Single Network Slice Support per AGW Node

[anusha-konda]

Proposal: Single Network Slice Support per AGW Node

Elevator Pitch

Intent of the proposal is to extend the current magma architecture to support single network slice per AGW and introduce
the base framework needed to support multiple slices per AGW.
Introducing NSSF as a new service, to select the optimal network slice available for the service requested by UE.
According to 3GPP TS29.531, section 5.2, Nnssf_NSSelection Service offerings by NSSF is to retrieve the information related to network slice.

Current proposal deals with interfaces towards Network Slice Selection service and the AMF interactions with NSSF during registration, pdu establishment procedures.

Out of scope:

• According to 3GPP TS29.531, section 5.3, Nnssf_NSSAIAvailability Service offerings are not mentioned in this proposal.
• Network slice selection in roaming scenarios is not considered.
• Network Repository Function (NRF) service offerings and interactions with other AGW services are not considered.

Total ask

Support of Single Slice per AGW on to Magma Architecture will be delivered at a total cost of: $261000

Project Details

To support single slice per AGW, enhancements to AGW services, subscriberdb, policydb, sessiond are detailed below.
NSSF is the new service that will be introduced in AGW to retrieve the network slice information.
The below explained features of NSSF shall provide base framework to support dynamic slice in AGW.

NSSF

• According to 3GPP TS29.531 v15.1.0, section 5.2.2.2, Nnssf_NSSelection service offers GET operation to retrieve the network slice info.
• To process the NSSF_NSSelection GET request, NSSF shall hold the info of Slice Instances, Configured Nssai in TA (PLMN+TAC).
• NSSF shall accept the configurations (through CLI and Orc8r)

• Below diagram represents SliceSelection(NSSF_NSSelection_Get as per 3GPP standard) interface, NSSF shall support to interact with AMF to select/retrieve slice info during registration procedure.

From the above figure

• UE initiates Registration request, with NSSAI – Requested NSSAI.
• MME(AMF) connects to SubscriberDB for authentication. SubscriberDB returns the security tokens to MME(AMF) to authenticate UE. MME(AMF) completes authentication of UE.
• MME(AMF) initiates GetSubscribedNssai(Nudm_SDM_Get as per 3GPP standard) to retrieve the Slice Subscription data of UE from SubscriberDB.
• SubscriberDB returns the Subscribed Nssai of UE, which was added by operator.
• MME(AMF) validates If requestedNssai not in SubscribedNssai, initiates rpc SliceSelection() to retrieve the network slice info.
• NSSF compares the UE requestedNssai and TAI info with the SupportedNssai per TA list. And with the below conditions returns AuthorizedNetworkSliceInfo
  • If no match, NSSF fills the rejectedNssai per TAI
  • Else if, requested Nssai matches SupportedNssai in TA, NSSF returns the AllowedNssai, NSIId (Network Slice Instance Identifier), AGWNodes list where slice is supported.
  • Else, NSSF fills the rejectedNssai per TAI
  • MME(AMF) verifies if itself is part of targetAmfSet from the NSSF response (AuthorizedNetworkSliceInfo), else send Registration reject.

Note: AMF Re-allocation is not considered in this proposal.

• MME(AMF) stores the NSIId in the UE context, and uses it during PDU establishment procedure.
• As this proposal deals with single slice per AGW, by default NSIProfile shall be created by operator to map the default Network Slice Instance to the supportedNssai in the list of TrackingAreas.
• As represented below, NSSF shall be responsible to provide the details of default NSIId when requested by AMF for the allowedSnssai.

NSSF Configuration

Below Orc8r APIs shall be supported, to configure NSSF. These APIs will be extended to support dynamic network slices in AGW.

NSSF CLI stub will be implemented in a similar line to operate AGW in headless mode.

---------------------------------------------------------------------------------------------
|      NSSF Orc8r API                          |        Description and Payload             |
|----------------------------------------------|---------------------------------------------
| /lte/{network_id}/nssf/configurednssai       | Configure Supported NSSAI per TAI.         |
|                                              | Attributes:                                | 
|                                              |           ConfiguredNssaiList              |
|                                              |           PLMN                             |
|                                              |           TAC                              |
|----------------------------------------------|--------------------------------------------|                                              |                                                       |
|  /lte/{network_id}/nssf/nsiprofiles          | Configure NSIProfiles.                     |
|                                              | Attributes:		                    |
|                                              |           ProfileName                      |
|                                              |           NSIId                            |
|                                              |           Nssai                            |
|                                              |           targetAmfSet                     |
|----------------------------------------------|--------------------------------------------|

NMS

• NMS UI shall provide options to configure Slice-APN mappings for subscribers.
• NMS UI shall be enhanced to configure policy based on IMSI + Slice + APN.

AMF

• During registration procedure, UE context shall be modified to maintain info about the allowed NSSAI list by fetching the subscribed NSSAI info from the subscriberDB and authorized slice info from NSSF.
• Shall modify the existing RPCs invocation to include slice towards mobilityd.
• Shall modify the existing RPCs invocation to include slice info towards sessiond while requesting addition/deletion a particular PDU session.

Delivery Approach

Features will be delivered in 3 milestones. Each milestone will have the following 4 process gates

• Design
• Development & Unit Testing
• Code review

Before finishing the last milestone, the feature shall pass the following process gates

• Integration testing
• System test
• User Acceptance test

Milestone1 – Design doc, AGW- NSSF Framework initialization + CLI stubs

• Deliver the design doc for NSSF support in AGW
• NSSF as new service in AGW. Init framework, db initialization, data structures.
• NSSF Proto and library generation
• Implement NSSF CLI stub to accept configurations
• AGW NSSF UT
• AGW system level scripts to bring up new service – NSSF

Milestone2 - AGW-NSSF-SliceSelection - Registration

• Implementation of gRPC interface SliceSelection(SliceInfoForRegistration) in NSSF service
• AMF extensions to interact with NSSF during registration and PDU establishment procedures, UTs
• Addition of positive and negative UT testcases in NSSF
• Addition of positive and negative UT testcases in AMF

Milestone3 - AGW-NSSF-SliceSelection – PDU Establishment

• Implementation of gRPC interface SliceSelection(SliceInfoForPDUSession)in NSSF service
• AMF extensions to interact with NSSF during registration and PDU establishment procedures, UTs
• Addition of positive and negative UT testcases in NSSF
• Addition of positive and negative UT testcases in AMF

Milestone4 - Orc8r support to configure NSSF

• Implement new service - SliceManager, initialization of new Orc8r service, gRPC ports, DB initialization,
• Implementation of swagger, obsidian handlers, validate functions, invoke configurator to store data in DB
• Slice Manager UT - for obsidian handlers
• Implement SliceManagerCloud RPC servicer which shall populate the data to AGW, Define protos (messages, interfaces)
• Implement UT for SliceManagerCloud RPC Servicer

Milestone5 - Orc8r and NMS Support to configure Subscriber Slice+APN mappings

• Define swagger models and APIs to accept subscribed nssai and default nssai.
• Define obsidian handlers, validation functions
• Updates to subscribedDB Unittest cases
• Add/Update UI pages to configure Subscriber - Slice + APN mappings
• Updates to NMS module unittestcases

Test plan

With the introduction of NSSF, below is the plan to verify single slice per AGW

• Regular 5G call flow verification with the inclusion of NSSF feature.
• Verification of negative cases for slice selection during control procedures.
• Verification of regression and scale tests.

Feature Roadmap

Feature will be delivered in 3 Milestones.

---

Milestone	Deliverable Summary
MS1	Design doc of NSSF. Launch NSSF as new service, NSSF CLI stub to configure SupportedNssai in TA, SliceProfiles in AGW headless mode
MS2	Implementation of SliceSelection gRPC interface of NSSF for SliceInfoForRegistration. Slice selection procedure by AMF during registration
MS3	Implementation of SliceSelection gRPC interface of NSSF for SliceInfoForPDUSession. Slice selection procedure by AMF during registration
MS4	Orc8r supports configuring NSSF. Implement New service in Orc8r.
MS6	Orc8r and NMS support to configure Subscriber Slice-APN mappings. Policy configs for IMSI + Slice + APN.

References

• https://www.etsi.org/deliver/etsi_ts/129500_129599/129531/15.00.00_60/ts_129531v150000p.pdf
• https://www.etsi.org/deliver/etsi_ts/123500_123599/123501/16.06.00_60/ts_123501v160600p.pdf
• https://www.etsi.org/deliver/etsi_ts/123500_123599/123502/15.03.00_60/ts_123502v150300p.pdf