This number uniquely identifies the interconnect mailbag to the interconnect entity sender; It is assigned by the interconnect entity sender; Together with the sender ID, it uniquely identifies the interconnect mailbag to the interconnect entity receiver; It is suggested that the interconnect entity sender and the interconnect entity receiver be able to maintain an audit trail of interconnect mailbags using this number; Each interconnect mailbag that is created by the sender should contain a unique control number; Interconnect mailbags that require retransmission should not have their control number changed