The enclosed ABNF syntax defines the structure of SIP messages, primarily based on the representation provided at: https://www.tech-invite.com/y-sip/tinv-rfc-SIP-abnf.html as of March 2025.
It incorporates the syntax from RFC 3261 https://datatracker.ietf.org/doc/html/rfc3261 and other related RFCs, ensuring all referenced rules are fully resolved for a complete and self-contained definition.
The definition is suitable for actually checking SIP message syntax with an appropriate tool, e.g., https://github.com/xsnpdngv/synx