NudmSDM Subscribe / Notify (TS 29.503 §5.3.2 / §5.3.3)

Mirrored documentation

Mirrored read-only from claudia-5gc @ v2.3.1. Edit upstream, not here.

Purpose

Allow NF consumers (AMF, SMF) to subscribe to UDM for notifications when subscription data changes in the UDR. Prevents NFs from holding stale cached subscriber data across AMBR/NSSAI updates applied by the operator (e.g., via management portal).

Specifications

Topic	Reference
Architecture	TS 23.501 §5.2.3.3
Procedure	TS 23.502 §4.2.2.2.2 step 14d
Stage 3	TS 29.503 §5.3.2 (Subscribe), §5.3.3 (Notify)
Data model	TS 29.503 §6.1.6.2.11 (SdmSubscription), §6.1.6.2.13 (ModificationNotification)

Sequence Diagram

sequenceDiagram
    participant AMF
    participant UDM
    participant UDR

    Note over AMF,UDM: Subscribe (TS 29.503 §5.3.2.2)
    AMF->>UDM: POST /nudm-sdm/v2/{supi}/sdm-subscriptions\n{callbackReference, monitoredResourceUri}
    UDM-->>AMF: 201 Created\nLocation: /nudm-sdm/v2/{supi}/sdm-subscriptions/{id}\nbody: SdmSubscription + subscriptionId

    Note over UDM,UDR: Data Change Trigger
    UDR-->>UDM: POST /nudm-mgmt/v1/{supi}/data-change\n(internal — fired by UDR after PATCH)

    Note over UDM,AMF: Notify (TS 29.503 §5.3.3.2)
    UDM->>AMF: POST {callbackReference}\n{resourceChanges: [{changeType, resourcePath, newValue}]}
    AMF-->>UDM: 204 No Content

    Note over AMF,UDM: Unsubscribe (TS 29.503 §5.3.2.7)
    AMF->>UDM: DELETE /nudm-sdm/v2/{supi}/sdm-subscriptions/{subscriptionId}
    UDM-->>AMF: 204 No Content

Information Elements

SdmSubscription (request/response body for POST)

IE	Type	M/O	Description
nfInstanceId	string (UUID)	O	Consumer NF instance UUID
callbackReference	URI	M	Callback URI for Nudm_SDM_Notify
monitoredResourceUri	URI	O	Specific resource to monitor
implicitUnsubscribe	bool	O	Auto-delete on deregistration
subscriptionId	string	O (in response)	Assigned by UDM

ModificationNotification (callback POST body)

IE	Type	Description
resourceChanges	array of ChangeItem	Describes what changed

ChangeItem

IE	Type	Description
changeType	enum (ADD/REMOVE/REPLACE)	Nature of change
resourcePath	string	JSON Pointer to changed field
newValue	any	New value after the change
originalValue	any	Previous value (optional)

Error Cases

Condition	HTTP Status	Cause
Missing callbackReference	400	MANDATORY_IE_MISSING
Subscriber not found in UDR	404	RESOURCE_URI_STRUCTURE_NOT_FOUND
Invalid subscription ID in DELETE	404	SUBSCRIPTION_NOT_FOUND

Implementation Notes

• Subscriptions keyed per SUPI, stored in memory (sync.Map). Thread-safe.
• subscriptionId is a ULID.
• Notification is asynchronous (goroutine); does not block the trigger call.
• UDR fires the internal trigger via POST /nudm-mgmt/v1/{supi}/data-change after any PATCH to subscription data, making UDM the fan-out hub.
• Notification client uses the same mTLS config as other outbound SBI calls in production.

Acceptance Criteria

1. POST /nudm-sdm/v2/{supi}/sdm-subscriptions returns 201 with Location + subscriptionId.
2. A data-change trigger via POST /nudm-mgmt/v1/{supi}/data-change fires a callback POST to all active subscribers for that SUPI within 2 s.
3. DELETE /nudm-sdm/v2/{supi}/sdm-subscriptions/{id} returns 204 and stops future notifications.
4. Missing callbackReference in POST returns 400 MANDATORY_IE_MISSING.