Global Mobility Management in Multi-access Networks

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© 2007
Global Mobility in Multi-access Networks
Rute Sofia
(rsofia@inescporto.pt)
http://telecom.inescporto.pt/~ian
2008 Fev 27

© 2008
This work is licensed under the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0
Unported License. http://creativecommons.org/licenses/by-nc-nd/3.0/
INESC-Porto, 2007.02.27
2
Overview
• What is global mobility
• The global perspectice
• Some use cases
• Notions
• Is it really needed? Yes vs. No factions
• Main requisites
• Main mobility management approaches of today
• Summary/Conclusions
• Some interesting research topics

© 2008
3
What is Global Mobility?
• Today, end-users have a highly nomadic lifestyle (e.g. frequent travelling; different
residential locations; different access locations)
– Least service disruption: access services, anywhere, anytime.
• End-users hold in average a cellular and a fixed access subscription
– One end-user may hold N subscriptions coming from X providers
– Multi-access technologies and architectures are involved (wireless/fixed/cellular)
• Wireless introduced the possibility to extend Internet access into new areas
– Wireless extends the fixed networks
– Wireless works as new backhaul
– Wireless allows bypassing local-loop legislation
– Potential for new services and new markets
• Multi-access architectures (wireless/fixed/cellular)
– One or more operators involved; different access technologies
Global Mobility: Internet access anywhere, anytime, independently of location,
terminal and access technology

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4
User on the Move
(Train, car…)
User Plane Session stays; re-registration not required –
SESSION CONTINUITY
Provider A
Domain 1
Domain 2
Domain 3
Domain 4
Domain 5
Domain 6
Fixed Wireless Mobile
Micro-Mobility Micro-Mobility Micro-Mobility
Provider B Provider C
Partial Macro-Mobility
The Global Perspective
Today
User on the Move
(Train, car…)
Session breaks; re-registration required –
nomadism but NO session continuity
User Perspective
Internet Services
(Google, Skype, …)
IMS Services
(Instant Messaging,
VoIP)
Service Provider
Perspective

© 2008
5
User on the Move
(Train, car…)
User Plane Session stays; re-registration not required –
SESSION CONTINUITY
Provider A
Domain 3
Domain 4
Domain 5
Domain 6Fixed Wireless Mobile
Provider B Provider CAccess/Network
Provider Perspective
A GLOBAL SOLUTION…Mobility Management
Functionality
Global Macro-Mobility
Any Access
Any Service
Seamless to the
User
The Global Perspective
Tomorrow
User on the Move
(Train, car…)
User Perspective
Internet Services
(Google, Skype, …)
IMS Services
(Instant Messaging,
VoIP)
Service Provider
Perspective
No visible interruption: session continuity
Domain 1
Domain 1 Domain 1
Domain 2 Domain 2 Domain 2

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6
Use Case 1
Hotspots /Internet-on-the-go
MN on the move
Provider A
Administrative
Domain 1
Provider B
Administrative
Domain 2
Same IP subnet
(L2 mobility
scheme)
Administrative
Domain 3
Administrative
Domain 4
Wireless Mobile
Hotspot 1
Correspondent Node 1
Different IP subnets
Hotspot 2

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Mobile Access
Fixed Access
Use Case 2
Multihoming
• End-user holds a mobile terminal with UMTS and WLAN interfaces
• On the street relies on UMTS
• At home prefers WLAN/DSL (higher throughput) -broadband access uses Wi-Fi as first-
hop
• Two interfaces = two different IP addresses
– Automatically activate an interface
– Automatically divert sessions from one interface to another?
• And if receiver has two different interfaces, which one to rely upon?
GGSN
UMTS
Access
WLAN
Access
Access
Router
Internet

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Use Case 3
FON, viral networks
Internet
Access
provider
• Fonera community
– Linus: buys social router (34,4 € plus 5 €
dispatch) for own use; shares broadband
access for free
– Bill: buys router and re-sells access; gets
50% of sales from vouchers
– Alien: gets access by means of vouchers
• Viral network
– Spread without operator control
– Backhaul is not changed!
• Limited mobility
– Just nomadism
• Simple AAA
– WEP, WPA
– No incentive for malicious usage
“Bill” user1
“Alien” user3
Pays 3€ per 24h usage
“Linus” user2@somewhere
“Linus” user1@home

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Mobility Management Notions (1/2)
Nomadism, aka Nomadicity
• The same service look & feel delivered independently of
user location or terminal
• Change of attachment point requires service re-activation
•Sessions (e.g., TCP) have to be re-initiated
• Requires global form of addressing (identification)
and global AAA
• Example: 3G global roaming
Session Continuity
• Sessions are seamessly diverted (handed over) from
an old identifier to a new
• Change of attachment point does not disrupt
active sessions
• Examples: L2 mobility support (micro-mobility);
Mobile IP (v4 and v6)
Optimized Global Mobility
Management requires
support for both
nomadism and session
continuity

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10
Mobility Management Notions (2/2)
• Global handover = Layer 2 handover + Layer 3 handover
• Layer 2 handover building blocks
– E.g.: in 802.11b, 500~2000ms, mainly scanning of available APs
• Layer 3 handover building blocks
• Movement detection (1-3s; Neighbor Discovery default values)
– Current router reachability
– Validity of current address
– Availability of new router on the network
– IP address configuration (stateless, stateful)
• Duplicate address detection (DAD) time (~1s)
• Layer 3 signaling procedures (example based on MIPv6)
• Binding update (in microseconds)
• Route optimization (in microseconds)
0 0.5 3 4 4.05
Layer 2 handover Movement detection DAD
Layer 3 signaling
Global Handover latency components
(example based on Wi-Fi+MIPv6)
Time (sec)

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11
Do we Really Need Global Mobility Management?
Yes vs No Factions
The “No” Faction
• Only some applications require session continuity
•No need for it in the near future
• Mobility management is not a service per se
• Mobility management must be centralized to work
• Mobility management is a layer 2 issue and has been dealt with
• Main stakeholders: 3GPP
The “Yes” Faction
• End-user nomadic lifestyle is increasing
•Global mobility management is necessary to convey adequately all subscribed services
• Global mobility provides basis for new services
•New business models and opportunities will come along
• A single operator should not take care of all mobility management
• Stakeholders: virtual and micro operators; wireless-based operators, end-users

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Main Requisites
• Support for multi-access networks
– Fixed, mobile, wireless
– Multi-mode terminals
– One or more operators involved
– Simultaneous handover support (source and receiver)
• Services provided anywhere, anytime
– Zero disruption!
– Independently of access technology and terminal
– Agnostic to ANY application (current OR FUTURE)
• Highly nomadic lifestyle requires…
– Adequate global AAA (or incentive to act honestly)
– Adequate global resource management
– Seamless handovers (session continuity)
– Ease of use (user-friendly approaches)
Can we do it with based upon current approaches?
One solution serves all, or shall approaches be combined?

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Major Mobility Approaches of Today
Transport
(OSI L4)
Network
(OSI L3)
Data/Link
(OSI L2,L1)
Application
(OSI L5-L7)
*SCTP: Stream Control Transport Protocol
SIP/IMS
M-SCTP*
HIP
Mobile IP
Layer 2 Mobility
(micro-mobility)
GPRS/UMTS
Wi-Fi
WiMAX
“Mobile” Ethernet

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3GPP Mobility Management
• Roaming agreements between different providers
• Connectivity: GTP tunneling – only one IP address is used
anywhere, anytime!
• Normally, Home GGSN is the mobility anchorpoint
• In some cases, the Visited GGSN may be the chosen anchorpoint!
• E.g., due to resources or proximity of services
• No session continuity possible with GTP!
• Current solution discussed – Mobile IP
•GGSN:Gateway GPRS Support Node
•SGSN: Serving GPRS Support Node
•UE: User Equipment
•RNC: Radio Network Controller
•HLR: Home Location Register
•PDP: Packet Data Protocol
•PLMN: Public Land Mobile Network
•NSP: Network Service Provider
•BG: Border Gateway
•GTP: GPRS tunneling protocol
•ER: Edge Router
• Potential Benefits
– Long experience in mobility
management
– ETSI TISPAN expands
IMS to fixed access
• Key Issues
– Requires specific client
– Only supports nomadism
– Only supports VoIP/IM
– Not suited for Internet-
based services

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WiMAX Mobility management
Main Features
• 802.16-2004 defines the fixed WiMAX
– Only nomadism
• 802.16e-2005 defines the mobile WiMAX
– Mobility: nomadism and session
continuity
– Intra-ASN handovers supported by L2
– Inter-ASN supported by Mobile IP
• ASN-GW as mobility anchor point
– Open system
– Contemplates global mobility
– Considers interoperability with other technologies
• Key Issues
– Coverage, collisions
– Specific security system has implications in interoperability
– Layer 2 features may require adaptation from upper layer
mechanisms
•UE: User Equipment
•NAP: Network Access Provider
•NSP: Network Service Provider
•ASP: Application Service Provider
•MSS: Mobile Subscriber Station
•CoA: Care-of-Address
•BS: Base Station

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Wi-Fi Mobility management
Internet
Mobile
Provider
WIMAX
Provider
AP1
AP2
AP3
AP14 DSL
Provider
Micro-handover
Macro-handover
Macro-handover
Main Features
• Handover triggered by signal threshold
• Scanning causes major latency of handover
(300~400 ms)
– Some optimized algorithm can reduce
scanning latency to ~50ms (still too large for
real-time applications)
– Easy to implement
– High deployment penetration
– Easily extends other access technologies
• Key Issues
– MAC Layer vendor-specific interpretated
– Low coverage
– collisions
– No global mobility method
– Weak security

© 2008
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Network layer Mobility Management (1/5)
Mobile IP
• HA: Home Agent
– Mobility anchor point
– Control plane: signalling, registration, data
redirection
– Data plane: routing
• MN: Mobile Node
– MIPv6/v4 client
– If MIPv6, integrated in the IPv6
stack – not an additional package!
• CN: Correspondent Node
– Third-party with whom MN
communicates
MN
Seamless handover
Provider A
Administrative
Domain 1
Provider B
Administrative
Domain 2
Administrative
Domain 3
Administrative
Domain 4
Different IP
subnets
MN
Wireless Mobile
Internet Services
CN 1
CN 2
Different IP
subnets
Same IP
subnet
(L2 mobility
scheme)

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Visited Network
Foreign Agent (FA)
Mobile Node
(MN)
Assigns (permanent) HoA to MN
If MN has registered its new CoA,
HA intercepts Packets to MN HoA
and tunnels them to FA
Home Address
(HoA)
MN
Internet
Registers CoA with HA via FA
Home Network
Home Agent (HA)
Assign CoA to MN and
forwards traffic arriving on
from the tunnel to the MN
1. Mobile Node moves
2. FA advertises IP address
3. MN registers CoA with HA
via FA
4. HA intercepts all packets
to HoA of MN and tunnels
them to CoA (FA)
5. FA decapsulates packets
and forwards them to the
MN
6.In the other direction,
packets do not need to be
tunneled to the HA ->
triangular routing
Network Layer Mobility Management (2/5)
Mobile IPv4
1
2
3
4
5
CoA: Care-of-address

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19
VN
MN
(HoA=IP1)
MN (CoA=IP2)
Internet
CN
HN
Home Agent (HA)
MIPv6 (Mobile IPv6)
Access Router2
3
3
1
1. MN moves
2. gets CoA from VN access
router (automatically)
3. MN registers CoA with
HA AND with active CNs
4. HA intercepts packets
sent to HoA and redirects
them to CoA (v6-in-v6*
tunneling)
5. active sessions get
actively diverted
GRE tunneling: Global Routing Encapsulation
HN: Home Network
VN: Visited Network
HoA: Home Address

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20
ADVANTAGES TO MIPv4
• Integrated into IPv6
•Mandatory in every implementation
• Larger address space
• No foreign agent
• Address autoconfiguration
• Integrated Neighbor/Router
discovery/unreachability
• Improved Security
•MIPv6 return routability procedure
•IPsec used to protect MIPv6 exchanges
• Automatic home agent discovery
• Support for route optimisation
• More efficient routing
•CN->MN packets sent directly
•MN->CN packets sent directly
MIPv6 OPTIMISATION APPROACHES
• Fast handover support
•Reduction of movement detection time
•Signaling load minimisation/network registration
time reduction
•Fast handovers for MIPv6, FMIPv6 (RFC 4068)
•Hierarchical MIPv6, HMIPv6 (RFC 4140)
•F-HMIPv6 (draft in progress)
• Smooth handover support
•Multihoming issues (IETF WG Monami6)
•Simultaneous bindings (draft in progress)
Default MIPv6 is slow for real-time and
interactive applications handovers, even
ignoring the data link layer handover delay
MIPv6 Advantages/Open Issues

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21
HMIPv6
• Reduces the MIPv6 signaling load – separates local from
global mobility
• Two different CoAs: Local CoA (LCoA), Regional (RCoA)
•MN does not need to frequently change CoA (but still
exchanges regular binding updates)
• MAP works as local HA: intercepts packets to the MN and
tunnels them to the LCoA
VN 1
MN
Internet
HN
HA
CN
VN 2
LCoA 1 LCoA 2
MN H@ => RCoA
MAP
FMIPv6
• Reduces the latency/packet loss between
handovers
• Anticipates the L3 handover (L2 trigger)
• Access router forwards data packets to
new location during the L3 handover
• Assumes that old AR knows neighbor AR
informationMN@PCoA
RCoA
LCoA1
LCoA2
VN 1
Internet
HNHA
CN
VN 2
1. L3 Information about new
AR obtained as soon as MN
“discovers” new possible L2
attachment
3. CN traffic redirected
while MIPv6 binding
exchange for NCoA is
being performed
MN@NCoA
2. Tunnel established by
previous access router,
between PCoA and NCoA
SOME MIPv6 Extensions

© 2008
22
Between network and transport Layers (1/3)
HIP: Host Identity Protocol (IETF RFC 4423)
–Originally intended as security protocol
•Supports multihoming
•Embodies some of the properties required for
mobility, e.g., identifier independent of
link/network layer addresses
•Communication secured by means of IPSec
–Bump in the Stack
•New Layer (host layer), between
network/transport layers
•New Host Identifier (HI)
•For applications, HI is used; for routing, IP
–End-host identified by a public key
•128-bit hashed key (called HIT tag) identifies
host on a session
•32-bit local scope identifier used for
compatibility to IPv4
•Binding to IP address is dynamic and can have
a 1-N relation
–Host Layer
•New namespace – extensions for DNS required
•New signaling protocol, 7 message types

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Between network and transport Layers (2/3)
HIP: The Overall Picture
Above the HI Layer, communication uses HI for identity
Below the HI layer, HI is replaced by IP for routing
SPD: Security Policy Database
SAD: Security Association Database

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Between network and transport Layers(3/3)
HIP: Summary
– Potential Benefits
• Security/anonimity
• Multihoming support
• Solution that can support global mobility (agnostic handovers to ANY application)
– Key Issues
• Requires OSI stack update – new layer between network/transport
• Requires DNS extensions (two new resource records)
• DNS – HIP mapping is problematic
– Mobility: frequent handovers imply frequent mappings of HI to locator
– Charging/local identifier association is tricky
– Mapping global tag to other identifiers problematic within a service/access provider

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Session Layer Mobility
SIP Session Identification Protocol (1/2)
Pre-Call Stage
– SIP Proxy Server
• Relays call signalling
• Keeps no session state
– SIP Redirect Server
• Redirects callers to other servers
– SIP Registrar
• Accept registration requests
• Keeps state about user (Location Server)
– SIP Address
• Globally reachable
• Address data format, e.g.,
user@somewhere.org
– Must include hostname; may include
username, port number, others
– Non-SIP URLs can be used (e.g.,
mailto)

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Session Layer Mobility
SIP Summary (2/2)
– SIP is generalized as signaling solution
– Can deal with NATs (STUN)
– Allows different levels of mobility
(personal, terminal, service)
– Can be used together with other
solutions
– Signalling path != data path – SIP
components do not interfere in the data
path
• Key Issues
– Does not support TCP-based
applications
– Does not provide global session
continuity
• But redirection with minor delay is
possible (for SIP-based
applications)
Mid-Call Stage

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27
“Mobile” Ethernet (1/4)
• Mitsubishi/NIICT paper/solution (2001)
• Relies on a virtual MAC address scheme
– Mostly thought for multihoming cases
• Architecture “glues” different segments forming a single IP subnet
– Signaling required to update MAC tables split (inter/intra segment)
• Layer 3 broadcasts (e.g., ICMPv6) treated as unicast
• Neighbor discovery servers hold mapping between IP/ virtual MAC
• Specific mobility management frames used

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28
“Mobile” Ethernet (2/4) - Registration
• MN (MD) enters AP range
• performs registration request
• AP forwards request to Edge Switch
• Edge Switch requests a Virtual MAC
address to a Neighbor Discovery
Server (NDS)
• Edge Switch creates entry for
obtained virtual MAC
• Switches in the Mobile Ethernet only
learn the virtual MAC

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29
Mobile Ethernet (3/4) - Handover
• MN (MD) moves between different APs
• Signaling server detects handover and
sends HO recommendation to Edge Switch
• Old Edge Switch sends state about virtual
MAC to new Edge Switch
• MN requests registration to new switch
• New edge switch updates virtual MAC entry

© 2008
30
Mobile Ethernet (4/4)
• Glues segments together
• No need to change IP address – agnostic to application
• Good support for multi-homed devices
• May help to lower latency (anticipate the global handover)
• Key Issues
• Virtual MAC addresses are still flat – weak scalability (in terms of state/signaling
overhead)
• Does not solve problems related to IP changes
• Network segments that are far apart cannot be glued
• Network segments belonging to different providers cannot be glued
• Mapping between IP/MAC required;
• Several servers involved: NDS, SS
• Frequent handovers between two MACs (ping-pong effect) may not be adequately
supported

© 2008
31
Conclusions
• Current operational solutions fall short in providing global mobility
• Micro-mobillity is limited in scope and range
• Globally, only support for nomadism is considered
• Exception: mobile WiMAX considers MIP for global management
• There is NO “one serves all” solution
• SIP does not support TCP-based applications
• HIP requires a “bump-in-the-stack” – implies changing every single IP device and
holds no clear benefit to other approaches
• MIP seems to be the most flexible solution (agnostic to applications, technology, user)
BUT requires IPv6 support in devices (MIPv4 is not an option)
• Main approaches have common points
• Unique identifier or way to dynamically map identifiers (locator/IP address)
• Mobility anchorpoint
• Most of the current solutions can be used together to create a global solution
• E.g., SIP with MIP; SIO with HIP; HIP with MIP
Before choosing a solution, requirements must be analysed!
A global mobility management solution MUST be agnostic to application (current or
future), network technology, and end-user!

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32
Some Interesting Research Topics
– Which OSI Layer(s) are best suited to support mobility convergence?
– Multi-access handover issues
• Resource management
• Dealing with simultaneous movement
• AAA, single sign-on
– Handover optimization
• Influencing handover decision
– New metrics
– Consider user policies
– Context-awareness revisited
– Mobility patterns & models
• Mobility patterns influence architecture requirements
• Adequate support for de-centralized control requires a better analysis of potential
mobility patterns

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