Buu-Minh TaCharlie Perkins

Improved LTE mobility mgmt

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

Constraints Goals

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?

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

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”

Overall Architecture

eNodeB

UE

S-GW

P-GW

MME

Architecture (1)Internal HA

eNodeB

UE

S-GW

P-GW

MME

HA-DS-GW/P-GW

HA-CpMME

GTP

GTP

GTP

Architecture (1)Internal HA

Architecture (2)External HA

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

Procedures

Moving to a network using MobileIP Initial Attach

..\Initial Attach.vsd Initial Attach with external HA

..\Initial Attach - HA external.vsd

Extensions to NAS protocol and Mobile IPv6

New NAS Attach Request message (UEpMME, pre-existing HA)

Attach Request’Attach

Request[NAS

protected]

Ciphered Options

[NAS protected]

Identifier

HA address

Derived Key

Ciphered

derived key

1. Attach Request: current message sent by UE to MME (protected using EPS security association). Encapsulated into a NAS container IE.

2. Ciphered Options: avoid one round trip to the UE.3. Identifier: NAI.4. HA address: so the pMME can send the BU. 5. Derived Key: to establish a security association between

pMME and HA.6. Ciphered derived key: so the HA can know the derived key,

and verify it has been establish by the UE.

New NAS Attach Request message (UEpMME, non-existing HA)

Attach Request’

Attach Request[NAS protected] Identifier

Ciphered Options

[NAS protected]

1. Attach Request: current message sent by UE to MME (protected using EPS security association). Encapsulated into a NAS container IE.

2. Identifier: NAI.3. Ciphered Options: avoid one round trip to the UE.

Binding Update (pMMEP-GW)External HA

Binding Update

Header Identifier Home Address

Care-of Address

Binding Authorization Data

Create Session Request

Ciphered Derived

Key

1. Care-of Address: external address of the P-GW.2. Binding Authorization Data: signature on everything that

precedes, using the derived key.3. Create Session Request: extracted by the P-GW.4. Ciphered Key: same as in the Attach Request.

Binding Update (pMMEP-GW)Internal HA

Binding Update

Header Identifier TEID

1. TEID: eNodeB GTP Tunnel Enpoint.

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.

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.

Pre-Authentication signal flow

Pre-Authentication ..\Pre-Attach + Attach - HA external.vsd

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.

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

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