## 7 Discussion  
The sensor network architectures for monitoring underwater pipeline mentioned in this paper provide different advantages for different objectives and requirements. Wired sensor networks usually provide higher communication bandwidth than wireless sensor networks and underwater acoustic wireless sensor networks. While optical networks for wide areas can provide high bandwidths such as 4,476 Mbps for OC-96, 9,953 Mbps for 10-Gigabit Ethernet WAN PHY, 13,271 Mbps for OC-256, and 39,813 Mbps for OC-768/STM-256, wireless communication networks cannot reach these figures [37]. For example, the bandwidth is 0.250 Mbps for Zigbee, 24 Mbps for Bluetooth 3.0, 70 Mbps for WiMax, and 600 Mbps for IEEE 802.11n. This is due to the existence of noise and the  
Figure 15: Simulation results for the integrated wired/RF wireless sensor network. Percentage of successfully transmitted packets. NUM_DRN_PER_DDN = 75.  
high cost of signal collusions. The bandwidths are farther reduced significantly with acoustic communication in underwater networks. Using both high bandwidth interconnection devices and high bandwidth wired links, the network can be used for pipeline monitoring applications that demand high bandwidth such as camera-based monitoring. On the other hand, wireless/acoustic wireless networks provide better reliability for pipeline monitoring applications such as sudden damages detection. These applications are event based applications that do not need high communication bandwidth. Events occur only if there are exceptions discovered by the sensors which they need to communicate. The integrated wired/RF wireless sensor network and integrated wired/acoustic wireless sensor network architectures can provide reasonable bandwidth as well as good reliability for event-based applications even if some parts of the network are damaged. The network architectures mentioned in this paper also have different degrees of reliability. The wired network may fail with a single point failure. On the other end, using wide transmission ranges in RF wireless and underwater acoustic wireless networks can solve the problem of a network failure due to failure of one or more nodes. The reliability degree of the wireless network can be increased as we increase the transmission range. However, this increase of the wireless transmission range causes a significant increase in power consumption. Therefore, the battery will be consumed rapidly and the life of the network will be reduced significantly. In the integrated wired/wireless networks and the integrated wired/acoustic wireless networks, the limitation of power sources is not an issue. Therefore, the node can be designed to use a wide transmission range for communication to provide better reliability. Some network architectures discussed earlier depend on surface buoys. These architectures are RF wireless sensor networks and integrated wired/RF wireless sensor networks. Using buoys connected through wires to an underwater pipeline in very deep sea is not practically feasible since the wires will be vertically expanded for a long distance (from the depth of the pipelines to the surface) which will significantly increase the probability of damages. Considering this important point, using integrated wired/acoustic sensor networks could provide better reliability in deep sea situations. Further to the benefit of increasing the reliability of the network, the availability of wireless nodes that are embedded in the wired networks can be used for other applications. One possible application is using external RF wireless or underwater acoustic wireless sensor nodes to monitor some aspects of the pipeline such as monitoring if there is any movement, sound, or hazards around the area of pipeline. The external nodes can send their information to the NCC through the integrated wired/RF wireless network or the integrated wired/acoustic wireless network. The integrated wired/wireless network represents the backbone for transferring the collected information to and from the NCC.