Complex sentence: The source system sets "Identification" in each datagram to a unique value for all datagrams using the same source IP address, destination IP address, and "Protocol" values for the lifetime of the datagram on the internet.
Split into simpler sentences: The source system sets "Identification" in each datagram to a unique value. For all datagrams using the same source IP address, destination IP address, and "Protocol" values for the lifetime of the datagram on the internet.