Improved LTE mobility mgmt
Buu-Minh Ta
Charlie Perkins
Constraints & Goals
Constraints



eNodeB and MME
shouldn’t be changed
Use existing LTE
authentication
procedures
Use existing policy
interface via HA
Goals



Smooth and quick
handovers
Identify Mobile IP
features needed to
support inferred LTE
design goals
Present at IETF, publish
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
Architecture (1)
Internal HA
HA-D
P-GW
S-GW/P-GW
P-GW
GTP
MME
MME
HA-C
S-GW
pMME
S-GW
GTP
GTP
eNodeB
eNodeB
UE
UE
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
(UEpMME, 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
(UEpMME, 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 (pMMEP-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 (pMMEP-GW)
Internal HA
Binding Update
Header
Identifier
1. TEID: eNodeB GTP Tunnel Enpoint.
TEID
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, PGW 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