This is the message sequence:
1. MS sends channel request (one-phase data) on RACH
2. Network sends Immediate Assignment on AGCH, Uplink PDCH
3. MS sends sequence of RLC/MAC data blocks on assigned PDTCH
4. Network sends PUA on PACCH
5. MS sends PCA to ack the PUA
This is fine so far. Then:
6. Network sends PDA on PACCH.
This is where there is confusion. If the network sends one or two PDAs then there is no PCA back. If it sends three PDAs then it gets three PCAs back.
Some key parameters are:
Uplink assignment is dynamic.
USF granularity is 4 blocks.
USF is 0.
The timeslot is dedicated to this MS, so all bursts have USF 0 on them.
RRBP is 1, though changing this doesn’t seem to change anything.
All control acks are by normal burst rather than access burst.
Everything behaves as expected, except for the need for three PDAs before I get a PCA. I can’t find any reason for that in the specs, and if anyone has any clue why the phone behaves this way then I’d be interested to find out.