Mobility Management - Technische Universität Ilmenau · Mobility Management 23 Integrierte Hard-...

Integrated HW/SW Systems GroupIlmenau University of Technology

Mobility Management

Prof. Dr.-Ing. habil. Andreas Mitschele-ThielDipl.-Ing. Ali Diab

Mobility Management 2

Integrierte Hard- und Softwaresysteme

Outline

• Introduction

• Mobility Management Approaches in the TCP/IP Reference Model

• Link Layer Mobility Management

• Network Layer Mobility Management

• Conclusions

• Questions Catalog



Introduction



Motivation

• The Internet and mobile communication networks are experiencing an enormous growth

• Future networks will interconnect various heterogeneous networks by means of a common IP core, also referred to as All-IP

• Goals: always-on connectivity, higher bandwidth, reduced delay, lower cost, etc.

• Challenge: support mobility between cells connected through an IP core while satisfying real-time requirements



Problem Statement

Internet

153 . 12 . 0 . 0 165 . 115 . 0 . 0

153 . 12 . 24 . 118

UDP

TCP



Problem Statement

Internet

153 . 12 . 0 . 0 165 . 115 . 0 . 0

UDP

TCP

165 . 115 . 215 . 9

Dropping Slow start mechanism

Communication disruption should be minimized or even eliminated



Mobility Management Requirements

• Fast and smooth handoffs (lossless handoffs are the ideal case)

• Fixed identifier for the Mobile Node (MN)

• Inter-working properly with IP

• Minimized signaling cost

• No impairments of ongoing applications

• No additional security vulnerabilities

• Scalability, robustness and deployability



Mobility Management Approaches in the TCP/IP Reference Model



Which Layer Handles Mobility?

Application layer

Application layerPresentation layer

Session layer

Transport layer Transport layer

Network layer Internet layer

Data link layer

Network Interface Hardware

Physical layer

ISO/OSI TCP/IP

Link layer mobility

Network layer mobility

Transport layer mobility

Session layer mobility

Application layer mobility

Required to build radio links



Which Layer Handles Mobility?

• Link layer mobility management is responsible for the establishment of a radio link between the MN and the new Access Point (AP)

• No more procedures are required if the old as well as the new AP belongs to the same subnet

• If the new AP belongs to a new subnet, we need mobility support either– in the network layer, i.e. the Internet layer of the TCP/IP reference

model,– in the transport layer or– in the application layer



Mobility Management in Different Layers, Why?

• Link layer mobility– Required when changing the point of attachment– Responsible for establishment of a wireless link

• Network layer mobility– Transparency to higher layer protocols, e.g. TCP and UDP– Applications on mobiles can further communicate with existing

applications without any modifications– Change of network architecture is allowed

• Transport layer mobility– End-to-end mobility management while keeping the Internet

infrastructure unchanged– End hosts take care of mobility, i.e. TCP and UDP are updated to

support mobility



Mobility Management in Different Layers, Why?

• Session layer mobility– Migration of sessions between devices

• Application layer mobility– No changes to current networks– Extending IP telephony infrastructure to fulfill mobility requirements – Usage of SIP protocol and support for mobility by change of the

mapping between a name of a user (e.g. mail address) and the IP address

• Hybrid layer mobility– Optimization of the performance of a certain layer mobility

management approach using information from other layers or the Integration of solutions from several layers

– Synchronization between layers is essential



Link Layer Mobility Management



Link Layer Handoff

• Responsible for the establishment of a radio link between the MN and the AP

• The handoff comprises 4 phases– Recognizing the loss of the wireless connection– Search for and detection of a new adequate AP– Re-/Authentication with the new discovered AP– Re-/Association with the new discovered AP



Recognizing the Loss of the Wireless Connection

• Connection loss is detected based on– Weakness of the received signal or – Failed frame transmissions

• Weakness of the received signal– Most frequently used approach– A layer 2 handoff is prompted, if the received signal strength goes

below a certain threshold

• Failed frame transmissions– Slower than received-signal-strength-based approach – The MN first assumes a collision as reason for failed frame

transmissions; if not, radio signal fading is assumed; if not, an out of range is declared



Search and Detection of A New Adequate AP

• Passive scanning

AP operating in frequency B

AP operating in frequency A

Beacon Beacon100 msec

t

t

t

Change to frequency A

BeaconBeacon

Change to frequency B

Change to frequency C



Search and Detection of A New Adequate AP

• Active scanning

Probe request

Probe delay MinChannelTime

No activities on this channel

Probe response

t

t

t

Change to frequency A

Change to frequency B

AP operating in frequency B

AP operating in frequency C

MaxChannelTime

Probe request

Probe delay MinChannelTime



Re-/Authentication With the New Discovered AP

• The MN authenticates itself to the new AP

• Two authentication methods are defined for the IEEE 802.11 standard– Open system: null-authentication (default method)– Shared key authentication: none null-authentication

• Exchange of authentication request & authentication response messages

• More messages can be exchanged between the authentication request & response; details depend on the authentication algorithm



Re-/Association With the New Discovered AP

• Exchange of association request & association response messages

• After this phase, the wireless link is established



Link Layer Handoff

• Large variation for the same hardware with same configuration mainly due to stochastic behavior of radio interface

• Scanning is the main factor in the latency, it accounts for – about 90 % of the overall handoff

delay and – 80 % of the messages

exchanged (depends on mobility and radio conditions)

MNProbe requests

Probe responses

APs

New APAuthentication request

Authentication response

Association request

Association response



Research Issues

• Speeding up the layer 2 handoff requires accelerating the scanning phase– Periodic scanning

• Scanning the medium while the MN is still connected to the old AP• When the signal strength of the current AP is decreasing, the MN

switches to another frequency for a short time and scans for other available APs

– Selective scanning• Use of a channel mask to reduce the channels that must be scanned

– Information about neighbors• Utilizing information about neighbor APs to reduce the number of

channels that must be scanned



Network Layer Mobility Management



Overview

• End-to-end mobility management

• Implemented in – Network layer of the ISO/OSI reference model or– Internet layer of the TCP/IP protocol suite

• Termed as layer 3 mobility management as well

• Benefits – Transparency to higher layer protocols, e.g. TCP and UDP– Applications on MNs can further communicate with existing

applications without any modifications

• However– The infrastructure has to be adapted



Network Layer Mobility Management Approaches

• Terminal-based mobility management approaches– Mobility support in the network and MNs– MNs participate in mobility procedures

– Status• Wide range of solutions has been developed• Employed in current networks

– Disadvantages• MNs have to be updated, which is mostly not preferable by users

– Classification• Terminal-based macro mobility management solutions• Terminal-based micro mobility management solutions



Network Layer Mobility Management Approaches

• Network-based mobility management– Mobility support in the network only (terminals with legacy IP stack can

be mobile)– No interaction between the network and MNs

– Status• Under development

– Disadvantages• Many features are hard to realize, e.g. route optimization• Focus is on support of global mobility; achieving fast and smooth handoffs

is not the focus yet

– Classification• Network-based macro mobility management solutions• Network-based micro mobility management solutions



Terminal-Based Mobility Management

• Macro mobility management approaches– Aim at global mobility support– Base protocols: Mobile IPv4 (RFC 3344) & Mobile IPv6 (RFC3775)

• Micro mobility management approaches– Performance improvements through localizing the mobility processing

inside administrative domains– Introducing of new intermediate nodes to the network– Hierarchical network topology is typically required– Categorized in

• Proxy Agent Approaches (PAA) and• Localized Enhanced Routing Schemes (LERS)



Macro Mobility Management – Mobile IPv6 (MIPv6)

Access Router (AR)

AR

AR

AR

Corresponding Node (CN)Internet

Home Agent (HA)

No support for mobility (standard IPv6 router)

Mobility support; use of two IP addresses (Home Address

(HoA) & Care of Address (CoA))Periodic broadcast

of Router Advertisements (RA)

CN



MIPv6 - Handoff

AR

AR

AR

AR

CNInternet

HA

Binding Updates (BUs)

CN



MIPv6 - Handoff

AR

AR

AR

AR

CNInternet

HA

Binding Acknowledgements (BAs)

CN



MIPv6 – Data Communication

AR

AR

AR

AR

CNInternet

HA

CN

Uplink data packets are dealt with as standard IP

packets



MIPv6 - Pros & Cons

• Pros– Enabling end-to-end mobility– Transparency to upper layer protocols– Works properly with IP

• Cons– Overhead due to encapsulation– High handoff latencies due to contacting the HA and the CN each

time the MN changes the point of attachment Communication disruption

– Considerable signaling load due to frequent BUs especially when MNs move at high speeds

– Sub-optimal routing and increased end-to-end delay due to triangular routing where CN is not MIPv6 enabled (binding updates) or due to lack of security



Micro Mobility Management

Administrative domain

Administrative domain

Intermediate node

Movements between different domains are typically handled

by MIP, also called inter- domain mobility

Internet

HA

Movements inside the domain are controlled by the intermediate node,

also called intra-domain mobility

HA is not aware of each change in the point of

attachment



Proxy Agent Approaches (PAA)

• Extend the principle of MIP to provide micro mobility

• Introduce new intermediate nodes to the network to process the mobility inside an administrative domain locally

• Data packets destined to the MN are forwarded to the intermediate node, which tunnels them towards the MN’s current point of attachment

• Examples– Hierarchical MIPv6 (HMIPv6), Anchor Foreign Agent (AFA),

Seamless MIP (S-MIP), etc.



HMIPv6

InternetHA

AR3AR1

Mobility Anchor Point (MAP)

AR2 AR6AR4

MAP

AR5

MN registers a Regional CoA (RCoA), i.e. a CoA in the MAP’s subnet, in its HA as the MN’s CoA; the location of the MN inside the domain is defined by the local

CoA (LCoA), which is a CoA in the current AR subnet

RCoA

LCoA

HA is not aware of the MN’s mobility as long as the

RCoA has not been changed

CN



HMIPv6 – Handoff

InternetHA

AR3AR1

MAP

AR2 AR6AR4

MAP

AR5

RCoA

LCoA

The MN configures a new LCoA

RA

Local BU

BA

CN



HMIPv6 – Data Communication

InternetHA

AR3AR1

MAP

AR2 AR6AR4

MAP

AR5

CN



HMIPv6 – Pros & Cons

• Pros– Localizing of mobility management inside administrative domains– Improving the performance: reduced handoff latency compared to

MIPv6, reduced packet loss, etc.– Reducing the signaling load traveling towards the HA

• Cons– Restrictions on the network topology– Single point of failure (all traffic passes through the MAP)– Increased signaling and packet forwarding overhead inside the

domain– Security issues: how to authenticate arriving MNs?



Localized Enhanced Routing Schemes (LERS)

• Similar principle as PAA approaches

• Typically introduce a new dynamic layer 3 routing protocol inside the domain (per-hop routing)

• Data packets destined for the MN are forwarded to the intermediate node controlling the domain, which forwards them hop per hop towards the MN

• All nodes in the domain should be mobility-aware

• Examples– Cellular IP, HAWAII



Cellular IP

InternetHA

CN

Gateway

BS1

BS3 BS4

BS2

BS5

The gateway controls the domain

IP-based routing of data packets inside the domain is

replaced by a special CIP routing and location

management

The MN registers the address of the gateway as its CoA;inside the domain, the MN

uses its HoA

Beacon messages flooded periodically all BSs know how to route packets towards the gateway



Cellular IP – Hard Handoff

InternetHA

CN

Gateway

BS1

BS3 BS4

BS2

BS5

BeaconRoute-update

Update its routing cache and starts forwarding data packets towards

the new location of the MN



Cellular IP – Semi-Soft Handoff

InternetHA

CN

Gateway

BS1

BS3 BS4

BS2

BS5

Semi-soft packet

Update its routing cache and starts forwarding data packets towards the MN via the old and

new BS

The MN detects a handoff in the near future it switches for a short time to the radio of

the new BS



Cellular IP – Semi-Soft Handoff

InternetHA

CN

Gateway

BS1

BS3 BS4

BS2

BS5

Route-update

Update its routing cache and stops forwarding to the old BS

After the layer 2 handoff, the MN sends a route-update packet to stop the bicast



Cellular IP – Data Communication

InternetHA

CN

Gateway

BS1

BS3 BS4

BS2

BS5

Uplink packets are forwarded hop by hop towards the gateway; they

are used to refresh the routing caches

Routed using IP towards their destination



Cellular IP – Pros & Cons

• Pros– Localizing of mobility management inside administrative domains– Improving the performance: reduced handoff latency, less lost packets,

etc.– Reducing the signaling traveling towards the HA– Mobile to mobile communication in the domain is routed via the gateway

• Cons– Restrictions on the network topology– Single point of failure (all traffic travels through the gateway)– Signaling and packet forwarding overhead inside the domain– A new layer 3 dynamic routing protocol is implemented, which highly

reduces the throughput of TCP– Every node in the domain have to be mobility-aware– Security issues: authentication of arriving MNs, authentication of route-

update messages, etc.



Network-Based Mobility Management

• Macro mobility management approaches– Aim at global network-based mobility support– Base protocols: Proxy MIPv6 (RFC 5213)– Developed by the IETF-NETLMM working group

• Micro mobility management approaches– Use similar principles as terminal-based micro mobility management

approaches– Performance improvements through localizing the mobility processing

inside administrative domains– Introduction of new intermediate nodes to the network and deploying

a hierarchical topology– Example: Terminal Independent MIP (TIMIP)



Macro Mobility Management – Proxy MIPv6

Mobile AccessGateway

(MAG)

MAG

MAG

MAG

Corresponding Node (CN)Internet

Localized Mobility Anchor (LMA)

MN does not have to understand mobility; from the MN´s point of view, it is located in its home network and

the whole domain represents a single point of attachment

Support of mobility is required in the MAGs; each MAG emulates the home network of each MN

served by it

Unicast RA with the Home Network Prefix

(HNP) of the MN

RA



Proxy MIPv6 – Handoff

MAG

MAG

MAG

MAG

CNInternet

LMA

The MAG detects a detach event

De-Registration Proxy Binding Update(DeReg PBU)

Proxy Binding Acknowledgement (PBAck)

Start a timer to delete the mobility binding of the MN



Proxy MIPv6 – Handoff

MAG

MAG

MAG

Internet

The MAG detects an attach event&

acquires the MN-ID and profile, from AAA server for example

PBU

LMA

MAG

Accepts the binding, allocates MN-HNP and sets

up a tunnel to the MAG

PBAck

A unicast RA with the MN-HNP the MN assumes that it is located in its home network and thus there is no need for a

re-configuration of its IP address

RA

CN



Proxy MIPv6 – Data Communication

MAG

MAG

MAG

CNInternet

LMA

MAG



Proxy MIPv6 – Pros & Cons

• Pros– Transparency to MNs (MNs with no mobility support can be mobile)– Protocol is robust against control messages dropping (no control

messages are sent on wireless links)– Reduced signaling cost – Terminating the tunnel in the MAG instead of MNs reduces the data

traffic volume sent over the wireless link

• Cons– Triangular routing increased end-to-end delay– Overhead due to the encapsulation– Handoff latency due to contacting the LMA each time the MN moves

from one point of attachment to another communication disruption– Route optimization is not possible



Research Issues

• Fast and smooth handoffs without restricting the network or introducing new nodes

• Privacy through location-independent addressing

• IP-based mobility between different access topologies, also called vertical handoffs

• Support of route optimization for network-based mobility management

• Security & scalability



Conclusions

• Mobility management in future networks is IP-based

• Mobility can be implemented in different layers of the TCP/IP reference model; each layer has positive and negative impacts

• Network layer mobility approaches are the most deployed solutions– Terminal-based approaches interact with MNs to support mobility– Network-based approaches do not involve MNs in mobility support– Both approaches are categorized into macro and micro mobility

management approaches• Macro mobility approaches aim at supporting global mobility• Micro mobility approaches aim at accelerating the mobility management

through processing of mobility locally



Control Questions

• Where do we need mobility support in case the MN has moved to an AP belonging to a different subnet? Why do we need such mobility support?

• What are the advantages obtained when supporting mobility in the network layer?

• Propose a solution to accelerate the layer 2 handoff procedure.

• What are the differences between terminal-based and network-based mobility management approaches?

• Compare between MIPv6 and HMIPv6?

• What are the differences between PAA and LERS approaches?

• What is the main idea behind network-based mobility management? How can such mobility support be realized?

• Propose some mechanisms to improve Proxy MIPv6?



References

• E. Weiss, A. Otyakmaz, E. López, B. Xu, “Design and Evaluation of a new Handoff Protocol in IEEE 802.11 Networks”, Proceedings of the 11th European Wireless conference 2005, Nicosia, Cyprus 2005.

• IEEE Computer Society, “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, Standard IEEE 802.11, ISBN: 0-7381-5656-6 SS95708, June 2007.

• C. Perkins, “IP Mobility Support for IPv4”, RFC 3344, August 2002.

• D. Johnson, C. Perkins, J. Arkko, “Mobility Support in IPv6”, RFC 3775, June 2004.

• H. Soliman, C. Castelluccia, K. El-Malki, L. Bellier, “Hierarchical Mobile IPv6 mobility management (HMIPv6)”, RFC 4140, August 2005.

• A. G. Valko, “Cellular IP - A New Approach to Internet Host Mobility”, in the proceeding of ACM Computer Communication Review, January 1999.

• S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, B. Patil, “Proxy Mobile IPv6”, RFC 5213, August 2008.

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