Busy periods in M/M/infinity systems with heterogeneous servers.

Boris Tsybakov Busy periods in M/M/infinity systems with heterogeneous servers. 153-156 2006 52 Queueing Syst. 2 http://dx.doi.org/10.1007/s11134-006-4435-8 db/journals/questa/questa52.html#Tsybakov06