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UNDERGROUND COMMUNICATIONS Improve Underground Safety with Higher Network Intelligence A new system supports underground safety requirements more cost-efficiently by using a mineÕs operational network infrastructure to manage critical safety functions By Christoph Müller, Dipl. Ing Underground mining accidents and resulting legislation have shown the importance of communication systems installed in underground mines. Traditionally, underground communication means telephone and analog communication systems like intercom radios or audio frequency-based analog intercom systems. All these systems have strong disadvantages in terms of coverage distance and transmission quality. Often, multiple different systems are installed in parallel. For quality and cost reasons, the use of Ethernet has become more and more popular in underground infrastructures. Underground communication has mainly involved data networking and voice communication (Voice over Internet Protocol, or VoIP) leading to the use of Ethernet as a universal "all-over-IP"-based communication system. Wireless LAN (WLAN) systems are being used for wireless voice and data communication using Pocket PCs or handheld VoIP phones as hardware devices. The use of personal mobile devices—and thus the people carrying them—offers the means for workers carrying these devices to be tracked automatically throughout the mine via the nearest access point. WLAN tags also may be used to track workers not equipped with these mobile devices. Raising Network Resilience Safety regulations demand that mine communications systems and devices be available at all times. However, as shown in Figure 1, the 'resilience' of different communication systems is limited, especially in terms of their cabling: • A phone system uses star-structured, point-to-point cabling of each individual phone to the PBX. If something cuts a trunk line, all phones in the area of this trunk line are out of service. • Intercom loudspeaker systems and many leaky feeder systems use line-based structures in which all communication devices are connected along a single cable. If the cable is cut, all devices from the cut point to the end of the line are out of service. Thus, traditional communication systems provide only a limited degree of resilience and availability in an emergency, with a high probability that even a single failure will result in an inability to communicate with workers in certain areas. A network structure using ring topology provides single-failure safety, which means that a single interruption in the network system does not prevent other components from remaining functional. Meshed ring structures are capable of providing multiple redundant transmission paths between two or more participants in the network, providing redundancy in large parts of the communication system. Since ring and mesh structures can be realized with Ethernet networks, this leads to improved applicability of Ethernet communications for safety-related applications over traditional communication technology, provided that the active components (network nodes as switches and access points) are equipped with battery-backup power supplies. Because Ethernet is routinely used in underground operations for voice, video and data traffic, it is already present in many mines and consequently, expanding its functionality to carry mine safety-related information saves substantial cost compared with installing and maintaining separate communication systems— which also may lack resilience. Traditional communication systems either employ central telephone PBX hardware, or with Ethernet, central servers to control network logic; e.g., assigning IP addresses, for example. Telephone PBX hardware and network servers are generally installed in a surface location. One consequence of this is that these systems—and thus probably most modes of communication—may not be available during an underground emergency that results in damage to the cabling to these central systems. An additional disadvantage of today's processing of information acquired underground is the fact that information is available only after having been processed in central computer systems located on the surface. Consequently, this information is not available to the people underground when they need it most: during an emergency when the communication to above ground may be cut. Staying Alive Figure 1ÑCommon network configurations for underground communications system. 44 E&MJ; • MARCH 2013 Due to these limitations, future unified communication systems supporting underground mine safety should offer the following capabilities: • The network must be able to "stay alive" underground even when all connections to the surface are interrupted. • Safety-related information must be processed underground, without need of interaction with central systems and allowing distribution of vital information from, say, gas and other environmental sensors, over the underground network. In this context, standardization of the information exchange becomes important. With the support of the European Union's Research Fund for Coal and Steel, a system has been developed over the past three years by MineTronics that provides this functionality in underground networks. This system is now being introduced in underwww.e-mj.com