This commit implements proper PDU Session Release handling across
RRC, PDCP, F1AP, E1AP to ensure clean resource cleanup when
a PDU session is terminated.
Key changes:
NGAP:
In `rrc_gNB_process_NGAP_PDUSESSION_RELEASE_COMMAND()`:
* Populates E1AP Bearer Modification for each released session
* If a CU-UP is connected, triggers `bearer_context_mod()` for PDU teardown
PDCP:
* Added `nr_pdcp_release_drbs()` to remove all DRBs linked to a given PDU session
* Called from `e1_bearer_context_modif()` for correct clean-up during session release
F1AP UE Context Modification:
Replace direct RRC message transfer with F1AP UE Context Modification Request
to properly handle PDU session release according to 3GPP TS 38.331.
3GPP TS 38.331 `5.3.5.6.4 DRB release` says: whether or not the RLC and MAC entities associated
with a PDCP entity are reset or released is determined by the CellGroupConfig. Thus,
updated CellGroupConfig needs to be received by the UE. This has to be retrieved by CUCP
from the DU. Therefore:
After receiving an NGAP_PDUSESSION_RELEASE_COMMAND, the CUCP shall:
1) forward (store for later) the NAS PDU to the UE, if present as per 3GPP TS 38.413, and
2) send a UE Context Modification to the DU with the list of DRBs to release
and the RRC container (RRCReconfiguration with NAS PDU)
After reception of UE Context Modification Response, the list of drbs to release
is prepared based on PDU session status PDU_SESSION_STATUS_TORELEASE
in rrc_gNB_generate_dedicatedRRCReconfiguration and then encoded
in drb_ToReleaseList for a new RRCReconfiguration with the new cellGroupConfig.
Key changes:
* rrc_gNB_generate_dedicatedRRCReconfiguration_release() now uses F1AP UE Context
Modification Request instead of direct RRC transfer
* Only DRBs to be released are now added to the list.
* The ASN.1 memory allocation is entirely done in build_RRCReconfiguration_IEs
* No longer needed to store ASN1 struct in UE context
GTP-U:
* Previous implementation had incomplete tunnel cleanup during PDU session release
- Missing distinction between N3 (PDU session level) and F1-U (DRB level) tunnels
- Lack of proper DRB identification for F1-U tunnel deletion
Major Changes:
* GTP tunnel teardown now handled in `e1_bearer_context_modif()` using the correct
F1 or N3 GTP instance (`newGtpuDeleteOneTunnel()`)
* Enhanced Tunnel Deletion Logic (cucp_cuup_handler.c):
- Separate handling for N3 tunnels (1 per PDU session) and F1-U tunnels (1 per DRB)
- Added proper DRB identification for F1-U tunnel cleanup
- Improved error handling with detailed logging for each tunnel deletion
- Enhanced logging to distinguish between N3 and F1-U tunnel operations
* New PDCP API Function (nr_pdcp_oai_api.c/h):
- Added nr_pdcp_get_drb_ids_for_pdusession() function
- Enables retrieval of all DRB IDs associated with a specific PDU session
- Supports proper F1-U tunnel cleanup by providing DRB identifiers in CUUP
* Enhanced GTP Interface (gtp_itf.cpp/h):
- Modified newGtpuDeleteOneTunnel() to accept tunnel_type parameter
- Improved logging to distinguish between PDU session and DRB tunnel types
- Better error messages for tunnel deletion failures
- Enhanced debugging information for remaining tunnels
Clean-up:
* Ensured xid tracking works consistently between PDU Session Establishment (with NAS PDU)
and dedicated RRCReconfiguration
* Add function to release GTP-U tunnel in Bearer Context Modification Request handler
* Do not send rrc_gNB_send_NGAP_PDUSESSION_RELEASE_RESPONSE when no PDU session are to
be released: it is sent upon completion of the RRCReconfiguration and needs to contain
released PDU Sessions (mandatory IE), therefore it is no necessary to send it in case
there is no PDU session to release.
Related to #867
Co-authored-by: rmagueta <rmagueta@allbesmart.pt>
according to TS 38.331, RRCReconfiguration messages can be carried
in a container by different RRC messages, e.g. HandoverPreparationInformation,
HandoverCommand, RRCResume etc.. therefore before the introduction of new
RRCReconfiguration messages, e.g. for handover, a new design seems to be necessary
in order to improve modularity and maintainability of the code.
The goal of this commit is to make the generation of RRCReconfiguration
messages more modular by (1) preparing the RRCReconfiguration parameters
data in RRC (2) pass it to ASN1 for IEs allocation (3) encode to buffer
The following changes are introduced:
(1) introduce struct nr_rrc_reconfig_param_t to store the RRC parameters relevant
to encode the RRCReconfiguration IEs
(2) add RRC function get_RRCReconfiguration_params to fetch nr_rrc_reconfig_param_t
data from the UE context and
(3) pass it to the ASN1 encoder, e.g. do_RRCReconfiguration
(4) add a function build_RRCReconfiguration_IEs to allocate memory and build the
ASN1 NR_RRCReconfiguration_IEs_t and
(5) adopt it in do_RRCReconfiguration
(4) add free_RRCReconfiguration_params for memory management of nr_rrc_reconfig_param_t data
(6) add test for rrc_reconfiguration
get_RRCReconfiguration_params:
This function prepares RRCReconfigurationParams for RRC encoding.
Motivation of this change: depending on the RRCReconfiguration
message to be encoded, the ownership of ASN1 memory allocation
should belong to the ASN1 layer, therefore this function is
preparing the nr_rrc_reconfig_param_t data to pass to the
ASN1 encoder to build the ASN1 message and encode to buffer
The function is preparing the params for the IEs that are
either mandatory or shared among different RRC messages.
Specific fields that depend on the message to be encoded are then
added afterwards in the caller. The input param to indicate
re-establishment has been split between SRBs and DRBs, since
depending on the scenario the PDCP re-establishment can vary.
This will be addressed in a later commit.
This function is also handling xid.
build_RRCReconfiguration_IE:
The long term goal is to transfer ownership of memory allocation in ASN1 encoding to
build_RRCReconfiguration_IE, then by calling ASN_STRUCT_FREE_CONTENTS_ONLY
on dl_dcch_msg, all IEs allocated in the context are freed after encoding to buffer.
In the long term, createDRBlist, createSRBlist can also be brought into the context
of build_RRCReconfiguration_IEs and free the ASN1 structure after encoding.
This improves maintability and helps preventing memory leaks.
Currently, what is not allocated in the context, is nulled and freed outside.
free_RRCReconfiguration_params:
this function frees memory allocated to build the nr_rrc_reconfig_param_t data,
including the NR_DRB_ToAddModList_t and NR_SRB_ToAddModList_t. The function
freeDRBlist has been removed since no longer necessary.
dedicated_NAS_msg_list:
dedicated_NAS_msg_list handling has also been refactored, by:
(1) fetch the NAS PDUs from the UE context in get_RRCReconfiguration_params,
which translates to (2) passing an array of dedicatedNAS-MessageList + size
to the ASN1 encoding function where (3) the ASN1 encoding logic for the
dedicated_NAS_msg_list IE has been moved
Note, 3GPP TS 38.331:
dedicatedNAS-MessageList: SEQUENCE (SIZE(1..maxDRB)) OF DedicatedNAS-Message
