commit 3278f0fb3cb3b945f1358cf7fa4b236b860f9752
author Pau Espin Pedrol <pespin@sysmocom.de> Mon Jun 13 13:00:53 2022 +0200
committer Pau Espin Pedrol <pespin@sysmocom.de> Mon Jun 13 13:51:55 2022 +0200
tree 946a897c5b0f7f3baf6dc58406107ec22e0dd4b8
parent f62e01a0778e472dfd3c8981e72592bb225f1119

iuup: Fix Handling of subsequent Initialization msgs

Once the IuUP FSM moved away from Init state, it stopped handling
Initialization messages received from peers and simply ignored them
starting from that point. As a result, if the first IuUP Init ACK it
sent to the peer was lost, the peer would keep retrying with more IuUP
Init and getting no answer.
In any case, it seems possible and desirable that a peer may send an
IuUP Init at a later point, as pointed out vaguely in 3GPP TS 25.415.

sec 6.5.2.1:
"""
Upon reception of a frame indicating that an Initialisation procedure is
active in the peer Iu UP entity, the Iu UP protocol layer forwards the whole
protocol information contained in the INITIALISATION control frame to the
upper layers. It also stores the RAB sub-Flow Combination set (and thus
replaces a possible previous set) in order to control during the transfer of
user data, that the Iu UP payload is correctly formatted (e.g. RFCI matches
the expected Iu UP frame payload total length). The peer Iu UP entity
receiving the INITIALISATION control frame shall choose a version that it
supports among the proposed versions indicated by the sender for which it
has enough initialisation information.
"""

sec B.2.2 "Initialisation State":
"""
After sending a positive acknowledgement of the last INITIALISATION control
frame, the Iu UP instance enters SMpSDU data transfer ready state. Note that
CN does not know if the initialisation ACK was correctly received by the RNC
(and Initialisation procedure successfully completed) until it receives RAB
assignment response, or use data from the RNC. The CN must therefore be able
to continue receiving INITIALISATION control frames by re-entering the
Initialisation state (from Support Mode Data Transfer Ready State), if the CN
has started to send user data before receiving the indication that
Initialisation was successfully completed
"""

sec B.2.3 "Support Mode Data Transfer Ready State":
"""
In case of handover or relocation, Initialisation procedures may have to be
performed and Iu UP instance may have to enter the initialisation state.
"""

Related: SYS#5995
Change-Id: I5cb740702805693cc7f0a550e2e093f9bfdd507c