This document summarizes a mathematical model of a single server queueing system with batch arrivals of customers. Key features of the model include: customers may arrive in batches and join an orbit if the server is busy, the server is unreliable and may break down requiring repair, and the server may take a vacation after completing a service. The document presents the transient state equations that govern the system and defines probability generating functions to obtain the transient and steady state solutions. Performance measures and reliability indices are also derived from the model.