Abstract: Crossbar is used to classify data packets in optical burst switching (OBS) edge nodes. This paper introduces input serial polling (ISP) algorithm, which is usually adopted in crossbar. An algorithm, named variable input serial polling (VISP), is proposed to support variable length data packets assembling. The details of the implementation of VISP algorithm in field programmable gate array (FPGA) is presented. Resource occupation and working frequency are compared between ISP and VISP.