f natural and man-made disasters are critical. For these reasons, co-location facilities are located in secure buildings with few windows and no company logos to identify them. They are also monitored by security cameras and heavily guarded by security firms. Carriers rent space in co-location facilities because no provider has outside cabling everywhere. In addition, certain providers have no cabling facilities. Instead, they own switches, which they connect to other carriers' networks. In both of these circumstances, rather than construct their own buildings to house their switches, car- riers lease space in carrier hotels. They place their equipment in cages or lease space in equipment cabinets in the carrier hotel. Locked wire cages surround the equipment and access to the equipment is available only to employees of the company that owns the equipment. For even more reliability, some providers place redundant equipment at more than one co-location site. Leasing space in carrier hotels saves network providers the expense of establishing and maintaining the following: Physical security against break-ins Access to large amounts of power Access to backup power Backup generators Dual air conditioning systems Uninterrupted power supplies Fire detection and fire suppression equipment Alarms to fire and police departments Staff members to plan and maintain the facilities Construction of earthquake-resistant facilities Carriers such as Level 3, AT&T, and Verizon have carrier-owned co-location facilities. These are generally in the same building as the carrier's Point of Presence (POP). Carriers offer a bundle of services at these facilities, including connections to routes connected to the co-location facility and connections to the carrier's POP, which is often located in the same building as the co-location services. AT&T and Verizon buy services from each other's co-location sites to reach customers whose locations are outside of areas in which they own access networks. Summary Another type of co-location facility 