N2 handover
This MR introduces full support for N2 handover, covering handover
decision, preparation, execution, and notification between source and
target NG-RAN nodes.
Key features:
1. Handover Decision & Preparation:
- Implement N2 handover decision based on UE measurement reports.
- Generate the Handover Preparation Information message, including
RRCReconfiguration.
- Send Handover Required message from the source NG-RAN to the AMF.
2. Handover Execution:
- Decode and handle the Handover Request on the target NG-RAN.
- Process the Handover Command on the source gNB, triggering
RRCReconfiguration.
- Initiate Handover Notify after successful completion.
3 NGAP & RRC Enhancements:
- Implement NGAP encoding/decoding functions for Handover Required,
Handover Request, Handover Command, Handover Failure, and Handover
Notify (3GPP TS 38.413).
- Adds NG-RAN Status Transfer support (UL/DL) for PDCP COUNT
preservation during mobility:
- support for NGAP Uplink and Downlink RAN Status Transfer messages
(TS 38.413 §9.2.3.13-14) to enable proper PDCP COUNT value
transfer during handover or recovery: NGAP encoding/decoding for
RAN Status Transfer, PDCP helpers to extract and apply COUNT (HFN
+ SN) per DRB. This aligns with TS 38.300 §9.2.3.2.1 and TS 23.502
§4.9.1.3.3, ensuring PDCP status preservation in AM.
4. Testing:
- Introduce a Telnet command to manually trigger N2 handover using UE
ID and neighbor PCI.
- Add configuration file for testing N2 handover with a target gNB.
This commit completes the NGAP Mobility Management procedure for N2 handover.
Upon failure on source gNB the Handover Cancel message is sent to the AMF which
in return responds with an ack.
Upon reception of NG RAN Status at the target CU-CP, send PDCP Status
via E1 Bearer Context Modification to the target CU-UP and update PDCP Count
upon reception of the message.
For the sake of simplicity, re-used and extended legacy e1_send_bearer_updates.
Further refactoring is not addressed in this commit.
Once fetched the PDCP Status from the PDCP entity over E1, the CU-CP triggers
the NG RAN Status Transfer procedure to transfer the PDCP Status to the target
CU.
This commit is also introducing the RRC callback.
The E1 Bearer Context Modification Request shall send a PDCP Status Request IE
during handover, e.g. the HO context is set to source, and it is not target, i.e.
only in N2 not in F1.
The current function "e1_send_bearer_updates" used to fill the E1 Request has been
refactored only for the sake of this commit and to avoid duplicated and redundant code.
The function itself deeper analysis and eventually a refactoring that will not be addressed
in this commit.
* the command gets in input the neighbour PCI and the UE ID
* the telnet ci function to retrieve the UE context was extended in the process
* add function to trigger handover on the same gNB for testing purposes
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
* add trigger function to (1) add the callbacks and (2) initiate
handover on the target NG-RAN
* add handover failure callback on target NG-RAN: the Handover
Failure is a procedure that belongs to the target NG-RAN and
it is different from the Handover Cancel procedure
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
This commit introduces the NG Mobility Management Procedure known as
Handover Notification. The outbound message is sent by the target NG-RAN
and is known as Handover Notify. The procedure is used to indicate to
the AMF that the UE has arrived to the target cell and the NG-based
handover has been successfully completed
* after RRCReconfiguration complete, in the N2 callback for HO success
* add NGAP encoder for the message
* RRC callback to trigger Handover Notify message
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
* add NG Handover Command message decoder
* process in RRC: encode RRCReconfiguration message
from the received HandoverCommandMessage
* trigger RRCReconfiguration for handover
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
* generate Handover Command for the source NG-RAN
to be added to the target to source transparent
container of the Handover Acknowledge message
* add Handover Acknowledge callback for N2
* send NG Handover Acknowledge to AMF
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
This commit completes the NG Mobility Management Procedure known as
Handover Resource Allocation. The outbound message is sent by the
target NG-RAN and is known as Handover Request Acknowledge.
Major changes:
* add RRC callback to trigger the generation of NG Handover
Request Acknowledge on the target NG-RAN
* add NG Handover Request Acknowledge encoder
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
This commit introduces the NG Mobility Management Procedure known as
Handover Resource Allocation. The inbound message is sent by the AMF
and is known as Handover Request.
Major changes:
(0) Add Handover Resource Allocation initiating message decoding
* add case for NGAP initiating message and unsuccessful message decoding
(1) handle Handover Request on the target NG-RAN
(2) decode NG Handover Request message
(3) process payload, e.g. create UE context,
store IDs, set UP security and trigger bearer setup
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
This message is sent from the Target NG-RAN to the AMF.
The commit introduces:
* NGAP encoding function
* N2 callback for the target gNB
* handle the failure in RRC, inform NGAP
* send NGAP message to AMF via SCTP
Note: UE context in NGAP is fetched from the amf_ue_ngap_id
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
(1) add N2 ho decision based on measurements
(2) add trigger for N2 HO on source CU
(3) generate NG Handover Preparation Information message,
including RRCReconfiguration, to be passed to the
NG Handover Required message
(4) call RRC callback for Handover Required message
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
This commit introduces the NG Mobility Management Procedure known as
Handover Preparation. The outbound message is sent by the source NG-RAN
and is known as Handover Required.
* introduce NGAP library for Mobility Management
* introduce NGAP IEs encoder functions for Handover Required and relevant common IEs
* handle RRC trigger in NGAP and Send NGAP Handover Required to the AMF
Co-authored-by: batuhan duyuler <batuhan.duyuler@firecell.io>
During the N2 HO review has been found that the HO context
was not allocated at trigger time but later in the flow. This
might lead to issues in some scenarios (e.g. in N2 HO)
and it was fixed in this commit.
During the review of the N2 HO MR it has been found that the wrong type
plmn_identity_t (S1AP) was used in RRC. Now updated to the platform type plmn_id_t.
Refactor measConfig
- Refactor and minor improvements in get_MeasConfig function;
- Add support for band in neighbourConfiguration (It is currently
possible to handover cells with different frequencies, as long as they
are in the same band, but this MR allows the handover to also be done
between cells in different bands).
Interoperability testing with srsRAN DU shows than when receiving
RRCReconfigurationCompleteIndicator in a UEContextModificationRequest
the DU replies in the UEContextModificationResponse with an empty
CellGroupConfig.
This CellGroupConfig is encoded as 2 zero bytes. Let's ignore this
message when we receive it, don't forward it to the UE in a
RRC Reconfiguration, as it should per standard (38.473 8.3.4.2):
If the CellGroupConfig IE is included in the DU to CU RRC Information
IE contained in the UE CONTEXT MODIFICATION RESPONSE message, the
gNB-CU shall perform RRC Reconfiguration as described in TS 38.331 [8].
The CellGroupConfig IE shall transparently be signaled to the UE as
specified in TS 38.331 [8].
To be removed/reworked in the future if the interoperability
situation improves.
Measurement gaps
Scheduling measurement gaps to provide sufficient time for the UE to
re-tune its transceiver to the target carrier, complete the set of
measurements and then re-tune its transceiver back to the original
carrier.
The changes done in this commit are to contribute the supporting changes
for the existing "Initial support for RedCap" feature in gNB.
In this patch, handle and store the RedCap related IE's present in "NR
UE Capability Information" msg which are
- 'supportOfRedCap-r17'
- 'supportOf16DRB-RedCap-r17'
- 'longSN-RedCap-r17'
- 'am-WithLongSN-RedCap-r17'
use 'longSN-RedCap-r17' and 'am-WithLongSN-RedCap-r17' IEs to set the SN
length to either 12 Bit or 18 Bit accordingly.
Previously, we only supported intra-frequency handovers, so the
measurements where only for intra-frequency, reusing the same
measurement object. Now that we would support inter-frequency handover,
also add multiple MeasObjects for each neighbor.
bugfix: UE AMBR is optional
This was a problem with open5gs and more than one PDU session. The core network
sets UE AMBR only once, leading to failure in the gNB for the second PDU session.
(A proper handling of AMBR has to be develop at some point in the gNB.)
This was a problem with open5gs and more than one PDU session.
The core network sets UE AMBR only once, leading to failure in the gNB
for the second PDU session.
(A proper handling of AMBR has to be develop at some point in the gNB.)
Various fixes for UE handling, HO doc updates
- On release request, search both attach and connected list to free a UE.
- on DU disconnect, only release the correspnonding UE contexts.
- When no AMF for the UE, auto-release the UE (NGAP would also send an
answer, but better check first)
- implement a "grace period" before the DU/MAC automatically releases a
UE: this is to avoid cases in which (for whatever reason) the UE
release request is not honored by the CU. In order to not fill up UE
contexts unnecessarily, the DU will eventually (after 10s) drop the UE
context
- some clarification in HO tutorial
Mark non-existing AMF UE NGAP ID through invalid INT64_MAX number
(permitted range is up to 2^40-1). Check for this range in the RAN
function, as we might otherwise pass the invalid AMF UE NGAP ID to the
agent, which would assert with
nr-softmodem: /oai-ran/openair2/E2AP/flexric/src/lib/3gpp/enc/enc_gnb.c:83: enc_gNB_UE_asn: Assertion `gnb->amf_ue_ngap_id < 1UL << 40' failed.
In other words, don't send KPM messages for a UE which has no valid AMF
UE NGAP ID yet (which follows from the fact that the spec requires an
AMF UE NGAP ID; the previous behavior of simply sending 0 could be
considered a bug, because it's not the UE's true AMF UE NGAP ID).
NR RRC Reject UE
Improvements in procedures to handle RRCReject message both at gNB and
UE. At gNB we send RRC Reject if the UE cannot be given resources to go
into connected mode.
Direct leak of 512 byte(s) in 1 object(s) allocated from:
#0 0x7f37634e5e2b in realloc.part.0 (/lib64/libasan.so.8+0xe5e2b) (BuildId: 7f1aa7e2e600e8c9d54ce6e3d36f3d31bfe7949a)
#1 0x000000fbb9ad in encode_dyn_cb /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/per_encoder.c:23
#2 0x000000fc279e in asn_put_few_bits /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/asn_bit_data.c:220
#3 0x000000fc279e in asn_put_few_bits /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/asn_bit_data.c:192
#4 0x000000fc2ce5 in asn_put_many_bits /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/asn_bit_data.c:293
#5 0x000000fb8c33 in OCTET_STRING_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/OCTET_STRING_uper.c:306
#6 0x000000fd191a in SEQUENCE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_SEQUENCE_uper.c:403
#7 0x000000fd191a in SEQUENCE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_SEQUENCE_uper.c:403
#8 0x000000fcb140 in CHOICE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_CHOICE_uper.c:177
#9 0x000000fd191a in SEQUENCE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_SEQUENCE_uper.c:403
#10 0x000000fcb140 in CHOICE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_CHOICE_uper.c:177
#11 0x000000fcb140 in CHOICE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_CHOICE_uper.c:177
#12 0x000000fd191a in SEQUENCE_encode_uper /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/constr_SEQUENCE_uper.c:403
#13 0x000000fbc1ed in uper_encode /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/uper_encoder.c:27
#14 0x000000fbc73a in uper_encode_to_new_buffer /home/richie/w/f1-refactor-ue-context/build/openair2/RRC/LTE/MESSAGES/uper_encoder.c:85
#15 0x000000e10fbd in do_RRCReconfiguration /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/MESSAGES/asn1_msg.c:586
#16 0x000000805712 in rrc_gNB_encode_RRCReconfiguration /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:652
#17 0x000000893860 in nr_rrc_f1_ho_acknowledge /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB_mobility.c:280
#18 0x0000008079ac in rrc_CU_process_ue_context_setup_response /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:2139
#19 0x0000008330d8 in rrc_gnb_task /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:2771
#20 0x7f3763428ee5 in asan_thread_start(void*) (/lib64/libasan.so.8+0x28ee5) (BuildId: 7f1aa7e2e600e8c9d54ce6e3d36f3d31bfe7949a)
During refactoring, I had asan errors in the next line. It took me some
time to figure out that a DRB ID 0 is not valid (cf.
get_next_available_drb_id() and get_drb(), they enforce this).
Direct leak of 48 byte(s) in 1 object(s) allocated from:
#0 0x7fea71ee6f0b in malloc (/lib64/libasan.so.8+0xe6f0b) (BuildId: 7f1aa7e2e600e8c9d54ce6e3d36f3d31bfe7949a)
#1 0x0000007f29c0 in malloc_or_fail /home/richie/w/f1-refactor-ue-context/common/utils/utils.h:86
#2 0x0000007f29c0 in cuup_notify_reestablishment /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:872
#3 0x000000808002 in rrc_CU_process_ue_context_setup_response /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:2126
#4 0x0000008330d8 in rrc_gnb_task /home/richie/w/f1-refactor-ue-context/openair2/RRC/NR/rrc_gNB.c:2770
#5 0x7fea71e28ee5 in asan_thread_start(void*) (/lib64/libasan.so.8+0x28ee5) (BuildId: 7f1aa7e2e600e8c9d54ce6e3d36f3d31bfe7949a)
