A Comparative Analysis on the Signaling Load ofProxy Mobile IPv6 and Hierarchical Mobile IPv6

Myung-Kyu Yi, Jin-Woo Choi, and Young-Kyu YangCollege of IT, Kyungwon University

5-3 Seromkwan, San 65, Bokjeong-Dong, Sujeong-Gu,Seongnam, Gyeonggi-Do, 461-701, South Korea

{kainos,cjw49,ykyang}@kyungwon.ac.kr

Abstract—In this paper, we investigate the performance of theproxy mobile IPv6 and compare it with that of the hierarchicalmobile IPv6. It is well known that performance of proxy mobileIPv6 is better than that of hierarchical mobile IPv6. For the moredetailed performance analysis, we propose an analytic mobilitymodel based on the random walk to take into account variousmobility conditions. Based on the analytic models, we formulatethe location management cost and handoff management cost.Then, we analyze the performance of the proxy mobile IPv6and hierarchical mobile IPv6, respectively. The numerical resultsshow that the proxy mobile IPv6 can has superior performanceto hierarchical mobile IPv6 by reducing the latencies for locationupdate and handoff.

I. INTRODUCTION

Recently, the rapid and widespread dissemination of power-ful notebook computer and wireless communication promisesto provide users with network access at any time and in anylocation. In order to communicate, all mobile devices mustbe configured with an IP address in accordance with the IPprotocol and its addressing scheme. The problem occurs whena user roams away from its home network and is no longerreachable using normal IP routing. This results in the activesessions of the device being terminated. A natural solution isto use IP layer mobility.

Mobile IPv6 (MIPv6)[1] is the IETF proposed standardsolution for handling terminal mobility among IP subnets. Itallows a computer to roam freely on the Internet while stillmaintaining the same IP address. Each Mobile Node (MN)is identified by two IP addresses: its Home Address (HoA)and its Care-of Address (CoA). The HoA is a static addressthat is used to identify higher layer connections. The CoA isa temporary IP address for routing purpose when the MN isattached to a foreign link. When an MN moves from its homelink to a foreign link, it first forms a CoA based on the prefix ofthe foreign link. Then, the MN informs its Home Agent (HA)and any active Correspondent Node (CN) by sending a BindingUpdate (BU) message. The BU message contains the MN’sHoA and its CoA. The HA needs to store this information inorder to forward packets address to the MN’s home address.Therefore, data packets addressed to the MN are routed toits home network, where the HA now intercepts and tunnelsthem to the CoA toward the MN. When the MN moves backto its home link, it will notify the HA to delete the binding.In MIPv6, however, the CoA of an MN changes whenever

it moves from one IP subnet to another. This could lead tofrequent registrations with the HA. Thus, Hierarchical MobileIPv6 (HMIPv6)[2] is proposed by IETF to reduce signalingcost. The HMIPv6 is a mobility management protocol aimedat reducing wireless signalling and improving handover per-formance while moving within a particular domain. It usesa new MIPv6 node called the Mobility Anchor Point (MAP)to handle Mobile IP registration locally. When an MN movesinto a new MAP domain in HMIPv6 networks, it needs toconfigure two CoAs: an Regional Care-of Address (RCoA) onthe MAP’s link and an on-link CoA (LCoA). While the LCoAis simply referred to as the CoA in MIPv6, the RCoA is auto-configured by the MN when receiving the MAP option. If theMN changes its current LCoA within a local MAP domain,it only needs to register the new address with the MAP.Therefore, the HA and external CNs need not be informedabout local mobility within an IPv6 network. In HMIPv6, allpackets addressed to the MN’s RCoA are intercepted by theMAP and tunnelled to the MN’s LCoA.

MAG AAA LMA CNMN

MN Attachment

AAA Query

AAA ReplyRouter

AdvertisementProxy Binding Update

Proxy Binding Acknowledgement Router

Advertisementdata packet

data packet

data packet

Fig. 1. Message flow in PMIPv6

However, MIPv6 and HMIPv6 require additional stacks andsignaling for the MN. This could bring overhead such asbattery power and computation resource consumption. Net-work based mobility support mechanism is another approachto solve the problems and support the IP mobility. It is calledProxy Mobile IPv6 (PMIPv6)[3] and is based on MIPv6.PMIPv6 enables IP mobility for a host without requiring itsparticipation in any mobility-related signaling. There are twomain components for the PMIPv6, a Local Mobility Anchor

(LMA) and a Mobile Access Gateway (MAG). The LMAperforms home agent roles, as defined in MIPv6, for the MNin the proxy mobile IPv6 domain. The LMA is the topologicalanchor point for the MN’s home network prefix (HNP) and itmaintains MN’s binding state. The MAG performs mobilityrelated signaling to the LMA for the MN and tracks theMN’s movements. Fig. 1 illustrates the message flow of overalloperations in PMIPv6. When an MN enters a PMIPv6 domainand attaches to an access link, the MAG retrieves the MN’sprofile using its current identifier. Then, the MAG will senda Proxy Binding Update (PBU) message to the LMA inorder to register the current point of attachment of the MN.Accordingly, a binding cache entry and a tunnel for the MN’shome prefix will be created. Then, the LMA reply Proxy BindAcknowledgement (PBA) message with the MN’s HNP. Afterreceiving the Router Advertise (RA) message, the MN createsits IP address. For packet routing, the LMA will route allreceived packets over the established tunnel to the MAG. TheMAG forwards these packets to the MN. Certainly, the MAGwill relay all the received packets over the tunnel to the LMAand then they will be routed towards the CN.

In this paper, we propose an analytic mobility model basedon the random walk to take into account various mobilityconditions for performance analysis of PMIPv6 and HMIPv6.Based on the analytic models, we formulate the location man-agement cost and handoff management cost. Then, we analyzethe performance of the proxy mobile IPv6 and hierarchicalmobile IPv6, respectively.

The rest of the paper is organized as follows. Section2 introduces an analytic mobility model for performanceevaluation and Section 3 formulates signaling cost functionsusing the analytic model. Section 4 shows the numerical resultsbased on the analytic model. Finally, conclusions are presentedin Section 5.

II. ANALYTIC MOBILITY MODEL

In this section, we develop an analytic model to derive thecost functions and compare the performance of the PMIPv6and HMIPv6 schemes. We assume the existence of a subnet-based cellular networks. Our network mobility model is rep-resented by a bounded-degree, connected graph G = (V,E)where the node-set V represents the subnets and the edge-setE represents the access paths between pairs of subnet. LetN = |V | be the number of nodes or subents in the networkG. For a node v ∈ V , let Γ(v) denote the set of neighbors ofv in G as shown in Fig. 2.

We propose to use random walk on a connected graph Grepresenting our network model. A random walk on a graphis stochastic process which occurs in a sequence of discretesteps. A random walk on the graph G induces a Markov chainMG as follows[4]. The states of MG are the nodes of G andfor any two nodes i and j, the transition probability betweenthe corresponding states is given by Pi,j . We denote Γ(i) asthe set of neighbors in subnet i. For all other subnets, Pi,i =Pi,j = 1

|Γ(i)+1| for j ∈ Γ(i), and zero otherwise.

Subnet 8

Subnet 1Subnet 2

Subnet 3

Subnet 4

Subnet 5

Subnet 6

Subnet 7

Fig. 2. Wireless cellular network model

TABLE ITRANSITION PROBABILITY MATRIX AND STEADY-STATE

PROBABILITIES(SSP)

SubnetsTransition Probability

SSPS1 S2 S3 S4 S5 S6 S7 S8

S1 0.33 0.33 0.00 0.00 0.00 0.00 0.00 0.33 0.0369S2 0.20 0.20 0.20 0.20 0.00 0.00 0.20 0.00 0.0608S3 0.00 0.03 0.94 0.03 0.00 0.00 0.00 0.00 0.4046S4 0.00 0.20 0.20 0.20 0.20 0.00 0.20 0.00 0.0606S5 0.00 0.00 0.00 0.33 0.33 0.33 0.00 0.00 0.0361S6 0.00 0.00 0.00 0.00 0.04 0.92 0.04 0.00 0.3017S7 0.00 0.20 0.00 0.20 0.00 0.20 0.20 0.20 0.0611S8 0.33 0.00 0.00 0.00 0.00 0.00 0.33 0.33 0.0381

III. SIGNALING COST FUNCTIONS

In this section, we present analytic signaling cost functionto compare PMIPv6 and HMIPv6.

A. Analysis of Signaling Cost in HMIPv6

AR / MAG

AAA

MAP / LMA

HA CN

a

b

c

d

Internet

f

e

Fig. 3. Network Model

For simplicity, we assume that each LMA is located on theMAP as shown in Fig. 3. Moreover, we define the distanceparameters used for the performance evaluation as follows:

◦ a : The number of hops between MN and AR/MAG.◦ b : The number of hops between AR/MAG and

MAP/LMA.◦ c : The number of hops between AR/MAG and AAA.◦ d : The number of hops between MAP/LMA and HA.◦ e : The number of hops between MAP/LMA and CN.◦ f : The number of hops between HA and CN.◦ δh : The processing cost of binding update at the HA.◦ δm : The processing cost of binding update at the MAP.◦ Pj,i : The transition probability from subnet i to subnet

j.◦ Πi : The steady state probability of state i estimates the

location probability of a user in subnet i.◦ Rr : The refresh rate that an MN renews its location.◦ ti : The time duration that an MN stays in a subnet.

We assume that performance metric is the total signalingcost which consist of the handoff management cost andlocation management cost in HMIPv6 as follows:

CHMIPT = CHMIP

H + CHMIPL (1)

We use Cg and Cl to present the location management costin global binding update and local binding update, respectively.Based on the random walk model, we can get the totalsignaling cost of HMIPv6 scheme as follows:

CHMIPL =

N∑i=1

{Πi · Cg +

N∑j=1,j �=i

Πj · Cl

}Rrti (2)

The first term is the registration costs from the MAP toits HA. The second term is the average registration costs foran MN’s movement from subnet i to subnet j in Eq.(2). Forsimplicity, we assume that the transmission cost for bindingupdate message is proportional to the distance in terms of thenumber of hops between the source and destination mobilityagents such as HA, MAP, CN and MN. Using the proportionalconstant δU , Eq.(2) can be rewritten as follows:

CHMIPL =

N∑i=1

{Πi · ((4a + 4b + 2d)δU + δh + δm)

+N∑

j=1,j �=i

Πj · (2(a + d)δU + δm)}

Rrti (3)

In HMIPv6, IP handoff latency can be expressed as the sumof the movement detection delay and address configurationdelay. Therefore, we can get the handoff management cost asfollows:

CHMIPH =

N∑i=1

{ N∑j=1,j �=i

Πj · Pj,i · (tMD + tDAD)}

Rrti (4)

B. Analysis of Signaling Cost in PMIPv6

We assume that performance metric is the total signalingcost which consist of the handoff management cost andlocation management cost in PMIPv6 as follows:

CPMIPT = CPMIP

H + CPMIPL (5)

We use C′l to present the location management cost in local

binding update in PMIPv6. Based on Eq.(2), the average totalsignaling cost of PMIPv6 scheme as follows:

CPMIPL =

N∑i=1

{Πi · Cg +

N∑j=1,j �=i

Πj · C ′l

}Rrti (6)

The first term is the registration costs from the LMA to itsHA. The second term is the average registration costs for anMN’s movement from MAG i to MAG j in Eq.(6). Basedon the message flow in PMIPv6, Eq.(6) can be rewritten asfollows:

CPMIPL =

N∑i=1

{Πi · ((4a + 4b + 2d)δU + δh + δm)

+N∑

j=1,j �=i

Πj · (2b · δU + δm)}

Rrti (7)

Since the PMIPv6 employs the per-MN-prefix model, themovement detection delay and address configuration delay arenot incurred in PMIPv6. However, it requires authenticationprocedure before the MAG sends a PBU message to the LMA.Therefore, we can get the handoff management cost in PMIPv6as follows:

CPMIPH =

N∑i=1

{ N∑j=1,j �=i

Πj · Pj,i · (tRA + tAAA)}

Rrti (8)

Based on the message flow for authentication process inPMIPv6, Eq.(8) can be rewritten as follows:

CPMIPH =

N∑i=1

{ N∑j=1,j �=i

Πj · Pj,i · ((3a + 2c)δU )}

Rrti (9)

IV. NUMERICAL RESULTS

In this section, we will demonstrate some numerical results.Table I and II show some of the parameters used in ourperformance analysis that are discussed in [4], [5], [6], [7],[8].

TABLE IIPERFORMANCE ANALYSIS PARAMETERS

Parameter Value Parameter Value

ti 0.01 - 1000 Rr 0.01-1000δh 30 δm 20δU 0.1 a 1 - 10b 3 c 1 - 10d 10 e, f 10

tMD 0.2 - 0.6 tDAD 1

We define the relative signaling cost of PMIPv6 scheme asthe ratio of total signaling cost for PMIPv6 scheme to that

of HMIPv6 scheme. A relative cost of 1 means that the costsunder both schemes are exactly the same.

1 2

Rel

ativ

e Si

gnal

ing

Cos

t

a

0.960

0.961

0.962

0.963

0.964

0.965

0.966

0.967

0.968

PMIPv6

HMIPv6

Fig. 4. Effect of a on the relative signaling cost

Fig. 4 shows the impact of delay between the MN andAR/MAG, a, on the relative signaling cost for b = 3, c = 3,Rr = 0.1, and ti=10. We can see that the performance of thePMIPv6, on the whole, results in the lowest total signaling costcompared with HMIPv6. This is because wireless link delayfor binding update is high, which incurs a high signaling costin HMIPv6. However, PMIPv6 is least affected because theMN is not involved in mobility-related signaling.

10 10

Rel

ativ

e Si

gnal

ing

Cos

t

R

0.925

0.930

0.935

0.940

0.945

0.950

0.955

0.960

0.965

r

-2 -1

PMIPv6

HMIPv6

Fig. 5. Effect of Rr on the relative signaling cost

Fig. 5 shows the Rr, on the relative signaling cost fora = 1, b = 3, c = 3, and ti = 10. As shown in Fig. 5, therelative signaling cost increases as Rr increases. We can seethat the performance of the PMIPv6, on the whole, resultsin the lowest total signaling cost compared with HMIPv6scheme. These results are expected because the PMIPv6scheme tries to reduce the signaling loads by reducing theaddress configuration delay. Moreover, the PMIPv6 does notrequire tunnelling overhead over the air.

Fig. 6 shows the impact of delay between the MN and AAA,c, on the total signaling cost for a = 1, b = 3, Rr = 0.1,

Rel

ativ

e Si

gnal

ing

Cos

t

PMIPv6

HMIPv6

0.925

0.926

0.927

0.928

0.929

0.930

0.931

0.932

0.933

0.934

0.935

1 2 3 4 5 6 7 8 9 10

c

Fig. 6. Effect of c on the relative signaling cost

ti = 10. We can see that PMIPv6 results in the lowest totalcost compared with HMIPv6 scheme. From the above analysisof the results, the PMIPv6 scheme has a considerable perfor-mance advantages over HMIPv6 scheme. So, we conclude thatthe PMIPv6 achieves significant performance improvementsby reducing the IP latencies of location update and handoff.

V. CONCLUSIONS

In this paper, we studied performance of PMIPv6 andcompare it with that of HMIPv6. For the more detailedperformance analysis, we proposed an analytic mobility modelbased on the random walk to take into account various mobilityconditions. Based on the analytic models, we formulatedthe location management cost and handoff management cost.Then, we analyzed the performance of the proxy mobileIPv6 and hierarchical mobile IPv6, respectively. The numericalresults show that PMIPv6 can has superior performance toHMIPv6 by reducing the IP latencies for location update andhandoff.

ACKNOWLEDGMENT

This research was supported by the Ministry of Knowl-edge Economy, Korea, under the ITRC(Information Tech-nology Research Center) support program supervised bythe IITA(Institute of Information Technology Advancement)(IITA-2008-C1090-0801-0040)

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[3] Sri Gundavelli, Kent Leung, Vijay Devarapalli, Kuntal Chowd-hury,“Proxy Mobile IPv6,” IETF Request for Comments 5213, August2008.

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