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AbstractThis paper deals with a service system in which the processor must serve two types of impatient units. In the case of blocking, the first type units leave the system whereas the second type units enter a pool and wait to be processed later.We develop an exhaustive analysis of the system including embedded Markov chain, fundamental period and various classical stationary probability distributions. More specific performance measures, such as the number of lost customers and other quantities, are also considered. The mathematical analysis of the model is based on the theory of Markov renewal processes, in Markov chains of M/G/1 type and in expressions of 'Takacs' equation' type.Analysis of an M/G/1 queue be presented in a different way. Suppose that the pool permanently has information about the state of the channel and that the unit at the head of the pool could occupy the channel when this becomes free. Taking into account that a unit of the first type can be lost, the processor may consider the possibility of reserving a priority period of time for such a unit delaying the entrance at service for the units in the pool. In this case we can think of / as a 'priority parameter'.The model described above has applications in the study of the access of messages to a central processor in computer networks. The service time distribution, the units in the pool and the distribution of the successive retrials in the queueing terminology correspond to the transmission time, blocked terminals which can be stored in a buffer and retransmission policy. So our model has related applications in the study of packet switching networks and communications protocols arising in the modelling of local area networks. For a more detailed discussion of other similar protocols used in computer networks, see Hammond and O'Reilly [7]. Many queueing systems are closely related to our model. The particular case A1 = 0
was first introduced by Fayolle [6]. Farahmand [5] and Artalejo and Martin [1] examined the M/G/1 queue with similar retransmission control policies: the delays between successive attempts follow an exponential law with parameter ,u, but the pool discipline is not FCFS. Other similar models can be found in the literature about multiclass retrial queues; see Falin et al. [4] and its references. In related work, Neuts and Ramalhoto [8] analyzed a service model in which, at the end of the transmission, the channel is required to search the next unit to be processed.The rest of the paper is organized as follows. In Section 2, we consider a formula of 'Takacs' equati...