Information Technology Reference
In-Depth Information
420
0.002
M-first(M=2)
M-first(M=3)
M-first with spot-checkin
g
(M=2)
M-first with spot-checking(M=3)
Credibility-based voting
(
random)
Credibility-based voting(rr1)
ε
acc
M
-
f
i
r
s
t
(
M
=
2
)
M-first(M=3)
M-first with spot-checking(M=2)
M-first with spot-checking(M=3)
Credibility-based voting(random)
Credibility-based voting(rr1)
400
380
0.0015
360
340
320
0.001
300
280
260
0.0005
240
220
0
200
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
c
c
(a) Error-rate
(b) Computation time
T
Figure 18.
M
-first voting with spot-checking vs. Credibility-based voting for colluding
rate
c
(
acc
=0.001
,
s =0.1
,
f =0.35
,
q =0.1
,
p
d
=0
, random scheduling without
blacklisting).
M
degrades the performance of VC systems. For example, the computation time of
3
-first
voting is around 320, while that of credibility-based voting ranges from 280 to 295.
4500
0.004
M-fir
s
t(M=2)
M-first(M=3)
M-first with spot-checking(M=2)
M-first with spot-checking(M=3)
Credibility-based voting(random)
Credibility-based voting(rr1)
ε
acc
M-first(M=2)
M-first(M=3)
M-first with spot-checking(M=2)
M-first with spot-checking(M=3)
Credibility-based voting(random)
Credibility-based voting(rr1)
4000
0.0035
3500
0.003
3000
0.0025
2500
0.002
2000
0.0015
1500
0.001
1000
0.0005
500
0
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
pd
pd
(a) Error-rate
(b) Computation time
T
Figure 19.
M
-first voting with spot-checking vs. Credibility-based voting for defection
rate
p
d
(
acc
=0.001
,
s =0.1
,
f =0.35
,
q =0.1
,
c =1.0
,
P
up
(steady)=0.8
, random
scheduling with blacklisting)
Defection rate
p
d
Fig.19 and Fig.20 show error rate and computation time of each method
for defection rate
p
d
at
P
up
(steady)=0.8
. This figure shows error rates of all methods stay
constant, while computation times increase with
p
d
. As shown in eq.(16), the computation
time is proportional to
1/(1−p
d
)
. Thus, the actual values of computation times in real VCs
become larger than those in the basic model (
p
d
=0
), since workers in real VCs frequently
