Yeah, I looked at C.2 and thought ‘OK, there’s no acknowledgement’ but then C.2 might refer to a DL TBF establishment as a result of an Immediate Assignment, rather than during an existing uplink TBF.
I saw a message flow in an Agilent document earlier today that showed PCA in response to a Packet D/L Assignment, so my plan just now is to focus on the message format, even though I’m sure I’ve tried everything to get it to work so far.