There are two types of PSEs: midspan and endspan. Midspan controllers, also known as power injectors, literally inject power onto existing Ethernet cables and are situated between the LAN switch and the powered device. Data is routed through a midspan PSE without modification. These controllers are especially convenient for PoE installation into existing networks without having to replace the switch. An endspan device, on the other hand, is a switch that has built-in PoE capabilities. Therefore, no midspan is needed. An endspan PSE would be used to build a new network from the ground up. Since midspans only have access to the power layer, they will use the new 2-event classification for PoE+ to communicate high power capabilities. The LLDP uses the data layer, so endspan controllers have the option to negotiate power with the PD using this additional classification method.