Heikki Lindholm, Lirim Osmani,Sasu Tarkoma, Hannu Flinck*,

Ashwin Rao

State Space Analysis to Refactor the Mobile Core

University of Helsinki *Nokia Networks

HomeSubscriber

Server(HSS)

ServingGateway(SGW)

EvolvedNode B

(eNodeB)

Network Functions in LTE Networks

Policy Control &ChargingFunction(PCRF)

MobilityManagement

Entity(MME)

UserEquipment

(UE) Inte

rnet

Mob

ile N

etw

ork

Radi

o Ac

cess

Net

wor

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Mob

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ore

PacketData

NetworkGateway(PGW)

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• Shortcomings of current architecture– Signaling Storm– Stateful gateways

• Demands from network operators– Reduce costs– Move functionality close to radio access network

Motivation for Refactoring

ServingGateway(SGW)

EvolvedNode B

(eNodeB)

PacketData

NetworkGateway(PGW)

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With virtualization at our disposal, can we simplify the architecture?

ForwardingElement

ForwardingElement

A Desirable Architecture

Policy Manager

UserEquipment

(UE) Inte

rnet

Mob

ile N

etw

ork Radio Access

NetworkMobile Core

ForwardingElement

Control PlaneUser Plane Logically Centralized Controller

Forwarding rules govern where packets are forwarded

Program forwarding elements to comply with the policy

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How do we refactor the mobile core?

• Device ID• Radio State • Location• Control-plane State• User-plane State

Grouping of State Variables

Abstracting usage of state variables

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• Initial Attach• Idle • Wake-up• Mobility• Service Request• … many more

Procedures using State Variables

Paper

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Network Function Device ID Location Radio State

Control-plane State

User-plane State

eNodeB ✔ ✔ ✔ ✔ ✔

MME ✔ ✔ ✗ ✔ ✔

SGW ✔ ✔ ✗ ✔ ✔

PGW ✔ ✔ ✗ ✔ ✔

HSS ✔ ✗ ✗ ✔ ✔

PCRF ✔ ✔ ✗ ✗ ✔

State Variables after Attach

Network Functions replicate state variables

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Network Function Location Control-plane State User-plane State

eNodeB P - P C P C

MME P C P C P C

SGW - C P C P C

PGW - C P C P C

HSS - - - C P -

PCRF - C - - P C

How are State Variables Replicated?

P : ProducerC : Consumer

• Can we group the Producers?• Can we move Consumers close to the Producers?

Take decisions at Producers?

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• Module for managing each variable group– Multiple variable groups modified in each

procedure– Incurs additional signaling between modules

• Module to serve each procedure– Merge modules from network functions that serve

the same procedure– Flexibility to determine physical location of

modules

Approaches to Refactor

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ForwardingElement

ForwardingElement

Proposed Architecture

Policy Manager

UserEquipment

(UE) Inte

rnet

Mob

ile N

etw

ork Radio Access

NetworkMobile Core

ForwardingElement

Control PlaneUser Plane

Mobile CoreControl Agent

Logically Centralized Mobile Core Controller

Attac

h

Idle

Wak

e

Mob

ility

Attac

h

Idle

… …

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Publish SubscribeSHIM for backward compatibility

• Formal Analysis – Analyze dependency network of Procedures and

State Variables– Essential to gather insights on the requirements

from the mobile core• Simulations/Emulations– Modifying LTE simulator/emulator

Next Step

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• Can we leverage virtualization technologies to simplify the architecture of the mobile core?

• Abstract the state variables• Producer/Consumer relationship between

network functions• Pub-sub architecture to serve the mobile core

Conclusion

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ashwin.rao@helsinki.fi

Thank You!

State Space Analysis to Refactor the Mobile Core

University of Helsinki Nokia Networks

Backups

• Route packets• Control network access• Support client mobility• Provide network security• Manage network functions

Main Functions of the LTE Core

Modularity based on Abstraction

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Why should future network functions be based on the existing protocol interactions?

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What do we gain from a refactored

centralized control plane?

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Could you have reached the same architecture by considering the

generic functions that any mobile network will need?

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• Network Access Control• Packet Routing and Transfer• Mobility Management• Security• Network Management

Main Functions of the Core

Complete List of Procedures

1) Device ID Primary keys in device/subscription lookupsIMSI, GUTI, …

2) Location Cell level location informationTAI, Tracking area list, ECGI, …

3) Radio Session State Radio link related informationC-RNTI, DRB, AS security context, …

4) Control-plane State Identifiers for control plane connectionsS5/S8/… IPs and TEIDs, NAS security context, …

5) User-plane State User-plane state identifiersS1u/S5u/…, QoS, bearer info, …

Grouping of State Variables

– Is this the best grouping?– Why not consider events first?– Backward compatibility issues?– What about other procedures?

TODO: Backups

ServingGateway(SGW)

EvolvedNode B

(eNodeB)

Network Functions in LTE Networks

Policy Control &ChargingFunction(PCRF)

MobilityManagement

Entity(MME)

HomeSubscriber

Server(HSS)

UserEquipment

(UE) Inte

rnet

Mob

ile N

etw

ork

Radi

o Ac

cess

Net

wor

k

Mob

ile C

ore

PacketData

NetworkGateway(PGW)

Control PlaneUser Plane