The characteristics of a time-delayed system with time-dependent delay time is investigated. We demonstrate the nonlinearity characteristics of the time-delayed system are significantly changed depending on the properties of time-dependent delay time and especially that the reconstructed phase trajectory of the system is not collapsed into simple manifold, differently from the delayed system with fixed delay time. We discuss the possibility of a phase space reconstruction and its applications.PACS numbers: 05.45.Xt, 05.40.PqThe effect of time delay due to a finite propagation speed of information is usually considered as the form of delay-differential equation:ẋ = f (x(t), x(t − τ 0 )), where τ 0 is the fixed delay time [1,2,3,4,5,6,7,8,9,10,11,12]. It has been found that the system actually exhibits many different behaviors depending on the nonlinearity and the delay of the system and that the dimension of the attractor rises linearly with the delay time, even though the number of degree of freedom is small [8,9,10,11]. In the last decade, models based of delay time have been extensively investigated in various fields such as optics [1], biology [2,3] and chemistry [4] for the purpose of understanding its fundamental role and of applying it to control [5] and communication [6,7].The models based on fixed delay time, however, often fail to properly cover such real factors as (a) memory effect of the oscillator, (b) approximately known delay time, and (c) time-dependent delay time [13,14,15]. To cover these factors, Volterra first proposed a model based on distributed delays [13]. The model has been used in various areas [14,15,16]. It has been shown very recently that the distributed delay induces a death phenomenon in a much larger set of parameters than that of the fixed delay [15]. Thus the Volterra's model has enabled us to understand the realistic effects of delay times in dynamical systems.Meanwhile, in studying the population dynamics and epidemic problems the delay time has been considered as a function of state variable [17] and there have been extensive investigations in that direction. However, there are many real situations in which the dynamics of delay time can not be described by an analytic function, e.g., neural networks and internet [18]. So it is reasonable to introduce time-dependent delay time as a stochastic process in those cases. In this point of view we shall investigate the effects of time-dependent delay time (TDT) * Electronic address: whkyes@empal.com † Electronic address: chmkim@mail.paichai.ac.kr ‡ Electronic address: yjpark@ccs.sogang.ac.kr in dynamical systems governed by a stochastic process and the effects in time-delayed systems remain much less studied.The main goal of this paper is to show how TDT alters the characteristics of time-delayed systems. In addition, we analyze these characteristics with regards to application to communication. We consider the modified Mackey-Glass model. The Mackey-Glass model [2] was introduced as a model showing the regeneration of blood cells ...