Hi I received some questions during the course that I did not have time to answer. Here they are:

Lecture 3: Transient solution. I added a comment on the transient solution of the two state markoc chain. See slide 9.

Lecture 10: Average waiting time calculation. As one of you pointed out, requests can arrive when the server is in vacation, and other requests are already waiting. I added a bit more detailed derivation now on slide 11. Still I skipped some steps.

Stability of queues: An infinite buffer queuing system is stable if $\rho <1$. We have seen this while deriving the results for M/M/1. Following Loynes' stability theorem this can be proved for more general cases. The proof is complex.