CoreSite owns and/or operates 22 data centers in the U.S. and has about 2.5 million net rentable square feet in operations, mostly in the key markets of Northern Virginia, Los Angeles, and San Francisco. It focuses on retail co-location--leasing smaller spaces to dozens of tenants per data center and resulting in a less concentrated customer base than wholesale data center providers. CoreSite's top 10 customers account for about a third of its annualized rental revenue. Of its 1,200 customers, more than 450 are network service providers, which exchange traffic at CoreSite locations. Interconnection revenue, driven primarily by connections between networks and connections between enterprises and their networks or cloud service providers, comprises just under 15% of total revenue.