In this correspondence, we investigate the accuracy of low-complexity discrete-time Markov chain models in characterizing the packet-loss process associated with a transport network whose behavior can be described in terms of a single bottleneck node, modeled by a single multiplexer. The results are useful since network behavior is often characterized in terms of a single bottleneck node and it is of some interest to establish the accuracy of Markov chain models in predicting the packet-loss process on even such a simplified network model. We demonstrate that, although higher order Markov chain models can achieve increasingly more accurate descriptions, the Gilbert model has some serious deficiencies in predicting the packet-loss statistics of the single-multiplexer model for a variety of packet arrival processes. We show that this has some serious consequences for the performance evaluation of forward error correction (FEC) coding schemes using Markov chain models compared to that predicted by an exact queueing analysis of the single-multiplexer model.

In wireless networks, channel state information is hard to obtain in a reliable and timely manner due to the rapid change of wireless environments. In this paper we propose instead the use of source information, which is always available at the encoder and can be easily and accurately obtained from video sequences, to achieve error-resilience. With use of exponential weighted moving average (EWMA) estimation for the motion-level information associated with video frames, a source-adaptive intra-coding rate selection scheme is described to provide error-resilience to N successive video frames. Based on our proposed cross-layer packetization scheme, a novel intra-frame packet interleaving scheme is implemented together with a fixed FEC coding strategy at the application-layer to combat the severe bursty losses over wireless channels, and the performance of the combined approach is investigated. Our objective and subjective results demonstrate the effectiveness of our approach in dealing with the bursty packet losses on both wireless single-hop and multi-hop networks without any additional system complexity or delay.

For video communications over wireless ad-hoc networks, there are fundamentally two different kinds of packet losses: packet losses due to channel over-pumping, where the operating transmission rate is higher than the prevailing channel capacity, and packet losses due to transmission errors. To eliminate the first kind of packet losses, rate-control is necessary in order to adapt to the time-varying channel capacity. For the second kind of packet losses, error-resilient coding techniques should be used. In this paper, we propose a cross-layer rate-control scheme based on an analytical study of how the effective video transmission rate is affected by the prevailing operating parameters. Furthermore, in order to provide error-resilient real-time video delivery over such wireless ad-hoc networks, a cross-layer delay-constrained joint source-channel coding (JSCC) approach, to be used in conjunction with rate-control, is proposed and investigated. Simulation results demonstrate the effectiveness of this combination of cross-layer rate-control and delay-constrained JSCC for supporting error-resilient video delivery over wireless ad-hoc networks operating under a delay constraint.

The Gilbert model (1-st order Markov chain model) and the single-multiplexer model are two frequently used models in the study of packet-loss processes in communication networks. In this paper we investigate the accuracy of the Gilbert model, and higher-order Markov chain extended Gilbert models, in characterizing the packet-loss process associated with a transport network modeled in terms of a single-multiplexer. More specifically, we quantitatively compare the packet-loss statistics predicted by the Gilbert models with those predicted by an exact queueing analysis of the single-multiplexer model. This topic is important since low-complexity Gilbert models are frequently used to characterize end-to-end network packet-loss behavior. On the other hand, network congestion behavior is often characterized in terms of a single bottleneck node modeled as a multiplexer. It is of some interest then to establish the relative accuracy of Gilbert models in predicting the packet-loss behavior on even such a simplified network model. We demonstrate that the Gilbert models have some serious deficiencies in accurately predicting the packet-loss statistics of the single-multiplexer model. The results are shown to have some serious consequences for the performance evaluation of forward error correction (FEC) coding schemes used to combat the effects of packet losses due to network buffer overflows.

In this paper, we investigate the effect of path correlation on video communications when path-diversity routing techniques are employed together with forward error correction (FEC). We study the statistical properties of packet losses when correlation between paths exists and demonstrate that the effects of path correlation on received video quality depend on various factors, such as the effectiveness of error control strategies (passive error concealment, FEC, etc.) and the existing channel conditions. We demonstrate that, contrary to common belief, path correlation need not be detrimental to the system performance. The results are expected to have some impact on the development of explicit multi-path routing strategies.

Packet video transmission over wireless networks is expected to experience packet losses due to noise, interference, multipath and the motion of mobile hosts. Such packet losses often occur in bursts which may cause substantial degradation to the transmitted video quality. In this paper, we propose the use of a cross-layer unequal error protection (UEP) approach which is achieved by assigning an unequal amount of forward error correction (FEC) to each group of link-layer packets according to the corresponding motion level of the slice acquired at the application layer. Also, a novel packetization scheme and an intraframe packet interleaving scheme are proposed to be used together with FEC/UEP in order to combat the bursty packet losses in 3G wireless environments. Our results demonstrate that the proposed approach is very effective in dealing with the packet losses occurring on wireless networks without incurring any additional implementation complexity or delay.

Properties of heterogeneous network traffic have been investigated from different aspects, resulting in different understanding. Specifically, one previous work discovers that the variance of network traffic exhibits a linear relationship with respect to the mean. Such a linear relation suggests that the traffic is "Poisson-like", and thus "smooth". On the other hand, prior work has shown that the heterogeneous traffic can be long-range dependent, and is thus bursty. The focus of this work is to investigate these seemingly contradictory issues, and to provide a unified understanding on the burstiness of heterogeneous traffic. In particular, we use a simple statistic, the variance of the traffic, for our investigation. We first study variance-mean relations at a single time scale. We then investigate the behavior of variances at multiple time scales, which determines the temporal correlation structure. Finally, we provide a unified view to include most important understanding of the network traffic.

Cheng Ma and Chuanyi Ji (1998) and Chuanyi Ji et al. (1999) showed empirically that independent (Haar) wavelet models were parsimonious, computationally efficient and accurate in modeling heterogeneous network traffic measured by both auto-covariance functions and buffer loss rate. We also proved analytically that such models were capable of capturing any decay rate of auto-covariance functions at large lags. In this work, we focus on comparing independent (Haar) wavelet models against independent wavelet models with higher vanishing moments. It is shown that as the vanishing moments increase, the independent wavelet models have better performance in approximating the auto-covariance function at small lags. The computational cost for all independent wavelet models is O(N) for a trace of length N.

In our previous work, we showed empirically that independent wavelet models were parsimonious, computationally efficient, and accurate in modeling heterogeneous network traffic measured by both auto-covariance functions and buffer loss rate. In this work, we focus on auto-covariance functions, to establish a theory of independent wavelet models as unified models for heterogeneous network traffic. We have developed the theory on the approximation capability of independent wavelet models for heterogeneous traffic in terms of the decay rate of auto-covariance functions at large lags. Average auto-covariance functions of independent wavelet models have been derived and shown to be linear combinations of basis functions. Through a simple analytical expression, we have shown that the decay rate of the auto-covariance functions of independent wavelet models is determined explicitly through a single quantity called the rate function of variances of wavelet coefficients. By specifying analytical forms of the rate function, independent wavelet models have been shown as unified models of heterogeneous traffic in terms of auto-covariance functions. The simplicity of the theory thereby provides both quantitative and qualitative explanations why independent wavelet models are unified models of heterogeneous traffic.

In this work, we investigate the performance of distributed admission control with QoS provisioning and dynamical channel allocation for mobile/wireless networks. We first provide a QoS metric feasible for admission control with dynamically allocated channels. We then derive a criterion analytically using the QoS measure for distributed call admission control with dynamic channel allocation. When maximum packing is used as the dynamic channel allocation scheme, the results obtained are independent of any particular algorithm which implements dynamic channel assignments. Our results thereby provide the optimal performance achievable for the distributed admission control with the QoS provisioning by the best dynamic channel allocation scheme in the given setting.

We investigate the performance of distributed admission control with QoS provisioning and dynamical channel allocation for mobile/wireless networks. We first provide a QoS metric feasible for admission control with dynamically allocated channels. We then derive analytically a criterion using the QoS measure for distributed call admission control with dynamic channel allocation. Since maximum packing is used as the dynamic channel allocation scheme, the results obtained are independent of any particular algorithm which implements the dynamic channel assignment. Our results thereby provides the optimal performance achievable for the distributed admission control with the QoS provisioning by the best dynamic channel allocation scheme in the given setting.