Bit-rate characteristics of a VBR MPEG video encoder for ATM networks

A variable-bit-rate (VBR) MPEG video compression encoder is introduced, and the performance of a statistically multiplexed asynchronous transfer mode (ATM) network supporting a number of such VBR video sources is evaluated. Bit-rate characteristics obtained from a detailed simulation are provided for a VBR MPEG encoder for CCIR601 video (operating in the 5-10 Mb/s regime) appropriate for medium-quality multimedia or broadcasting applications. The results presented include bit-rate traces and signal-to-noise-ratio data for typical test sequences, along with summary statistics such as the marginal distribution of frame rate. Data from a study of statistical multiplexing on an ATM network are also given. Simulation results for an ATM statistical multiplexer with N>>1 VBR MPEG sources are presented in terms of key performance measures such as cell loss rate and delay versus throughput. The results confirm that ATM channel efficiencies of approximately 80-90% can be obtained at reasonable cell loss rate and delay levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The arrangement of data in a variable bit rate (VBR) video codec, making it suitable for the transmission over ATM (asynchronous transfer mode) networks, is addressed. Attention is focused on two aspects specifically belonging to the ATM environment: the impairment due to the loss of ATM data cells and the statistical analysis of a real VBR video source. A particular implementation of a hybrid DCT (discrete cosine transform) broadcast video codec, which adheres to the recent specifications proposed by the European Telecommunications Standards Institute, is addressed. In order to optimize the performance with respect to cell losses, a specific solution based on the concept of organizing data into video packets is explored. The statistical characteristics of the available VBR video source are investigated, using a real-time acquisition system. >

A fuzzy approach to MPEG video transmission in ATM networks

Many studies have been conducted involving the transport of constant and variable bit rate MPEG-2 video in asynchronous transfer mode (ATM) networks; however, many of these studies have considered fairly homogeneous scenarios in which the only other traffic present in the ATM network, if any, are other MPEG-2 video sources. In this study the requirements of supporting MPEG-2 video communications in an ATM network under unloaded and heavily loaded network conditions, in which the generated traffic sources are bursty in nature, are considered. To complete the study an experimental video on demand (VoD) testbed, developed as part of a collaborative research effort between the Communications Research Center of Canada (CRC), Nortel and the University of Ottawa, was employed. To determine the characteristics of the MPEG-2 video traffic generated by the VoD application in the ATM network in the presence of other traffic, cell interarrival time measurements and cell rate snapshots at the ATM cell level were considered. Results obtained show that the end-to-end flow control implemented in the application layer in the video-on-demand (VoD) system and the traffic controls implemented intermediate network elements (e.g., routers, switches) have significant impacts on the characteristics of the MPEG-2 traffic carried in the ATM network. Moreover, the impact of the intermediate network elements on the characteristics of the MPEG-2 traffic increases with the amount of non-MPEG-2 video.

Performance evaluation methods that have been used so far failed to capture the real characteristics of network traffic. This is especially true when the service times are general such as the variable bit rate (VBR) video, which is proven to be self-similar. In the paper, diffusion approximation methods are proposed to analyse a dynamic scheduler for self-similar VBR video traffic in asynchronous transfer mode (ATM) networks. The proposed scheme employs a coupled queueing system that has been used extensively in the modelling of computer and communication systems. Diffusion approximations methods are used to decouple a queueing system which represents an ATM network node into separate G/G/1 queues. Real MPEG video traces are used in the discrete event simulation. Results are compared with the approximation, and are found to work very well under different traffic conditions.

The authors compare constant bit rate (CBR) and variable bit rate (VBR) video services in an asynchronous transfer mode (ATM) environment. The simplified network model of CCITT SGXV is used to estimate the statistical multiplexing gain for VBR service. Current NNI (network node interface) capacities, 150 or 600 Mb/s, are determined to be too small to effectively support standard television signals that are VBR coded at average bit rates of 5-10 Mb/s. It is also shown that the leaky bucket technique is superior to the sliding window technique for an average bit rate usage parameter control from the service point of view. If sliding window is used, higher picture quality and shorter delay are not always guaranteed in VBR video services. >

Many recent studies have been conducted involving the transport of constant and variable bit rate MPEG-2 video in Asynchronous Transfer Mode (ATM) networks; however, many of these studies have considered fairly homogeneous scenarios in which the only other traffic present in the ATM network, if any, are other MPEG-2 video sources. In this study the traffic pattern of MPEG-2 video communications in an ATM network under heavily loaded network conditions, in which the generated traffic sources are bursty in nature, is considered. To complete the study an experimental VoD testbed, developed as part of a collaborative research effort between the Communications Research Centre of Canada (CRC), Nortel and the University of Ottawa, was employed. To determine the characteristics of the MPEG-2 video traffic generated by the VoD application in the ATM network in the presence of other traffic, cell interarrivai time measurements were considered. Results obtained show that the end-to-end flow control implemented in the application layer in the VoD system and the traffic controls implemented intermediate network elements (e.g., routers, switches) have significant impacts on the characteristics of the MPEG-2 traffic carried in the ATM network. Moreover, the impact of the intermediate network elements on the characteristics of the MPEG-2 traffic increases with the amount of non-MPEG-2 video traffic present in the network.

For video sources the Moving Picture Experts Group (MPEG) compression scheme has become the defacto standard for video compression since then. However, even with the huge reduction of bits that MPEG compression provides, it does not smooth the video traffic. Indeed the variable bit rate (VBR) MPEG compression algorithm guarantees that the MPEG stream will be bursty. A service, where an asynchronous transfer mode (ATM) client requests and receives from an ATM server VBR MPEG coded video sequences, is considered. An algorithm for streaming VBR MPEG coded video delivery over ATM networks, which dynamically allocates the transmission parameters, is proposed. A scheme for optimal choice of the prediction window's size is also presented. The results obtained show that the proposed dynamic allocation algorithm can provide an efficient solution for VBR MPEG coded video transport with guaranteed quality of service (QoS) over ATM networks.

In recent years, there has been a strong interest in transmitting compressed video over packet switched networks, such as asynchronous transfer mode (ATM). Previous work has dealt with transmitting MPEG over constant bit rate (CBR) and variable bit rate (VBR) services of ATM. The available bit rate (ABR) service of ATM is expected to be much more cost effective than CBR or VBR. However, there hasn't been much work done on running interactive client/server applications (for example, video on demand) over ABR. We have developed a framework to design interactive video systems transmitting MPEG video over the ATM ABR service. We have developed models to determine the network connection parameters required to run interactive client/server multimedia applications over an ATM network using the ABR service. We solve our model using real-time dynamic equilation (RTDE) analysis. We conclude that by proper dimensioning of the buffers at the client and the server, it is possible to run interactive video over the ATM ABR service.

Variable bit-rate (VBR) MPEG video traffic is highly bursty due to group of pictures structure, and shows time-variant statistical characteristics due to scene changes. These characteristics make it more difficult to manage network resources, and leads to the significant reduction in network utilization. We deal with the issues related to efficiently transmitting VBR MPEG video traffic over asynchronous transfer mode networks, while maintaining consistent visual quality and improving network utilization on the basis of real-time applications. First, we propose a joint encoder and channel-rate control scheme that comply with not only negotiated traffic parameters, but also constraints imposed by encoder and decoder buffers. Second, we propose a dynamic bandwidth renegotiation method by combining the above scheme with a traffic smoothing method that can make the peak rate close to the sustainable rate. The efficiencies of the proposed methods are compared with a few other competitive schemes such as transmission methods for unconstrained VBR and the constant bit-rate scheme with average bandwidth equal to that of the proposed methods.

Designing new network adaptation and ATM adaptation layers for interactive multimedia applications

Video traffic is expected to account for a significant share of the traffic volume in future asynchronous transfer mode (ATM) networks. MPEG-2, proposed by the 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 propose 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. The simulation results show that overall cell loss and delay are reduced significantly at the ATM switch node.

Traffic prediction and dynamic bandwidth allocation over ATM: a neural network approach

This paper presents a dynamic bandwidth allocation system for real-time variable bit rate (VBR) video transport in asynchronous Transfer mode (ATM) networks. This system takes advantage of scene changes in the video trace on a scale larger than a second, and it adapts the bandwidth as needed. An improvement on efficiency is achieved by assigning bandwidth for the transport of VBR video and having more than one predictor in parallel with different prediction horizons, hence this scheme reduces the processing time for the bandwidth adaptation with no significant degradations on the queue statistics. The link capacity required for a specific session is a function of the input traffic, which is characterized by its spectral characteristic. In particular, we use the low frequency band of the power spectrum, which is extracted from the stochastic input by a low pass filter. The predictor is a neural network (NN) called ”Pi-Sigma Network”, and the output of this predictor is interpreted according to the prediction horizon in use.

In recent years, there has been a strong interest in transmitting compressed video over packet switched networks, such as asynchronous transfer mode (ATM). Previous work has dealt with transmitting MPEG over constant bit rate (CBR) and variable bit rate (VBR) services of ATM. The available bit rate (ABR) service of ATM is expected to be much more cost effective than CBR or VBR. However, there hasn't been much work done on running interactive client/server applications (for example, video on demand) over ABR. We have developed a framework to design interactive video systems transmitting MPEG video over the ATM ABR service. We have developed models to determine the network connection parameters required to run interactive client/server multimedia applications over an ATM network using the ABR service. We solve our model using real-time dynamic equilation (RTDE) analysis. We conclude that by proper dimensioning of the buffers at the client and the server, it is possible to run interactive video over the ATM ABR service.