The Identifier and Sequence Number can be used by the client to match the reply with the request that caused the reply.
The data received (a timestamp) in the Timestamp is returned in the reply together with two additional timestamps. The timestamp is a 32 bits in length and is then number of milliseconds since Midnight UT .
The Originate Timestamp is the time the sender last touched the message before sending it, the Receive Timestamp is the time the echoer first touched it on receipt, and the Transmit Timestamp is the time the echoer last touched the message on sending it.
If the time is not available in milliseconds or cannot be provided with respect to midnight UT then any time can be inserted in a timestamp provided the high order bit of the timestamp is also set to indicate this non-standard value.
