Transcript Adaptive_Playout_Scheduling_Using_Time

Adaptive Playout Scheduling Using Timescale Modification in Packet Voice
Communications
Yi J. Liang, Nikolaus Farber, Bernd Girod
Information Systems Laboratory, Department of
Electrical Engineering, Stanford University
ICASSP 2001
Objective
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To improve tradeoff between delay and loss.
Adaptively adjusting the play out schedule of individual
packet according to the varying network condition, even
during voiced period.
Different Playout Scheduling
Notations
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tis : sent time
tir : received time
tip : played out time
L0 = ti+1s - tis : packetization time (constant)
dib = tip – tir : buffering delay
din = tir – tis : network delay
Li = ti+1p - tip : achieved length of audio packet I
dimax : maximum allowable total delay
Timing Relationship for Adaptive Scheduling
Two Issues of Evaluating Different
Scheduling Schemes

Average buffering delay
1
db 
P

i
i
(
d

d
 max n )
iP
where P  {i | t ip  tri }
Late loss rate
 l  (| R |  | P |) / N
R : total packets received
N : total packets sent
Basic Operation of the Playout Process
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To estimate di+1n and ti+1p with din, di-1n, …
To calculating Li by definition and scaling current packet i
if necessary
If dimax is chosen close to din, the buffering delay can be
reduced.
Basic Operation of the Playout Process
(continued)

According to the user-specified loss rate
di+1max is set to the small value satisfying
ˆl 


i 1
d n  d max
d n 0
, ˆl
i
i
h
(
d
)
/
h
 n  (d n )
hi(dn) is the histogram of past delays accumulated at time i
Basic Operation of the Playout Process
(continued)

i 1
The expected buffering delay dˆb is
dˆbi 1 
i 1
d max
i 1
d max
d n 0
d n 0
i 1
i
i
(
d

d
)
h
(
d
)
/
h
 max n n  (dn )
Scaling of Voice Packets
Performance Comparison
Performance Comparison (continued)
Concluion
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The proposed algorithm effectively reduces buffering delay
and loss rate by adapting the playout schedule to the
varying network delay n high dynamic way.
Simulation results based on Internet measurement have
shown significant reductions in average buffering delay
and loss rate produced by the proposed playout scheme.