This configures the VCI portion of the ATM cell header for this circuit, again with a valid range that varies by the underlying interface, from as few as 6 bits, 0-63, on a DXI/HSSI port up to 12 bits, 0-4095, on an STM-1/STS-3c interworking card. An admin migrating a circuit from a lower-capacity ATM interface to a higher-capacity trunk needs to recheck this value, since a VCI valid on the old port might now conflict with a different addressing convention on the new one. For example, a VCI of 55 works fine on an ATM UNI DS3/E3 port with a 0-255 range, but the admin must verify no collision exists if that same circuit is later moved onto an STM-1/STS-3c port sharing address space with many more circuits.