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OPNET Simulation Modeling and Analysis of

Enhanced Mobile IP

Taeyeon Park and Arek DadejCooperative Research Centre for Satellite Systems

Institute for Telecommunications Research, University of South Australia

Mawson Lakes Boulevard, Mawson Lakes, SA 5095, Australia

Email: typark@spri.levels.unisa.edu.au, arek.dadej@unisa.edu.au

Abstract To facilitate simulation studies of Mobile IP perfor-mance and comparative analysis of enhanced Mobile IP handovermechanisms, we have developed a simulation model of MobileIP using OPNET modeling environment. In this paper, weprovide basic design concepts and implementation details of thesimulation model, as well as descriptions of the advanced featuresof IP mobility architectures implemented as part of the model,e.g. buffering and regional registration. Based on the analysisof simulation results obtained using the developed simulation

models, a few suggestions are made for the use of Mobile IPand related enhanced mechanisms in selected wireless Internetscenarios.

I. INTRODUCTION

Mobile Internet Protocol (Mobile IP) [11], [13] was devel-

oped to provide seamless support for routing of IP datagrams

to mobile hosts. The fundamental assumption behind the

development of Mobile IP was backward compatibility with

the existing Internet infrastructure based on TCP/IP protocol

suite originally developed for fixed networks. Although Mobile

IP was originally aimed at the mobile wireless computing

environment built within the realms of the Internet tradition,

its principles are also being adopted in the new generationall-IP cellular networks that will replace the traditional mobile

telephony networks.

To get the maximum benefits from deployment of new

generation all-IP networks, and to avoid costly design mis-

takes, it is very important to carefully evaluate Mobile IP and

related protocol mechanisms for various usage scenarios and

operating conditions that may occur in the next generation

mobile Internet. In this paper, we describe implementation of

a Mobile IP simulation model. The model covers a number of

advanced Mobile IP mechanisms e.g. movement detection [3],

[14], buffering [5], [9], [2], [6] and bicasting [11], [7] for

handover smoothing, and regional registration [4].

This paper is organized as follows. In Section II, we give abrief overview of Mobile IP and some of its inherent problems.

Section III describes design philosophy behind the simulation

models of Mobile IP entities. Some basic and enhanced IP

mobility mechanisms implemented in the model are explained

in the subsequent sections. Sections VI and VII describe the

setup of simulation experiments, simulation results and their

analysis. In Section VIII, we conclude with the summary of

contributions and with comments on the intended future use

of the simulation model.

MNFAHA

Data tunneling (fwd)

Registration / deregistration

Agent discovery

CN

Direct forwarding by standard IP routing

Fig. 1. Operation of Mobile IPv4

II . BRIEF OVERVIEW OF MOBILE IP

A. Basic Operation

The basic sequence of operation for Mobile IPv4 (MIPv4)

is as follows:

1) Datagram sent by correspondent node (CN) to mobilenode (MN) arrives on home network via standard IP

routing.

2) Datagram is intercepted by home agent (HA) and is

tunneled to the care-of address.

3) Datagram is detunneled and delivered to the MN.

4) For datagrams sent by the MN, standard IP routing

delivers each datagram to its destination. In Fig. 1, the

foreign agent (FA) is the MNs default router.

The datagram forwarding service in both directions ensures

that all datagrams are correctly delivered to their destinations

regardless of where the MN currently is. To correctly track

the location of the roaming MN, three basic services are

needed: agent discovery (to discover the serving FA in a visited

network), registration (of the MN with the FA and of the

MNs current location with the HA), and movement detection

(to detect the need for Mobile IP handover). The interacting

entities and the corresponding scope for each of these services

are depicted in Fig. 1.

B. Known problems and directions for solutions

The following issues have been identified within the Mobile

IP community as high priority work items that need to be

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addressed in order to accelerate widespread wireless Internet

deployment and to meet the high service quality standards

expected of the next generation wireless Internet.

Handover performance fast handover is needed for real-

time multimedia traffic and when high frequencies of

handovers may be expected [7]

Security good protection, e.g. using Authentication, Au-

thorization and Accounting (AAA), from security attacks,is needed in the highly vulnerable wireless environment

Integration of Quality of Service (QoS) harmonization

with QoS models, such as Differentiated Services (Diff-

Serv) or Multi Protocol Label Switching (MPLS), needs

to be achieved in order to guarantee both good mobility

support and good quality of service [1]

Deployment and migration effective handling of firewall

and/or Network Address Translation (NAT) traversal, as

well as smooth transition between, or coexistence of,

MIPv4 and Mobile IPv6 (MIPv6)

In this paper, we focus on the issues in handover perfor-

mance.

III. DESIGN OF SIMULATION MODELS

This section explains the design philosophy followed in the

development of the models, as well as discusses the Mobile

IP related functional entities supported in the model.

A. Design concepts

The general design philosophy followed in the development

of our models is modularity and simplicity. Firstly, modularity

means ease of extension and flexibility in respect to functional

changes, thus allowing development of a complete set of

models required in the Mobile IP performance studies starting

from a very basic set of models. A complete set of models

may include implementations of various Mobile IP extensiontypes and a large number of micro/local mobility handling

mechanisms that aim at fast handovers and integration with

the various flavors of QoS control models that may be used in

the wireless Internet. Secondly, simplicity helps in focusing on

the functional and performance aspects of Mobile IP chosen

for the particular study and ensures easy maintenance of

the developed model. As an example, the modularity and

simplicity of the model mean that by turning on or off one of

the IP mobility enhancing mechanisms featured in the model,

we can focus on the impact of the selection of this particular

enhancement on the Mobile IP signaling load and the overall

QoS performance, with minimum or no effort required to

change the model to suit the specific Mobile IP networkingscenario under investigation.

B. Basic entities and modified OPNET library modules

Simulation models of Mobile IP entities consist of MN, FA,

and HA, together implementing Mobile IP functionality based

on [11].

According to the modeling principles used in OPNET, we

have constructed each entity with separate Node Model. Each

node model consists of several component modules including

processor/queue modules and streams providing connections

between modules. Even though most constituents of a node

model depend on the type of node, common component

modules include udp/tcp transport modules, ip encap/ip rte

network modules, and arp/mac modules. Every node should

be equipped with more than one physical link, e.g. Ethernet,

Point-to-Point, or WLAN (Wireless Local Area Network). The

last and most important component module of a node model

is the processor module implementing/determining the role of

the given node in the network. This is coded into a Process

Model. Examples are the MN process model, the FA process

model, and the HA process model that are used in the MN,

FA, and HA node models respectively. The IPIP process model

implements IP-within-IP encapsulation [12] functionality and

is used in both FA and HA node models.

In addition to developing new node models and process

models, we have modified some OPNET library models, such

as ip rte/ip encap, arp, and wlan mac modules. In the ip rte

module, we need to update the Common IP Routing Table

upon receiving a remote interrupt from the MN module to

request a change of the Default Gateway. In the arp module,gratuitous and proxy Address Resolution Protocol (ARP) send

routines are added and calls to those routines are inserted in a

few places in the code. The wlan mac module is modified to

contain newly defined Beacon frame formatting and handling,

to enable MNs movement among multiple WLAN Access

Points (APs) in one OPNET subnet plane.

C. Supported functionalities

Table I summarizes the functions supported and unsupported

in the models. In the table, the abbreviated names for message

types are as follows Agent Solicitation (SOL), Agent Ad-

vertisement (ADV), Registration Request (RRQ), Registration

Reply (RRP), Regional RRQ (R-RRQ), and Regional RRP(R-RRP).

IV. BASIC MOBILE IP MECHANISMS

As the basic set of mechanisms for the support of Mobile

IP, we implemented several mechanisms including agent dis-

covery and movement detection (ADMD) mechanisms, home

registration and deregistration, and IP tunneling mechanism.

In the following subsections, we explain each of these mech-

anisms in detail.

A. Agent discovery and movement detection

Various kinds of ADMD mechanism are considered in

the model. First, Eager Cell Switching (ECS), chosen as adefault mechanism in the simulation study, is designed to

trigger immediate handover to the new FA as soon as the MN

receives an ADV message from that FA. Its maximum ADMD

latency equals to the maximum ADV send interval used by

the new FA, whereas the mean value approaches half of the

maximum. Second, Lazy Cell Switching (LCS) mechanism

allows handover to a new FA only after three consecutive

packets from the previous FA are lost (the number of lost

packets can be varied). As can be easily seen, the maximum

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TABLE I

SUMMARY OF SUPPORTED FUNCTIONALITY

Features Supported Unsupported

Architectural entities MN, HA, and FA -Messages and extensions SOL, ADV, RRQ, RRP, R-RRQ, R-RRP, -

and all extension typesCare-of address types FA-COA Collocated-COAEncapsulation/tunneling IP-in-IP (forward tunnel Minimal Encapsulation,

and buffer forward tunnel) Generic Routing Encapsulation

and IP-in-IP (reverse tunnel)ARP types ARP, Proxy ARP, and -

Gratuitous ARPReplay protection Timestamp-based Nonce-basedAdditional mechanisms Enhanced optimal buffering, Route optimization,

Regional Registration with Security and AAAhierarchical FA management

and mean ADMD latency of the LCS method are four times

the max. ADV send interval (under assumption that the radio

coverages of the current and the new FAs overlap) and three

and a half times the max. ADV send interval, accordingly.

Though the ADMD latency for LCS is larger than that of ECS,LCS is still useful in situations where high handover frequency

is expected due to high mobility rate and high randomness

in mobility pattern. The last method, Active Cell Switching

(ACS), is obtained from the basic ECS mechanism by adding

layer-2 (L2) triggering of the handover sequence. The MN

solicits an ADV message from the new FA upon receiving

a L2 trigger notifying that L2 handover has been completed

or L2 link to the current FA is about to be broken (the latter

depends on the pre-set threshold value of signal strength). The

ACS mechanism reduces max. ADMD latency to about an

average round trip time (RTT) between the MN and the new

FA, which is normally much shorter than the nominal ADV

send interval.

B. Registration and deregistration

Registration mechanism is a core service in the Mobile IP.

When MN roams away from its home network and arrives in

the radio coverage area of a visited FA, it needs to register

its current location with its HA via the FA. While MN is

registered with a visited network, it can then issue another

registration request to another FA. This is called handover

(throughout this paper, the term handover is preferred to

the term handoff). The handover results in a change to the

active/current mobility binding. In some cases, when simulta-

neous binding is supported and enabled, the active mobility

binding (as opposed to other bindings) can be determinedfrom the context information held by the MN. While MN is

away from its home network, the HA acts as a housekeeper to

pass all the datagrams destined to the roaming MN. For that

purpose, the HA performs gratuitous ARP and proxy ARP on

behalf of the MN. Although a basic policy in Mobile IP is

to employ soft-state protocol operation, in some cases explicit

deactivation of mobility bindings may be required before a

timer involved in the soft-state mechanism has expired. For

such cases, as well as cases where the MN returns to its home

IPIP

IPH data

IPH dataIPH

IPH data

ip_ip(entry)

(ENCAP)

ip_encap

ip_rte

using gratuitous/proxydestined to the MN

ARP mechanisms.

Intercept packets

Check if registered ?

haMBindingTable

Fig. 2. HA acting as a Tunnel Entry Point

network and wants to remove the mobility bindings, explicit

deregistration mechanism may be used. When MN returns

home, it should issue gratuitous ARP to let other nodes on

the home network know that it has returned.

C. Tunneling (Encapsulation and decapsulation)

Among several tunneling mechanisms mentioned in [11],

we support at present only IP-within-IP [12]; it should be

supported in all cases as the default mandatory tunneling

mechanism. The operation of the mechanism differs depending

on where the mechanism resides (i.e. in HA or in FA). For

normal forward tunneling from HA to FA, the IPIP module

in the HA node should act as a tunnel entry point as shownin Fig. 2, while the one in the FA node acts as a tunnel exit

point as shown in Fig. 3. For the reverse tunneling case, i.e.

when the tunnel begins at the FA and ends at the HA, the roles

change and are opposite to those in the forward tunneling case.

V. ADDITIONAL MOBILITY ENHANCING MECHANISMS

To study performance of different types of Mobile IP han-

dovers, we implemented buffering and bicasting mechanisms

as they are widely accepted as handover smoothing techniques.

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IPIPIPH dataIPH

IPH data

IPH data

ip_rte

ip_ip(exit)

Check if visitor ?

Send to the MN directlyusing link layer address(hw_addr) through thedesignated interface.

Protocol==IPIP ? ip_encap(DECAP)

faVisitorTable

Fig. 3. FA acting as a Tunnel Exit Point

To reduce registration latency in networks with hierarchical

FAs, we have implemented regional registration functionality.

In the following subsections, we explain each mechanisms inmore detail.

A. Optimal buffering sequence

Buffering is generally accepted throughout the Mobile IP

community as a handover smoothing technique. The term

handover smoothing is used here to describe the reduction

in packet loss incurred by the handover.

To get maximum benefit from the use of buffering, we have

designed an optimal buffering sequence involving the MN,

old/current FA (oFA), new FA (nFA), and HA or gateway

FA (HA/GFA), as shown in Fig. 4. The basic principles for

controlling when the buffering is done, and for forwarding of

the buffered data, are as follows:

When a buffering request is made from the MN to

the oFA1 via BUF CTL REQ (Store) message, direct

forwarding of packets should be carried out as long as

the direct communication between the MN and the oFA

is possible, in parallel to the buffering at the oFA. This

helps eliminate any packet loss that might occur if the

overflow of buffer pool happens due to its limited size.

The BUF CTL REQ (Forward) message is sent just after

sending a RRQ, or as an extension of the RRQ message.

This ensures minimum delay of the buffered packets

delivered to the MN. To avoid packet duplication problem

(due to the simultaneous forwarding and buffering at the

oFA), last pkt idof the packet that the MN has receivedlast should be sent as a parameter of the BUF CTL REQ

(Forward) message.

While buffering technique is considered to guarantee zero

(or at least minimum) packet loss when designed properly as

described in the section above, it can cause unwanted buffering

delay for certain classes of user application traffic, such as

real-time multimedia traffic.

1At the time of making the buffering request, the oFA means the currentFA servicing the MN.

Buffering and direct forwarding of datapackets to the MN while in contact with oFA

RRQ

Store into a buffer

Indirect forwarding of buffered datapackets from oFA to the MN via nFA

BUF_CTL_REQ (STO)

MN nFA oFA HA/GFA

RRQBUF_CTL_REQ (FWD)

RRP

Direct forwarding via nFA

Just buffering at oFA

L2 HANDOVER

RRP

Data packet (Direct)Control message Data packet (Tunneled)

Fig. 4. An Optimal Buffering Sequence

B. Bicasting with pre-registration

Bicasting is another handover smoothing technique well

known in the Mobile IP community. Bicasting techniques may

be categorized according to the entity that performs bicasting.

First and most common case is when the HA (or GFA if

regional registration is used) acts as a bicasting entity. In this

case the HA/GFA sends the packets destined to the MN both tothe oFA and to the nFA. This kind of bicasting can be achieved

easily without any additional mechanisms if the basic Mobile

IP supports simultaneous mobility binding via S bit of the

RRQ message. Another case is when the current FA acts as a

bicasting entity. The current FA sends packets both to the MN

and to the prospective new FA(s). An example of this kind of

bicasting can be found in the Bidirectional Edge Tunnel [7].

Bicasting can reduce greatly the packet loss resulting from

large handover latency as buffering technique does. Bicasting

is, however, more beneficial than buffering in that it also re-

sults in the minimum amount of packet delay, comparable with

the delay experienced when no handover is made. It should

be noted that the minimum packet delay can be achieved onlyif we make a pre-registration with the (prospective) new FA,

using a sort of handover prediction that determines the possible

future FA(s) likely to serve the MN.

C. Regional registration and hierarchical FA management

Regional registration as defined in [4] means a registration

local to the visited domain that does not need to go through

to the home network unless the MN goes out of the current

visited domain. It is believed that such local registration can

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reduce Mobile IP related signaling delay, especially when the

distance between the visited network and the home network

of the MN is large. In Section VII-C, we have compared

the overall signaling overhead for the regional and basic

(non-regional) registration methods while varying the relative

distance between the FA hierarchy and the HA.

We have implemented regional registration mechanism

along with hierarchical FA management procedures according

to [4]. As a part of hierarchical FA management in the FA

hierarchy (for example, see Fig. 5), we have modified the

ADV message to include the Hierarchical FA Extension, where

the hierarchical FA information can be gathered dynamically

or configured statically. The original approach dealt with in

[4] requires the MN to send explicit request for a regional

registration when it receives the ADV with the I bit set.

We have developed a modified approach in which FA de-

termines which registration type, home, regional, or global,

is appropriate when it receives a normal (meaning global)

registration request from the MN. The modified approach does

not affect the MN. The FA (or FA group in an FA hierarchy)

takes care of all relevant activities by itself. The explicitbenefit of that approach as compared with the original one

is a reduction in size of the ADV message, thus saving in

bandwidth consumption over the wireless link.

VI. SIMULATION SETUP

Fig. 5 shows the network topology that we have used

in our simulations to investigate the basic characteristics of

Mobile IP handover mechanisms. In the figure, the R x denotes

border routers in each subnetwork, i.e. routers that connect

the subnetwork to the Internet. For the home subnetwork, the

HA functionality may be incorporated in the border router

R h. Similarly, for the foreign subnetwork, the gateway FA

functionality that resides in the FA1 may be integrated in theborder router R v. In hierarchical terms, the FA1 can act as a

gateway FA. Otherwise, it acts as a normal router or normal FA

depending on the functionality implemented and the specific

needs of the network. The FA hierarchy constructed this way

may be used for the purpose of regional registration, or as a

flat FA topology/structure in other cases. For FAs acting as leaf

access routers (FA4 - FA7), it is assumed that the FAs have also

been equipped with base station (BS or, in 802.11 terms, AP)

functionality. The collocation of FA and BS functionalities

in the same node also implies that any number of layer-2

handovers may occur as long as layer-3 IP address (a care-

of address in Mobile IP sense) has not changed.

We have introduced FA-HA path delay 2 to simulate distance

between the foreign subnetwork (in the visited domain) and the

home subnetwork. To represent that in terms of delay in time

domain, we have varied appropriately the delay attribute of

the point-to-point link between the border router R v and the

Internet Cloud.

2It reflects both geographical distance and abstract distance. While theformer is well represented by transmission delay, the latter consists of propa-gational delay and processing delay at every router along the communicationpath.

MN

Movement Trajectory

FA2

FA4 FA5 FA6 FA7

Visited (Foreign)Domain

R_v

FA1

FA3

R_h HACN R_c

CorrespondentSubnetwork

Home Subnetwork

Internet

Fig. 5. Network Topology Used in the Simulation

Wireless LAN is configured as IEEE 802.11, with 11 Mbps

data rate and no RTS/CTS or fragmentation used. Each

WLAN radio coverage is set to 250 meters; that ensuresnon-overlapping radio coverage of separate APs, eventually

requiring a sort of hard handover upon crossing the coverage

boundaries.

Mobility pattern of the MN is characterized by a horizontal

linear path with constant ground speed of 30 km/h (the speed

has been varied from 1 to 30 km/h when needed to observe

the impact of the moving speed on various performance mea-

sures). The moving speed (30 km/h) implies that MN moves

faster than typical pedestrians but also slower than typical

passenger vehicles in a metropolitan area. Consequently, this

choice of mobility pattern results in moderate handover rates.

The application traffic exchanged between the CN and the

MN is configured to represent IP Telephony using Voice-over-IP techniques where CN and MN act as clients to each other.

The voice traffic exchanged between the MN and CN can start

and stop in each direction in a random manner.

VII. SIMULATION RESULTS AND ANALYSIS

Using the simulation setup described in the previous section,

we have simulated a basic set of handover scenarios and

obtained preliminary results. In the simulation, performance

measures selected for the purpose of simplified experiments

were gathered, namely packet delay, jitter and packet loss

during handover. Basic Mobile IP handover operates according

to the standard specification defined in [11], whereas han-

dover methods utilizing bicasting and buffering are enabled inaddition to the basic Mobile IP handover where required.

A. Movement detection performance

Fig. 6 shows comparative results of various ADMD methods

when basic Mobile IP mechanism without regional registration

or buffering is solely used for MN to handover between

FAs. As expected from the discussion in Sec. IV-A, LCS

method shows the worst performance among the methods

compared. ACS is comparable to ECS in performance, giving

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0 50 100 150 200 250 3000

100

200

300

400

500

600

700

800

900

FAHA path delay (msec)

Averagehandoverlatency(msec)

LCSHOlatECSHOlatACSHOlatLCSADMDlatECSADMDlatACSADMDlatLCSREGlatECSREGlatACSREGlat

Fig. 6. Comparison of Average Handover Latency for Various ADMDMethods

a little bit better results at the expense of L2 triggering

cost. When considering that overall handover latency is, by

definition, the sum of ADMD latency and registration latency,the contribution of ADMD latency only goes below that of the

registration latency around 150 msec of FA-HA path delay forthe LCS method. For ECS and ACS, it is around 37 and 16

msec respectively. These results imply that the ECS or ACSshould be strongly recommended for the scenarios of moderate

FA-HA path delay (below 150 msec).

B. Mobile IP signaling overhead

Fig. 7 and Fig. 8 show the change of application throughput

and the corresponding Mobile IP signaling load when the

moving speed of the MN at ground level varies from 1 to 30

km/h. For the simulation, no regional registration or bufferingother than basic Mobile IP mechanism are used and ECS is

applied to decide move detection. In those figures, a and beach mean the send interval of ADV message at layer 3 and

Beacon frame at layer 2 in the unit of second.

As the moving speed of the MN increases, the overall

throughput is going down partly because of the corresponding

increase in the signaling load and also partly because of the

increase of disconnection time over full communication time

due to handover. The higher speed of the MN implies higher

handover rate, thus results in the higher disconnected time

during which no packet can be exchanged. It also induces

larger signaling overhead per unit time period.

For fixed value ofa, move detection method, ECS does notaffect overall handover latency. However, the value of b doessince layer-3 handover in our simulation setup includes the

time for completion of layer-2 handover that can be shortened

by shorter value ofb. In Fig. 7, as beacon interval b increasesthroughput decreases more rapidly at higher moving speed of

the MN. This tells us that for larger values of b throughputis more affected by communication blackout period (due to

frequent handovers). On the other hand, for smaller values of

b throughput is more affected by signaling overhead.

5 10 15 20 25 309.6

9.65

9.7

9.75

9.8

9.85

9.9

9.95

10

Moving Speed of MN (Vconst in km/h)

Average

Throughput(Kbits/sec)

a=1.0, b=0.1a=1.0, b=0.5a=1.0, b=1.0

1

Fig. 7. UDP Application Throughput

5 10 15 20 25 300

50

100

150

200

250

300

350

400

Moving Speed of MN (Vconst in km/h)

AverageSignalingLoad(bits/sec)

a=1.0, b=1.0a=3.0, b=1.0a=5.0, b=1.0

1

Fig. 8. Mobile IP Signaling Load

C. Regional registration performance and FA-HA path delay

In Fig. 9 through to Fig. 11, we have shown various

performance results for combinations of non-regional/regional

registration and basic/buffering cases. Except for the NBacase, all other methods show comparable results, with the

average handover latency 3 around 100 msec when we set100 msec for a, and 10 msec for b. This proves that ourbuffering mechanism ensures timely delivery of user traffic as

soon as MN begins to register through newly discovered FA.

Also, regional registration helps complete local registration in

a relatively short time, independent of the value of FA-HA

path delay.

In Fig. 10, for all cases, throughput decreases as FA-HA

path delay increases, since the higher path delay restricts the

amount of user traffic along the HA-FA path from CN to

MN transferred in a given time interval. Better performance

3We define handover latency as difference between time when the firstpacket is received from new FA after handover and time when the last packetis received from old FA before handover. If buffering is used, the first packetthrough the new FA may be the one buffered at the old FA and then forwardedto the new FA.

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0 50 100 150 200 250 3000

100

200

300

400

500

600

700

FAHA path delay (msec)

Averagehandoverlatency(msec)

NBaNBuRBaRBu

Fig. 9. Comparison of Average Handover Latency

0 50 100 150 200 250 3000.99

0.991

0.992

0.993

0.994

0.995

0.996

0.997

0.998

0.999

1

FAHA path delay (msec)

Normalizedthroughput

NBaNBuRBaRBu

Fig. 10. Comparison of Normalized Throughput

in respect to normalized throughput can be achieved when

buffering is used. This is because buffering guarantees zero

packet loss regardless of its poor performance in respect to

packet delay. Otherwise, regional registration, which reduces

handover latency, and thus packet loss during handover, seems

to enhance the performance in the case without buffering.

While regional registrations can improve performance in

situations of higher FA-HA path delay, they also incur about 33

% more average signaling load when three-level FA hierarchy

is used as in Fig. 5. The signaling overhead does generally go

up as the number of levels in the FA hierarchy increases, even

though the increase of overhead is much more dependent onthe network topology employed. Some aspects of increased

signaling load, such as increased size of the ADV message

due to inclusion of the full FA hierarchy information may

outweigh the benefits of regional registration when bandwidth-

constrained wireless links are involved.

VIII. CONCLUSION

We have developed and verified a set of Mobile IP simu-

lation models using OPNET network simulation environment.

0 50 100 150 200 250 3000

5

10

15

20

25

30

FAHA path delay (msec)

Average

signalingload(Kbps)

NBaNBuRBaRBu

Fig. 11. Comparison of Average MIP Signaling Load

Preliminary simulation study was undertaken to verify the cor-

rectness of the developed simulation models, and to investigate

some basic performance characteristics of Mobile IP featuringa few additional handover enhancement mechanisms.

Simulation results provide us with some insight as to

the characteristics of the considered Mobile IP mechanisms.

For example, buffering can be used to guarantee minimum

(even zero) packet loss during handover, but it may increase

instantaneous packet delay variation undesirable with real-

time applications, such as Voice-over-IP. Another example

conclusion is that regional registrations should be carefully

considered before implemented in the network, since they

reduce signaling delay but not signaling load.

We are currently researching adaptive mobility control

scheme that explores a variety of Mobile IP scenarios and

algorithms. This smart IP Mobility control architecture dy-namically adapts to the operating conditions and the specific

network neighborhood the MN roams into. The developed

simulation model is currently undergoing extensions to incor-

porate additional features necessary to simulate the Adaptive

Mobility Control Architecture [10].

ACKNOWLEDGMENT

This work was supported by the Commonwealth of Aus-

tralia through its Cooperative Research Centres Program. We

would like to thank anonymous reviewers for their valuable

comments in the course of reviewing process.

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[2] D. S. Eom, H. S. Lee, M. Sugano, M. Murata and H. Miyahara,Improving TCP handoff performance in Mobile IP based networks,Computer Communications 25(7):635646, May 2002.

[3] N. A. Fikouras and C. Gorg, Performance Comparison of Hintedand Advertisement Based Movement Detection Methods for Mobile IPHand-offs, Computer Networks, 37(1):5562, 2001.

[4] E. Gustafsson, A. Jonsson, and C. Perkins, Mobile IPv4 RegionalRegistration, IETF Internet-Draft, draft-ietf-mobileip-reg-tunnel-06.txt,work in progress, March 2002.

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[5] M. Khalil, H. Akhtar, E. Qaddoura, C. E. Perkins, and A. E. Cerpa,Buffer Management for Mobile IP, IETF Internet-Draft, draft-mkhalil-mobileip-buffer-00.txt, work in progress, October 1999.

[6] G. Krishnamurthi, R. Chalmers, and C. Perkins, Buffer Management forSmooth Handovers in IPv6, IETF Internet-Draft, draft-krishnamurthi-mobileip-buffer6-01.txt, work in progress, March 2001.

[7] MIPv4 Handoffs Design Team, Low Latency Handoffs in MobileIPv4, IETF Internet-Draft, draft-ietf-mobileip-lowlatency-handoffs-v4-04.txt, work in progress, June 2002.

[8] OPNET Modeler Radio, http://www.opnet.com.

[9] S. R. Pandy and S. Jamadagni, Improved Low Latency Handoff inMobile IPv4, IETF Internet-Draft, draft-shiva-improved-lowlatency-handoff-v4-01.txt, work in progress, February 2002.

[10] T. Park and A. Dadej, Adaptive Handover between Terrestrial andSatellite Wireless Networks, Proc. CRCSS Conference 2002, Canberra,Australia, pp.46, 1215 February 2002.

[11] C. Perkins, Editor, IP Mobility Support for IPv4, IETF, RFC 3344,August 2002.

[12] C. Perkins, IP Encapsulation within IP, IETF, RFC 2003, October1996.

[13] J. Solomon, Mobile IP: The Internet Unplugged, Prentice Hall,Englewood Cliffs, 1998.

[14] D. Trossen, G. Krishnamurthi, H. Chaskar, J. Kempf, Issues in

candidate access router discovery for seamless IP-level handoffs, IETFInternet-Draft, draft-ietf-seamoby-cardiscovery-issues-03.txt, work inprogress, June 2002.

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