Today's applications generate bursty traffic in packet networks, causing unavoidable congestions, delays and losses. Thus, for applications such as real-time multimedia it is desirable for information to be compressed and prioritized so that the application can degrade gracefully under adverse network conditions.
PET focuses on fault tolerant transmission of prioritized data over packet switched networks.
The idea is that the prioritized message is encoded into packets in a such way that any destination can recover the message in priority order based solely on the number of packets received and processed.