Ismail Dalgic

Performance evaluation of 10Base-T and 100Base-T Ethernets carrying multimedia traffic

The performance of 10Base-T and 100Base-T Ethernet segments carrying audio/video traffic is presented. End-to-end delay requirements suitable for a wide range of multimedia applications are considered (ranging from 20-500 ms). Given the specific nature of the network considered and the maximum latency requirement, some data is lost. Data loss at the receiver causes quality degradations in the displayed video in the form of discontinuities, referred to as glitches. We define various quantities characterizing the glitches, namely, the total amount of information lost in glitches, their duration, and the rate at which glitches occur. We study these quantities for various network and traffic scenarios, using a computer simulation model driven by real video traffic generated by encoding video sequences. We also determine the maximum number of video streams that can be supported for given maximum delay requirement and glitch rate. We consider various types of video contents (video conferencing, motion pictures, commercials), two encoding schemes (H.261 and MPEG-1), and two encoder control schemes [constant bit rate (CBR) and constant-quality variable bit rate (CQ-VBR)] and compare their results. Furthermore, we consider scenarios with mixtures of video and data traffic (with various degrees of burstiness), and determine the effect of one traffic type over the other.

Constant quality video encoding

Lossy video compression algorithms, such as those used in the H.261 and MPEG standards, result in quality degradation seen in the form of tiling, edge business, and mosquito noise. The number of bits required to encode a scene so as to achieve a given quality objective depends on the scene content; the more complex the scene is, the more bits are required. Therefore, in order to achieve a given video quality at all times, the encoder parameters must be appropriately adjusted according to the scene content. The authors propose a video encoding scheme which maintains the quality of the encoded video at a constant level. This scheme is based on a quantitative video quality measure, and it uses a feedback control mechanism to control the parameters of the encoder. The authors evaluate this scheme by applying it to test sequences, and compare it with constant bit rate and open-loop variable bit rate schemes in terms of quality and rate. They show that their scheme achieves better quality than the other two schemes for a given total number of bits, particularly when the content has scene changes over time.

Evaluation of 10Base-T and 100Base-T Ethernets carrying video, audio and data traffic

Multimedia applications integrate a variety of media, namely, audio, video, images, graphics, text, and data. These media have different bandwidth, delay, and loss requirements. Data traffic is predominantly bursty and it requires reliable service from the network, but it can tolerate delay. In contrast, audio and video traffic is stream-oriented, it can tolerate some loss of data, but it requires delivery within a bounded delay. To support multimedia communications, it is desirable to use existing network infrastructures, which are designed specifically for data applications. In such existing network infrastructures, Ethernet is the most popular LAN scheme used. The authors have simulated 10Base-T and 100Base-T Ethernet segments carrying constant bit rate audio/video streams and data traffic (bursty and non-bursty). Given the stream rate, stream delay and loss constraints, as well as the date load and burst size, they have determined the number of streams supportable.<<ETX>>

Feedback-control scheme for low-latency constant-quality MPEG-2 video encoding

This paper describes a coding control scheme for MPEG-2 which maintains the perceived video quality constant, and is suitable for real-time and low latency encoding. We have chosen a proportional integral derivative (PID) scheme for the controller, and we adopt the same approach in designing the particular PID feedback function. The main reason for using a PID feedback function is the good tradeoff that it offers between computational complexity, ease of design, and performance. We have chosen to use a new video quality metric called moving picture quality metric (MPQM). This metric models the human visual system and matches subjective evaluations correctly, outperforming existing quality metrics for video. Simulations results are shown for typical video sequences. A comparison with CBR encoding also is presented.

On the performance of networks carrying multimedia traffic

The subject matter of this chapter is the performance of networks carrying multimedia traffic. The focus is particularly on audio/video traffic, since they constitute the types of media with the most stringent requirements, especially in terms of bandwidth and delay. The dependence of video traffic characteristics on the video encoding scheme and its control, as well as on the content, is illustrated by giving results for several example cases. The performance of Ethernets and ATM networks carrying video traffic is then addressed. The performance evaluation is undertaken by means of computer simulation, using real video sequences. All the delays in the system, starting with the camera, and ending with the display, are taken into account. Given the specific nature of the network considered and the maximum latency requirement, some data is lost. Loss of data at the receiver causes glitches in the display of video. The effect of data loss is thus measured in terms of the spatial extent, duration, and rate of glitches experienced as a function of the number of video streams, the delay requirement of the video application, and the video rate. Conversely, the performance of a network is measured in terms of the number of video streams that can be supported for a given maximum delay requirement and a given glitch rate, duration, and spatial extent.