Network Integration in 3G and 4GWireless Networks

Michael Lin∗, Heesook Choi†, Travis Dawson†, Thomas La Porta∗∗Department of Computer Science and Engineering, Pennsylvania State University, State College, PA

†Sprint Nextel ATL, Burlingame, CA

Abstract—3G wireless data networks have emergedas the first high speed, ubiquitous data networks. 4Gwireless networks are poised to replace 3G networksas the next generation of mobile data networks, butthe transition will be lengthy and expensive. Wirelessauthentication across 3G and 4G data networks is typi-cally an arduous task, requiring complete disconnectionfrom the existing network before performing a lengthyfull authentication on the new network. We introducean efficient interworking method for CDMA2000 1xEV-DO and WiMAX data networks that allows existingauthentication credentials to be leveraged in moreefficient interworking protocols at both tightly- andloosely-coupled network integration levels, as wellas a proactive handoff scheme that takes advantageof our tightly-coupled interworking. We perform adetailed simulation and mathematical analysis of ourinterworking and handoff protocols and find that ourinterworking scheme reduces interworking delays byup to 75% in the WiMAX to CDMA case and 85% inthe CDMA to WiMAX case.

I. INTRODUCTION

With the proliferation of smartphones and mobileInternet devices such as the iPhone, Blackberry, andwireless-enabled netbooks, ubiquitous, mobile, con-nected computing has become mainstream. How-ever, as mobile devices have become more popu-lar, more powerful and easier to use, their trafficdemands have increased to the extent that they arecausing service outages and performance degra-dation on currently deployed 3G networks. 4Gwireless standards promise to increase throughputand ease network load, but upgrading networksto 4G standards is expensive, difficult, and time-consuming. During the transition period, 3G and4G networks will co-exist, and service providerscan increase their operational efficiency by balanc-ing load across both networks.

Wireless networks are typically homogeneousand vertically integrated—a service provider com-mits to a wireless standard, such as GSM/UMTS orCDMA2000, and implements it throughout its en-

tire network, from the network core to the base sta-tion. However, there can be economic and technicaladvantages to creating a heterogeneous network.Integrating a newer, faster network with an exist-ing, widespread network allows a service providerto incrementally upgrade its network while main-taining coverage. Even after a transition, due to dif-ferent radio technology strengths and weaknesses,complete coverage may be most efficiently achievedusing a combination of 3G and 4G technologies.

Despite these potential advantages, interoperabil-ity between the disparate portions of a heteroge-neous network remains the most important concernfor service providers. If interworking is too costly,difficult, or places too high of a strain on the net-work, service providers will not choose to maintaina heterogeneous network.

In this paper, we introduce an efficient inter-working protocol that allows cross-authenticationbetween 3G CDMA2000 1xEV-DO (CDMA) and4G WiMAX data networks. We introduce CDMAforeign mode and WiMAX foreign mode operation,which allow a user from a WiMAX service providerto connect to a CDMA network and vice versa. Ourinterworking procedures use existing, extensiblestandards, and rely on existing key material wher-ever possible. As a result, foreign mode authenti-cation is roughly as efficient as native mode au-thentication and maintains each network’s securityrequirements. Additionally, we introduce a proac-tive, seamless handoff procedure across CDMA andWiMAX networks.

Using an analytical model, we show that a proac-tive handoff can reduce re-authentication delay byup to 85% in the case of handing over to a WiMAXnetwork, and up to 75% in the case of handing overto a CDMA network. Additionally, detailed simula-tion results show that interworked processing loadand queue waiting times are at worst identical to,and in many cases better than, existing loads and

waiting times.In brief, the contributions of this paper are as

follows:• CDMA and WiMAX foreign mode protocols• CDMA and WiMAX foreign mode handoff

protocols• Performance results showing that foreign

mode operation performs no worse than, andin some cases better than native mode opera-tion

The remainder of the paper is organized as fol-lows. In the next section, we discuss related work.Section III is a brief overview of authenticationmethods for CDMA and WiMAX networks. Wediscuss the impact of interworking on networkunification architectures in Section IV. Section Vdescribes the interworking procedure in detail. Wepresent analytical and simulation results in Sec-tion VI.

II. RELATED WORK

In our review of the literature, we have notfound any descriptions of CDMA and WiMAX in-terworking in specific, but our work is comparableto a large body of work on interworking betweenother types of networks, such as GSM/UMTS andwireless LANs (WLAN). The CDMA standardsbody, 3GPP2 [1], defines a method for interworkingbetween 3GPP2 networks and WLANs in [2]; thisis treated with more detail by Buddhikot, et al.in [3]. We adapt the 3GPP2 key exchange procedurein our CDMA-WiMAX interworking. The 3GPP2also describes the basic requirements needed forCDMA-WiMAX interworking in [4], but does notgive any technical detail. The WiMAX Forum has acomplementary document [5] that is similarly highlevel.

Buddhikot, et al. [6] describe a general interwork-ing server for 3G wireless and WLANs. They in-troduce the de facto standard descriptive classifica-tions of interworking: tightly-coupled and loosely-coupled. A tightly-coupled interworking architec-ture treats a WLAN as an access network for the3G network, with authentication information beingsent directly to the 3G network without travers-ing the Internet. Loosely-coupled interworking re-lies on the Internet for interworking. Although, asdefined, tightly-coupled and loosely-coupled referto 3G/WLAN interworking, the abstractions theyrepresent can be applied to any networks thatsupport multiple modes of access. Haase, et al. [7]

introduce a unified mobility management gatewaythat allows for interworking between wireless andtraditional wired voice networks.

III. WIRELESS AUTHENTICATION

This section provides an overview of wirelessauthentication in CDMA and WiMAX networks.We begin by establishing some common wirelessnetworking concepts.

Wireless networks are divided into two distinctcomponents: the access network and the core net-work. The two networks are typically connectedthrough a single gateway, which we refer to as theaccess gateway. Core and access networks are closelyassociated, and interworking between different coreand access networks is cumbersome.

Although each wireless standard defines its ownunique network functions, wireless networks sharea similar general architecture. The network is di-vided into a core network, which handles AAA ser-vices (authentication, authorization, and account-ing), IP mobility management, Internet connectiv-ity, and other network services, and an access net-work, which includes base stations and networkcomponents that govern network access and local-ized mobility management, including handoffs anduser location. The access network is connected tothe core network through an access network gate-way that controls access registration, user location,and other localized services.

Due to the threat of man-in-the-middle or falsebase station attacks [8], mutual authentication be-tween the device and network is now common-place. In particular, WiMAX requires mutual au-thentication, and it is an option, but not requiredin CDMA.

In the following subsections we briefly de-scribe the actual authentication procedures used inCDMA and WiMAX. To minimize confusion, wewill refer to network functions by their abstractnames (AAA server, base station, access networkgateway) in the remainder of the paper.

A. CDMA AuthenticationCDMA2000 1xEV-DO is a 3G high speed data

access standard that is part of the 3GPP2 standardsfamily. CDMA authentication involves the base sta-tion (BS), the Packet Data Serving Node (PDSN),the AAA server, and the Mobile IP Home Agent.The PDSN is the access network gateway. Users areidentified with a Network Access Identifier (NAI),of the form user@domain.com.

CDMA2000 1xEV-DO uses Mobile IP authenti-cation extensions to authenticate users with theAAA server while assigning them an IP address.The user’s home AAA server is the final authorityon authentication, but authentication data can becached in the PDSN/FA and HA.

B. WiMAX Authentication

WiMAX is a high speed data-only 4G wire-less network standard. Like CDMA 1xEV-DO,WiMAX’s core network uses Mobile IP for IP mo-bility management, although the implementationdetails differ. The primary network elements inWiMAX authentication are the base station, Ac-cess Service Network-Gateway (ASN-GW), and theAAA server. The ASN-GW serves as the access net-work gateway. WiMAX uses the same NAI formatas CDMA.

WiMAX uses the Extensible Authentication Pro-tocol (EAP) between the user, ASN-GW, and theuser’s home AAA server. EAP is an extensibleauthentication framework that supports multipleauthentication standards. For example, mutual au-thentication can be achieved using EAP-SIM, EAP-TLS, or EAP-TTLS. In practice, EAP-TLS is the mostcommonly used form of authentication.

IV. NETWORK INTEGRATION ARCHITECTURES

Interworking can occur at different levels inthe network architecture, with tighter interworkingconfigurations offering greater network efficiency,and looser configurations greater flexibility. How-ever, efficiency comes at the cost of more difficultintegration, and can lead to unnecessary traffictraversing the vulnerable network core. Existingresearch [6] defines loosely-coupled and tightly-coupled interworking between networks. In addi-tion to these architectures, we introduce a thirdinterworking configuration, unified core, which in-tegrates two networks at an intermediate levelbetween loosely-coupled and tightly-coupled inter-working.

A. Separate Service Provider

A separate service provider architecture is analo-gous to the loosely-coupled architecture definedin [6]. In this configuration, each service providermaintains disparate, complete access and core net-works, with independent AAA services. Althoughthis provides only minimal network integration, itdoes allow providers to maintain control over their

ASN-GW/PDSN/FA

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Fig. 1. Unified Core and Access Network Architecture

own core networks, as well as allowing the inte-gration of vastly different networks. Furthermore,service and roaming agreements between serviceproviders that make use of this architecture allowproviders to easily extend their coverage withoutthe large investment needed to expand their ownnetwork.

B. Unified Core Network

A unified core network shares core networkservers, including those that provide essential ser-vices, such as AAA servers and Mobile IP HomeAgents, and optional network features, such asecho cancellation or streaming video. If a wirelessservice provider owns multiple, incompatible ac-cess networks, a unified core network can providefaster, more reliable access to network authentica-tion and applications while maintaining existingaccess network infrastructure. Each network is dif-ferentiated at the access network level, with distinctaccess network gateways.

C. Unified Core and Access Networks

A unified access network (Figure 1), also knownas a tightly-coupled architecture, allows multipleair interfaces to be used with a single access net-work gateway. A unified access network gatewayallows the fast transmission of localized user mo-bility information that is necessary for seamlesssoft handoffs between different air interfaces, mak-ing handoffs as fluid as in native mode. We de-scribe a protocol for soft handoffs using a unifiedCDMA and WiMAX access network gateway inSection V-C.

V. CDMA AND WIMAX INTERWORKING

In this section we propose an interworking pro-cedure between CDMA and WiMAX networks and

introduce vertical handoff methods. In each in-terworking scenario (WiMAX foreign mode andCDMA foreign mode), there is a home network anda foreign network. The home network is the user’soriginating network and is the network with whichthe user must ultimately authenticate. Users cangain access to a foreign network only if the foreignAAA server can authenticate with their home AAAserver.

Interworking protocols must maintain the se-curity standards of the networks between whichit operates. We summarize the relevant securitydemands for CDMA and WiMAX below:• WiMAX Foreign Mode Mutual authentication

between the mobile station (user and device)and the network; authentication is requiredbetween the user, access gateway, and AAAserver; authentication relies on user and servercertificates

• CDMA Foreign Mode Authentication of userto network; authentication is required betweenthe user, access gateway, and AAA server;authentication relies on private keys

We propose two new authentication methods,one for each interworking scenario. Our WiMAXforeign mode solution relies on existing EAP meth-ods and a new application of existing key material,while our CDMA foreign mode solution introducesa new extension to Mobile IP authentication. Ad-ditionally, we introduce inter-network soft handoffprotocols for both WiMAX and CDMA foreignmode that rely on a unified access network gate-way.

A. WiMAX Foreign Mode

This subsection describes WiMAX foreign mode,where the WiMAX network is the foreign network.WiMAX foreign mode allows CDMA users to au-thenticate for service on WiMAX networks usingexisting authentication credentials, while maintain-ing WiMAX networks’ requirement of mutual au-thentication. Additionally, soft handoffs are possi-ble if the access network is unified; this is discussedin detail in Section V-C.

To authenticate for network access, users mustauthenticate with the WiMAX access network andthe user’s home AAA server. We propose theuse of EAP-AKA authentication, using secret keysgenerated as described in [2], to provide mutualauthentication for CDMA users on WiMAX net-works. The MN-AAA key provisioned in every

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Fig. 2. WiMAX foreign mode message flows with EAP-AKAauthentication.

CDMA2000 1xEV-DO device is used to generatea new, shared key. Once the key is established,we use the EAP-AKA [9] authentication methodfor mutual authentication. One of the principles ofWiMAX security is that mutual authentication isrequired for network access; EAP-AKA, using a keyderived from the MN-AAA key, provides mutualauthentication between the user and his home AAAserver. Figure 2 illustrates the message flow.

The use of EAP-AKA for CDMA users on foreignWiMAX networks enables interworking withoutmaking any changes in WiMAX access networkelements such as the BS and ASN-GW. The accessnetwork servers need only to forward the EAP mes-sages it receives from the user to the foreign AAAserver. However, user equipment and the homeAAA server must support EAP-AKA functionality.In addition, the home AAA server must be ableto securely deliver the Master Secret Key to theASN-GW, which will be possible through existingchannels.

B. CDMA Foreign Mode

CDMA foreign mode is the complement toWiMAX foreign mode, in which WiMAX users con-nect to CDMA networks using existing WiMAX au-thentication credentials. We introduce a new MobileIP authentication extension that enables the use ofWiMAX certificates for authentication on a CDMAnetwork. Our proposed extension requires no extramessages in the Mobile IP authentication messageflow, which reduces its performance impact andsimplifies implementation. Furthermore, by relyingon tried and tested security concepts, our designalso reduces the opportunity for the introductionof new security flaws.

Typically, CDMA networks only require authenti-cation between the user and his home AAA. There-

MS HA Home AAA

- Generate K_R - MN-HA=HMAC(K_R, DataMS->HA)

- S = E(KPu, K_R)

DataMS->HA, MN-HA, (CertMS, S)CertMS, S

- Check CertMS - K_R=D(KPr,S)

K_R

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DataHA->MS, MN-HA

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Home AAA, HA, and MS authenticate each other

KPu: AAA's public keyKPr: AAA's private key

Fig. 3. CDMA foreign mode certificate exchange.

fore, WiMAX users need only to perform MobileIP authentication with his home AAA server onceconnected to a CDMA 1xEV-DO network. How-ever, WiMAX users will not have the shared keysnecessary to complete the Mobile IP authenticationprocedure, and the foreign AAA server will nothave the certificate needed to authenticate withthe WiMAX user. Therefore, as in CDMA foreignmode, WiMAX foreign mode must still rely onusers’ home AAA servers for authentication.

We propose an interworking method that inte-grates both device authentication and the exchangeof credentials into Mobile IP using the GeneralizedMobile IP Authentication Extension [10]. The exten-sion is already used in native mode CDMA authen-tication; we add support for mutual authenticationusing certificates. We define two new GeneralizedMobile IP Authentication Extension subtypes: Cer-tificate and Key Material.

The Certificate extension contains the user’s cer-tificate, used in WiMAX native mode authentica-tion, and the Key Material extension contains anencrypted key, K R, generated by the user. Figure 3shows the certificate exchange, and Figure 4 showsthe authentication message flow between the user,the foreign network, and the user’s home network.

To support our interworking scenario, users musthave a cryptographically secure random numbergenerator to generate K R. There is no requiredchange for the PDSN/FA or HA; the FA and HAcan simply forward the Generalized Mobile IP Au-thentication Extension. AAA servers must validateusers based on the certificate in the extension,decrypt the key if the certificate is valid, and sendthe key to the HA, all of which require only minorchanges.

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Fig. 4. CDMA foreign mode message flow.

C. Handoff ProceduresThe interworking we describe above allows

cross-network authentication in all network unifica-tion scenarios described in Section IV. Additionally,in a unified core and access network with a uni-versal access network gateway, inter-protocol softhandoffs are possible.

We describe two handoff scenarios, parallel toCDMA and WiMAX foreign mode: CDMA accessand WiMAX access. The major difference betweenthe two access types is that CDMA 1xEV-DO net-works require authentication at the service networklevel—with the AAA server—but not at the accessnetwork level, while WiMAX networks require au-thentication at both the access and service networklevels.

1) CDMA Access: As noted earlier, CDMA net-works do not mandate access authentication. Thissimplifies the handoff procedure, since it negatesthe need for a separate authentication step beforecompleting the handoff. Instead, the access networkgateway tracks the Mobile IP tunnel and IP addressassigned to the user prior to the handoff, and re-establishes them after the handoff. This is onlypossible if the network is unified at the accessnetwork level: the access network gateway mustbe able to communicate with both types of accessnetworks. The handoff is then completed with onlya single step: the establishment of a PPP connectionbetween the user and the access gateway.

2) WiMAX Access: Unlike CDMA networks,WiMAX networks require access authentication,which provides mutual authentication and key ex-

MS CDMA-BS FA/ASN-GW/PDSN AAA

Server

Establish a PPP connection

WiMAX-BSHandoff

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Synchronizing/Raning/Capability Neg.

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Data service

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Fig. 5. Proactive handoff flows from a CDMA to a WiMAXnetwork.

change. However, the delay caused by performing acomplete network access authentication is sufficientthat service may be interrupted when the userroams onto a WiMAX network. WiMAX standardsdefine an optimized handoff procedure that reducesinitial network entry time. We propose a similarproactive authentication procedure for handoffs be-tween CDMA and WiMAX.

When users are in a CDMA cell on the edgeof a WiMAX cell, WiMAX authentication, such asEAP-TTLS or EAP-TLS, is proactively triggered bythe access gateway and processed between the MS,access gateway, and AAA server. The integratedaccess gateway acts as the Authenticator in theWiMAX network and caches the key materials itreceives from the AAA server, rather than sendingthem directly to the base station. Users also cachethe key materials generated from the proactiveWiMAX authentication.

Once a user is associated with a WiMAX basestation, the serving base station requests the cachedWiMAX key materials from the access gateway. TheBS and user perform the necessary three-way hand-shake and key exchanges, but with reduced delaydue to the pre-emptive authentication step. Thethree-way handshake is still necessary to ensurethat the user and BS agree on the encryption key.Figure 5 shows the message flows of the optimizedhandoff between CDMA and WiMAX networks.

VI. SIMULATION AND PERFORMANCE ANALYSIS

In this section, we first present experimentally-backed simulation results that clarify the perfor-mance of our interworking authentication methods,then we analyze the performance of our proposedhandoff method in a queueing model.

To inform our simulation and models, we mea-sured network authentication delays on a smallwired testbed between the mobile device, PDSN,ASN-GW, AAA server, and HA, for both CDMAand WiMAX native mode operation. Our measure-ments are based on packet delay times on a small,wired testbed network. We normalized delays foreach message at each network element based ona native mode CDMA authentication—the delaysfor a native CDMA authentication sum to 1, andother authentication delays are expressed as per-centages of this total time. The normalized delaysform the basis for our simulation and analyticalresults. Our simulation architecture models eachcore network server and the access gateways, withunlimited buffer sizes and 16 parallel processors.Each server’s service rate, µ, is based on our mea-sured delays. Processing load is measured as theoccupancy rate of a server’s processors.

We study network performance at two levels.First, we examine the behavior of messages andload at each server in the network. This gives usmicro-level insight into the specific bottlenecks ofvarious authentication scenarios. Then, we presentresults for end-user performance, specifically hand-off latency between networks that require re-authentication. This gives us a macro-level per-formance overview. Next, we present our detailedsimulation results.

A. Simulation ResultsWe simulated authentication procedures under

CDMA and WiMAX native and foreign mode ina separate service provider configuration. We sim-ulated networks with 50k, 100k, 200k, and 500ksubscribers, with 2 AAA servers and 4 access gate-ways each. We measured two variables at eachelement: waiting time, as measured by the averagetime a message spends in a buffer before beingserviced, and processing load, measured as averageprocessor occupancy.

Due to the design of our interworking extensionsand message flows, almost no additional messagesare necessary to authenticate across network types,which significantly reduces the performance impactof interworking. Figures 6(a) and 6(b) show the pro-cessing time and waiting time at the AAA server,Figure 7(a) shows buffer sizes at the CDMA PDSN,and Figures 7(b) and 7(c) show the load at theWiMAX ASN-GW. Neither CDMA foreign modenor WiMAX foreign mode produces a significantlyhigher load on the core or access network than

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native mode, and in some cases, the foreign modeload is actually lower.

Figure 6(a) illustrates the effect of network au-thentication on processing load at the AAA serveras the number of subscribers increases. Due to thecentral role of the AAA server in authentication,its load remains high in all authentication methodsbut one. Figure 6(b) illustrates a similar effect inwaiting times, with essentially linearly increasingwaiting times, except for CDMA authentication, thehorizontal line along the x-axis. CDMA authentica-tion is the only outlier, which indicates a differentserver is the bottleneck in CDMA authentication.Notably, WiMAX foreign mode waiting times andserver load are not significantly different from na-tive mode, indicating the low overhead of foreignmode operation.

The PDSN load percentages and waiting timesin Figures 6(c) and 7(a) show that CDMA authen-tication is in fact bottlenecked at the PDSN. It alsoillustrates the difference between foreign and na-tive mode CDMA authentication. In foreign modeoperation, the AAA server is highly congested, butthe load at the PDSN is significantly lower.

Figures 7(b) and 7(c) show the performance atthe ASN-GW. In both foreign and native mode, theASN-GW is less of a bottleneck than the PDSN,although we can see that in native mode the ASN-GW’s processing load increases, as do its waitingtimes, indicating a potential bottleneck in very largenetworks. Again, the design benefit of foreign modeoperation is apparent in the high performance offoreign mode operation.

B. Handoff Delay

We use a M/M/1 queueing model to comparethe performance of CDMA and WiMAX foreignmode handoffs with a complete disconnection-and-

re-authentication cycle. We use the same normal-ized delay information as in our simulations.

In a M/M/1 queue, long-term system behavioris determined by the Poisson arrival rate of eachmessage at each network element, λe,i, and theexponential service rate at each network element,µe,i, where e ∈ E, the set of all network elements,and i ∈ I, the set of all messages in an authentica-tion message flow. Total delay at element e, whichincludes queueing delay and processing delay, isgiven by the following equation:

1µe,i − λe,i

(1)

Then the total delay for a message flow, I, is asfollows:

∑∀i∈I,∀e∈E

1µe,i − λe,i

(2)

Service rates for each element are based on mea-sured delay on a sample authentication messageflow in a test network. As in the simulation results,service rates are normalized based on the nativemode authentication message flow for a CDMAnetwork: the CDMA native mode message flowdelays sum to 1.

Figures 8(a) and 8(b) show the results of our anal-ysis. Since de-authentication and re-authenticationis a symmetric operation, its performance remainsthe same in each case. Notably, the delay incurredfrom re-authentication is significantly higher thanfrom a foreign mode handoff. The combinationof our proactive handoff procedure and efficientinterworking lead to a significant reduction in re-authentication time: 75% in the WiMAX to CDMAcase, and 85% in the CDMA to WiMAX case.

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Fig. 8. Authentication delays

VII. CONCLUSION

In this paper we introduced efficient interwork-ing procedures between CDMA 1xEV-DO andWiMAX data networks. Our procedures leveragethe extensible nature of existing authentication pro-tocols and require no architectural changes for basicinterworking to be achieved. In addition to ba-sic interworking, we introduce a seamless handoffprocedure between CDMA 1xEV-DO and WiMAXthat relies on tighter integration between accessnetworks.

REFERENCES

[1] 3gpp2. [Online]. Available: http://www.3gpp2.org[2] “cdma2000 Packet Data Services: Wireless Local Area Net-

work (WLAN) Interworking-Access to Internet,” 3GPP2,2007.

[3] M. Buddhikot, G. Chandranmenon, S. Han, Y.-W. Lee,S. Miller, and L. Salgarelli, “Design and implementationof a wlan/cdma2000 interworking architecture,” Commu-nications Magazine, IEEE, vol. 41, no. 11, pp. 90–100, Nov.2003.

[4] “cdma2000 wireless ip network standard: Simple ip andmobile ip access services. Technical Report X.S0011-002-D,”3GPP2, 2006.

[5] “WiMAX Forum network architecture (Stage3: Detailedprotocols and procedures)[annex:WiMAX-3GPP2 Inter-working].” WiMAX Forum, 2008.

[6] M. Buddhikot, G. Chandranmenon, S. Han, Y. Lee,S. Miller, and L. Salgarelli, “Integration of 802.11 and third-generation wireless data networks,” in INFOCOM 2003.Twenty-Second Annual Joint Conference of the IEEE Computerand Communications. IEEE Societies, vol. 1, March-3 April2003, pp. 503–512 vol.1.

[7] O. Haase, K. Murakami, and T. LaPorta, “Unified mobil-ity manager: enabling efficient sip/umts mobile networkcontrol,” Wireless Communications, IEEE, vol. 10, no. 4, pp.66–75, Aug. 2003.

[8] U. Meyer and S. Wetzel, “A man-in-the-middle attack onumts,” in WiSe ’04: Proceedings of the 3rd ACM workshop onWireless security. New York, NY, USA: ACM, 2004, pp.90–97.

[9] J. Arkko and H. Haverinen, “Extensible AuthenticationProtocol Method for 3rd Generation Authentication andKey Agreement (EAP-AKA),” RFC 4187 (Informational),Internet Engineering Task Force, Jan. 2006, updated byRFC 5448. [Online]. Available: http://www.ietf.org/rfc/rfc4187.txt

[10] C. Perkins, P. Calhoun, and J. Bharatia, “Mobile IPv4Challenge/Response Extensions (Revised),” RFC 4721(Proposed Standard), Internet Engineering Task Force, Jan.2007. [Online]. Available: http://www.ietf.org/rfc/rfc4721.txt