VI. RESULTS AND DISCUSSION
We used OMNET++ to conduct our simulation studies. Our
main issues were: (i) making reliable connections and (ii)
evaluating the end-to-end delay in our converged network. We
did a comparative study of both loose and tight coupling. Our
network setups for loose coupling and tight coupling are in
shown in Fig. 3 and Fig. 4, respectively.
In our simulation we utilized a single gateway that separates
the two heterogeneous networks, that is, the WSN and the
LTE-A cellular network. For simplicity, we deployed 10 nodes
in our WSN. We did this since we were mainly concerned
with end-to-end connections. The reliability of the converged
network was limited by the low power, lossy channel of the
WSN. Utilizing IEEE 802.5.4 and 6LoWPAN are among the
best options for this type of network (Low Power Lossy
Network) and were therefore utilized in our simulations. We
were also cognizant of potential bottlenecks at the dual mode
gateway. This however, was an issue of scalability and could
easily be addressed by providing multiple gateways.
Nonetheless, issues of scalability were not the focus of our
research and hence were not addressed in our simulation
studies. The delay at the gateway as a result of buffering and
protocol conversion processing was negligible with respect to
the delay caused by the noisy channel of the WSN. Thus, this
was ignored.
Fig. 6 depicts the end-to-end transmission delay time in
loose coupling and tight coupling. The graphs imply that by
using the proposed tight coupling method the end-to-end delay
time can be decreased significantly from 900 milliseconds at
the maximum to 500 milliseconds, which would be a
significant enhancement for real time networks or systems
with low latency restrictions. Also, this would meet the
requirements for various applications of real-time M2M
networks.