Generic 模型消息中TID域是啥意思，官方文档的解释我已经看过了，还是不太明白，求解释
The TID field is a transaction identifier indicating whether the message is a new message or a
retransmission of a previously sent message, as described in Section 3.4.1.2.2.
To retransmit the message, a Generic OnOff Client shall use the same value for the TID field as in the
previously sent message within 6 seconds from sending that message.
