The compressor communicates the uncompressed header template via an RSVP Path message. Also included in the message are a set of operands for reconstructing the header from the transmitted compressed header and the stored header template. The compressor sends one or more SHC objects via an RSVP Path message. The template consists of the first n bytes of a packet. All of the fixed fields are set to their appropriate values.
Fields are always delimited on byte boundaries.
Each operand is simply an offset and a length. They serve to delimit the variable fields within the template. Several additional operations are signaled via flags. The concern the updating of TTL, the IP checksum, and the IP length field. The 'L' flag indicates that the IP length field should be inferred from the received packet length.