Over land, under sea, and through the air, a fierce battle continues to rage to shave each extra millisecond off trading speeds.

This fight was first centred on custom-built fibre-optic cables, which could quickly relay trading messages from firms' servers to exchange data centres. Next, came microwaves. Now, a variant on microwave technology known as millimetre-wave transmissions is in use, and point-to-point laser links are also under development.