## 2 Literature Review
### Buffer Allocation Problems
For example, the co-occurrence of keywords such as manufacturing, material handling, and machine shop practice suggests a strong association between these concepts in buffer allocation and queueing networks. Performance evaluation and throughput are often explored together, indicating the significance of evaluating system performance in terms of throughput. The co-occurrence of keywords such as system analysis, topology, and blocking implies the importance of studying the system's structure and characteristics, including network topology and the impact of blocking on performance. Moreover, keywords such as integer programming and genetic algorithms suggest utilising optimisation techniques for solving buffer allocation problems in queueing networks. These methods are commonly employed to find optimal solutions by balancing conflicting objectives. Uniform or homogeneous buffers possess equivalent capacities or sizes throughout the queueing network. Conversely, non-uniform buffers, also called heterogeneous buffers, exhibit varied capacities or sizes across different buffers in the queueing network, enabling each buffer to accommodate different entities. From an optimisation standpoint, the suitability of uniform buffers in a queueing network relies on the specific goals and requirements of the analysed system [65]. While uniform buffers can simplify the analysis, they may only sometimes represent the optimal choice regarding performance or resource utilisation. Uniform buffers foster balanced resource utilisation across the network, which can be advantageous in scenarios prioritising uniformity to ensure fairness and prevent bottlenecks. However, in certain situations, non-uniform buffers may offer superior resource utilisation. For instance, when demand or arrival rates significantly differ across different network parts, allocating larger buffers to high-demand areas can avert congestion and optimise resource allocation. Uniform buffers may not be optimal for minimising queueing delays. In the presence of heterogeneous arrival rates or service times, non-uniform buffers facilitate the allocation of buffer capacity based on demand at each network stage. By allowing larger buffers at bottleneck points or areas with high variability in arrival rates, non-uniform buffers can diminish queueing delays and enhance the overall system's performance [66]. The cost associated with buffer size plays a vital role in optimisation. Uniform buffers simplify resource allocation and buffer management but can result in over-provisioning in specific network segments. Conversely, appropriately sizing non-uniform buffers based on demand patterns can optimise resource utilisation and potentially reduce costs by eliminating unnecessary buffer capacity. Non-uniform buffers offer greater flexibility and adaptability to dynamic changes within the system. In situations where the demand pattern or service times vary, non-uniform buffers enable better adjustment to changing requirements. This flexibility leads to improved performance and responsiveness compared to uniform buffers, which may need to be more adaptable to varying conditions [67]. Figure 2: Co-occurrence network of keywords in buffer allocation and queueing networks for manufacturing systems.