Hi all: I have performed an Operations Directorate review of draft-ietf-payload-rtp-ancillary-06 "This memo describes an RTP Payload format for SMPTE Ancillary data, as defined by SMPTE ST 291-1. SMPTE Ancillary data is generally used along with professional video formats to carry a range of ancillary data types, including time code, Closed Captioning, and the Active Format Description (AFD)." This draft is a protocol specification for a particular (but very general) kind of payload carried in an RTP stream. It is clearly written and easy to follow, but it does assume that the reader understands - more or less - how video is encoded in a video stream. In section 2.1, the phrase 'start of active video (SAV)' is used to define SAV. A little more explanation of SAV would help readers who are unfamiliar with video encoding. The Data_Count field is clearly explained, but I'm left puzzled. If bit 8 is an even-parity bit for bits 7-0, and bit 9 is the Logical NOT of bit8, why do you need to have two parity bits? Still in section 2.1, the second-to-last paragraph is an 'Operations' comment about suitable values for "the amount of time between when an ANC data packet becomes available to a sender and the emission of an RTP payload containing that ANC data packet." Is that a parameter that needs to be set somewhere, or just a helpful implementation comment? I suspect it's the latter of those. There's another 'Operations' comment in section 3.1, Media Type Definition, under Interoperability. It points out that - essentially - all equipment a single Operator uses to carry video stream should implement the same set of smpte291 features. Section 3.2 is 'Mapping to SDP'; I presume that's the Session Description Protocol, RFC 4566? If so, it wrongly refers to RFC 4855, which describes something other than SDP. That needs to be corrected. Last, a tiny typo in sectoion 3.3: 'may with to receive' should be 'may wish to receive' Overall this is a straightforward document, I believe it's ready to publish, apart from changes in response to my comments above. Cheers, Nevil -- --------------------------------------------------------------------- Nevil Brownlee Computer Science Department Phone: +64 9 373 7599 x88941 The University of Auckland FAX: +64 9 373 7453 Private Bag 92019, Auckland 1142, New Zealand