Improving the Efficiency of the ISO Checksum Calculation

In this paper we describe techniques for efficient calculation of the ISO checksum which, to our knowledge, are not discussed in current literature. We propose that future versions of the ISO protocols employ checksums computed using logical "bytes" twice as large as the actual ones. Measurements are presented comparing times required to calculate the XNS, IP, and ISO checksums with and without these techniques, and the proposed new checksum. Our refinements yield improvements of 5 to 10 per cent in speed. Our proposed replacement checksum can be computed twice as quickly in some instances.