Unreliable servers are an important performance analysis component. In this paper we construct a novel approximation for the steady state joint solution of a tandem feedback unreliable server queue, and compare its behaviour to other approximation techniques and simulation. The queue transition structures are interesting, as they incorporate off-diagonal terms which create a MAP-like arrival process. The system is solved using spectral expansion in preference to matrix geometric methods, as this provides better stability and accuracy in finite queues. The results suggest that this novel approach of approximating joint behaviour in this manner can be of value in providing computationally inexpensive approximations to network solutions of this type.
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