The fragment offset field within the RTP/JPEG header, according to [RFC 2435], should be used as if no header extension would be present. Additionally, if a packet does not contain an entropy-encoded scan data segment, but contains a header extension the fragment offset field shall not be zero if any packets containing an entropy-encoded scan data section for the same frame have been transmitted. If the initial packet of a frame contains no header extension, according to this standard, its fragment offset field shall be zero, otherwise it should be zero