S. Selvakumar et Sv. Raghavan, DIFFERENTIAL PRIORITY-BASED ADAPTIVE RATE SERVICE DISCIPLINE FOR QOS GUARANTEE OF VIDEO STREAM, Computer communications, 20(13), 1997, pp. 1160-1174
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.