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5G Network Slicing


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This presentation is an introduction to the 5G network slicing based on 3GPP Release 15 standards

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5G Network Slicing

  1. 1. 5G Network Slicing Sridhar Bhaskaran 3GPP Standards Expert (SA2, CT4, CT3 and CT1)
  2. 2. Network Slicing in 3GPP - History Release 13 Release 14 Release 15 ● Dedicated Core Networks (DECOR) introduced ● Selection and Redirection of MME based on subscribed UE usage type ● MME further selects SGW / PGW based on UE usage type ● One UE = one UE usage type ● No indicator in RRC to let eNB select right MME ● All changes are core network centric ● Enhanced DECOR (eDECOR) ⇒ Introduces UE assisted Dedicated Core Network selection ● UE provisioned with a default Dedicated Core Network ID (DCN ID) by HPLMN ● Serving Network provides a DCN ID for that PLMN ● UE stores per PLMN DCN ID ● DCN ID carried in RRC ● eNB selects right MME based on DCN ID ● MME selects SGW / PGW based on UE usage type ● One UE = one DCN ID ● All PDN connections of the UE in same DCN ● Brand new 5G core network and system architecture ● One UE can connect to multiple slices ● AMF (equivalent of MME) is common to all slices ● Slice identified by Specific Network Slice Selection Assistance Information (S-NSSAI) ● S-NSSAI contains Slice Type and Slide DIfferentiator ● NSSAI = Set of S-NSSAI ● UE provisioned with a configured NSSAI per PLMN ● UE provided with allowed NSSAI by serving PLMN ● UE can be connected upto 8 S-NSSAIs (slices) simultaneously ● Requested NSSAI carried in RRC during initial access (when 5G-GUTI not available) ● Selection of NFs based on S-NSSAI
  3. 3. Slicing in LTE DECOR and eDECOR
  4. 4. How DECOR Works? UE eNB Initial MME Target MME HSS Attach Request Authentication Information Request Authentication Information Answer (Auth vectors, UE usage type) Check if this MME serves the UE usage type. If not initiate NAS redirectionReroute NAS Message Request (MMEGI of target MME, NAS message) Initial UE Message(NAS Message - Attach Request) Attach Procedure Continues with Target MME
  5. 5. Some key aspects of DECOR ● UE usage type is mapped to a Dedicated Core Network (DCN) ● MMEs that belong to a DCN are grouped together under a MME Group Id (MMEGI) ● Within a set of Tracking Areas (TA List), there can be multiple DCNs (and hence multiple MMEGI) ● During SGW selection MME uses TAI + UE usage type in DNS query to discover an SGW that belongs to the DCN. ● During PDN Connection establishment, the MME uses APN + UE usage type in the DNS query to discover PGW that serves the APN and belongs to the DCN.
  6. 6. Enhancements to DECOR (eDECOR) - R14 UE eNB Target MME HSS RRC Message (DCN-ID, NAS(Attach Request)) Select MMEGI based on DCN-ID received in RRC Attach Procedure Continues with Target MME S1AP Initial UE Message (NAS message(Attach Req), DCN ID) Attach Accept (DCN-ID) ● UE stores the DCN-ID provided by MME in per PLMN DCN-ID ● UE uses that DCN-ID in subsequent initial NAS messages (Attach, TAU) in that PLMN
  7. 7. Limitations of DECOR / eDECOR ● One UE = one DCN ID at a given time ● So at any given time one UE can be connected to only one DCN ● All PDN connections (even if it belongs to different APN) part of same DCN ● Simultaneous use of same application network (APN) via different 3gpp core networks not possible ○ E.g One UE simultaneously connected to multiple VPN (i.e APN name could be same) ⇒ In this case network isolation for each VPN not possible. ● UE selection of a slice based on application not possible (i.e UE can not tell over RRC which PDN connection needs to be routed to which DCN as all PDN connections are routed to same DCN)
  8. 8. Slicing in 5G
  9. 9. 5G Core Network Architecture Courtesy:
  10. 10. EPC vs 5G Network Slicing UE RAN MME SGW PGW (APN1) PGW (APN2) PGW (APN3) ● 1 UE - connect to one Dedicated Core Network (DCN) ● 1 DCN can support multiple applications (APN) ● Same application support in multiple DCNs require repeated configurations for same APN but different DCN in DNS UE RAN AMF SMF1 SMF2 SMF3 UPF1 DN-1 UPF2 DN-2 UPF3 DN-3 ● 1 UE - can connect to multiple core network slices ● Each slice identified by an S-NSSAI ● AMF is common to all slices UE uses ● SMFs specific to each slice ● SMFs selected via NRF specific to the slice (S-NSSAI) ● NRFs + SMFs can be in different administrative domain from AMF ● SMFs select UPF ● Traffic routing of each slice is independent and isolated ● RAN supports slicing at the radio ● Network Slice Selection Policies provided to UE to select a slice for a given application LTE - Evolved Packet Core (EPC) 5G Core Network (5GC) 10
  11. 11. 5G Control Plane Protocol Stack
  12. 12. Why MM - SM Split? ● Unlike EPC, the NAS stack in 5G is split between AMF and SMF. The SM part of NAS stack is handled at SMF. ● Why is this split needed? ○ Reason: Network slicing ○ Some slices don't need session management at all (e.g some IoT UEs that only support SMS). ○ For such cases, there is no need to have SM stack in the slice.
  13. 13. Key Concepts ● S-NSSAI: Specific Network Slice Selection Assistance Information. An S-NSSAI identifies a network slice. It contains ○ Slice/Service Type (SST) - refers to expected network slice behavior in terms of features and services. ○ Slice Differentiator (SD) - optional information - complementing SST to differentiate among multiple slices of same Slice type. ● NSSAI: A collection of S-NSSAI. ● Configured NSSAI: NSSAI provisioned in the UE applicable to one or more PLMNs. ● Allowed NSSAI: NSSAI provided to the UE by serving PLMN via NAS signaling. ● Requested NSSAI: NSSAI provided by UE to serving PLMN during Registration ● NSSP: Network Slice Selection Policy - contains policy rules to let UE select an HPLMN specific S-NSSAI for an application type. ● URSP: UE Route Selection Policy - NSSP is contained within URSP in UE ● NSI: Network Slice Instance - a collection of NF instances that serve a given S-NSSAI. NSI is not visible to UE and the RAN. It is a completely core network concept
  14. 14. What is Stored in UE? ● Configured NSSAI per PLMN (including HPLMN) and/or Configured NSSAI applicable to many PLMN(s) [i.e standard NSSAI to use for any PLMN] ○ Configured NSSAI provided by HPLMN initially = Set of Subscribed S-NSSAI ● For Configured NSSAI provided by serving PLMN, some rules to map HPLMN provided S-NSSAI to serving PLMN configured S-NSSAI is also provided. ● List of rejected S-NSSAI by serving PLMN at PLMN level and/or current Registration Area (set of TAs) level. ● NOTE: Number of configured NSSAI the UE can store other than that of HPLMN provided NSSAI is upto UE implementation. ● Ref: Clause 5.15.4 of 3GPP TS 23.501
  15. 15. Requested NSSAI Selection in UE - During Registration Procedure Registration Procedure Starts Is Allowed NSSAI for the serving PLMN available? Is Configured NSSAI for the serving PLMN available? Requested NSSAI = Allowed NSSAI or its subset Requested NSSAI = Configured NSSAI or its subset Yes Yes No No Requested NSSAI = NULL Reference: Clause of 3GPP TS 23.501
  16. 16. Requested S-NSSAI Selection in UE - During PDU Session Establishment PDU Session Establishment Procedure Starts Is URSP with NSSP available? Is mapping from Configured NSSAI of HPLMN to Allowed NSSAI available? Derive a S-NSSAI based on NSSP (NOTE: URSP with NSSP is provided by HPLMN). The derived S-NSSAI is of HPLMN scope No S-NSSAI included in PDU Session Establishment Request (NAS SM Message) Include an S-NSSAI mapped to an S-NSSAI in Allowed NSSAI Include an appropriate S-NSSAI from Allowed NSSAI Yes No Yes No Reference: Clause of 3GPP TS 23.501
  17. 17. Role of AMF ● During Registration Procedure: ○ Query UDM to get subscribed NSSAI ○ Verify if S-NSSAI(s) in requested NSSAI are permitted based on Subscribed NSSAI (AMF to map requested S-NSSAI to Configured NSSAI for HPLMN for roamers) ○ If allowed NSSAI not available in AMF UE context ■ Either query NSSF to determine Allowed NSSAI (or) ■ Based on local configuration determine if the AMF can serve the UE ● During PDU Session Establishment Procedure: ○ If NRF for the S-NSSAI included by UE already available at AMF - query the NRF to select an SMF from that slice instance ○ Else query the NSSF to select a slice instance for the S-NSSAI and get an NRF for that slice instance. Then query the NRF to select the SMF. ● At any time: ○ Update UE with new Configured NSSAI for the Serving PLMN along with mapping of this configured NSSAI to Configured NSSAI for the HPLMN. ■ Uses UE Configuration Update NAS procedure. ○ Update the URSP (and NSSP) in the UE when requested by PCF.
  18. 18. Role of NSSF ● During Registration Procedure: ○ Based on requested NSSAI and subscribed NSSAI provided by AMF select the network slice instance(s) to serve the UE for the set of S-NSSAI. ■ Correspondingly select the set of NRFs to be used in each of these selected network slice instance(s) ○ Alternatively NSSF may defer the selection of network slice instance(s) for S-NSSAI to PDU session establishment procedure. ○ Select a target AMF set or list of candidate AMFs ○ Determine allowed NSSAI ○ Provide mapping of each S-NSSAI of allowed NSSAI to subscribed S-NSSAI(s), if required ○ Return the above to AMF ● During PDU Session Establishment Procedure: ○ Based on requested S-NSSAI, select a network slice instance. ○ Determine the NRF to be used in that slice instance (within same PLMN) ○ Return the above to AMF
  19. 19. Role of NRF ● NRF is a Network Repository Function - a registry that maintains the NF profile and the NF services supported by each NF that has registered with it - within that network slice instance. ● During Registration Procedure: ○ AMF may query the NRF provided by NSSF to select target AMF or an NRF that is locally configured at AMF, to get the list of candidate AMFs. ● During PDU Session Establishment Procedure: ○ AMF queries the NRF from the network slice instance corresponding to the UE requested S-NSSAI to select an SMF from that network slice instance.
  20. 20. AN - AMF Interaction for Supported S-NSSAI Access Network (AN) AMF AN to AMF: S-NSSAIs supported in each TA. AMF to AN: Set of S-NSSAIs that the AMF can connect to. N2 Association Setup / Update Procedure
  21. 21. Registration Procedure in Non Roaming/Roaming Case UE NG-RAN AMF NSSF NRF UDM Registration Req over RRC (included Req NSSAI from allowed/configured NSSAI if GUTI not available) Route to AMF as per R-NSSAI or to a default AMF Get slice specific subscription data Slice selection request (Req NSSAI, Sub NSSAI, TAI, Mapping of Req NSSAI to HPLMN NSSAI for roamers) Slice selection response (Allowed NSSAI, Mapping information of allowed NSSAI to HPLMN NSSAI for roamers, NRF, Target AMF set, rejected S-NSSAI with cause) Query NRF and find target AMF / redirect registration to target AMF and continue rest of registration procedure
  22. 22. PDU Session Establishment Procedure in Non Roaming Case UE AMF NSSF NRF SMF PDU Session Establishment Request(DNN, S-NSSAI) Query NSSF if NRF for S-NSSAI is not available Return NRF address for the selected Network Slice Instance Query NRF to select SMF (DNN, S-NSSAI) Return SMF Address PDU Session Establishment Procedure Continues with Selected SMF
  23. 23. PDU Session Establishment Procedure - SMF Selection in Home Routed Roaming Case (Option 1) AMF vNSSF vNRF hNRF (slice Level) hNSSF Query vNSSF if vNRF for S-NSSAI is not available Return vNRF address for the selected Network Slice Instance Query vNRF to select vSMF (DNN, requested S-NSSAI) and hSMF (DNN, requested S-NSSAI mapped to HPLMN S-NSSAI), hNRF infor NF Discovery Request (DNN) Slice selection request Slice selection response (appropriate hNRF to use) NF Discovery Response (v-SMF, h-SMF address)
  24. 24. PDU Session Establishment Procedure - SMF Selection in Home Routed Roaming Case (Option 2) AMF vNSSF vNRF hNRF (PLMN Level) Slice specific local hNRF Query vNSSF if vNRF for S-NSSAI is not available Return vNRF address for the selected Network Slice Instance Query vNRF to select vSMF (DNN, requested S-NSSAI) and hSMF (DNSS, requested S-NSSAI mapped to HPLMN S-NSSAI) NF Discovery Request (DNN, S-NSSAI) Directly query slice instance specific NR if local configuration of slice instance specifc NRF based on S-NSSAI / NSI-ID available. NF Discovery Response (v-SMF, h-SMF address)
  25. 25. Use Cases Enabled by 5G Slicing 1 UE - common AMF - but multiple slices with slice specific SMF, UPF and PCF Courtesy:
  26. 26. Other Use Cases Enabled by 5G Slicing ● For vertical applications - operators can spawn SMF, UPF, PCF in separate slice instance(s) for that vertical market and route UE traffic for those vertical applications. ● Testing of new features in the network by deploying a specific slice and configuring a specific set of UEs to use that slice (through UE Configuration Update NAS procedures).
  27. 27. Thank You