Traffic management of multimedia over ATM networks

Abstract

ultimedia consists of voice, video, and data in the same application. When multimedia is transmitted over a network, video traffic consumes most of the bandwidth, and also requires a high level of quality of service (QoS) guarantee from the network. In order to reduce the bandwidth requirement, video is therefore compressed before transmission over the network. Video compression is based on removing the temporal and spatial redundancy of information in a video stream.An MPEG compressed video consists of different types of frames (I, B, and P), of varying bit rates. A number of these frames are grouped together to form a group of pictures (GoP). A GoP begins with an I-frame, followed by B-and Pframes. If a GoP includes n frames with (m -1) B-frames between consecutive P-frames, the GoP is denoted MmNn. Compression greatly reduces the bit rate of the multimedia stream. However, compressed video is highly bursty in nature. The bit rate changes abruptly from frame to frame; the Iframe has the highest bit rate among the three frame types, and the B-frame usually has the smallest rate. The bursty nature of the multimedia stream necessitates managing the traffic efficiently when transmitted over an asynchronous transfer mode (ATM) network. This gives rise to a number of traffic management issues related to transmission of multimedia traffic over ATM.Advantages of ATM networks, such as high trunk speed, low bit error rate, flexible service type (bandwidth on demand), and high multiplexing capacity make it very suitable for transporting multimedia with QoS guarantees. Statistical multiplexing of bursty video sources in an ATM network improves the bandwidth utilization of the network and lowers the service cost. Furthermore, the multiplexing of multimedia streams reduces the burstiness and bandwidth requirement of the aggregate traffic. However, coincidence of the peaks of many video streams may result in congestion in the network and degrade the quality of the video. Congestion control is important to guarantee the quality of multimedia. Moreover, in multiplexed transmission, efficient bandwidth allocation among the multiple multimedia streams will improve network resource utilization. A network can be managed much more efficiently if the traffic entering the network is smooth. For transmitting video, the bursty multimedia stream can be shaped to smooth out the multimedia traffic stream. Flow control is used to regulate the traffic rate between the sender and the receiver (e.g., a client/server type of system) so that a fast/slow transmitter will not result in overflow/underflow at the receiver. Note that the video quality at the receiver is degraded for either overflow or underflow.When multimedia is transmitted over a dynamically variable bandwidth channel, such as the available bit rate (ABR) service of ATM networks, depending on the level of network congestion, the amount of network bandwidth available to the multimedia source varies over time. In case of congestion, the bit rate of the source can be scaled down to h...