This attribute specifies the throughput importance of the packets when
forwarded over VNS connections. In times of congestion the discard
priority of a packet is used to determine whether the packet should be
discarded to reduce the heavy traffic load. Packets with lower discard
priority (numerically higher vdp) are more likely to be discarded than
packets with higher discard priority (numerically lower vdp). Discard
priority one (vdp 1) should be used for the most important traffic,
whereas discard priority three (vdp 3) should be used for the least
important traffic.