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UNDERGROUND COMMUNICATIONS Figure 2ÑA Mining Infrastructure Computer (MIC). ground mines with the safety support functions following in a stepby-step procedure. For broadband network communication in underground mines, a wired backbone is essential. This wired backbone is set up using rugged industrial fiber optic cables because maximum effective length for copper Ethernet cable is limited. In most underground infrastructures today, single mode fiber is a de-facto standard. To achieve redundancy, most underground fiber optic installations today are designed to connect devices in ring structures. A pure ring, however may not be suitable to provide a highly resilient network because a ring cut in two places may leave a large number of network nodes disconnected between the damaged points. One method to overcome this is to use intelligent network nodes that are not only able to provide ring redundancy but also meshed links. These network nodes, called Mining Infrastructure Computers (MIC), also provide location-based operational functions such as tracking of assets or people (See Figure 2). Just as a mine physically consists of a meshed network of underground tunnels, a modern network can follow these structures, with some limitations. And, just as miners use an alternate route when one tunnel is blocked, a network can employ alternate routing when the original route is unavailable. The MIC, as an active underground component, is not just a network switch or access point. Each MIC is a distributed independent network node that is able to communicate with miners even if all network connections are down; in other words, MICs keep an underground network "alive" in an emergency. This is the precondition for distributed processing of potential safety information, which then can be transmitted to workers in the network areas available after an emergency. To supply miners with relevant safety information after lines to the surface are cut, the MIC needs certain static information. Traditionally, all information about locations of emergency exits and emergency equipment (fire fighting equipment, rescue chambers or first aid equipment) is provided by signage on tunnel walls. In the new safety support network, however, this information is downloaded to all underground MICs and can be made available to miners. With this information, MICs can function as a navigation system with two electronic maps available for computation of location based safety information. One map is a static version indicating tunnel layout of the mine (similar to street layout in map software) and the location of safety equipment and exits. The MICs also create a second, dynamic overlay map indicating real time availability of network links. MICs can use this information to provide underground 'navigation' information to miners; for example, an active or usable network link can be interpreted to indicate that the tunnel through which the cable is routed is physically passable. This is extremely important information in a mining emergency. It may help organize evacuation plans as well as speed up search and rescue operations. www.e-mj.com MARCH 2013 • E&MJ; 45