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We consider a single-server retrial model with many classes of customers. The arriving customers follow independent Poisson inputs and, a new customer meeting server busy may join the corresponding (class-dependent) orbit queue with a class-dependent probability. Otherwise, this (blocked) customer leaves the system. We consider constant retrial rate discipline, when only one (the oldest) orbital customer makes the attempts to occupy server following a class-dependent exponential distribution. This setting includes the systems with incoming and outgoing calls.

Applying regenerative approach, we derive some explicit expressions for the steady-state probabilities. In case the service times are exponentially distributed, we obtain some performance measures by the matrix-analytic method. At that we combine both methods to efficiently derive explicit solutions for the Markovian model. Moreover, we provide necessary and sufficient stability conditions. Analytical results are numerically illustrated by simulation.