Even on a dry day, the MTA's 300 pumping rooms remove an estimated 13 million gallons of water from the tunnel network, just to keep the system dry enough to run.

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And traffic between geographically separated company networks can be routed through a virtual private network (VPN) tunnel instead of being exposed to the open Internet.

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This loop also passes through the Sasso San Gottardo, a demilitarised tunnel that is part of a network of clandestine Swiss Army caves and tunnels built into the mountain and used as bunkers during WWII and the Cold War.

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Once it is plugged in to the network behind the router it creates an SSL tunnel back to head quarters.

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Mr Hammond said the Hindead Tunnel was one of the missing links in Britain's trunk road network.

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The only limitations appear to be those inherent in the mobile phone network - losing the signal if you are going through a tunnel, for example.

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