RFC 3828 / START HERE
UDP-Lite, before the details
UDP-Lite means Lightweight User Datagram Protocol.
It carries datagrams: individual network messages. The payload is the application data after the transport header. An application can choose a checksum-covered prefix and leave a payload tail unchecked. A checksum detects accidental changes; it is not a security signature.
The idea in one picture
Application choice
Covered prefix
Unchecked tail
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
Some error-tolerant audio or video codecs can use partly damaged data better than a lost datagram. RFC3828 defines a separate transport: its entire header and IP-derived pseudo-header always remain checked. Full coverage is the recommended default.
A familiar example
A voice application might protect its important format bytes while tolerating some damaged media bytes. It must explicitly opt in and check what it receives. The benefit requires suitable link behavior; ordinary links can discard damaged packets first.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Choose what must surviveUDP-Lite means Lightweight User Datagram Protocol. An error-tolerant audio or video application may prefer some damaged data to a missing datagram. It explicitly chooses a sensitive prefix and an unchecked tail.→
- Read the header and coverage boundaryEach of four header fields is16 bits. Checksum Coverage replaces UDP’s Length field and counts octets from the first UDP-Lite header octet, including all 8 header octets.→
- Compute the mandatory checksumA pseudo-header is checksum input derived from IP, not extra bytes transmitted inside UDP-Lite. Its length is the full UDP-Lite datagram length even when coverage is partial.→
- Separate coverage from correctnessThe receiver validates the datagram format and checksum before passing the payload to an application willing to receive this coverage. A successful checksum says nothing about bytes outside its coverage.→
- Find the lower-layer gatePartial transport coverage helps only if an error-prone link supports suitable partial error detection. A packet dropped by the link never reaches UDP-Lite.→
- Use a distinct protocol within its limitsIP protocol136 selects UDP-Lite. UDP uses17. Sharing UDP’s port-number space does not make the two transports interchangeable.→
This introduction explains RFC 3828 (2004). Read the original RFC ↗