feat: add NR NTN access detection by donivtech · Pull Request #684 · omec-project/amf

donivtech · 2026-04-24T14:06:09Z

Closes #683.

Detects NR Non-Terrestrial Network access by checking for the NRNTN-TAI-Information protocol extension (ID 287 per 3GPP TS 38.413) inside UserLocationInformationNR.IEExtensions received over NGAP, and tracks the result on the UE context.

Changes

New context.NtnAccessInfo struct (carries Detected bool today; shaped to hold future satelliteBackhaulCat / geoSatelliteId / NTN TAI list without reshaping AmfUe/RanUe).
AmfUe.NtnAccess, RanUe.NtnAccess, AmfUe.IsNtn() helper.
Detection inside RanUe.UpdateLocation (NR branch), running after the NR TAI/CGI parsing succeeds so a malformed message cannot leave NTN state out of sync with the stored location.
Detection itself uses ngap.HasUserLocationInformationNRExtension from omec-project/ngap@v1.9.1 (added in omec-project/ngap#87).
6 table-driven cases in context/ran_ue_test.go covering the NTN-state semantics on RanUe.updateNtnAccess.

Detection semantics — sticky

Detected is set true the first time the NRNTN-TAI-Information extension is observed for a UE during the current UE context. It is not cleared while the UE context lives. The extension is PRESENCE optional per 3GPP TS 38.413 and gNBs include it at their discretion — typically on context-establishing events (initial UE message, handover) but often not on routine uplink/location reports. Treating an absent extension as evidence of "not NTN" would cause IsNtn() to flap on routine NGAP traffic for a UE that genuinely is on NTN; sticky-on avoids that.

Scope

Detection-only groundwork. No protocol behavior changes, no SBI payloads change, nothing reads the flag yet. Follow-up patches will extend NtnAccessInfo and wire NTN into the SBI path once satelliteBackhaulCat / geoSatelliteId are available in omec-project/openapi.

Test plan

go build ./... clean
go vet ./... clean
go test ./... all pass (6 new sticky-semantics cases in context/ran_ue_test.go)
make lint (golangci-lint via Docker) — 0 issues

Add the NGAP protocol IE/extension identifier 287 assigned to NRNTN-TAI-Information per 3GPP TS 38.413. This IE-extension is optionally carried inside UserLocationInformationNR.IEExtensions and indicates that the UE is being served over NR Non-Terrestrial Network access. The full Rel-17 IE type (NRNTNTAIInformation SEQUENCE) is not yet defined here; this commit only adds the bare ID so that callers checking presence of the extension can reference a canonical constant rather than hard-coding 287. The type definition and the remaining Rel-16/17/18 IE IDs are expected to land as part of the broader NGAP release uplift. Used by omec-project/amf#684 (NTN access detection). Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com>

Add a small NGAP-aware helper that reports whether a given UserLocationInformationNR carries a protocol extension with the specified ProtocolIE-ID inside its IEExtensions container. Generic over the extension ID, so callers can compose it with any existing or future ProtocolIEID* constant (NRNTN-TAI-Information being the immediate use case from omec-project/amf#684). Keeping NGAP-aware inspection helpers in this repo makes the eventual N2 release uplift easier to scope: all NGAP-touching code lives here. Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com>

* feat: add NRNTN-TAI-Information protocol IE/extension ID Add the NGAP protocol IE/extension identifier 287 assigned to NRNTN-TAI-Information per 3GPP TS 38.413. This IE-extension is optionally carried inside UserLocationInformationNR.IEExtensions and indicates that the UE is being served over NR Non-Terrestrial Network access. The full Rel-17 IE type (NRNTNTAIInformation SEQUENCE) is not yet defined here; this commit only adds the bare ID so that callers checking presence of the extension can reference a canonical constant rather than hard-coding 287. The type definition and the remaining Rel-16/17/18 IE IDs are expected to land as part of the broader NGAP release uplift. Used by omec-project/amf#684 (NTN access detection). Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com> * feat: add HasUserLocationInformationNRExtension helper Add a small NGAP-aware helper that reports whether a given UserLocationInformationNR carries a protocol extension with the specified ProtocolIE-ID inside its IEExtensions container. Generic over the extension ID, so callers can compose it with any existing or future ProtocolIEID* constant (NRNTN-TAI-Information being the immediate use case from omec-project/amf#684). Keeping NGAP-aware inspection helpers in this repo makes the eventual N2 release uplift easier to scope: all NGAP-touching code lives here. Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com> * Create patch release Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com> --------- Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com> Co-authored-by: Vinod Patmanathan <vinod.patmanathan@forsway.com>

donivtech · 2026-05-05T07:30:48Z

ngap#87 merged and v1.9.1 tagged. Force-pushed: bumped go.mod to ngap v1.9.1, dropped the local constant and helper, now using ngap.HasUserLocationInformationNRExtension(loc, ngapType.ProtocolIEIDNRNTNTAIInformation) directly.

gab-arrobo · 2026-05-05T16:02:28Z

ngap#87 merged and v1.9.1 tagged. Force-pushed: bumped go.mod to ngap v1.9.1, dropped the local constant and helper, now using ngap.HasUserLocationInformationNRExtension(loc, ngapType.ProtocolIEIDNRNTNTAIInformation) directly.

I think you need to rebase your PR and address any conflict because the amf is already using ngap v1.9.1 (https://github.com/omec-project/amf/blob/main/go.mod#L14)

donivtech · 2026-05-05T16:23:11Z

Good catch, rebased now. Diff are just the context/ changes.

Copilot

Pull request overview

Adds groundwork in the AMF UE/RAN UE context layer to detect NR Non-Terrestrial Network (NTN) access from NGAP UserLocationInformationNR by checking for the NRNTN-TAI-Information extension, and stores the result on UE context objects for future use.

Changes:

Introduces context.NtnAccessInfo and AmfUe.IsNtn() helper.
Tracks NTN detection on RanUe during NR UpdateLocation and propagates it to AmfUe.
Extends AmfUe with an NtnAccess field to persist/access the detection result.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
context/ran_ue.go	Detects NR NTN by presence of the NRNTN-TAI-Information extension during NR location updates and propagates NTN state to `AmfUe`.
context/ntn.go	Adds `NtnAccessInfo` and `AmfUe.IsNtn()` helper to represent/query NTN access.
context/amf_ue.go	Stores NTN access state on `AmfUe` via a new `NtnAccess` field.

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gab-arrobo · 2026-05-05T17:01:21Z

@donivtech, please check Copilot's comments (make sure the comments are valid) and address them if applicable

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

donivtech · 2026-05-07T17:38:55Z

Reverted to sticky-on. NRNTN-TAI-Information is PRESENCE optional per TS 38.413, and UpdateLocation is called from 11 NGAP handlers; non-sticky would flap on routine traffic where the extension is omitted. Doc strings spell this out.
Moved the NTN check to after NR TAI/CGI parsing (Copilot remove export port and clean make output #5) so a malformed message can't desync NTN state from the stored location.
Fixed copyright to Forsway Scandinavia AB on both new files.
Rebased on current main.

donivtech · 2026-05-07T22:12:57Z

I initially had this sticky, switched to per-message after Copilot suggested it, but reverted because absence of the optional IE shouldn't be treated as evidence of no NTN access. It would cause false negatives during a session.

gab-arrobo · 2026-05-13T05:13:27Z

I initially had this sticky, switched to per-message after Copilot suggested it, but reverted because absence of the optional IE shouldn't be treated as evidence of no NTN access. It would cause false negatives during a session.

I am currently trying to finalize the migration of the SBI to 3GPP release 18. As soon as those changes are merged, I will come back to this PR. I hope it does not take too long. Sorry for the delay.

donivtech · 2026-05-13T13:55:34Z

No worries. Thanks for the heads up.

Detect Non-Terrestrial Network access by checking for the NRNTN-TAI-Information protocol extension (ID 287 per 3GPP TS 38.413) in UserLocationInformationNR received via NGAP, and track the result in a new NtnAccessInfo struct on AmfUe and RanUe. This is detection-only groundwork. No protocol behavior changes: nothing reads the flag yet. Future patches can extend NtnAccessInfo with satellite backhaul category, GEO satellite ID, and NTN TAI list as those fields become available in omec-project/openapi and omec-project/ngap. Signed-off-by: Vinod Patmanathan <vinod.patmanathan@forsway.com>

gab-arrobo · 2026-05-21T14:40:13Z

@donivtech, are the changes from PR still needed when we migrate the NGAP to release 18?

gab-arrobo · 2026-05-21T15:44:27Z

 	EventSubscriptionsInfo map[string]*AmfUeEventSubscription `json:"eventSubscriptionInfo,omitempty"`
 	/* User Location*/
 	RatType                  models.RatType      `json:"ratType,omitempty"`
+	NtnAccess                *NtnAccessInfo      `json:"ntnAccess,omitempty"`


Based on the latest SBI changes (openapi models), I think these changes are not applicable. Instead of creating NtnAccessInfo (Detected: true or false), should not you rely on the models.RatType such as the ones below to make the "Detected" decision? What do you think? Also, do you need NGAP rel-18 as part of these changes?

... RATTYPE_NR_LEO RatType = "NR_LEO" RATTYPE_NR_MEO RatType = "NR_MEO" RATTYPE_NR_GEO RatType = "NR_GEO" RATTYPE_NR_OTHER_SAT RatType = "NR_OTHER_SAT" ...

donivtech · 2026-05-22T09:45:54Z

Using RatType is agreed in principle. But it's worth noting the current asymmetry. openapi/v2 brought the Rel-18 RatType values (NR_LEO/MEO/GEO/OTHER_SAT), but ngap/v2 is module path bump, so the ASN.1 schema is unchanged from Rel-15. AMF doesn't yet have NGAP to distinguish between LEO/MEO/GEO. The only NTN signal we get is the presence of of the bare NRNTN-TAI-Information extension (ID 287). Contents are not decoded.

What could be done today is to set ue.RatType = RATTYPE_NR_OTHER_SAT whenever the extension is detected (coarse classification). Orbit specific can come once N2 release-18 work lands the proper IE decode.

I can refactor to drop NtnAccessInfo, set RatType to NR_OTHER_SAT from UpdateLocation when the extension is observed. Want me to do that here?

No NGAP Rel-18 dependency, just the presence-check helper we already have in ngap/v2.

gab-arrobo · 2026-05-22T19:42:15Z

openapi/v2 brought the Rel-18 RatType values (NR_LEO/MEO/GEO/OTHER_SAT), but ngap/v2 is module path bump, so the ASN.1 schema is unchanged from Rel-15. AMF doesn't yet have NGAP to distinguish between LEO/MEO/GEO.

So, upgrading the NGAP to release 18 would resolve this limitation, correct? If so, let me see if I can complete the N2 upgrade in the coming days

donivtech · 2026-05-24T11:59:15Z

Yes, that would resolve it cleanly. Prefer waiting for the N2 upgrade so the orbit specific RatType lands in one shot.

gab-arrobo · 2026-06-02T06:48:12Z

Yes, that would resolve it cleanly. Prefer waiting for the N2 upgrade so the orbit specific RatType lands in one shot.

@donivtech,
NGAP is upgraded now to rel 18. Please take a look at it. Also, see the new "Find*" (e.g., https://github.com/omec-project/ngap/blob/main/extensions.go#L18). Do we still need the extensions.go file (https://github.com/omec-project/ngap/blob/main/extensions.go)?

donivtech mentioned this pull request Apr 24, 2026

fix: set RatType correctly during registration #685

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donivtech force-pushed the feat/ntn-access-detection branch from 7c00259 to 807d151 Compare April 27, 2026 07:07

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donivtech mentioned this pull request Apr 29, 2026

feat: add NRNTN-TAI-Information protocol IE/extension ID omec-project/ngap#87

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donivtech force-pushed the feat/ntn-access-detection branch from 807d151 to ec87ad6 Compare May 5, 2026 07:14

donivtech force-pushed the feat/ntn-access-detection branch from ec87ad6 to 3988068 Compare May 5, 2026 16:07

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donivtech force-pushed the feat/ntn-access-detection branch from 3988068 to 5a860b8 Compare May 6, 2026 12:40

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donivtech force-pushed the feat/ntn-access-detection branch 2 times, most recently from c84e3dc to 6fe40ea Compare May 7, 2026 17:34

donivtech force-pushed the feat/ntn-access-detection branch from 6fe40ea to 95109cf Compare May 18, 2026 09:32

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Detection semantics — sticky

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