The age of information (AoI) has been studied actively in recent years as a performance measure for systems that require real-time performance, such as remote monitoring systems via communication networks. The theoretical analysis of the AoI is usually formulated based on explicit system modeling, such as a single-server queueing model. However, in general, the behavior of large-scale systems such as communication networks is complex, and it is usually difficult to express the delay using simple queueing models. In this paper, we consider a framework in which the sequence of delays is composed from a non-negative continuous-time stochastic process, called a virtual delay process, as a new modeling approach for the theoretical analysis of the AoI. Under such a framework, we derive an expression for the transient probability distribution of the AoI and further apply the theory of stochastic orders to prove that the high dependence of the sequence of delays leads to the degradation of AoI performance. We further consider a special case in which the sequence of delays is generated from a stationary Gaussian process, and we discuss the sensitivity of the AoI to second-order statistics of the delay process through numerical experiments.

The audio quality provided by some simple FEC schemes is studied. We deal with an M/M/l/K queueing model and assume that some of packets are lost due to noise or interference in the transmission as well as buffer overflow in the router. We consider the following two schemes: One is the Fixed/Variable Scheme that fixes the volume of original data and varies the volume of redundant data in a packet, and the other is Variable/Fixed Scheme that varies the volume of original data and fixed the volume of the whole data. We showed the cases where the Fixed/Variable Scheme improves the audio quality of the system.