1. Larsen, R.L. and Agrawala, A.K., Control of a Heterogeneous Two-server Exponential Queuing System, IEEE Trans. Soft. Eng., 1983, vol. 9, pp. 526–552.
2. Lin, W. and Kumar, P.R., Optimal Control of a Queuing System with Two Heterogeneous Servers, IEEE Trans. Automat. Control, 1984, vol. 29, pp. 696–703.
3. Rykov, V.V., On Monotonicity Conditions for Optimal Policies for Controlling Queuing Systems, Autom. Remote Control, 1999, no. 9, pp. 1290–1301.
4. Efrosinin, D.V. and Rykov, V.V., Numerical Study of the Optimal Control of a System with Nonhomogeneous Servers, Autom. Remote Control, 2003, no. 2, pp. 302–309.
5. Morrison, J.A., Two-server Queue with One Server Idle Below a Threshold, Queuing Syst., 1990, vol. 7, pp. 325–336.