APRS-IS depends very much on a timestamp created at the time that a record from an iGate is received.
Very few stations transmit a timestamp in the packet header even though accurate time is usually available when the GPS provides valid position data.
So in a network where packets are carried through many digipeaters (a result of the end user supplying an inappropriate PATH), and many of these digipeaters having several iGates listening, there is a need to weed out duplicates.
The mechanism to discard duplicates falls down when the duplicate submission is delayed significantly, and some network infrastructure is notorious for latency.
