Adaptive Access Regulation for VBR Video Streams

摘要

Streaming of prerecorded video is used by a growing number of applications in the Internet. Therefore, it is likely that in a WLAN (Wirless LAN) hot spot several such VBR (Variable Bit Rate) video streams have to compete for the available resources. Moreover, since usually no Quality of Service reservation is available in a WLAN, the video streams possibly have to face varying bandwidth and losses due to congestion. Instead of applying congestion and error control mechanisms like quality scaling, FEC (Forward Error Correction) or delay-bound retransmissions on an individual basis for each of the streams, in this paper we suggest to regulate the access to the WLAN by a scheduling instance that decides about the actions to be taken in case of congestion. We analyze how this task can be fulfilled by an access scheme based on EDF (Earliest Deadline First) and an algorithm called MAP (Minimum Schedule Assisted Prefetching), which has previously been introduced for the scheduling of video streams. In contrast to EDF, MAP keeps track of the status of the individual streams and allocates bandwidth based on minimum schedules. This allows us to both support network-friendly, controlled retransmissions and allocate resources more efficiently than the EDF scheduler. In our simulation, we demonstrate that based on its admission control function, MAP may reduce the bandwidth required during the transmission, so that in case of congestion, less videos need to reduce their data rate. In addition, we show how this abundant bandwidth may be used to retransmit lost data.