CARE-OF-PREFIX ROUTING FOR MOVING NETWORKS IN

MOBILE IP NETWORK

Toshihiro SUZUKI, Ken IGARASHI, Hiroshi KAWAKAMI, Akira MIURA

NTT DoCoMo, 3-5, Hikarinooka, Yokosuka-shi, Kanagawa, 239-8659 Japan

Keywords: Mobile IP, moving network, routing, addressing, handoff, NEMO

Abstract: The future ubiquitous network will serve so many mobile terminals that it is extremely important to control

them efficiently. One useful approach is to group terminals having similar movement characteristics and

manage them in units of groups. Another important issue is the mobility management of moving networks,

such as a network on a train or in a car, or a personal area network. Moving networks may be defined for a

variety of situations and can lead to a lot of attractive applications. Moving network mobility support is

indeed one of the most interesting research topics. In this paper, we clarify the difference between host

mobility support and the conventional moving network mobility support, propose a mechanism for moving

network mobility support and shows it is better than the conventional ones.

1 INTRODUCTION

Since the future ubiquitous network must serve

several billion Mobile Nodes (MNs) (i.e., mobile

terminals), it is extremely important to control them

efficiently. Given this number of MNs, one key

technique is to group MNs having similar movement

characteristics, and manage them in units of groups.

Another urgent topic is to enhance the mobility

management of local networks, such as a network on

a train, in a car, or a personal area network. This

moving network mobility support and moving

networks can be applied to a variety of situations and

can lead to a lot of attractive applications. This

mobility management is indeed one of the most

interesting research topics today. Many groups

including IETF are actively researching IP routing

techniques to support moving network mobility.

NTT DoCoMo Network Laboratories are also

studying it as a key technology for IP

(IP based IMP

Platform) (Yumiba, 2001), a platform we have

proposed for the next-generation mobile network.

The representative requirements for moving

network mobility support in IP are the same as those

for host mobility support (mobility management for

moving hosts rather than a moving network). They

are:

(1) Route optimization

(2) Minimization of the packet header size

(3) Reduction in handoff signal overhead.

“Pinball” Routing (Thubert, 2004), in which

packets are always transmitted via Home Agent

(HA) (Johnson, 2004), cannot satisfy requirement (1)

because it requires excessive network resources.

Given requirement (2), we must minimize packet

overhead by dispensing with encapsulation.

Requirement (3) demands that handoff be achieved

seamlessly with minimal packet loss and short

handoff latency. Therefore, it is important to reduce

the amount of handoff signals. The NEMO WG has

proposed only partial solutions to these three

requirements.

In this paper, we clarify the difference between

host mobility support and the conventional moving

network mobility support, and propose a solution

that satisfies all the requirements. Its effectiveness

was confirmed by using network simulator 2 (called

ns2).

Section 2 briefly describes the difference

between host mobility support and the conventional

moving network mobility support, and the

requirements for moving network mobility support.

Section 3 proposes the basic techniques of a new

routing method applicable to moving networks.

Section 4 introduces a new routing mechanism that

uses these basic techniques for Mobile IP (MIP)

(Johnson, 2004). Section 5 compares the proposed

routing mechanisms with conventional ones.

114

Suzuki T., Igarashi K., Kawakami H. and Miura A. (2004).

CARE-OF-PREFIX ROUTING FOR MOVING NETWORKS IN MOBILE IP NETWORK.

In Proceedings of the First International Conference on E-Business and Telecommunication Networks, pages 114-120

DOI: 10.5220/0001383201140120

 SciTePress

2 DIFFERENCE BETWEEN HOST

MOBILITY SUPPORT AND THE

CONVENTIONAL MOVING

NETWORK MOBILITY

SUPPORT

The characteristics and brief evaluations of NEMO

Basic Support (hereafter referred to as Basic)

(Devarapalli, 2004) and Reverse Routing Header

(RRH) (Thubert, 2004), both of which are currently

proposed in NEMO WG for moving network

mobility support, are shown below.

Basic constructs a bidirectional tunnel between a

Mobile Router (MR) and the HA of that MR.

Packets from/to MNs in a moving network are

always carried via this tunnel (Fig. 1). When the

moving network moves, handoff is achieved by

reconstructing a tunnel. Specifically, a bidirectional

tunnel is reconstructed between the Care of Address

(CoA) (Johnson, 2004), which an MR is allocated by

the new AR (Access Router), and the HA address of

the MR. CoAs of MNs in the moving network

remain unchanged even if handoff occurs. This hides

the move of the moving network from the MNs in

the moving network. Furthermore, even if there are

many MNs in the moving network, handoff can be

achieved easily because only this bidirectional tunnel

needs to be reconstructed. Therefore, there is a high

possibility that requirement (3) can be met. However,

the undesirable effect of Pinball Routing is

significant if the HA of the MR is far from the

moving network. Additionally, packet overhead is

greatly increased because packets are doubly

encapsulated, once for the bidirectional tunnel and

another for the CoA of the MN. Therefore, Basic

cannot meet requirements (1) and (2).

RRH satisfies requirement (1) (Fig. 2).

Specifically, routing is optimized as follows. All

CNs are informed of the CoA of the MR, and the

packets destined to MNs in the moving network are

transmitted with Routing Header Option (RHO) in

IPv6 (Deering, 2004). That is, the CoA of the MR

and the CoA of the MN are attached. With regard to

Requirement (2), RRH yields packet header sizes

that lie between those of Basic and host mobility

support. When the moving network moves, it is

necessary to inform all CNs of the change in the

CoA of the MR. The more CNs there are, the more

handoff signals are sent. Therefore, RRH cannot

meet requirement (3).

As mentioned above, neither of the two

conventional mechanisms can satisfy all

requirements. This is due to the assumption made by

NEMO WG for the moving network. NEMO WG

assumes that the prefix inside a moving network, i.e.

Moving Network Prefix (MNP), is fixed

(Devarapalli, 2004) (Thubert, 2004). Given this

assumption, MNP is not changed even if a moving

network moves. Therefore, to connect to an MN in

the moving network, it is necessary to use the CoA

of the MR in addition to the CoA of the MN in the

moving network. This increases the packet header

size. The MR-CoA is needed to construct a

bidirectional tunnel in Basic, or to set it in the RHO

in RRH.

The technologies proposed in Section 3 dispense

with this assumption. That is, MNP is changed to

adapt to the hierarchical address for the AR to which

the moving network is connected. This enables

packets to be routed to an MN in the moving

network using only MN-CoA in the moving network,

as in the case of host mobility support.

3 PROPOSED BASIC

TECHNIQUES

3.1 Care of Prefix

As described in Section 2, the conventional

mechanisms require the use of both of MR-CoA and

MR’s HA

UPDATE

DATA

TUNNEL

MR’s HA

UPDATE

DATA

TUNNEL

Figure 1: Basic

UPDATE

DATA

RHO

UPDATE

DATA

RHO

Figure 2: RRH

MNP=A:A:A::/40

A:A::/30

A:B::/30

MNP=A:B:A::/40

move

MN1’s CoA = A:A:A::a/40

MN2’s CoA = A:A:A::b/40

MN1’s CoA = A:B:A::a/40

MN2’s CoA = A:B:A::b/40

MN1’s CoA = A:A:A::a/40 Æ A:B:A::a/40

MN2’s CoA = A:A:A::b/40 Æ A:B:A::b/40

AR1 AR2

MN1

MN2

MN1

MN2

MNP=A:A:A::/40

A:A::/30

A:B::/30

MNP=A:B:A::/40

move

MN1’s CoA = A:A:A::a/40

MN2’s CoA = A:A:A::b/40

MN1’s CoA = A:B:A::a/40

MN2’s CoA = A:B:A::b/40

MN1’s CoA = A:A:A::a/40 Æ A:B:A::a/40

MN2’s CoA = A:A:A::b/40 Æ A:B:A::b/40

AR1 AR2

MN1

MN2

MN1

MN2

Figure 3: Care of Prefix

CARE-OF-PREFIX ROUTING FOR MOVING NETWORKS IN MOBILE IP NETWORK

115

MN-CoA to route packets to an MN in the moving

network, which increases packet overhead.

Therefore, it is necessary to find a solution that

minimizes packet overhead. The solution should be

to use only one CoA, as in the case of host mobility

support. The Care of Prefix (CoP) (Suzuki, 2003)

technique is used to implement this. Specifically, an

MR is allocated a CoP by the AR to which the

moving network is connected. This CoP is an MNP

in the hierarchical topology that embraces the

moving network. After that, the MR uses this CoP to

assign a CoA to the MNs in the moving network. In

this way, packets for an MN in the moving network

can reach the MN using only MN-CoA (Fig. 3).

The method of allocating the CoP is shown in

Figure 3, using the IPv6 method as an example.

Suppose that the net mask of the AR, which is an

edge router of the core network, is 30 bits long. The

moving network is allocated a CoP with a 40-bit

mask to form a hierarchical structure that embraces

the moving network.

In this way, MNP (i.e. CoP) reflects the

hierarchical topology of the core network so that

MN-CoA can be resolved from anywhere within the

core network. In addition, a CoA can be generated

from a CoP without any risk of duplication. Since

the CoP is uniquely allocated to each moving

network, duplicate CoAs are not generated for MNs

that are connected to the same AR.

CoP makes it possible to meet requirements (1)

and (2) at the same time because a CN can directly

send packets to an MN in a moving network using

only MN-CoA in the same manner as in host

mobility support. However, when handoff occurs,

the CoAs of all MNs in a moving network must be

changed. This dramatically increases the number of

handoff signals sent to the HAs of all MNs, and

similarly the number of those sent to all CNs if route

optimization is implemented. Therefore, it is difficult

to meet requirement (3).

3.2 Concatenated HAs

As mentioned in Section 3.1, the use of CoP cannot

meet requirement (3). One problem is that handoff

signals must be sent to the HAs of all MNs in a

moving network. To solve this problem, we propose

Concatenated HAs (Suzuki, 2003) (Fig. 4).

In this technique, each HA of each MN does not

hold its CoA. Instead, it holds the information that

the MN is in a certain moving network. Specifically,

the information of MN-MR concatenation is

registered with the HA of each MN, while the CoAs

of all MNs are registered with the HA of that MR.

This makes it possible to limit the number of entities

updated at handoff. At handoff, only the HA of the

MR requires updating rather than the HAs of all

MNs.

3.3 Aggregate Router

As mentioned in Section 3.1, there is another

problem that prevents requirement (3) from being

satisfied. It is that handoff signals must be sent to all

CNs. To solve this problem, we propose the

AGgregate Router (AGR) (Fig. 4). The purposes of

the AGR are twofold: localize handoff signals and

aggregate the handoff signals that are sent to all

CNs. Specifically, the AGR manages the mobility of

the moving network as well as the HA of MR, i.e.,

the AGR maintains the CoAs of all MNs in the

moving network, and each CN holds the binding

information that indicates that MN-CoA is the AGR

address. If the CoAs of all MNs in the moving

network are changed due to handoff, the MNs do not

need to send handoff signals to each CN. They only

send handoff signals to the AGR. This localizes the

handoff signals. Furthermore, we aggregate them if

MR sends a handoff signal to AGR instead of all

MNs. Moreover, the binding information that MN-

CoA is AGR address can also be registered at each

HA of each MN in the moving network..

All packets destined to MNs in a moving

network are carried via the AGR. Therefore, the

AGR should be placed at the optimal location

considering the movement characteristics of the

moving network, the location of each CN and so

forth. If necessary, the AGR must be relocated. The

AGR location should be chosen so that no

roundabout communication paths are created

between MNs to CNs as a result of network

movement (factor (1)). Also, the frequency of AGR

relocations should be minimized (factor (2)). If the

AGR is located near the moving network, i.e. in the

lower part of the core network, each communication

path can be optimized and the handoff procedure can

be localized (factor (3)). However, this increases the

frequency of AGR relocations due to handoff. On

the other hand, if the AGR is located in the higher

part of the core network, the communication paths

may not be optimal and the handoff procedure may

MN1 Æ CoA_MN1

MN2 Æ CoA_MN2

Æ MR1

Handover

AGR

MR1

AR1

AR2

AR3

AR4

MN1

MN2

MN1

MN2

CN1

CN2

MN1’s HA

MN2’s HA

MR1’s HA

Concatenated HAs

MN1 Æ CoA_MN1

MN2 Æ CoA_MN2

Æ MR1

Handover

AGR

MR1

AR1

AR2

AR3

AR4

MN1

MN2

MN1

MN2

CN1

CN2

MN1’s HA

MN2’s HA

MR1’s HA

Concatenated HAs

Figure 4: Concatenated HAs and Aggregate Router

ICETE 2004 - WIRELESS COMMUNICATION SYSTEMS AND NETWORKS

116

not be localized. Fortunately, AGR relocation, which

is an expensive procedure, rarely occurs. As

described above, there is a trade-off between factors

(1)-(3). The determination of the optimal AGR

location requires attention to all these factors.

HoA CoA

MN1 #1

MN2 #2

……..

Moving Network

……..

Common Individual

Figure 5: Hierarchical Address Management

3.4 Hierarchical Address

Management

Even if the techniques described in Sections 3.1 to

3.3 are used, it is still necessary to inform the AGR

and the MR’s HA of the updated CoAs, as all CoAs

are changed when a moving network moves. The

volume of handoff signals depends on the number of

MNs in a moving network. Therefore, the data

volume of handoff signals can become very large.

To achieve seamless handoff, it is important to

reduce the number of handoff signals. Hierarchical

Address Management provides a solution to this

problem (Fig. 5).

In Hierarchical Address Management, the CoA of

each MN in a moving network is divided into the

common information and the individual information.

The common information indicates the location of

the moving network, and this is changed when

handoff occurs. On the other hand, the individual

information indicates the location of each MN in a

moving network, and this need not be changed even

if handoff occurs. CoP, as mentioned in Section 3.1,

makes this address management possible because an

AR allocates an individual prefix using the same

subnet mask as given to the moving network to

avoid generating duplicate CoAs. The MR connected

to the core network, the AGR, and the MR’s HA

manages the binding information using this

management technique. Thus, handoff can be

achieved by updating only the common information.

As mentioned above, Hierarchical Address

Management solves the problem by reducing

handoff signal volume, not quantity.

In short, Hierarchical Address Management

along with Concatenated HAs and AGR make it

possible to meet requirement (3) for seamless

handoff.

4 CARE-OF-PREFIX ROUTING IN

A MOBILE IP NETWORK

Combining the basic techniques described in

Sections 3.1 to 3.4 can yield a new routing

mechanism for moving network mobility support

that has the same performance as host mobility

support. We call it Care-of-Prefix Routing (CoPR).

Figure 6 provides an overview of CoPR. Here, the

HA of each MN in the moving network holds the

binding information indicating that the CoA of each

MN is the AGR address. Thus, Concatenated HAs is

omitted. The following details the specification of

CoPR.

Figure 7 shows the sequence for connecting

MR1 to AR1. AGR1 sends its address to AR1 and

AR2, which are connected as the subordinate of

AGR1. When MR1 connects to AR1, MR1 sends a

Router Solicitation (RSol) (Johnson, 2004)

containing a request for a CoP. Next, AR1 sends a

Router Advertisement (RAdv) (Johnson, 2004)

containing the CoP (A:1::) to MR1 and AGR1. After

that, MR1 creates its on-Link CoA (LCoA) (Johnson,

2004) (A::1), sets the AGR1 address as its Alternate

CoA (ACoA) (Johnson, 2004), and registers its CoP.

MR1 then sends a Binding Update (BU) (Johnson,

2004) containing its LCoA and CoP to AGR1, which

registers the binding information. Also, MR1 sends a

Æ AGR1

Handover

AGR1

MR1

AR1

AR2

AR3

AR4

MN1

MN2

MN1

MN2

CN1

CN2

MN1’s HA

MN2’s HA

MR1’s HA

Æ AGR1

CoP

LCoA = A::1

ACoA = AGR1

CoP = A:1::/64

A::/48

B::/48

LCoA = B::1

ACoA = AGR1

CoP = B:1::/64

LCoA = A:1::1

ACoA = AGR1

LCoA = A:1::2

ACoA = AGR1

LCoA = B:1::2

ACoA = AGR1

LCoA = B:1::1

ACoA = AGR1

MN1_HoA Æ AGR1

MN2_HoA Æ AGR1

MN1_HoA Æ A:1::1

MN2_HoA Æ A:1::2

MN1_HoA Æ B:1::1

MN2_HoA Æ B:1::2

2MN2

A:1::/64

(CoP)

MN1

2MN2

B:1::/64

(CoP)

MN1

Æ AGR1

Handover

AGR1

MR1

AR1

AR2

AR3

AR4

MN1

MN2

MN1

MN2

CN1

CN2

MN1’s HA

MN2’s HA

MR1’s HA

Æ AGR1

CoP

LCoA = A::1

ACoA = AGR1

CoP = A:1::/64

A::/48

B::/48

LCoA = B::1

ACoA = AGR1

CoP = B:1::/64

LCoA = A:1::1

ACoA = AGR1

LCoA = A:1::2

ACoA = AGR1

LCoA = B:1::2

ACoA = AGR1

LCoA = B:1::1

ACoA = AGR1

MN1_HoA Æ AGR1

MN2_HoA Æ AGR1

MN1_HoA Æ A:1::1

MN2_HoA Æ A:1::2

MN1_HoA Æ B:1::1

MN2_HoA Æ B:1::2

2MN2

A:1::/64

(CoP)

MN1

2MN2

B:1::/64

(CoP)

MN1

Figure 6: Care of Prefix Routing on MIP

Figure 7: MR joins

MR1_HoA=HoA.x

MN1_HoA=HoA.y

MR1

AR1 AR2

AGR1

HA1(MR1)

AGR address Notification

RSol CoP req

RAdvAGR1, A:1::

BU(SA=A::1, DA=AGR1, HoAOpt=HoA.x, CoP=A:1::)

BindingCache

MR1.CoPA:1::

HoA.xA::1

BindingCache

HoA.xAGR1

BC search

HoA.xA::1

encap

RHO proc

IPinIP (DA=A::1)

decap

BA proc

LCoA gen



A::1

ACoA gen



AGR1

CoP reg



A:1::

BU (SA=A::1, DA=HA, ACoA=AGR1, HoAOpt=HoAx )

BA (SA=AGR1, DA=AR1.x, RHO=HoA.x)

BA (SA=HA1, DA=AGR1, RHO=HoA.x)

CARE-OF-PREFIX ROUTING FOR MOVING NETWORKS IN MOBILE IP NETWORK

117

BU to the HA of MR1 to register the AGR1 address

as its ACoA.

Figure 8 shows the sequence for connecting

MN1 to MR1 in the case where MR1 is already

connected to AR1. MN1 creates its LCoA (A:1::1)

and its ACoA (AGR1 address) from the RAdv

received from MR1. Next, MN1 sends a BU with its

LCoA to AGR1, and a BU containing the ACoA to

its HA. At that time, AGR1 caches the relation that

MN-CoA1 is from the CoP of MR1.

Figure 9 shows the sequence of route

optimization from CN1 to MN1. MN1 sends a BU to

ACoA (AGR1 address). In this situation, CN1 can

send packets destined to MN1 via AGR1 using

RHO. AGR1 encapsulates this packet with the LCoA

(A:1::1) of MN1 after locating the LCoA (A:1::1) of

MN1 in its binding cache and transmits this packet

to MN1.

Figure 10 shows the sequence triggered by

moving network handoff. MR1 updates its CoP and

informs AGR1 of the update, after getting the new

CoP (B:1::). The subnet mask of this new CoP

should be the same as that of the previous CoP

(A:1::). When AGR1 updates the CoP of MR1,

AGR1 also updates all the LCoAs of all MNs since

they are also subordinates of MR1. More precisely,

only the common information is updated, since MN1

creates its new LCoA after receiving RAdv, which

contains the new CoP (B:1::) sent by MR1. In CoPR,

MN-CoA1 (B:1::1), which AGR1 manages, has

already been updated so that it is not necessary for

MN1 to send a BU to AGR1. In this way, BUs can

be omitted from each MN in the moving network to

the AGR. If the AGR address is changed, it is

necessary to update ACoAs of MN1 and MR1.

5 PERFORMANCE EVALUATION

We have evaluated CoPR, Basic and RRH, using

network simulator 2. Figure 11 shows the parameters

and the topology used in the simulation.

This simulation assumed that the AGR location

was optimal, as shown in Figure 11. The simulation

time was 10 seconds, and the first 2 seconds were

discarded to eliminate the influence of jitter. We

evaluated each mechanism assuming 1, 5, 10, 100,



CNs

MR’s HA

MN’s HA

MNs

2sHandoff interval

G.723.1(6.3Kbps)

* Num. of MNs

(packet size: 24byte)

Data trans. Rate

(CNs -> MNs)

20msL2 disconnected time

11Mbps (1ms)Wireless Link (link delay)

100Mbps (1ms)Wired Link (link delay)

Movement range

AGR



CNs

MR’s HA

MN’s HA

MNs

2sHandoff interval

G.723.1(6.3Kbps)

* Num. of MNs

(packet size: 24byte)

Data trans. Rate

(CNs -> MNs)

20msL2 disconnected time

11Mbps (1ms)Wireless Link (link delay)

100Mbps (1ms)Wired Link (link delay)

Movement range

AGR

Figure 11: Simulation Conditions

AGR1

MN1

BC search

HoA.yA:1::1

encap

RHO proc

IPinIP ( DA=A:1::1)

CN1

BindingCache

HoA.xAGR1

BA (SA=CN1, DA=AGR1, RHO=HoA.y)

BC search

HoA.yA:1::1

encap

RHO proc

IPinIP ( DA=A:1::1)

decap

BA proc

DATA (SA=CN1, DA=AGR1, RHO=HoA.y)

decap

BU (SA=A:1::1, DA=CN1, ACoA=AGR1, HoAOpt=HoA.y)

MR1_HoA=HoA.x

MN1_HoA=HoA.y

MR1_CoP=A:1::

ACoA=AGR1

MR1_LCoA=A::1

MN1_LCoA=A:1::1

Figure 9: Optimization of the route to CN

MR1

AGR1

RAdvAGR1, A:1::

decap

BA proc

MN1

HA2(MN1)

MR1_HoA=HoA.x

MN1_HoA=HoA.y

MR1_CoP=A:1::

BU(SA=A:1::1, DA=AGR1, HoAOpt=HoA.y)

BindingCache

HoA.yAR1.1y

BindingCache

HoA.yAGR1

BA (SA=HA2, DA=AGR1, RHO=HoA.y)

BC search

HoA.yA:1::1

encap

RHO proc

IPinIP ( DA=A:1::1)

BA (SA=AGR1, DA=A:1::1, RHO=HoA.y)

RSol

LCoA gen



A:1::1

ACoA gen



AGR1

BU (SA=A:1::1, DA=HA2, ACoA=AGR1, HoAOpt=HoA.y)

Figure 8: MN joins

MR1

AR2

AGR1

RSol CoP req

MN1

RAdv (AGR1, B:1::)

LCoA gen



B::1

CoP reg



B:1::

BU (SA=B::1, DA=AGR1, HoAOpt=HoA.x, CoP=B:1::)

BindingCache

MR1.CoPB:1::

HoA.xB::1

HoA.yB:1::1

BA (SA=AGR1, DA=B::1, RHOr=HoA.x

BA proc

RAdv (AGR1, B:1::)

MR1_CoP=B:1::

MR1_LCoA=B::1

MN1_LCoA=B:1::1

After handoff (only changed addresses)

Before handoff

MR1_HoA=HoA.x

MN1_HoA=HoA.y

MR1_CoP=A:1::

ACoA=AGR1

MR1_LCoA=A::1

MN1_LCoA=A:1::1

LCoA gen



B:1::1

Figure 10: Handoff

ICETE 2004 - WIRELESS COMMUNICATION SYSTEMS AND NETWORKS

118

and 500 MNs in the moving network. The following

items were evaluated:

(1) E2E delay

(2) Amount of received data / total network

resources used

(3) Handoff signal overhead

(4) Handoff latency

(5) Amount of packet loss

Item 1 is the mean delay of packet transmission

from a CN to an MN in the moving network, and

indicates the degree of route optimization. Item 2

indicates the throughput on each hop. This should

increase if the route is optimized, packet header size

is minimized, and discarded packets are minimized.

The inverse of this measure indicates the network

resource that should be provided for given traffic.

Item 3 is the number of handoff signals, i.e. RSol,

RAdv, BU, and Binding Ack (BA) (Johnson, 2004),

per handoff. Item 4 is the mean time from handoff

initiation to completion. Item 5 is the total discarded

packets caused by the handoff. Items 3 to 5 also

indicate handoff performance.

Comparisons for items 1 and 2 for various

numbers of MNs are shown in Figures 12 and 13.

With respect to items 1 and 2, the results of

CoPR are good as shown in each figure. This is

because CoPR implements both route optimization

and minimization of packet header size.

With regard to item 1, CoPR is superior to Basic

in terms of performance regardless of the number of

MNs. The degree of superiority would increase if the

HA is separated from the MR, because the packets

must pass through the bidirectional tunnel from the

MR to its HA. On the other hand, CoPR and RRH

offer similar levels of performance since both of

them optimize routing.

With regard to item 2, the ratio of CoPR

performance to those of the conventional methods is

almost independent of the number of MNs. The ratio

is 1.90 when compared to Basic. This shows that

CoPR transmits data more efficiently than Basic.

This difference is due to the difference in

encapsulation distance of Basic and CoPR. Basic

uses a longer encapsulation distance, from the MR to

its HA, whereas CoPR encapsulates only the route

from the MN to the AGR. On the other hand, the

performance ratio is 0.94 for RRH. The reason is as

follows. In RRH, packets are transmitted with an

RHO that sets two CoAs, MR-CoA and MN-CoA,

from the CN to the MN. In comparison, in CoPR, the

packets are transmitted with an RHO that sets one

AGR address from the CN to the AGR, and also by

encapsulation from the AGR to the MN. Therefore,

CoPR is better and this ratio is larger if the CN is

farther from the moving network than considered in

this simulation environment. The reciprocal of item

2 represents the network resources needed to support

the traffic of a new service. In other words,

increasing item 2 makes it cheaper to put a service

into operation.

Items 3 and 4 for RRH change rapidly with the

number of MNs. Figures 14 and 15 show the

comparisons for various numbers of MNs.

With regard to item 3, both Basic and CoPR

offer low and constant values. On the other hand, in

RRH, increasing the number of MNs increases the

number of handoff signals. Specifically, if the

number of MNs is 500, CoPR has about the same

level of performance as Basic, while it requires

2,000 fewer handoff signals than RRH. The reason is

that RRH demands that all MNs in the moving

network send a BU to each CN and HA.

For item 4, the performance ratio of CoPR to

Basic is 0.38, regardless of the number of MNs. This

difference depends on the BU destination. If the HA

of the MR is located farther from the moving

network than considered in this simulation

environment, the degree of superiority of CoPR

would increase. On the other hand, the ratio of CoPR

to RRH depends on the number of MNs, e.g. 0.32

with one MN, 0.11 with 500 MNs. This shows that

CoPR has lower handoff latency than RRH. The

superiority of CoPR over RRH is due to the fact that

Basic

RRH

CoPR

Num. of MNs in Moving Network

E2E delay (s)

(Item 1)

1510100500

0.006

0.008

0.01

0.012

0.014

0.016

Basic

RRH

CoPR

Num. of MNs in Moving Network

Amount of received data / Total network resources used

(Item 2)

1 5 10 100 500

0.01

0.02

0.03

0.04

Figure 12: Comparison over Num. of MNs (Item 1).

Figure 13: Comparison over Num. of MNs (Item 2)

Basic

RRH

CoPR

Num. of MNs in Moving Network

Num. of handoff signals

Num. of MNs in Moving Network

(Item 3)

1510100500

100

1000

Basic

RRH

CoPR

Num. of MNs in Moving Network

Handoff latency (s)

(Item 4)

1 5 10 100 500

0.01

0.02

0.03

0.04

0.05

0.06

Figure 14: Comparison over Num. of MNs (Item 3)

Figure 15: Comparison over Num. of MNs (Item 4)

CARE-OF-PREFIX ROUTING FOR MOVING NETWORKS IN MOBILE IP NETWORK

119

the BU destination is only the AGR in CoPR,

compared to all CNs and all HAs in RRH. Therefore,

if the number of CNs and MNs in the moving

network is increased or the distance between an MN

and its HA, or between an MN and a CN is

increased, the handoff latency of RRH increases

dramatically. In short, CoPR is much better than

RRH.

Figure 16 shows the comparisons for different

numbers of MNs regarding item 5, i.e., the total

packet loss. As these figures show, the amount of

discarded packets on CoPR is the smallest of the

three methods, regardless of the number of MNs.

Additionally, the three methods have different time

ranges of discarded packets. For Basic, it is from the

L2 disconnect time until the binding information that

the MR’s HA manages is updated. For RRH, it is

from the L2 disconnect time until the binding

information that each CN manages is updated. For

CoPR, it is from the L2 disconnect time until the

binding information the AGR manages is updated.

This value of RRH becomes worse than those of the

other methods as the number of MNs increases. This

is because the number of handoff signals increases as

the number of MNs grows.

6 CONCLUSION

This paper clarified the difference between host

mobility support and conventional moving network

mobility support, and proposed new routing

mechanisms for moving network mobility support

that meet all requirements. Specifically, this paper

proposed four basic techniques: Care of Prefix,

which minimizes the packet header size,

Concatenated HAs and Hierarchical Address

Management, which reduce the number and volume

of handoff signals, Aggregate Router, which

aggregates and localizes handoff signals, and CoPR,

which is a mechanism for applying these basic

techniques to MIP.

We verified the effectiveness of our proposed

mechanisms using network simulator 2. Quantitative

analyses showed that CoPR is the best in terms of

five measures: E2E delay, amount of effective

received data / total used network resources, amount

of handoff signals, handoff latency, and amount of

discarded packets. As mentioned above, CoPR is

superior to the conventional solutions proposed in

NEMO. We will construct an experimental system

and verify the feasibility of the proposal

mechanisms.

ACKNOWLEDGMENTS

The authors would like to thank Mr. Yoshizawa and

Mr. Fukazawa of NTT COMWARE Corporation for

their useful advice on the simulation.

REFERENCES

IETF, Available: http://www.ietf.org/

Yumiba, H., Imai, K. & Yabusaki, M.. 2001. IP-Based

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Johnson, D., Perkins, C. & Arkko, J. 2004. Mobility

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http://www.isi.edu/nsnam/ns/

Devarapalli, V., Wakikawa, R., Petrescu, A. & Thubert, P.

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Suzuki, T., Hiyama, S., Igarashi, K., Kawakami, S. &

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Network, In IEICE General Conference.

Basic

RRH

CoPR

Time (s)

Total packet loss

(a) Case of one MN in Moving Network

246810

Basic

RRH

CoPR

Time (s)

Total packet loss

(b) Case of five MNs in Moving Network

246810

Basic

RRH

CoPR

Time (s)

Total packet loss

246810

Basic

RRH

CoPR

Time (s)

Total packet loss

(d) Case of 100 MNs in Moving Network

246810

100

200

300

400

500

Basic

RRH

CoPR

Time (s)

Tot al p acket loss

(e) Case of 500 MNs in Moving Network

246810

500

1000

1500

2000

2500

3000

3500

Figure 16: Comparison on each case (Item 5)

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