THE PH PH/1 QUEUE AT EPOCHS OF QUEUE SIZE CHANGE/

The PH/PH/1 queue is considered at embedded epochs which form the unio n of arrival and departure instants. This provides us with a new, comp act representation as a quasi-birth-and-death process, where the order of the blocks is the sum of the number of phases in the arrival and s ervice time distributions. It is quite easy to recover, from this new embedded process, the usual distributions at epochs of arrival, or epo chs of departure, or at arbitrary instants. The quasi-birth-and-death structure allows for efficient algorithmic procedures.