This Link says a that :Use of sequence numbers fixes the duplicate error.
When can duplicate message end up at a receiver?
If a node detects an error, it sends out an error flag and when all the other receiving nodes detect the error, they too send out error flags and destroy the received message. The transmitter then resends the message again.
Im not aware of the possibilities of a duplicate messages being received...
Plz Help as i must decide if sequence number must be used or not in my messages.