Translocation is modeled with the Rubinstein-Duke rules for hopping reptons along a one-dimensional lattice (tube). Identification of some coupled states guarantees a semi-periodicity of the process. The chain is driven through the pore by a bias potential promoting the transition of stored length in one direction. Accounting exactly for all allowed states the translocation time of polymers up to the 10-links length is determined. The crossover from reptation to faster dynamics through gradually allowing hernia creation and annihilation is found. Some computational details are presented.