Design a Data packet duplicate suppression mechanism on multicast face. ccnd's algorithm is: * Multicast datagram face should delay every outgoing Data packet for a random duration (on the order of 10ms). * During the delay of a packet, if an identical packet is received on the face, cancel the send. but it causes packet reordering and cannot adapt to link condition. This Task is to design a better algorithm for duplicate suppression. Category is currently "Faces", but the design MAY propose to put part of this feature in Forwarding/Tables if necessary.