Customer contact centres have a heavy reliance on customer service representatives (CSRs) and labour is often the largest single cost in the operation. How many CSRs to employ, how to schedule their working hours, the skills they should have, and how to route interactions between customers and CSRs, are a series of assignment problems that Operations Research (OR) has been studying for five decades. This review analyses twenty-five peer-reviewed papers, published between 1974 and 2017, that apply OR to CSR assignment. The papers were identified in major scholarly databases, screened against clearly defined inclusion criteria and grouped into five streams: queueing-based staffing, shift scheduling and multi-skill staffing, simulation-based optimisation, planning under forecast uncertainty, and dynamic call-to-agent routing. For each, the real-world problem, the role of OR, the model, the solution method and software, and validation are extracted, and strengths, limitations and extensions are identified through critical review.

A worked example applying the Hungarian method and Erlang-C staffing to a representative case shows a reduction in total handling time of about 27% relative to a naïve assignment and identifies the minimum staffing needed to meet an 80/20 service level. Synthesis shows that the trend is moving from deterministic assignment and covering models to stochastic, simulation-based, and robust formulations that include staffing, scheduling, and routing. Various research gaps are explored, including omnichannel service, human-AI collaboration, learning-based routing, and CSR fairness and well-being.

Keywords— Assignment problem; Call centre staffing; Customer service representatives; Shift scheduling; Skill-based routing; Operations research.