Discrete event simulation is an indispensable tool to understand the dynamics of communication networks and evaluate their performance. As the scale and complexity of these networks increases, simulation itself becomes a computationally prohibitive undertaking. Among all possible solutions, improving the performance of event manipulation operations is an important one. In this paper, we discover that in network simulation events are often inserted into the simulation kernel in their timestamp order. Based on this observation, we make some simple modifications on the conventional calendar queue. Experiments show that the new data structure can achieve two orders of execution speedup against the conventional calendar queue in some wireline network simulation and in wireless network simulation, the speedup scales well with the network size.