Special Feature

IP-based Mobility Management
Technology
Ichiro Okajima†, Masahiro Inoue, Koji Omae,
Hideaki Takahashi, and Narumi Umeda
Abstract
This article reviews recent progress in the study of IP-based mobility management technology forenhancing the mobility of cellular phones and other mobile nodes in fourth-generation mobile communications systems. The architecture and components of this management technology are described andsome experimental and simulation results are presented.

1. Introduction

a management architecture that satisfies them.

NTT DoCoMo is developing IP-based mobility
management technology, which is basic technology
needed for the deployment of fourth generation
mobile communications systems (4G systems) thatwill support broadband mobile communications services. IP-based mobility management technology
works at the Internet protocol (IP) layer to enable
seamless handoff* of mobile nodes (such as cellular
phones, personal digital assistants (PDAs), and notebook computers) while they are moving around in the
4G system and to give packets end-to-end reachability to and from mobile nodes. In short, this technology enables true mobility by permitting mobile nodes
to move about freely anywhere in the 4G system andinitiate and perform communications.
This article presents an overview of the architectureof IP-based mobility management and describes its
key components: multiple interface management,
active state mobility management, and dormant state
mobility management.

2.1 Requirements
There are three main requirements for mobility
management.
(1) High packet transmission quality
To support a diverse range of applications, goodpacket transmission quality is essential, including
low packet transmission delay, minimal packet transmission delay deviation, and a low packet loss rate.
(2) Modest control cost
To make efficient use of wireless links, which havesignificantly lower bandwidth capacity than wired
links, it is necessary to reduce the amount of signaling traffic associated with mobility management thatmust be transferred over the wireless links.
(3) Seamless mobility
The management scheme must implement seamless mobility that supports mobile nodes connected to
not only 4G cellular wireless links but also
IEEE802.11 and other wireless links and to Ethernet
and other wired links.

2. IP-based mobility management architecture

2.2 Configuration and protocol stackIn principle, mobility management can be implemented at any layer from the link layer to the application layer. However, if mobility management is
implemented at the link layer, the applicability wouldThis section outlines the key requirements formobility management in the 4G system and presents† NTT DoCoMo, Inc.
Yokosuka-shi, 239-8536 Japan
E-mail: okajimai@nttdocomo.co.jp

40* Handoff: The act of transferring a wireless signal from one cell site
to another. Equivalent to handover.

NTT Technical Review

Special Feature

be limited to the same type link, and this would contravene Requirement (3). Moreover, if mobility management is implemented at the transport layer or theapplication layer, it would have to be implemented
separately for each different transport and application
layer protocol, which would increase the amount ofsignaling traffic and thus fail to satisfy Requirement(2). In contrast, if we implement mobility management at the IP layer, which is common to all link
layer, transport layer, and application layer protocols,then Requirements (2) and (3) can both be satisfied.
This approach can handle the wireless link disconnections associated with handoffs and delays in packet route setup processing that are the primary factors

in the degradation of packet communication quality,
so Requirement (1) is also satisfied. Consequently,
this approach satisfies all three of the basic requirements. Figure 1 shows a schematic representation of
our IP-based mobility management scheme and protocol stack, assuming the use of IPv6 (Internet protocol version 6), which has an enormous address spacethat can support an extremely large number of mobile
nodes. Three of the key terms related to mobile nodes
shown in Fig. 1 are explained below.
Multiple interface management (MIM) provides
the link layer that best matches user preferences to thelayers above from among the several link layers available for the mobile node while minimizing the power

Correspondent nodeHome agent

Internet
Paging agent
Mobility anchor point(MAP)

IP network

RouterRouter with built-in 4G
cellular access transceiver

4G cellular access point

IEEE802.11 access point

Mobile router

MobileIP network

Mobile node

Applications

TCP: transmission control protocol
UDP: user datagram protocol

Applications

TCP/UDPTCP/UDPHMIP-Bv6/IPPv6
MIM
802.11 4G
MN

IPv6HMIP-Bv6

IPv6

IPPv6

IPv6

MIPv6

IPv6

IPv6

4G Link

Link Link

Link Link

Link Link

Link Link

Link Link

Link Link

Link Link

Link

4G-AP

Routers

MAP

Routers

PA

Routers

HA

Routers

CN

•••

•••

•••

•••

Fig. 1. IP-based mobility management architecture and protocol stack.

Vol. 2 No. 9 Sep. 200441

Special Feature

consumption of the mobile node’s other link layersthat are not used.
HMIP-Bv6 (hierarchical mobile IPv6 with buffering at MAP) is a mobility management scheme thatuses a mobility anchor point (MAP) with buffering
capability for handoffs. It achieves reliable routing of
packets to the mobile node in the active state of communication with a low packet loss rate and low packet transmission delay.
IPPv6 (IPv6 paging protocol) is a mobility management protocol that uses a paging agent (PA) to
manage the location of mobile nodes in the dormant
communication state in local areas and to notify themobile node of the arrival of incoming packets, thus
enabling it to have less frequent packet route setup
processing.

3.1 Requirements
There are two main requirements for MIM.
(1) NIC selection based on user preferences
A network interface card (NIC) is the communication interface hardware that implements the link layer
protocol. NICs are rapidly coming down in price andlevels of chip integration are increasing, so it is only
a matter of time before a mobile node can support
multiple NICs. When that happens, MIM will need to
be able to determine what NICs are available on amobile node and select the one that best matches theuser’s preferences.
(2) Lower battery consumption
To conserve the mobile node’s battery power, MIM
must efficiently manage the power consumption of
the NICs.

3. Multiple interface management

3.2 MIM configuration
Figure 2 shows an MIM configuration that satisfies
the above requirements [1]. It is built into the mobilenode.
(1) User preference information
User preference information is input via an MIM

This section defines the requirements for interface
management with multiple kinds of link layers andthen presents an overview of NTT DoCoMo’s proposed MIM.

MIM GUI
Application protocols
TCP/UDPHMIP-Bv6/IPPv6

User preference
information

MIM

Optimum NIC selection function

IEEE802.11
NIC
IEEE802.11
link

4G cellular NIC

Ethernet NIC

4G cellular
link

IEEE
802.11access point

4G
Cellularaccess point

IP packet flow

LAPI signaling flow

Ethernetlink
Ethernethub
MIM internal data flow

Fig. 2. MIM configuration.

42

NTT Technical Review

Special Featuregraphical user interface and stored in a database. Typical information will include the user’s preferences
for bit rate, transmission quality, and transmission
cost.
(2) Optimal NIC selection function
The MIM periodically checks to make sure that the
NIC being used best matches the user preferences
and, if necessary, changes NICs. The MIM also helps
conserve battery power by turning off the power to all
NICs that are currently not selected. This optimal
NIC selection function utilizes the link layer application programming interface (LAPI) [2] to control thelink layer and exchange status information between
the link layer and the higher layer. For example, if theuser prefers a high bit rate, this function selects the
NIC that provides the highest bit rate.
4. Active state mobility management
This section defines the requirements for active
state mobility management, outlines NTT DoCoMo’s
proposed HMIP-Bv6 scheme, and presents somerecent evaluation results for this scheme.
4.1 Requirements
There are three main requirements for active state
mobility management.
(1) Mobile node and mobile network mobility
Support of standalone mobile nodes is essential, but
the mobility of mobile networks such as groups ofmobile nodes traveling in a train or bus must also be
supported.
(2) Ease of deployment
To promote rapid and cost-effective deployment of
4G systems, the equipment must be easy to introduce.
(3) High packet communication quality
To support a broad range of applications, the management scheme must satisfy the requirements inTable 1 for voice and other realtime traffic to minimize degradation of quality during handoffs, while atthe same time minimizing the slowdown of throughput during handoffs to accommodate data traffic.
4.2 HMIP-Bv6 scheme
In the conventional mobile IPv6 (MIPv6) [3] andhierarchical mobile IPv6 (HMIPv6) [4] schemes,
mobility is achieved by a home agent (HA) and a
MAP, which forwards packets destined for mobile
nodes, but these schemes do not satisfy the above
requirements due to bursty packet losses that occur
during handoffs. This led us to propose a new
approach called hierarchical mobile IPv6 with buffering at MAP (HMIP-Bv6), which adds a number of
new capabilities to the HMIPv6 scheme [5], [6]. The
four described below are achieved through extensions made only to the mobile node, MAP, and HA.
(1) Agent discovery function
This function enables a mobile node to dynamically discover a MAP. This enables the mobile node to
select the optimal MAP when there are multiple
MAPs on the IP network by comparing the relative
distances to MAPs, packet processing loads, andother criteria. We define this capability in an agent
discovery protocol [7] and can also use it to discoverPAs, as mentioned in section 4. Another advantage ofthis approach is that no data about MAPs and PAs
needs to be preconfigured in the mobile nodes orrouters, which simplifies the deployment of MAPs
and PAs on the IP network.
(2) MAP buffering function
Packets destined for a mobile node are buffered in
the MAP to prevent packet loss during handoffs. Thisis illustrated for the HMIP-Bv6 scheme in Fig. 3.
(3) Subnet prefix management function
This function manages all the subnet prefixes in
HAs and MAPs used by the mobile network [8] andsupports mobility for all nodes on the mobile network.
(4) Care-of address fast configuration function
This function speeds up the configuration process-

Table 1. Voice communication quality requirements and measured results.
HMIPv6MIPv6

HMIP-Bv6

Evaluation criteria

Requirement [12]No. of packets lost per handoff

3

16.24

17.66

12.93

14.38

0.00

0.00

Packet loss rate (%)

0.1

1.02

1.10

0.81

0.90

0.00

0.00

End-to-end packet transmission
delay deviation (ms)

50

0.00

2.91

0.00

2.99

21.02

28.60

Average end-to-end packet
transmission delay (ms)400

111.87108.94111.87108.94111.88109.54

Simulation Experiment Simulation Experiment Simulation Experiment

Failed to meet requirements

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Special Feature

Mobile node

Router 1

MAP

HA

CN

Handoff needs to be done
Binding update (with buffering on)

Binding acknowledgment
Link layer handoff
PacketbufferingCare-of addressconfiguration

Router 2
Binding update (with buffering off)
Binding acknowledgment

Transmission of data
packets that havebeen buffered

Data packets
Control packets

Fig. 3. HMIP-Bv6 scheme.

ing during handoffs for care-of addresses (packet forwarding addresses of mobile nodes), thereby reducing the packet transmission delay after handoffs.
4.3 Evaluation of HMIP-Bv6 scheme
The packet transmission quality of three schemes(MIPv6, HMIPv6, and HMIP-Bv6) was evaluatedthrough simulations and experimental trials. This section presents our findings.
4.3.1 Evaluation method
1) Evaluation criteria
Using the network model shown in Fig. 4, we evaluated the quality of voice and data communications at
the mobile node when the voice and data were sentfrom the correspondent node to the mobile node. For
VoIP (voice over IP) speech communications, the criteria were the number of packets lost per handoff,
packet loss rate, end-to-end packet transmission
delay deviation, and average end-to-end packet transmission delay. For data communications, the criterion was the time required to transfer a file.
2) Network model
The network model consists of a correspondent
node, an HA, and an IP network interconnected by
the Internet. A MAP and several routers are deployedon the IP network and a mobile node performs hand44

offs between routers. Packet transmission delays
through the Internet and the IP network were 50 ms[9] and 10 ms [10], respectively.
3) Traffic models
We used two traffic models. For voice traffic, thepacket rate was 50 packets per second and the packet
size was 80 bytes [11]. For data traffic, a 5-Mbyte file
was downloaded by FTP (file transfer protocol).
4.3.2 Measured results
The measured voice communication quality and therequirements are shown in Table 1. The HMIP-Bv6
scheme was able to satisfy the requirements for thenumber of packets lost per handoff and packet loss
rate as a result of the effectiveness of the MAP packet buffering, but the other two schemes failed to meetthese requirements. All of the schemes met therequirement for end-to-end packet transmission delay
deviation and average end-to-end packet transmission delay.
Figure 5 shows the measured data communication
quality. Download times were measured for all threeschemes for mobile node handoff intervals of 8, 16,
and 32 s and without handoff. The experimental measurements and simulation results showed similar tendencies. The downloads took longer as the interval
between handoffs decreased for the MIPv6 and
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Special Feature

Packet transmission
delay through the Internet: 50 ms
Home agent

Correspondentnode
MAP
Packet transmission
delay through an IP network: 10 ms
Router(i.e., active state).
(2) Seamless resumption of communication
The packet communication quality
must be equivalent to the quality
requirements of the active state mobility
management so that the dormant state
mobility management can resume communications with high packet communication quality whenever the mobile nodetransits from the dormant state to theactive state.

Mobile node

5.2 IPPv6 configuration
IPPv6 has been proposed as a dormant
state mobility management scheme thatsatisfies the above requirements [13].
120
Experimental results
This protocol has five functions, which
Simulation results
Without handoff
100
are implemented in mobile nodes and32-s intervals
PAs.
16-s
intervals
80
8-s intervals
1) PA discovery function
60
The mobile node can discover PAs. It
dynamicallydiscovers the nearest PA
40
using the agent discovery protocol.
202) Dormant state detection function
Figure 6(a) shows the transition of the0
MIPv6
HMIPv6
HMIP-Bv6
mobile node to the dormant state. By
monitoring how long a mobile node is in
Fig. 5. Data communication quality.
a continuous state of non-communication, IPPv6 can determine transitions to
HMIPv6 schemes, but stayed more or less constantthe dormant state and send an area registration
for the HMIP-Bv6 scheme. The main factor degradrequest to the PA.
ing download speed is the loss of the TCP (transmis3) Paging area formation function
sion control protocol) data segment. Since this does
Figure 6(a) also shows the mobile node’s location
not occur in the HMIP-Bv6 scheme, the download
management in terms of paging area units. Sincetime was unaffected by handoff.
there is no need to form a new paging area as long as
the mobile node moves within the same paging area,
5. Dormant state mobility management
the volume of control signals is significantly less thanwith active state mobility management.
This section defines the requirements for dormant4) Paging function
state mobility management and overviews and evaluFigure 6(b) shows how paging request messages
ates NTT DoCoMo’s proposed IPPv6.
are sent throughout the paging area of a mobile node
when packets destined for the mobile node are
5.1 Requirements
received. It also shows the transition of the mobile
There are two main requirements for dormant statenode to the active state when the mobile node
mobility management.
receives the paging request.
(1) Reduction of control signals5) Mobile node address packet buffering function
Mobility management must be implemented in
The PA buffers packets destined for a mobile nodesuch a way that the volume of control signals is subto prevent packet loss while the mobile node is being
stantially less when the mobile node has no packets to
notified of incoming packets by the paging function.
send or receive (i.e., dormant state) than when themobile node does have packets to send or receive
Download time (s)Fig. 4. Network model.

Vol. 2 No. 9 Sep. 200445

Special Feature

HA
Internet
Internet
IP networkq Incoming packets

y Area registration
requestPA

Routerw Arearegistration
requestIP network

w PacketbufferingPAe IP paging

r IP paging responset Packet routing
RouterRouter
4G-AP

802.11AP

802.11AP

4G-AP
4G-AP

Mobile node

4G-AP

q Non-communication state
Mobile noder Transition betweent Transition between
e Transition
subnets (sending
paging areas
between accessnot required)points (sending
not required)(a) Dormant state transition
AP: access point(b) Paging function
Paging area

Fig. 6. IPPv6 operation.

1.4

No. of control packets (normalized simulation results)

5.3 Evaluation of the IPPv6 scheme
The effectiveness of IPPv6 at reducing thenumber of control packets was evaluatedthrough simulation. Figure 7 shows the number of control packets versus the mobile node
handoff interval for four different numbers ofsubnets per paging area. The number of control
packets was normalized by the number of control packets in active state mobility management. The traffic session of mobile nodes had
an average interval of 1800 s. The shorter thehandoff interval of mobile nodes was (i.e., themore frequently the mobile nodes moved), themore effective IPPv6 was at reducing the number of control packets. This was true for all
numbers of subnets. When the paging area
consisted of seven subnets and the averagehandoff interval was 20 s, IPPv6 halved thenumber of control packets. Thus, IPPv6 greatly reduced the number of control packets.
6. Conclusion

This article described IP-based mobility
management technology that enhances the mobilityof mobile nodes in 4G systems. Featuring multiple
interface management, active state mobility management, and dormant state mobility management, it satisfies all the key requirements, including high packet
communication quality, modest control costs, andseamless mobility.

7 subnets
19 subnets
37 subnets
61 subnets

1.2

1

0.8

0.6

0.4

0.2

0

20

60

121
181
Handoff interval

244

(s)

Fig. 7. Reduction in number of control packets achieved by
IPPv6 (simulation results).

References
[1]
[2]

[3]
[4]

46

Interval between sessions = 1800 s

T. Ikeda, I. Okajima, and N. Umeda, “Link Manager for IP-Based
Mobile Communications System,” IEICE, B-5-58, Sep. 2001.
R. Kobayashi, M. Inoue, I. Okajima, and N. Umeda, “Management
Information Exchange which should be Commonly Shared among the
Link Layers for IP-Based Mobile Communications System,” IEICE,
B-5-128, Sep. 2003.
D. Johnson, C. Perkins, and J. Arkko, “Mobility Support in IPv6,”
draft-ietf-mobileip-ipv6-24.txt, June 2003.
H. Soliman, C. Castelluccia, K. El Malki, and I. Bellier, “HierarchicalNTT Technical Review

Special Feature

[5]

[6]

[7]

[8]

Mobile IPv6 Mobility Management (HMIPv6),” draft-ietf-mobileiphmipv6-08.txt, June 2003.
K. Omae, I. Okajima, and N. Umeda, “Hierarchical Mobile IPv6
Extension for IP-based Mobile Communications System,” IEICE, IN
Research Group, IN 2001-178, Feb. 2002.
H. Takahashi, R. Kobayashi, I. Okajima, and N. Umeda, “Transmission Quality Evaluation of Hierarchical Mobile IPv6 with Buffering
Using Test Bed,” Proceedings of IEEE VTC 2003 Spring, Apr. 2003.
K. Omae, M. Inoue, I. Okajima, and N. Umeda, “Hierarchical Agent
Discovery for Hierarchical IP Mobility Management Protocol,”IEICE, B-5-116, Mar. 2003.
I. Okajima, N. Umeda, and Y Yamao, “Architecture and Mobile IPv6

Extensions Supporting Mobile Networks In Mobile Communications,” Proceedings of IEEE VTC 2001 Fall Vol. 4, Oct. 2001.
[9] http://average.matrix.net/[10] http://www.iij.ad.jp/[11] ITU-T Recommendation G.729 Annex A, “Reduced complexity
8kbit/s CS-ACELP speech codec,” Nov. 1996.
[12] ITU-T Recommendation Y.1541, “Network Performance Objectives
for IP-Based Services,” Feb. 2002.
[13] M. Inoue, I. Okajima, and N. Umeda, “IP Paging for IP-based Mobile
Communications System,” IEICE, RCS2004-3, Apr. 2004.

Ichiro Okajima

Hideaki Takahashi

Senior Research Engineer, Wireless Laboratories, NTT DoCoMo, Inc.
He joined NTT DoCoMo in 1991. He is
engaged in research on 4G mobile communications systems. He is a member of the Institute ofElectronics, Information and Communication
Engineers (IEICE).

Wireless Laboratories, NTT DoCoMo, Inc.
He joined NTT DoCoMo in 2001. He is
engaged in research on 4G mobile communications systems. He is a member of the Information
Processing Society of Japan (IPSJ).

Masahiro Inoue

Narumi Umeda

Research Engineer, Wireless Laboratories,
NTT DoCoMo, Inc.
He joined NTT DoCoMo in 1995. He is
engaged in research on N-STAR satellite mobile
communications systems and 4G communications systems. He is a member of IEICE andIEEE.

Director, Communication Systems Laboratory,
Wireless Laboratories, NTT DoCoMo, Inc.
He received the B.E. and M.E. degrees in electronic engineering from Hokkaido University,
Sapporo, Hokkaido in 1985 and 1987, respectively. He joined NTT Laboratories in 1987. In
1992, he transferred to NTT Mobile Communications Network, Inc. (now NTT DoCoMo, Inc.).
He has been engaged in research on the radio linkcontrol for the personal digital cellular (PDC)
system and IMT-2000. His current researchinterests are in the radio control for 4G mobile
communications systems (beyond 3G). He was aco-recipient of the Japan Institute of Invention
and Innovation (JIII) Imperial Invention Prize in1998 and the best paper award of the International Conference on Telecommunications at
ICT2002. He is a member of IEICE and IEEE.

Koji Omae
Wireless Laboratories, NTT DoCoMo, Inc.
He joined NTT DoCoMo in 2000. He is
engaged in research on 4G mobile communications systems. He is a member of IEICE.

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