Formal Approach to Mobility Modeling

IETF 78 – IRTF MOBOPTS

Ashutosh DuttaBryan Lyles

Henning Schulzrinne

1

Outline

• Motivation• Abstract functions of mobility

event• Why mobility model• Next Steps?

2

Motivation• Cellular mobility typically involves handoff across

homogeneous access technology – Optimization techniques are carefully engineered to improve

the handoff performance• IP-based mobility involves movement across access

technologies, administrative domains, at multiple layers and involve interaction between multiple protocols– Mechanisms and design principles for optimized handover

need better analysis– Currently there are ad hoc solutions for IP mobility

optimization, not engineering practice – No formal methodology to systematically discover or

evaluate mobility optimizations – No methodology for systematic evaluation or prediction of

"run-time" cost/benefit tradeoffs

3

Backbone

AdministrativeDomain B

L2 PoA

Corresponding Host

128.59.10.7

IPch

207.3.232.10

210.5.240.10

128.59.11.8

N2

N1N1

N2

N1- Network 1 (802.11)N2- Network 2 ( CDMA/GPRS)

ConfigurationAgent

L3 PoA 207.3.232.10

MobileHost

AuthenticationAgent

Authorization Agent

RegistrationAgent

RegistrationAgent

Administrative Domain A

ConfigurationAgent

Authorization Agent

SignalingProxy

AuthenticationAgent

SignalingProxy

Layer 3 PoA

L2 PoA Layer 2 PoA

Layer 2 PoA

L3 PoA

Mobility Illustration in IP-based 4G network

128.59.9.6

L3 PoA

A

B

CD

900 ms media interruption

802.11 802.11

h/o delay900 ms

802.11 802.11

4 Seconds media interruption h/o delay 4 s

Handoff Delay~ 18 s

802.11 CDMA

18 Seconds media interruptionh/o delay18 s

4

Mobility/Function

AccessType

Network Discovery

Resource Discovery

TriggeringTechnique

DetectionTechnique

Configuration Key exchange/Authentication

Encryption BindingUpdate

MediaRerouting

GSM TDMA BCCH FCCH ChannelStrength

SCH TMSI SRES/A3 DES MSCContld.

Anchor

WCDMA CDMA PILOT SYNCChannel

ChannelStrength

Frequency TMSI SRES/A3

AES NetworkControl

Anchor

IS-95 CDMA PILOT SYNCchannel

ChannelStrength

RTC TMSI Diffie-HellmanAKA

Kasumi MSCContld.

AnchorMSC

CDMA1X-EVDO

EVDO PILOTChannel

SYNCChannel

ChannelStrength

RTC TMSI Diffie-Hellman/CAVE

AES MSC PDSN/MSC

802.11 CSMA/CA

Beacon11R

11R802.21

SNR atMobile

Scanning.ChannelNumber,SSID

SSID,Channel number

Layer 2 authenticate802.1XEAP

WEP/WPA802.11i

Associate IAPP

Cell IP Any Gatewaybeacon

Mobilemsmt.

APbeaconID

GW Beacon MAC AddressAP address

IPSec IPSec RouteUpdate

IntermediateyRouter

MIPv4 Any ICMPRouter adv.FA adv.

ICMPRouterAdv.

FA adv.L2 triggering

FA adv FA-CoACo-CoA

IKE/PANAAAA

IPSec MIPRegistration

FARFAHA

MIPv6 Any StatelessProactive

CARD802.2111R

RouterAdv.

RouterPrefix

CoA IKE/PANAAAA

IPSEC MIP updateMIP RO

CHMAPHA

SIPM Any StatelessICMP Router

802.2111R

L3RouterAdv.

Router Prefix, ICMP

CoAAORRe-Register

INVITE exchange/AAA

IPSEC/SRTP/S/MIME

Re-INVITE B2BUACHRTPtrans

Abstraction of mobility functions

5

HandoverEvent

Network discovery &selection

Networkattachment

Configuration Securityassociation

Bindingupdate

Mediareroute

Channeldiscovery

L2 association

Routersolicitation

Domainadvertisement

Identifieracquisition

DuplicateAddressDetection

AddressResolution

Authentication(L2 and L3)

Keyderivation

Identifierupdate

Identifiermapping

Bindingcache

Tunneling

Buffering

Forwarding

Bi-casting/Multicasting

Serverdiscovery

IdentifierVerification

Subnetdiscovery

P1 P2 P3 P4 P5 P6

P11

P13

P12

P21

P22

P23

P31

P32

P33 P41

P42P51

P52

P53

P54

P61 P62

P63

P64

System decomposition of handover process

6

Dependency analysis among handover operationsHandoff Process Precedence

RelationshipData it depends on

P11 – Channel Discovery P00 Signal-to-Noise Ratio valueP12 – Subnet discovery P21,P22 Layer 2 beacon ID

L3 router advertisementP13 – Server discovery P12 Subnet address

Default router addressP21- Layer 2 association P11 Channel number

MAC address Authentication key

P22- Router solicitation P21, P12 Layer 2 bindingP23- Domain advertisement P13 Server configuration

Router advertisementP31 – Identifier acquisition P23,P12 Default gateway

Subnet address Server address

P32 – Duplicate addressdetection

P31 ARPRouter advertisement

P33 – Address resolution P32, P31 New identifierP41 – Authentication P13 Address of authenticatorP42 – Key Derivation P41 PMK (Pairwise Master Key) P51 – Identifier update P31,P52 L3 Address

Uniqueness of L3 addressP52 – Identifier verification P31 Completion of COTIP53 – Identifier mapping P51 Updated MN address

at CN and HAP54 – Binding cache P53 New Care-of-address mappingP61 – Tunneling P51 Tunnel end-point address

Identifier addressP62 – Forwarding P51, P53 New address of the mobileP63 – Buffering P62, P51 New identifier acquisition P64 – Multicasting/Bicasting P51 New identifier acquisition 7

Resource usage per mobility eventsSub transitions

Sub-operations Resource Consumption

Bytes exchanged

CPU samples

Power (nano joules)

t00 Layer 2 un-reachability test 43 5 51600t01 Layer 3 unreachability 86 3 103200t11 Discover layer 2 channel 109 3 130800t12 Discover layer 3 subnet 110 4 132000t13 Discover server 126 5 540000t21 Layer 2 association 99 2 118800t22 Router solicitation 70 4 84000t23 Domain advertisement 226 4 271200t31 Identifier acquisition 1426 5 1711200t32 Duplicate address detection 164 6 196800t33 Address resolution 60 3 72000t41 Layer 2 open authentication 94 3 112800t42 Layer 2 EAP 2842 6 3410400t43 Four-way handshake 504 4 604800t51 Master key derivation (PMK) 0 10 0

t52 Session key derivation (PTK) 0 6 0

t61 Identifier update 204 4 422400t62 Identifier verification 148 6 177600t63 Identifier mapping 0 8 0t64 Binding cache 0 3 0t71 Fast binding update 110 3 132000

t72 Local caching 0 6 0

t81 Tunneling 60 2 72000t82 Forwarding 100 2 120000t83 Buffering 120 3 144000t91 Local id mapping 40 4 48000

t92 Multicasting/bicasting 192 2 230400 8

Why Mobility Model ?Problem: In the absence of any formal mechanism it is difficult to

predict or verify the systems performance of un-optimized handover or any specific handoff optimization technique

Specific expected results– Generate automatic schedule of handoff operations given a

set of resource constraints, performance objectives and dependence relationship

– A methodology to verify the systems performance of a specific optimization technique as well as systems behavior (e.g., deadlocks)

– Ability to design a customized mobility protocol that will define its own set of elementary operations for each of the desired handoff functions

– Specification of the functional components of mobility protocols and tools that search for context specific optimizations, such as caching, proactive feature and cross layer techniques

Possible Next Steps?• In order to transition ad hoc optimization

approaches to engineering best practice we need the following:– Framework or model that can analyze the mobility event

in a systematic way, can verify and predict the performance under systems resource constraints

– A set of fundamental design principles to optimize handoff components across layers

– A set of well defined methodologies to verify the optimization techniques for mobility in an IP-based network

– Need best current practices for mobility deployment• Write a document with mobility design principles

and systematic approach to building a mobility model – cite some sample illustrative models if possible 10