All the upward forces of transition are 0.5 (the arrival rate). The downward force from 1 to 0 is 1/3 (the exponential parameter for a single customer). The other downward forces are all 2/3 (since states 2:0, 2:1 and 2:2 all correspond to 2 customers currently being served). The probabilities in the jump chain are ratios of forces, eg the probability of entering state 0 when the process leaves state 1 is given by force from 1 to 0 / total force out of 1 = (1/3) / (1/2 + 1/3)