This paper deals with a retrial queueing system M/M/C/K with exponential abandonment
at which positive and negative primary customers arrive according to Poisson processes.
This model is of practical interest: it permits to analyze the performance in call
centers or multiprocessor computer systems. For model under study, we find the ergodicity
condition and also the approximate solution by applying Value Extrapolation method
which includes solving of some algebraic system of equations. To this end, we have
resolved the algebraic system in question by different numerical methods. We present
also numerical results to analyze the system performance.