Variable Bit Rate Sources Research Articles

A Poisson Hidden Markov Model for Multiview Video Traffic

Multiview video has recently emerged as a means to improve user experience in novel multimedia services. We propose a new stochastic model to characterize the traffic generated by a Multiview Video Coding (MVC) variable bit-rate source. To this aim, we resort to a Poisson hidden Markov model (P-HMM), in which the first (hidden) layer represents the evolution of the video activity and the second layer represents the frame sizes of the multiple encoded views. We propose a method for estimating the model parameters in long MVC sequences. We then present extensive numerical simulations assessing the model's ability to produce traffic with realistic characteristics for a general class of MVC sequences. We then extend our framework to network applications where we show that our model is able to accurately describe the sender and receiver buffers behavior in MVC transmission. Finally, we derive a model of user behavior for interactive view selection, which, in conjunction with our traffic model, is able to accurately predict actual network load in interactive multiview services.

Kalman optimized model for MPEG-4 VBR sources

This paper presents a traffic prediction method for MPEG-4 (Moving Picture Experts Group) VBR (Variable Bit Rate) videos. No previous knowledge of the traffic statistics is needed when Kalman optimized method is applied to modeling and predicting MPEG-4 video traffic. The GoP (group of pictures) loss probabilities in actual traffic are a very close approximation to those in our prediction traffic and the prediction errors are very small. Simulations show our prediction method for future GoP is effective and applicable to real time video traffic prediction and resource reservation.

Efficient Transmission of MPEG-2 Coded Video Traffic over ATM Networks

Video traffic is expected to account for a significant share of the traffic volume in the future asynchronous transfer mode (ATM) networks. MPEG-2 proposed by Moving Picture Expert Group is one of the most promising compression techniques for such applications. One of the critical issues in MPEG-2 is to realize effective variable bit rate (VBR) video transfer thorough ATM networks. The Leaky Bucket (LB) scheme has been widely accepted as the usage parameter control (UPC) mechanism to police the VBR sources. We proposed a new Adaptive Dynamic Leaky Bucket (ADLB) congestion control mechanism, which is based on the LB scheme. Unlike the conventional LB, the leak rate of the ADLB is controlled using delayed feedback information of available bandwidth sent by the network. This scheme allows sources to get varying amounts of bandwidth over time, while reserving a minimum guaranteed bandwidth (MCR) for the entire duration of the connection. At the time of congestion, the leak rate of the ADLB is adjusted according to the feedback indicating the currently available bandwidth to the connection. The simulation results show that the end-to-end cell transfer delay and cell loss of each source has been improved significantly.

Effective bandwidth estimation and testing for Markov sources

This work addresses the resource sharing problem in broadband communication networks that can guarantee some quality of service (QoS), and develops some results about data source and traffic modelling, especially in aspects of model testing and parameter estimation. The multiplexing of variable bit rate (VBR) sources poses a mathematical and statistical problem: the estimation of the resource requirements of a source or set of sources. The estimation method shall be simple enough to be practically implemented in the connection acceptance control (CAC) function. In this paper, the VBR video sources are taken as a typical case of variable rate, with real-time constraints. This association of requirements makes the case especially interesting. A Markov model is assumed for the VBR sources. The validity of such models is under research; they seem to be appropriate at least in certain time scales. The model is tested against real video traces. In order to estimate the resource allocation or “channel occupation” of each source, the concept of equivalent bandwidth proposed by Kelly [Notes on effective bandwidth, in: F.P. Kelly, S. Zachary, I.B. Ziedins (Eds.), Stochastic Networks: Theory and Applications, Oxford University Press, Oxford, 1996, pp. 141] is used; it is based on a consistent mathematical theory, and has proven to be robust and useful for technical applications. A calculation of the equivalent bandwidth of a Markov source, given its parameters, can be found in the literature [IEEE ACM Trans. Networking 1 (4) (1993) 424]. But in fact, one can only estimate model and parameters. In this work, an estimation of the equivalent bandwidth is given, which can be obtained from real data. The convergence and the consistency of the estimation are studied, and practical bounds are found. Illustrative calculations are performed from real video traces that were obtained using a software MPEG coder, developed by the authors. The mathematical and statistical results are valid for whatever phenomenon that can be modelled as a Markov process.

A survey of statistical source models for variable-bit-rate compressed video

It is predicted that, in the near future, the transport of compressed video will pervade computer networks. Variable-bit-rate (VBR) encoded video is expected to become a significant source of network traffic, due to its advantages in statistical multiplexing gain and consistent video quality. Both systems analysts and developers need to assess and study the impact these sources will have on their networks and networking products. To this end, suitable statistical source models are required to analyze performance metrics such as packet loss, delay and jitter. This paper provides a survey of VBR source models which can be used to drive network simulations. The models are categorized into four groups: Markov chain/linear regression, TES, self-similar and i.i.d/analytical. We present models which have been used for VBR sources containing moderate-to-significant scene changes and moderate-to-full motion. A description of each model is given along with corresponding advantages and shortcomings. Comparisons are made based on the complexity of each model.

Evaluation of ABR traffic management under various system time scales

In this paper, the effects of various time scales on the management of ABR (Available Bit Rate) traffic using feedback based control is studied. Since delay tolerable, the ABR applications can be allocated the remaining resources after CBR (Constant Bit Rate) and VBR (Variable Bit Rate) applications have been accommodated. To avoid excessive losses the transmission rate of the ABR applications should be modulated by the amount of remaining resources. That is, the ABR rate should be controlled through a feedback based rate control mechanism. In this paper, a network link shared by remote ABR and VBR applications is considered and the impact of various system time scales on the effectiveness of the feedback based flow control scheme is investigated by formulating and studying a tractable analytical model. These time scales are expressed in terms of the network transmission speed, the minimum tolerable ABR rate and the rate of change of the VBR source rate. While the negative impact of a decreased network time scale on the effectiveness of this control scheme is well established, the impact of the ABR and VBR time scales has not been investigated in the past. It turns out that for a given network time scale, the induced cell losses can be significantly reduced for increased ABR and/or VBR time scales and thus, the latter time scales should be taken into consideration while evaluating the effectiveness of an adaptive feedback based flow control mechanism. This study also suggests that higher efficiency can be achieved by enforcing large ABR time scales, leading to the introduction of a new class of transmission policies.

A bandwidth assignment algorithm on a satellite channel for VBR traffic

Variable bit rate (VBR) video is currently by far the most interesting and challenging real-time application. A VBR encoder attempts to keep the quality of video output constant and at the same time reduces bandwidth requirements, since only a minimum amount of information has to be transferred. On the other hand, as VBR video traffic is both highly variable and delay-sensitive, high-speed networks (e.g. ATM) are generally implemented by assigning peak rate bandwidths to VBR video applications. This approach may, however, be inefficient in a satellite network based on a TDMA scheme. To overcome this problem, we have designed a demand assignment satellite bandwidth allocation algorithm in TDMA, named V2L-DA (VBR 2-Level Demand Assignment), which manages the VBR video traffic according to a dynamic bandwidth allocation algorithm. In this paper we discuss how to tune the proposed algorithm in order to optimize network utilization when MPEG-1 VBR video traffic is being transmitted. Our results indicate that most of the time only 40% of the peak rate bandwidth is needed to satisfy the VBR source, so the remaining 60% of the peak rate bandwidth can be used to transmit the datagram traffic queued in the network stations. © 1997 John Wiley & Sons, Ltd.

Guaranteed quality-of-service wireless access to ATM networks

We study the problem of wireless access to asynchronous transfer modes (ATMs). We consider three classes of ATM sources: constant bit rate (CBR), variable bit rate (VBR), and available bit rate (ABR). We propose a polling scheme with nonpreemptive priority. Under such a scheme, we derive sufficient conditions such that all the CBR sources satisfy their jitter constraints and all the VBR sources satisfy their delay constraints. The remaining bandwidth is used by the ABR sources, for which we adapt a random access scheme proposed by Chen and Lee (1994). For this random access scheme, we derive the throughput-offer load characteristic, and thus the capacity. Based on this, we propose adaptive random access schemes that track the offer load to its optimal value. Our simulations show that our adaptive schemes maintain a high throughput with respect to the whole range of system load.

Long-range dependence in variable-bit-rate video traffic

We analyze 20 large sets of actual variable-bit-rate (VBR) video data, generated by a variety of different codecs and representing a wide range of different scenes. Performing extensive statistical and graphical tests, our main conclusion is that long-range dependence is an inherent feature of VBR video traffic, i.e., a feature that is independent of scene (e.g., video phone, video conference, motion picture video) and codec. In particular, we show that the long-range dependence property allows us to clearly distinguish between our measured data and traffic generated by VBR source models currently used in the literature. These findings give rise to novel and challenging problems in traffic engineering for high-speed networks and open up new areas of research in queueing and performance analysis involving long-range dependent traffic models. A small number of analytic queueing results already exist, and we discuss their implications for network design and network control strategies in the presence of long-range dependent traffic. >

A new approach for allocating buffers and bandwidth to heterogeneous, regulated traffic in an ATM node

A new approach to determining the admissibility of variable bit rate (VBR) traffic in buffered digital networks is developed. In this approach all traffic presented to the network is assumed to have been subjected to leaky-bucket regulation, and extremal, periodic, on-off regulated traffic is considered; the analysis is based on fluid models. Each regulated traffic stream is allocated bandwidth and buffer resources which are independent of other traffic. Bandwidth and buffer allocations are traded off in a manner optimal for an adversarial situation involving minimal knowledge of other traffic. This leads to a single-resource statistical-multiplexing problem which is solved using techniques previously used for unbuffered traffic. VBR traffic is found to be divisible into two classes, one for which statistical multiplexing is effective and one for which statistical multiplexing is ineffective in the sense that accepting small losses provides no advantage over lossless performance. The boundary of the set of admissible traffic sources is examined, and is found to be sufficiently linear that an effective bandwidth can be meaningfully assigned to each VBR source, so long as only statistically-multiplexable sources are considered, or only nonstatistically-multiplexable sources are considered. If these two types of sources are intermixed, then nonlinear interactions occur and fewer sources can be admitted than a linear theory would predict. A qualitative characterization of the nonlinearities is presented. The complete analysis involves conservative approximations; however, admission decisions based on this work are expected to be less overly conservative than decisions based on alternative approaches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

FEC and priority for VBR video distribution over ATM

Video services promise to become a major traffic component of future B-ISDN networks. Proliferation of video services, particularly for home-entertainment purposes, may involve the use of variable-bit-rate (VBR) video compression. Asynchronous transfer mode (ATM) technology will be the means of handling the switching and multiplexing problems that will arise, but it involves the risk of cell losses due to buffer overflow. This paper assumes the use of a VBR source encoding scheme which achieves a modest level of compression, so as to make a low-cost home decoder feasible, and generates data with two data level values with respect to the reconstruction process. The use of forward error correcting (FEC) codes has been proposed previously to reconstruct lost cells containing high-value video data. The paper focuses on the final ATM link to the home and compares the efficiency of FEC with simple priority treatment of high-value cells with respect to cell-discard in the ATM multiplexer. It is shown that priority is preferable to FEC with regard to quality, traffic handling capacity and simplicity, but requires longer buffers for the same rate of cell loss. Such buffers would increase the end-to-end delay of the video signals, presenting a potential problem for teleconference video applications, but the characteristic is not likely to be a problem for distribution applications.

Service integration issues on an ATM DQDB MAN

Metropolitan Area Network (MAN) technology has now reached a degree of maturity as far as the transport of connectionless services is concerned. In the near future, attention will therefore focus on the transport of connection-oriented services using the asynchronous technique, with a view towards the total integration of such networks with Broadband Integrated Services Digital Networks (B-ISDN). In such a context, this paper investigates the main problems associated with the use of a Distributed Queue Dual Bus (DQDB) MAN for the integrated transport of voice, video and data services, using only the asynchronous access mode. A network architecture containing functional blocks which perform adaptation functions for connection-oriented services is proposed, and results obtained by simulation of the Queued Arbitrated access protocol when the offered load derives from both constant and variable bit-rate sources are presented

Modeling and queueing analysis of variable-bit-rate coded video sources in ATM networks

Traffic models and queueing performance of variable-bit-rate (VBR) video sources in an asynchronous transfer mode (ATM) network are studied. A discrete-time discrete-state Markov chain is used to model the aggregate video traffic with each VBR-coded source being modeled by a renewal process, which has been successfully applied in the analysis of packet voice traffic. Three different methods including the stationary-interval (SI) method, the asymptotic method (ASM), and the hybrid method for queueing network analyzer (QNA) are used to approximate the average queue size. Results for different traffic conditions and different number of VBR sources are compared with the simulation results. It can be observed that as the number of sources increases the aggregate traffic becomes more predictable and the congestion at the common queue becomes smaller. This result verifies the fact that multiplexing a large number of identical video sources on a single high speed link statistically yields significant bandwidth saving. It is also interesting to note that the SI method provides an upper bound and the ASM method yields a lower bound for the average queue size for the type of traffic used in the study. When the number of VBR sources increases, the result deviates from the SI method and approaches the ASM method. In general, the QNA method provides a close match to the simulation result.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance evaluation of statistical multiplexing schemes in ATM networks

This paper presents a method of modelling and analysing asynchronous traffic mode (ATM) networks, i.e. we study the performance characteristics of different ATM systems where the input is an aggregate cell arrival stream resulting from the superposition of different ATM traffic sources with different traffic characteristics. ATM traffic sources may range from constant bit rate sources (CBR) to variable bit rate sources (VBR). Flexible statistical multiplexing schemes must be adopted in order for the ATM networks to handle the traffic sources more efficiently, and to increase the bandwidth utilization as much as possible. In particular, we investigate two ATM traffic modelling approaches: the on-off model, and the Markov Modulated Poisson Process (MMPP) model. The performance analysis gives as output analytical formulas for the cell waiting time distribution and the cell loss probability in an ATM multiplexer queue. The multiplexer queue may represent a single ATM switching node in which the aggregate cell arrival stream arrives.