Constraint-based routing is an invaluable part of a full-fledged Quality of Service architecture. Unfortunately, QoS routing with multiple additive constraints is known to be a NP-complete problem. Hence, accurate constraint-based routing algorithms with a fast running time are scarce, perhaps even non-existent. The expected impact of such an efficient constraint-based routing algorithm has resulted in the proposal of numerous heuristics and a few exact QoS algorithms. This chapter presents a

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... orough, concise and fair evaluation of the most important multi-constrained path selection algorithms known today. A performance evaluation of these algorithms is presented based on a complexity analysis and simulation results. Besides the routing algorithm, dynamic aspects of QoS routing are discussed: how to cope with incomplete or inaccurate topology information and (in)stability issues.