Each eNodeB in lte network is identified by one unique id i.e. global enodeb Id. Macro enodeb id is 20 bits long and each cell of this eNodeB has is identified by 28 bits long string. Left 20 most significant bits of cell identity is same as 20 bits of enodeb id and remaining 8 bits are used by each cell of enodeb to get unique number. 8 bits can constitute (0-254) unique numbers. Reason being, spec tells one enodeb can support up to 255 cells. By practically, a macro enodeb can have at max 3 cells.
At the radio physical layer, each cell is identified by its PCI values, which ranges value from 0 to 504.