This paper identifies the sequential decision principle that guarantees optimality for the sequential dynamic routing scheme, which is widely used among communication path establishment methods. In particular, the paper elucidates how this principle can be applied under the trunk reservation system—a general control mechanism for communication path establishment—and compares the performance with other routing schemes by applying it to practical situations. The results confirmed the principle that, in communication networks where a trunk reservation system is applied, calls should be assigned starting from the route with the minimum assignment cost. Furthermore, the experiments revealed that when an optimal sequential routing scheme that fundamentally prevents each link from being excessively occupied by overflow traffic is applied, a uniform trunk reservation system may actually cause degradation in routing system performance. In particular, this inefficiency characteristic resulting from the uniform trunk reservation system is shown to be more pronounced when the traffic level imposed on the communication network is at a moderate level.