Update AGW modules to be Network Slice aware

[moinuddin1980]

Proposal: Update AGW modules to be Network Slice aware

Elevator Pitch

The future 5G network will support a vast range of innovative services for customers, enterprises, various industrial verticals, federal level demands, and virtual mobile network operators (MVNOs).
According to their different quality of service (QoS) requirements, these services can be categorized as

1. Enhanced Mobile Broadband (eMBB) devours huge chunks of bandwidth (FWA)
2. Ultra-reliable Low-Latency Communications (urLLC require a lightning-fast response time for mission-critical applications
3. Massive Machine-Type Communications (mMTC) stress the number of simultaneous mobile connections

5G network will fulfill these service requirements through a core technology called Network slicing. It is a central pillar of the 5G network, managed with end-to-end (e2e) service orchestration.

Magma being an open-source software platform that gives network operators an open, flexible and extendable mobile core network solution and implementing network slicing feature will enable it to support various use cases such as Fixed Wireless Access (FWA), Private 5G etc.

This proposal intends to make the AGW network functions aware of network slice type support and provide different QoS requirements based on network slice type.

Total ask

Support of Network Slice aware AGW modules on Magma Architecture will be delivered in three milestones.

Contact Information

Moinuddin Khan (moinuddin.khan@wavelabs.ai)

Project Details

To introduce the network slice specific services the UE PDU sessions and multiple modules in AGW need to be aware of S-NSSAI. Currently the following AGW modules are considered as a minimum to support network slice aware UE services.

SubscriberDB extensions to support slice configuration

• Subscriber configurations shall be enhanced to accept SliceType-APN/DNN mappings for 5G UE.
• CLI commands shall be provided for configuring subscriber config with associated Slice and APN configurations.
  subscriberdb_cli.py update --lte-auth-key 465B5CE8B199B49FAA5F0A2EE238A6BC --lte-auth-opc E8ED289DEBA952E4283B54E88E6183CA --slice-apn-map {sst:1, sd:"sd1", apn-config: { apn_1: {5,15,1,1,1000,2000,1,,,,}}} --slice-apn-map {sst:1, sd:"sd2", apnconfig: { apn_2: {5,15,1,1,1000,2000,1,,,,}}} IMSI001010000000002
• Subscriber Slice-APN mappings are maintained and extracted by the SubscriberDB process in AGW and provide the APN info to the NFs via RPC responses.
• SubscriberDB shall support processing requests for Slice Selection Subscription data (like Nudm_SDM_Get) from AMF. And In response sends back Slice Selection Subscription data including Subscribed S-NSSAIs.

AMF extensions to support slice configs

• As part of handling NG setup request, shall populate the supported slice info list in NG setup response.
• As part of handling registration request, shall populate the supported slice info in registration accept.
• As part of handling PDU session establishment request, shall populate the slice info in PDU session establishment accept.
• As part of handling Service request, shall populate the allowed slice info in Service Accept.
• In order to support network slicing for UE registration procedure, the UE context shall be modified to maintain info about the allowed NSSAI list by fetching the subscribed NSSAI info from the subscriberDB.
• Shall modify the existing RPCs invocation to include S-NSSAI towards mobilityd.
• Shall modify the existing RPCs invocation to include S-NSSAI info towards sessiond while requesting addition/deletion a particular PDU session.
• Need to extend the support of slice in the stateless feature.

Mobilityd extensions to support slice configs

• UE IP address allocation logic with mobilityd shall consider slice identifier (S-NSSAI) as one constituent of search key.
• Hence, the existing RPCs exposed by mobility to other NFs need to be modified to accommodate the slice info.
• The IP address assignment shall happen from the default IP pool for both 4G and 5G UE sessions.
  1. As there is no network slicing for 4G sessions, while fetching the IP address from the pool, slice identifier will be set to zero or null
  2. For 5G sessions the slice identifier shall be properly set and shall be used as a constituent of the key for fetching IP address from pool

Sessiond extensions

• Modify the related gRPC interface to introduce the S-NSSAI for PDU session management
• Modify handling of AMF PDU session establishment request and response w.r.t S-NSSAI
• Modify PDU session creation/modification/fetching/deletion in RedisDB and in local memory (session map, session store & session state data structures) with S-NSSAI as constituent of key along with PDU session id and IMSI
• sessiond shall support S-NSSAI specific statistics

Delivery Approach

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

1. Design
2. Development & Unit Testing
3. code review

Before finishing the last milestone, the feature shall pass the following process gates 4. Integration testing 5. System test 6. User Acceptance test

Milestone1 – UE registration related subscriberDB and AMF network slicing changes

Tasks to make SubscriberDB and AMF network slice aware.

1. SubscriberDB extensions to store subscriber S-NSSAI details
2. Changes in gRPC interface between subscriberDB and AMF to accommodate S-NSSAI
3. Existing CLI command modification to accept slice-apn mappings
4. New UTs will be added and existing ones will be modified as required.

Milestone2 – IP address reservation taking network slicing into account

Tasks to make mobilityd network slice aware and allocate ip addresses taking S-NSSAI into consideration.

1. Mobilityd extensions to reserve UE IP per slice.
2. Modify the CLI commands to include S-NSSAI as key for reserving IP address
3. Enhancement to existing RPCs in between mobilityd and AMF to include S-NSSAI info
4. New UTs will be added and existing ones will be modified as required.

Milestone3 – PDU session management taking network slicing into account

Tasks to make AMF, sessiond network slice aware.

1. Enhancement to

   • UE context modification in AMF to handle S-NSSAI info
   • NG setup procedure to handle S-NSSAI info in AMF
   • processing Service request w.r.t network slice info and populate the allowed slice info in Service Accept.
   • existing RPCs between sessiond and AMF to include the S-NSSAI for PDU session management
   • processing of PDU session request and sending response w.r.t network slice info in sessiond
   • processing of gRPC PDU session response at AMF - slice specific statistics in sessiond

2. New UTs will be added and existing ones will be modified as required.

Test Plan

Primarily targeted to test the network slicing is achieved during the 5G call flow which is mapped to PDU session creation/deletion. Following is the set of tests or scenarios to test the feature.

Integration Testing will be performed using simulators

1. 5G call flow is working with Network Slicing
2. Existing 4G call flow should work with no slicing
3. Scale and other related tests to be performed
4. Negative scenarios related testing to be done

Feature Roadmap

Feature will be delivered in 3 Milestones.

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Milestone	Deliverable Summary
MS1	UE registration related subscriberDB and AMF network slicing changes
MS2	IP address reservation taking network slicing into account
MS3	PDU session management taking network slicing into account

Reference

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3GPP Specification	URL
TS29.531	https://www.etsi.org/deliver/etsi_ts/129500_129599/129531/15.00.00_60/ts_129531v150000p.pdf
TS23.501	https://www.etsi.org/deliver/etsi_ts/123500_123599/123501/16.06.00_60/ts_123501v160600p.pdf
TS23.502	https://www.etsi.org/deliver/etsi_ts/123500_123599/123502/15.03.00_60/ts_123502v150300p.pdf