Surender Kumar, Nidhi Sharma. Mathematical Study Of Waiting Time Of Service In Four Server Hierarchical Structured Feedback Queuing System With Revisit At Most Once To Any Of The Servers. REDVET [Internet]. 2023Sep.12 [cited 2025Sep.13];24(3):627-33. Available from: https://www.veterinaria.org/index.php/REDVET/article/view/1850