Kaufmann, Michael Algorithms and Complexity, MPI for Informatics, Max Planck Society;
https://rdcu.be/dwYiA (Publisher version)
Kaufmann, M., & Sibeyn, J. F. (1992). Optimal Multi-packet Routing on the Torus. In O. Nurmi (Ed.), Algorithms Theory - SWAT' 92 (pp. 118-128). Berlin, Germany: Springer.