A queue with skill based service under FCFS-ALIS : steady state, overloaded system, and behavior under abandonments

We consider a queueing system with servers S = {m_1, …, m_J}, and with customer types C = {a, b, …}. A bipartite graph G describes which pairs of server - customer type are compatible. We consider FCFS-ALIS policy: A server always picks the first, longest waiting compatible customer, a customer is always assigned to the longest idle compatible server. We assume Poisson arrivals and exponential service times. We derive an explicit product-form expression for the steady state distribution of this system when service capacity is sufficient. We analyze the system under overload, when partial steady state exists. Finally we describe the behavior of the system with generally distributed abandonments, under many arrivals - fast service scaling