Transmit distances can play a major part in 10 GbE deployment decisions and budgets. This graphic from HP shows the relationship between distance and cost. The relationship is not linear, meaning that CX4+ OMC will deliver about 20X the distance of regular CX4 but only at 2X the price. Twisted pair cabling such as CAT6A will carry 10 GbE up to 100 meters (330 feet), but this may not be long enough even for one data center, never mind WAN connections. At the extreme end, 10GBASE-ER (for “extended reach”) will transmit reliably up to 40 km, or nearly 25 miles.