We introduce UDF Lite - a lightweight version of UDP with increased flexibility in the form of a partial checksum. It allows senders to specify packets as partially insensitive to errors. The coverage of the checksum is specified by the sending application on a per-packet basis. Because of its close relationship to UDP, UDP Lite is easily integrated into an existing UDP implementation. UDP is a simple best-effort transport protocol that adds multiplexing and an optional checksum to IP. Unlike TCP, UDP does not provide reliability, in-oflder delivery or congestion control, which has made it especially popular among delay-sensitive real-time applications. Audio/video applications often prefer damaged packets over lost packets. One way for an application to allow delivery of damaged packets is to disable the UDP checksum. This would mean, however, that important application-specific headers might pass unverified. Also, in the next version of IP, Ipv6, the UDP checksum is mandatory since there is no header checksum in Ipv6. These applications could benefit from using UDP Lite instead of UDP. By reflecting the UDP Lite policy with a partial checksum onto the link layer, the gain can be even higher