
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20 25 3
0
throughput improvement (Mb/s)
speed (unit/s)
UCAN TTL=3
SCP TTL=3
UCAN TTL=4
SCP TTL=4
UCAN TTL=5
SCP TTL=5
Figure 5: Throughput measurements for SCP and UCAN
when 200 hosts move at maximum speeds ranging between
1 and 30units/s.
than UCAN. The reason is that UCAN will forward a
request to a TTL range, while SCP stops if the down-
link rate falls below a threshold. This way, nodes at
the fringes of the coverage area are not contacted.
6.2 Throughput
This section describes the throughput improvement
measurements for SCP and UCAN. The experiments
were run in the following way. For each of the maxi-
mum speeds of 2, 5, 10, 15, 20, 25 and 30 units/s, 10
random initial network configurations with 200 hosts
were chosen. The experiment was performed for 400
seconds for each such configuration. During the ex-
periment, each host moved continuously according
to the random waypoint model. We have addressed
the problem of the random waypoint mobility model
identified in (Yoon et al., 2003) by choosing the speed
of each device to be uniformly distributed in the inter-
val [1, MS − 1], where MS is the maximum speed, and
by discarding the first 200 movements for each exper-
iment, so that the initial configurations do not bias the
results. We have performed the experiment for TTL
values of 3, 4, and 5.
Figure 5 shows the results of the experiments. For
the same TTL, the curves of SCP and UCAN are al-
most identical, with UCAN having only a nominal
advantage, negated by a higher network load. The
improvement was measured against the throughput of
the link to the base station.
7 CONCLUSIONS
We have presented a routing and crediting protocol
that establishes a cooperative environment for hybrid
networks. SCP is secure against attacks to the cred-
iting scheme. This was achieved by using a special
crediting function that does not reward longer paths.
The advantage of our approach is that it minimizes the
number of expensive cryptographic operations needed
and relies on the users being rational. We showed ex-
perimentally that the elevated security of SCP does
not come at the expense of the network load or the
efficiency of the routes.
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