Congestion reduction in transmission of video over ABR networks

In the transmission of bursty traffic such as video and data, a network with a fixed capacity may have some unused bandwidth. The available bit rate (ABR) scheme in ATM networks can make use of this spare channel capacity as a lower priority service. ABR has been developed initially for delay-tolerant services such as data. The authors demonstrate how, with the help of a video transcoder, delay-sensitive services such as video may be transmitted over ABR. The transcoder further compresses the video bit stream according to the rates dictated by the network with minimum degradation to the picture quality. The video quality has been optimised by combining the classical minimum cell rate (MCR) with the subjectively acceptable minimum quality (SAMQ). The performance of two different coding formats for ABR sources, namely the constant bit rate (CBR) and variable bit rate (VBR) video input to the transcoder are compared. The authors also present techniques for further reduction of congestion at the multiplexing switches and report on the impact of the forward and backward link delays on the ABR performance with a video transcoder