To allow to send F1 messages to multiple DUs from the CU, we need to
send these messages via different assoc_id (SCTP association ID,
basically akin to a file descriptor). Currently, the assoc_id is stored
in a context at the F1 module and retrieved in
f1ap_itti_send_sctp_data_req().
To facilitate a later change towards indicating (from the RRC) to which
assoc_id (hence, DU) to send a message, we refactor all
CU_send_*()/DU_send_*() functions to take the assoc_id as a parameter to
which to send messages. In this commit, we then pass the assoc_id from
the context. A later commit changes this (at the CU) to pass the
assoc_id from the message to be sent.
Previous to this commit, the CU creates an F1 instance and initializes
GTP after a successful connection establishment, and tears the F1
instance down after the DU disconnects. This does not work when trying
to connect multiple DUs, or have them reconnect, as e.g., GTP
re-initialization fails (socket already bound).
This commit makes the CU F1 instance creation and GTP init at CU task
init (only once), and also frees the F1 instance only after the CU task
exits, which is at termination of the application, typically.
The RRC container is to be handled by the msg handler in
mac_rrc_dl_handler.c. Therefore, don't forward the RRC message, but copy
it into the message so the handler can take the action.
- store the assoc ID of a UE at the RRC
- if F1 receives an SCTP shutdown, it removes the endpoint
- F1 will also send an "F1 Lost Connection" message to the RRC
- it is not yet possible to reconnect a DU after it had already been
connected at the CU, since the CU F1AP task will try to rebind GTP,
which fails
This branch series implements the usage of the F1 Setup Request
internally at the gNB, even if CU and DU run in the same process. Until
now, the F1 Setup Request contained struct fields to pass IP
configuration to the F1AP module; this information is not necessary in
monolithic, nor should it be relevant when passing the information in
F1 Setup Request.
Therefore, this commit moves all IP connection-related information out
of the F1 Setup Request and into a separate structure instead. In order
to give the F1AP module the necessary connection information, the
DU_REGISTER_REQ message is introduced that combines the F1 Setup Request
and IP configuration, such that the F1AP module can setup the SCTP
connection and then send the F1 Setup Request message.
In a later commit, there will be a callback for F1 Setup Request at MAC
to simply register the DU at the CU. The monolithic callback will simply
forward the F1 Setup Request The F1AP callback will look up the IP
configuration and create DU_REGISTER_REQ message containing IP
configuration and F1 Setup Request, which is then handled by the F1AP
module. To this end, a separate function in gnb_config.c allows to read
IP information from configuration.
Instead of storing the F1 Setup Request implicitly in F1 context, we
provide the F1 Setup Request message to be encoded explicitly to the
encoding function.
This commit repairs the reestablishment after the introduction of the CU
UE ID in the CU, different from the DU UE ID. Now, the CU uses an
identifier different from the RNTI, used in the MAC, to refer to UEs.
To repair the reestablishment, a number of changes needed to be
introduced:
- Handle old_gNB_DU_UE_id in MAC
The MAC handles the old_gNB_DU_UE_id field in the DL RRC Message. The
commit adds encoding/decoding of the field. The MAC will drop the old
UE, but retain the CellGroup of the corresponding UE(!). Because a UE
releases the spCellGroup on reestablishment, the MAC does the same; it
needs to reapply the old configuration after a reconfiguration. For the
latter, introduce new variables to keep a "future" CellGroupConfig to be
applied (reconfigCellGroup) and a flag (expect_reconfiguration) that
applies the CellGroupConfig if a DL RRC Message transfer on DCCH, which
is assumed to be the reconfiguration.
- Add RNTI change in RLC
The RLC needs to reuse the old UE context. Hence, we simply change the
RNTI in the old context, and delete the new one.
- No PDCP UE ID change
The previous implementation of the PDCP used the RNTI; hence, the ID
needed to be switch (as above for the RLC). Since the PDCP now also uses
the CU UE ID, no identifier change is needed, and we remove all
corresponding code.
- No MAC modifications/update from CU
As foreseen by the spec, the CU does not modify or change the
cellGroupConfig in the RRC during reestablishment. This change will be
generalized in the future to all of the RRC. Also, the
nr_rrc_mac_remove_ue() function has been removed: the MAC handles any UE
changes autonomeously, without being triggered from the RRC explicitly.
- Remove reestablish_rnti_map
The RRC does not use RNTIs for UE identification. Hence, a
reestablish_rnti_map to link two UEs to each other is not necessary
anymore.
The UE had a list of known UEs. With the introduction of a separate
module for F1 UE ID handling that is also used in monolithic (to
separate CU UE ID from DU UE ID), this functionality is not needed, and
deleted in this commit.
Previously, the F1AP handler called various functions directly, instead
of sending an ITTI message to the RRC thread. This has two drawbacks:
- it can lead to data races if the RRC task uses functionality that is
being accessed by the F1 task through this function
- no homogeneity: all other handlers send an ITTI message, so this one
should too
- The CU/DU UE ID is used in DL RRC Message Transfer
- Note: The CU UE ID currently is still the RNTI
- on every DL RRC Message, the DU verifies that the UE exists
- Refactor RRC: common function to forward protected SRB PDUs
The RRC uses gNB_ue_ngap_id as its primary ID; the following commits
will introduce the usage of the (F1) gNB CU UE ID. This commits renames
the gNB_ue_ngap_id to rrc_ue_id to better reflect its usage as the RRC's
primary UE ID.
It will be used as the NGAP and F1 (CU) UE IDs.
ENB_MODE is a cmake option to swap the order of include directories.
This has historical reasons; before OAI used cmake, it was very
sensitive to the order of includes. Nowadays, the order does not matter.
Remove this option, and fix the compilation issues that arise while
doing so.
Robert Schmidt