DIFFERENTIAL PRIORITY-BASED ADAPTIVE RATE SERVICE DISCIPLINE FOR QOS GUARANTEE OF VIDEO STREAM

This paper deals with the issue of providing performance guarantee suc h as throughput, delay, and jitter for real-time multimedia applicatio ns in packet switched networks. Generally, video demands very high ban dwidth in such applications [1,2]. To achieve greater efficiency in vi deo transmission, we propose a scheme based on the semantics of the vi deo represented as a MPEG stream. All existing service disciplines suc h as Delay Earliest-Due-Date, Virtual Clock, Stop-and-Go, etc., are ge neric in their approach and do not differentiate among picture types o f a video stream. These disciplines assume that the packets of a strea m are independent and assign priority for all packets on an equal basi s to provide performance guarantee. The packets exceeding the specific ation, are marked as low priority and receive best effort service only . Low priority packets get dropped if insufficient resources are avail able, leading to the los of vital information in a video stream such a s I picture on which the other information (P or B picture) depend. In this paper, we introduce a concept called, Differential Priority, whi ch exploits the interdependency among pictures by assigning different priorities to different picture types, to minimize the loss of vital i nformation. The simulation studies confirm that the loss is less in ou r approach compared to the existing (single priority) approach. Furthe r, the existing service disciplines provide performance guarantee on a per packet basis. But it is the set of packets such as a slice, in a video stream, will be more meaningful compared to a single packet duri ng reconstruction of image at the destination. Based on this semantics , we propose yet another concept known as Slot, which is typically the transmission time of one slice of a video stream. The delay guarantee known as Slotted Deadline Guarantee (SDLG), is associated with it to provide guarantee to a set of packets in a slot rather than a single p acket. The advantages of SDLG are: (a) reduced work load for the sched uler in updating the priority data-structure and (b) better statistica l performance guarantee due to flexibility of deadline of packets with in a slot. These two results are established through analysis and simu lation. These motivated us to propose a semantics-based approach to pr ovide performance guarantee. The adaptive rate service discipline prop osed in this paper, exploits the semantics of the video stream, viz., the differential priority and the slot, to provide slotted deadline gu arantee. (C) 1997 Elsevier Science B.V.