Improved LTE mobility mgmt

1. Improved LTE mobility mgmt Buu-Minh Ta Charlie Perkins

2. Constraints & Goals Constraints Goals • eNodeB and MME shouldn’t be changed • Use existing LTE authentication procedures • Use existing policy interface via HA • Smooth and quick handovers • Identify Mobile IP features needed to support inferred LTE design goals • Present at IETF, publish

3. Issues • S-GW • What is its purpose? • Only intermediary on the GTP tunnel • Handovers between other networks? • Length of procedures… • How many roundtrips to establish the connection?

4. Initially planned response • Observation: Past projects have exhibited excellent performance using Mobile IP. • [S-GW + P-GW] = P-GW/S-GW  HA-D • pMME (proxy MME) HA-C • Keep existing PCEF/PCRF/PCC • Keep existing MME authentication

5. Why is S-GW separate from P-GW? • It’s not all that easy to figure out • Some purported justifications: • Aggregation of mobility events • Distribution of statistics gathering • Hiding aspects of radio technology • Enabling multi-homed eNodeBs • By now, the P-GW and S-GW seem tightly bound • A fully routed EPC seems likely to work “better”

6. Overall Architecture

7. Architecture (1)Internal HA HA-D S-GW/P-GW P-GW P-GW GTP MME MME GTP HA-C pMME S-GW S-GW GTP eNodeB eNodeB UE UE

8. Architecture (1)Internal HA

9. Architecture (2)External HA

10. Modifying Mobile IPv6 • Split HA into HA-D (== P-GW) + HA-C (== MME) • Enable HA to tunnel via GTP • HA-C  HA-D via GTP-C • Enable alternate security association (algorithm, data) • Enable Binding Authorization for HA • Enable alternative CoA • Problem: UE has no unique ID for eNodeB

11. Procedures

12. Moving to a network using MobileIP • Initial Attach • ..\Initial Attach.vsd • Initial Attach with external HA • ..\Initial Attach - HA external.vsd

13. Extensions to NAS protocol and Mobile IPv6

14. New NAS Attach Request message (UEpMME, pre-existing HA) • Attach Request: current message sent by UE to MME (protected using EPS security association). Encapsulated into a NAS container IE. • Ciphered Options: avoid one round trip to the UE. • Identifier: NAI. • HA address: so the pMME can send the BU. • Derived Key: to establish a security association between pMME and HA. • Ciphered derived key: so the HA can know the derived key, and verify it has been establish by the UE.

15. New NAS Attach Request message (UEpMME, non-existing HA) Attach Request: current message sent by UE to MME (protected using EPS security association). Encapsulated into a NAS container IE. Identifier: NAI. Ciphered Options: avoid one round trip to the UE.

16. Binding Update (pMMEP-GW)External HA Care-of Address: external address of the P-GW. Binding Authorization Data: signature on everything that precedes, using the derived key. Create Session Request: extracted by the P-GW. Ciphered Key: same as in the Attach Request.

17. Binding Update (pMMEP-GW)Internal HA TEID: eNodeB GTP Tunnel Enpoint.

18. Pre-Authentication with LTE network • Context: • UE is within reach of LTE network, but has not initiated attach and handover. • Goals: • Pre-authentication with pMME and MME to establish security association. • “Pro-active handover” to make the handover quicker.

19. Pre-Authentication with LTE network • How can we do it? • Pre-Authentication Request containing Attach Request to pMME. • pMME fakes the attach of the UE to a “virtual” eNodeB by forwarding the Attach Request to the MME. • Current Authentication and Identification procedures. • Pre-create the session within the P-GW • When the UE initiates the attach: • Continues the procedure (session already created, P-GW TEID available): Attach Accept • Basically, just need the eNodeB TEID to establish the tunnel.

20. Pre-Authentication signal flow • Pre-Authentication • ..\Pre-Attach + Attach - HA external.vsd

21. Additional steps • Consider client-triggered PMIP approach. • Map signaling to multi-stage HA into HMIP approach. • Insert preregistration sequences from SFF designs, attempt the application of FMIP context transfer.

22. Is it better? • With so many modifications, one wonders whether it is worth it to use Mobile IPv6 • But – compared to existing procedures, it is still much simpler – less signaling, fewer steps • Most of the complexity is due to constraint to avoid modifications to eNodeB/MME/GTP etc. • Have an almost complete spreadsheet

23. Next Steps • Build it • Experiment with new signaling designs • Try with simulators • Measure performance • Submit documents to [mext], [netext] • Submit documents to 3GPP SA2 • Wait for hell to freeze over