The sequenceId used in the RealNumber® DNO Live Download API identifies when a message was sent over the interface and is used to track and maintain the order of messages. The format is:
<date>:<millisecond timestamp>:<nanoseconds>
The date portion corresponds to the date when the message was sent over the API. The millisecond portion contains the milliseconds since Unix epoch timestamp of when the message was sent. The nanosecond portion can be considered random and is only used to guarantee order and uniqueness between two similar messages that are potentially created at the same millisecond timestamp. This would be an unusual occurrence but could happen when processing messages from a file for example.
For more information, please view RealNumber Live DNO.