Formal Approach to Mobility
Modeling
IETF 78 – IRTF MOBOPTS
Ashutosh Dutta
Bryan 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
Mobility Illustration in IP-based 4G network
Administrative
Domain A
Administrative
Domain B
Authorization
Agent
Registration
Agent
Authorization
Agent
Authentication
Agent
Authentication
Agent
Configuration
Agent
Signaling
Proxy
N1
Registration
Agent
Configuration
Agent
N2
N1
Backbone
IPch
Signaling
Proxy
L3 PoA
Corresponding
Host
Layer 2
PoA
207.3.232.10
A
L2 PoA
L3 PoA
N2
128.59.11.8
L2 PoA
Layer 3
PoA
B
C
D
L3 PoA
128.59.10.7
Mobile
Host
N1- Network 1 (802.11)
N2- Network 2 ( CDMA/GPRS)
Layer 2
PoA
207.3.232.10
802.11
802.11
210.5.240.10
128.59.9.6
802.11
Handoff Delay
~ 18 s
CDMA
802.11
802.11
900 ms
media interruption
h/o delay
900 ms
4
h/o delay
18 s
18 Seconds media interruption
4 Seconds media interruption
h/o delay 4 s
Abstraction of mobility functions
Mobility/
Function
Access
Type
Network
Discovery
Resource
Discovery
Triggering
Technique
Detection
Technique
Configuration
Key
exchange/
Authentic
ation
Encryption
Binding
Update
Media
Rerouting
GSM
TDMA
BCCH
FCCH
Channel
Strength
SCH
TMSI
SRES/A3
DES
MSC
Contld.
Anchor
WCDMA
CDMA
PILOT
SYNC
Channel
Channel
Strength
Frequency
TMSI
SRES/A
3
AES
Network
Control
Anchor
IS-95
CDMA
PILOT
SYNC
channel
Channel
Strength
RTC
TMSI
DiffieHellman
AKA
Kasumi
MSC
Contld.
Anchor
MSC
CDMA
1XEVDO
EVDO
PILOT
Channel
SYNC
Channel
Channel
Strength
RTC
TMSI
DiffieHellman/
CAVE
AES
MSC
PDSN/MSC
802.11
CSMA/
CA
Beacon
11R
11R
802.21
SNR at
Mobile
Scanning.
Channel
Number,
SSID
SSID,
Channel
number
Layer 2
authentic
ate
802.1X
EAP
WEP/WP
A
802.11i
Associate
IAPP
Cell IP
Any
Gateway
beacon
Mobile
msmt.
AP
beacon
ID
GW Beacon
MAC
Address
AP address
IPSec
IPSec
Route
Update
Intermediat
ey
Router
MIPv4
Any
ICMP
Router
adv.
FA adv.
ICMP
Router
Adv.
FA adv.
L2
triggering
FA adv
FA-CoA
Co-CoA
IKE/PA
NA
AAA
IPSec
MIP
Registratio
n
FA
RFA
HA
MIPv6
Any
Stateless
Proactive
CARD
802.21
11R
Router
Adv.
Router
Prefix
CoA
IKE/PA
NA
AAA
IPSEC
MIP
update
MIP RO
CH
MAP
HA
SIPM
Any
Stateless
ICMP
802.21
11R
L3
Router
Router
Prefix,
CoA
AOR
INVITE
exchange
IPSEC/
SRTP/
Re-INVITE
B2BUA
CH
5
System decomposition of handover process
Handover
Event
P1
P2
Network
discovery &
selection
P11
Channel
discovery
P13
P3
Network
attachment
P12
Subnet
discovery
P21
L2
association
Server
discovery
P4
Configuration
P5
Security
association
P6
Media
reroute
Binding
update
P31
Identifier
acquisition
P23
Domain
advertisement
P22
Router
solicitation
P33
Address
Resolution
P32
Duplicate
Address
Detection
P41
Authentication
(L2 and L3)
P53
Identifier
mapping
P42
Key
derivation
P51
Identifier
update
P62
P61
Tunneling
P54
Binding
cache
Forwarding
P63
Buffering
P64
P52
Identifier
Verification
Bi-casting/
Multicasting
6
Dependency analysis among handover operations
Handoff Process
P11 – Channel Discovery
P12 – Subnet discovery
Precedence
Relationship
P00
P21,P22
P13 – Server discovery
P12
P21- Layer 2 association
P11
P22- Router solicitation
P23- Domain advertisement
P21, P12
P13
P31 – Identifier acquisition
P23,P12
P32 – Duplicate address
detection
P33 – Address resolution
P41 – Authentication
P42 – Key Derivation
P51 – Identifier update
P31
P52 – Identifier verification
P53 – Identifier mapping
P31
P51
P54 – Binding cache
P61 – Tunneling
P53
P51
P62 – Forwarding
P63 – Buffering
P64 – Multicasting/Bicasting
P51, P53
P62, P51
P51
P32, P31
P13
P41
P31,P52
Data it depends on
Signal-to-Noise Ratio value
Layer 2 beacon ID
L3 router advertisement
Subnet address
Default router address
Channel number
MAC address
Authentication key
Layer 2 binding
Server configuration
Router advertisement
Default gateway
Subnet address
Server address
ARP
Router advertisement
New identifier
Address of authenticator
PMK (Pairwise Master Key)
L3 Address
Uniqueness of L3 address
Completion of COTI
Updated MN address
at CN and HA
New Care-of-address mapping
Tunnel end-point address
Identifier address
New address of the mobile
New identifier acquisition
New identifier acquisition
7
Resource usage per mobility events
Sub
Sub-operations
transitions
Resource Consumption
Bytes
exchanged
CPU
samples
Power
(nano
joules)
t00
t01
t11
t12
t13
t21
t22
t23
t31
t32
t33
t41
t42
t43
t51
Layer 2 un-reachability test
Layer 3 unreachability
Discover layer 2 channel
Discover layer 3 subnet
Discover server
Layer 2 association
Router solicitation
Domain advertisement
Identifier acquisition
Duplicate address detection
Address resolution
Layer 2 open authentication
Layer 2 EAP
Four-way handshake
Master key derivation (PMK)
43
86
109
110
126
99
70
226
1426
164
60
94
2842
504
0
5
3
3
4
5
2
4
4
5
6
3
3
6
4
10
51600
103200
130800
132000
540000
118800
84000
271200
1711200
196800
72000
112800
3410400
604800
0
t52
t61
t62
t63
t64
t71
t72
t81
t82
t83
t91
t92
Session key derivation (PTK)
Identifier update
Identifier verification
Identifier mapping
Binding cache
Fast binding update
Local caching
Tunneling
Forwarding
Buffering
Local id mapping
Multicasting/bicasting
0
204
148
0
0
110
0
60
100
120
40
192
6
4
6
8
3
3
6
2
2
3
4
2
0
422400
177600
0
0
132000
0
72000
120000
144000
48000
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