ) switch with speedup of two, i.e. emulating an FIFO OQ switch with bandwidth $R$ by $2K-1$ parallel switching fabrics each with bandwidth $r$, where $r=R/K$.