Early Packet Discard. A congestion control technique that selectively drops all but the last ATM cell in a Classical IP over ATM packet. When congestion occurs, EPD discards cells at the beginning of an IP packet, leaving the rest intact. The last cell is preserved because it alerts the switch--and the destination station--of the beginning of a new packet. Because IP packets from which cells have been discarded receive n o acknowledgment from the destination, they are automatically retransmitted from the source. Most vendors expect EPD to be used in conjunction with unspecified bit rate (UBR) service. Switches simply junk UBR cells when congestion occurs, without regard for application traffic. By discarding cells selectively, so that whole IP packets are resent, EPD makes UBR a safer option.