Simulation analysis of a communication link with statistically multiplexed bursty noise sources

Adaptive time scale modification of speech for graceful degrading voice quality in congested networks for VoIP applications

By rotating the half-wave plate, the variable communication bit rate between 5.12Gbps and 2.56Gbps has been verified at satellite-to-ground optical communication linkage, the communication link used Differential Phase Shift Keying(DPSK) modulation format and the wavelength is 1549.731nm. Without error correcting code and adaptive optics, an average bit error rate of 1.9E-9 was achieved while the link distance exceeded 1500km.

Evaluation of ABR traffic management under various system time scales

Since they are 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 rates of the ABR applications should be modulated by the amount of remaining resources. That is, the ABR rates should be controlled through a feedback based rate control mechanism. 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. 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 known, 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 when evaluating the effectiveness of an adaptive feedback based rate control mechanism.

The overall aim of the paper is concerned with transmission of a digital video signal over an asynchronous transfer mode (ATM) network, using a self-organizing fuzzy (SOF) controller. In ATM a traffic-shaping buffer is used to prevent excessive back-to-back cells being generated during the peak transmissions of Moving Picture Expert Group (MPEG) variable bit rate (VBR) data sources. The VBR data sources are unpredictable and have substantial variations in bit rate, which could result in data loss and therefore image quality degradation. In this research, a self-organizing fuzzy controller is applied to digital video to eliminate excessive delay or loss at the user network interface. A self-organizing fuzzy controller adjusts the traffic-shaping buffer output rate frame by frame to enable the VBR encoded video to conform to the leaky bucket's contract. A rule-based fuzzy (RBF) controller regulates the average arrival rate to the traffic-shaping buffer to prevent either overflow or starvation of the buffer on a group of picture (GOP) by GOP basis. The computer simulation results demonstrate that the use of a SOF controller reduces excessive delay and data loss at the user network interface as compared with a conventional policing mechanism in ATM.

The paper presents an implementation of a perceptually transparent variable bit rate (VBR) audio coder that complies with the MPEG-4 advanced audio coding (AAC) standard. The coder is based on the MPEG-4 reference software source code of CBR coder. With small modifications in the reference source code a coder guaranteeing perceptual transparency is achieved at compression ratios considerably better than that of the reference CBR coder. Comparison tests indicate that files generated by the perceptually transparent VBR coder applied to a standard set of test items are considerably smaller (in average 24%) than the smallest CBR files of the same quality.

In the paper we present the Adaptive Resource Allocation and Management (ARAM) algorithms developed to manage a Direct Broadcast Satellite (DBS) system supporting heterogeneous traffic mixes and operating under dynamic channel conditions. This traffic mix includes both: (i) data traffic that operates as an available bit rate flow and, (ii) video traffic that generates a variable bit rate flow. Both types of traffic use the Internet Protocol (IP) so they can be efficiently multiplexed on the same link. The dynamic channel conditions reflect time variation error rates due to external effects such as rain or jamming. ARAM attempts to maximize the utilization of the available capacity on the forward DBS link while maintaining Quality of Service (QoS) in the presence of congestion int he network and channel degradation effects. To achieve these ends, it utilizes adaptive control of video compression rates, data transmission rates, and channel forward error correction rates. One of the major features of ARAM is the admission control algorithm used to determine the number of variable bit rate flows admitted for service. In order to maximize the resource utilization, assignment of the variable bit rate services based on their peak rate is avoided. Instead, a flexible utilization of the bandwidth requiring the estimation of statistical multiplexing gain is used enabling more services to share the DBS link. Therefore in this paper, we focus on the ARAM admission control algorithm and assess its impact on QoS and DBS link utilization.

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.

The speech signal consists of a time-varying ensemble of different types of segments with distinct characteristics, which require different degrees of coding resolution in order to retain an overall high voice quality. A fixed-rate coder can capture such time-varying characteristics only if it operates at a high enough bit rate. At a low bit rate, a fixed-rate coder will not be able to capture all of these various segments well and will fail to render high voice quality. A multimode variable bit rate (VBR) coder uses an arsenal of modes, operating at different bit rates. These modes are designed to represent these different speech segments optimally with the right amount of coding resolution. Thus, a multimode VBR codec adapts the coding mechanism to the input speech and delivers high quality at low (average) rates. This paper presents the essential framework and the unique advantages of a multimode VBR codec and suggests algorithms for the different modes.

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

One of the great challenges for circuit switching systems to be the candidate of the broadband ISDN (integrated services digital networks) would be the supporting of variable bit rate services. Peak bit rate allocation wastes a lot of bandwidth in the case where the traffic is bursty. This paper proposes a novel approach, namely the dynamic time-slot allocation (DTSA), which provides a way of statistical multiplexing between the variable bit rate sources. The support of DTSA regarding the call admission control and switching is also described. A traffic model for characterizing the behavior of variable bit rate sources is proposed. A performance evaluation is given in terms of the segment loss rate and the statistical multiplexing gain through an analysis based on the proposed traffic model. Unlike the ATM (asynchronous transfer mode), the scheme presented might provide a smooth transition from narrowband ISDN to broadband ISDN.

It is important to establish the technology to accommodate best-effort TCP/IP traffic over wide area ATM networks. The UBR (unspecified bit rate) service category is the most typical service category for the best-effort traffic, especially in the LAN environment. On the other hand, the VBR (variable bit rate) service category with SCD (selective cell discard) option is considered as the service category which is appropriate for wide area networks due to its fairness and minimum guarantee of the cell transmission using not only PCR (peak cell rate) but SCR (sustainable cell rate) and MBS (maximum burst size). However, there is no actual evaluation for such service. We have, therefore, performed the experimental studies on TCP/IP over VBR with SCD service along with UBR and VBR without SCD cases. Through these experiments, we measured the link utilization of the effective data and the fairness between each obtained TCP/IP throughput during congestion of the ATM switch. From the results of the link utilization, the value is always over 90% under the various conditions. Therefore, even in the case of cell losses due to SCD or buffer overflow in ATM switch congestion, the average throughput is almost the same as the value which equals the trunk line speed divided by the number of the accommodated TCP/IP connections. From the results of the fairness, VBR with SCD has almost the same characteristics as UBR and obtains better TCP/IP throughput than VBR without SCD. Finally, we discuss the effectiveness of VBR with SCD and the other service categories, such as UBR and ABR (available bit rate), and conclude that VBR with SCD is one of the most suitable ATM service categories for wide area ATM networks.

The aim of this paper is to present a new shaped Variable Bit Rate (VBR) for video transmission, which plays a crucial role in delivering video traffic over the Internet. This new shaped algorithm, referred to as Slight Delay Shaped Variable Bit Rate (SD-SVBR). It is designed based on the Shaped VBR (SVBR) algorithm that is devised for real-time video application. This algorithm has been utilized by many researchers in many network conditions. However, SVBR inherits several limitations and weaknesses due to its embedded estimation or prediction processes. SVBR suffers from several problems, such as the occurrence of unwanted sharp decrease in video rate, bucket overflow, the existence of a low video rate, and the generation of a cyclical negative fluctuation. The new algorithm is capable of producing a high video rate and at the same time a better Quantization Parameter (QP) stability video sequence. Besides that, the video rate is shaped efficiently to prevent unwanted sharp increment or decrement, and to avoid bucket overflow. The experiments showed that SD-SVBR gains an impressive result. In almost all cases, it gains high video rate without bucket overflow, utilizes the bucket well, and interestingly, it is still able to obtain smoother QP fluctuation.

The currently specified variable bit-rate (VBR) service class for real-time traffic on broad-band networks severely sacrifices network utilization to provide QoS support for multimedia traffic. A new service class, called VBR+, has been proposed to balance the goals of providing acceptable QoS and achieving high network utilization. VBR+ is a flexible service class that extends the traditional VBR service with bandwidth renegotiation. Bandwidth renegotiation is well suited for the dynamic traffic profiles of multimedia applications. Renegotiation allows a more efficient network capacity allocation and potentially allows the network to operate at more aggressive statistical multiplexing regimes while maintaining acceptable QoS. Some quality degradation is caused by source rate control when the network is congested and renegotiation requests cannot be fully satisfied. This paper quantifies the trade-off between video quality and network utilization for VBR+ transport. The multiplexing performance of VBR+ traffic is obtained via simulation using MPEG-2 video traces obtained using NEC's VisuaLink codec. Results shows that VBR+ transport can maintain acceptable video quality at 70 - 80% link utilization. This represents a 20 - 30% improvement on utilization over the currently specified VBR service for comparable video quality.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We consider the multiplexing of several variable bit rate (VBR) connections over one variable bit rate connection where the multiplexing uses a multiplexing buffer of size B. The VBR trunk is itself a connection and has a multidimensional connection descriptor, reflecting peak and sustainable rates. Given a cost function for the VBR trunk and a connection admission control (CAC) method for the input connections, we focus on the problem of finding the VBR trunk connection descriptor that minimizes the cost function and is able to accept set given set of VBR input connections. First, we show that, under reasonable assumptions on the cost function, the optimization problem can be reduced to a simpler one. Then we consider the homogeneous, loss-free case, for which we give an explicit CAC method. In this case, we find that, for all reasonable cost functions, the optimal VBR trunk is either of the CBR type, or is truly VBR, with a burst duration equal to the burst duration of the input connections. We show that the optimal peak cell rate is fixed for a given B (thus for a CBR trunk), and a VBR choice can only be an improvement. Lastly, we take as an example of the cost function the equivalent capacity of the VBR trunk. These results are expected to form the basis for a general method for a connection manager at a multiplexing node in an integrated services packet network.