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Wireless Pers CommunDOI 10.1007/s11277-007-9266-3

Seamless proactive handover across heterogeneous accessnetworks

Ashutosh Dutta · Subir Das · David Famolari ·Yoshihiro Ohba · Kenichi Taniuchi ·Victor Fajardo · Rafa Marin Lopez ·Toshikazu Kodama · Henning Schulzrinne

Received: 22 May 2006 / Accepted: 22 January 2007© Springer Science+Business Media B.V. 2007

Abstract Dual-mode handsets and multimodeterminals are generating demand for solutions thatenable convergence and seamless handover acrossheterogeneous access networks. The IEEE 802.21working group is creating a framework thatdefines a Media Independent Handover Function(MIHF), facilitates handover across heterogeneousaccess networks and helps mobile users experiencebetter performance during mobility events. In thispaper, we describe this 802.21 framework and alsosummarize a Media-independent Pre-Authentica-tion (MPA) mechanism currently under discus-sion within the IRTF that can further optimizehandover performance. We discuss how the 802.21framework and the MPA technique can be inte-grated to improve handover performance. Finally,we describe a test-bed implementation and vali-date experimental performance results of the com-bined mobility technique.

A. Dutta (B) · S. Das · D. FamolariMobile Networking Research, Telcordia Technologies,1 Telcordia Drive, RRC - 1A220, Piscataway, NJ,08854, USAe-mail:adutta@research.telcordia.com

Y. Ohba · K. Taniuchi · V. Fajardo · R. M. Lopez ·T. KodamaToshiba America Research Inc., P.O. Box 429,Piscataway, NJ 08854, USA

H. SchulzrinneComputer Science Department, Columbia University,New York, NY, USA

Keywords IEEE802.21 · Heterogeneous hand-over · Seamless mobility · Media independentpre-authentication

1 Introduction

Future network devices will need to roam seam-lessly across heterogeneous access technologiessuch as 802.11, WiMAX, CDMA, and GSM,between wired networks such as xDSL and cable,as well as between packet switched and circuitswitched (PSTN) networks. Figure 1 shows anexample wireless Internet roaming scenario acrossheterogeneous access networks that involves intra-subnet, inter-subnet, and inter-domain mobility.Supporting seamless roaming between heteroge-neous networks is a challenging task since eachaccess network may have different mobility, QoSand security requirements. Moreover, interactiveapplications such as VoIP and streaming mediahave stringent performance requirements on end-to-end delay and packet loss. The handover processstresses these performance bounds by introducingdelays due to discovery, configuration, authenti-cation and binding update procedures associatedwith a mobility event.

The overall handover delay can be attributedto operational delays at all layers of the protocolstack including layer 2, layer 3 and the applica-tion layer. Performance can also be tied to the

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Fig. 1 Wireless internetroaming scenario

802.11a/b/g

BluetoothIPv6

UMTS/CDMANetwork

Domain2

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PSTN ga

Hotspot

CHRoamUser Ad Hoc

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specific access networks and protocols that areused for network access. For example, configuring aPPP (Point-to-Point Protocol) interface in a WANenvironment takes more time than configuring aninterface using DHCP (Dynamic Host Configu-ration Protocol) in a LAN environment. Accessnetwork-specific authentication and authorizationprotocols may introduce additional delays. It isobserved that traditional non-optimized handovertakes up to 4 s delay during inter-LAN movement.Thus in a typical deployment scenario, several hun-dred (∼200–300) packets may be lost during thehandover. Also, it may take up to 15 s to com-plete authentication and connection establishmentprocedures if the neighboring network is eitherCDMA or GPRS. Movement between two differ-ent administrative domains poses additional chal-lenges since a mobile will need to re-establishauthentication and authorization in the new dom-ain. Layer 2 handoff delay is more relevant when anauthentication process is involved to obtain layer2 connectivity. Experimental studies [1,21] withnetwork handovers indicate that the latency intro-duced due to scanning and authentication at layer 2is not acceptable for real time communications. Forexample, in IEEE 802.11 based wireless networks,the IEEE 802.11i security mechanism performs a

new set of exchanges with the authenticator in thetarget AP in order to initiate an EAP (ExtensibleAuthentication Protocol) exchange to an authen-tication server. Following a successful authentica-tion, a 4-way handshake with the wireless stationderives a new set of session keys for use in datacommunications. This process can significantly pro-long the handover event and calls for improved la-tency performance in layer 2 security mechanismsrelated to handover.

In order to provide an improved, secured mobil-ity management solution for real-time communi-cation involving heterogeneous handover, we havedesigned an optimization scheme that takes advan-tage of IEEE 802.21 [14] services and a newtechnique called Media independent Pre-Authen-tication (MPA) [8]. MPA enables mobile devicesto expedite layer 2 pre-authentication in the neigh-boring network, to proactively obtain an IPaddress, and to perform mobility related bindingupdates ahead of the anticipated handover. MPAalso helps to bootstrap layer 2 security in the tar-get network while the mobile is still connectedin the current network. MPA thus provides anaccess independent pre-authentication mechanismthat does not require support for different layer 2authentication and encryption mechanisms.

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The rest of the paper is organized as follows.Related work in mobility optimization is describedin Sect 2. Section 3 describes the IEEE 802.21framework, its core architecture and the functionalcomponents. An example of MPA assisted 802.21-based mobility is illustrated in Sect. 4. Results of atest-bed implementation involving the 802.21Information Service (IS), Event Service (ES), andMPA framework for two different types of hand-over scenarios are described in Sect. 5. Section 6highlights certain features of MPA that are differ-ent than existing make-before-break mechanismsand FMIPv6. Finally, Sect. 7 concludes the paper.

2 Related work

References [6,11,17,18,20,26,32,36] describe mob-ility management techniques that support fast-handover by enhancing currently availablemobility management protocols for both IPv4 andIPv6. Reference [32] attempts to reduce delay atlayer 2 by reducing the scanning time, whereasrefs. [6,26] devise mechanisms to reduce hand-over delay at layer 3 and application layer respec-tively. Similarly refs. [3,33] try to reduce the layer 2authentication delay during handover. NETLMMworking group within the IETF is working defininga design team document [18] that aims at reduc-ing the delay during intra-domain handoff. Thereis also relevant work undertaken by various stan-dards organizations. IEEE 802.11i defines a pre-authentication mechanism for use in 802.11 variantwireless networks. This mechanism allows mobiledevices to pre-authenticate by establishing link-layer security associations with one or more targetauthenticators by sending 802.1X messages directlyto the target authenticators bridged via the servingauthenticator. IEEE 802.11f has defined transferof security context from one AP to another. Pres-ently, IEEE 802.11r Task Group has been workingto define fast BSS transition mechanisms involv-ing a definition of key management hierarchy andmechanisms for link-layer pre-authentication andsetup of session keys before the re-association tothe target AP. These mechanisms are defined for802.11 technologies only and are only applicablewithin an access domain [e.g., same ESS (Extended

Service Set)] and do not support inter-ESS or inter-domain handover within 802.11 access technology.

Currently, there are several initiatives tooptimize mobility across heterogeneous networks.The MOBOPTS working group within the IRTF(Internet Research Task Force) and the DNA (Det-ecting Network Attachment) working group withinthe IETF have been investigating ways to supportoptimized handover by using appropriate triggersand events from the lower layers. References [4,7] describe mobility management techniques thatconsider both security and heterogeneous mobility.Although many of these techniques use cross-layermechanisms and “make-before-break” algorithmsto provide fast-handover, it is desirable to havea standardized method to handle mobility acrossheterogeneous networks in an efficient manner.The IEEE 802.21 [14] working group is currentlyworking towards a Media Independent Handoverframework and is creating a standard that facili-tates handover in a heterogeneous accessenvironments. This framework provides assistanceto underlying mobility management approaches byallowing information about neighboring networks,link specific events and commands that are nec-essary during handover process to be exchangedbetween 802.21 entities. MPA [8] is being discussedwithin the IRTF as a way to further improve ser-vice quality and user experience during handoverevents. In this paper, we discuss how MPA and802.21 can be used together to improve handoverperformance in heterogeneous access networks.We describe how the two approaches can be inte-grated and present experimental results obtainedon a prototype test-bed implementing the 802.21and MPA concepts. We also describe how MPAcan reduce layer 2 handover delay by bootstrap-ping layer 2 pre-authentication in the previous net-work. Lastly, we provide a brief comparison withthe existing fast-handover technique FMIPv6 [4].

3 IEEE 802.21 framework

The IEEE 802.21 framework is intended to facili-tate handover between heterogeneous access net-works by exchanging information and definingcommands and event triggers to assist in thehandover decision making process. The framework

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within 802.21 helps mobile devices to discover,characterize, and select networks within their cur-rent neighborhoods by exchanging informationabout available link types, link identifiers, and linkqualities of nearby network links. This process ofnetwork discovery and selection allows a mobile toconnect to the most appropriate network based oncertain mobile policies.

The heart of the 802.21 framework is the MediaIndependent Handover Function (MIHF) whichprovides abstracted services to higher layers bymeans of a unified interface. This unified interfaceexposes service primitives that are independent ofthe access technology. The MIHF can communi-cate with access specific lower layer MAC and PHYcomponents, including those of 802.16, 802.11 andcellular, as well as with upper layer entities. TheMIHF and its relationship with upper and lowerlayer elements are shown in Fig. 2. MIHF definesthree different services: Media Independent EventService (MIES), Media Independent CommandService (MICS) and Media Independent Informa-tion Service (MIIS). In the following subsections,we describe these three main functional compo-nents in greater detail.

3.1 Media Independent Event Service

Media Independent Event Service (MIES) pro-vides services to the upper layers by reporting bothlocal and remote events. Local events take placewithin the local stack of the mobile node, whereasremote events take place in another MIHF in thenetwork. The event model works according to asubscription and notification procedure. An MIHuser (typically upper layer protocols) registers tothe lower layers for a certain set of events and getsnotified as those events take place. In the case oflocal events, information propagates upward fromthe lower layer to the MIH layer and then to theupper layers. In the case of remote events, infor-mation may propagate from the MIH or Layer 3Mobility Protocol (L3MP) in one stack to the MIHor L3MP in a remote stack. Some of the commonevents defined include “Link Up,” “Link Down,”“Link Parameters Change,” “Link Going Down,”“Handover Imminent,” etc. As the upper layer getsnotified about certain events it makes use of the

command service to control the links to switch overto a new point of attachment.

3.2 Media Independent Command Service

The higher layers use the (Media IndependentCommand Services) MICS primitives to controlthe functions of the lower layers. MICS commandsare used to gather information about the status ofthe connected links, as well as to execute higherlayer mobility and connectivity decisions to thelower layers. MIH commands can be both localand remote. These include commands from theupper layers to the MIH and from the MIH tothe lower layers. Some examples of MICS com-mands are MIH Poll, MIH Scan, MIH Configure,and MIH Switch. The commands instruct an MIHdevice to poll connected links to learn their mostrecent status, to scan for newly discovered links, toconfigure new links and to switch between avail-able links.

3.3 Media Independent Information Service

Mobiles on the move need to discover availableneighboring networks and communicate with theelements within these networks to optimize thehandover. The MIIS defines information elementsand corresponding query-response mechanismsthat allow an MIHF entity to discover and obt-ain information relating to nearby networks. TheMIIS provides access to information, including net-work type, roaming partners, service providers ofthe neighboring networks, channel information,MAC addresses, security information, and otherinformation about higher layer services helpful tohandover decisions. This information can be madeavailable via both lower and upper layers. In somecases certain layer 2 information may not be avail-able or sufficient to make intelligent handover deci-sions. In such scenarios, higher-layer services maybe consulted to assist in the mobility decision-making process.

The MIIS specifies a common way of represent-ing information by using standard formats suchas XML (eXternal Markup Language) andTLV (Type-Length-Value). Having a higher layer

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Fig. 2 Mediaindependent handoverfunction location and keyservices (Source: IEEED01)

mechanism obtain information about neighboringnetworks of different access technologies alleviatesthe need for a specific access-dependent discoverymethod. We have implemented an MIIS based onthe Resource Description Framework (RDF) [29]and XML as part of our prototype.

4 Mobility optimization using 802.21 and MPA

Media-independent Pre-Authentication (MPA) isa mobile-assisted, secure handover optimizationscheme that works over any link-layer and withany mobility management protocol. With MPA, amobile node is not only able to securely obtainan IP address and other configuration parametersfrom a candidate target network (CTN), but is alsoable to send and receive IP packets using the obt-ained CTN IP address before it physically attachesto the CTN. This ability to communicate at layer-3before establishing layer-2 connectivity is a greatbenefit in terms of reducing handover delays.

The MPA procedure works as follows. An MPAmobile device first establishes a security associationwith a CTN via its existing network connection usi-ng the Protocol for carrying Authentication andNetwork Access (PANA) [24] to obtain config-uration information that will allow it to partici-pate in the new network. Next, a bi-directionaltunnel is established between the device and theAccess Router (AR) of the CTN. IP packets canbe sent over this tunnel. At this point, all the nec-essary layer 3 mechanisms have been completed

to enable handover, however the device has notyet established layer 2 connectivity with the CTN.Once this has been established, the bi-directionaltunnel can be removed and the handover is com-plete. By pre-authenticating, pre-configuring thelink and establishing a secure tunnel, the handovercan complete with reduced delays and fewer lostpackets.

MPA however, does not perform network dis-covery and relies on outside mechanisms to dis-cover CTNs. In this sense, MPA and 802.21 canbe very complementary to each other with 802.21providing network discovery and making availableinformation to assist in mobility decisions. MPAcan ensure that the security associations are inplace and that devices can authenticate with can-didate networks before mobility decisions are exe-cuted. These security associations can happen atdifferent layers of the protocol stack.

The service primitives defined in the 802.21framework can work with any type of layer 3 andabove mobility management protocol such as SIP[31], MIPv6 [16] or MIPv4 [27]. A mobile usesthe service primitives to communicate with policymanagers, device drivers and other mobility man-agement protocols during its movement.

Figure 3 shows an illustration of how MPA and802.21 can work in conjunction with a SIP-basedmobility management mechanism. As shown, themobile has two types of interfaces [Network X(e.g., 802.11) and Network Y (e.g., CDMA)]. Ini-tially, the mobile is using Network X as its pri-mary interface to establish a multimedia session

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Query more on Network Y

Response info for Network Y

MIH_Info.Request_

I

1MIH Old

ARSIP

MIH1

2

Mobile Terminali Network X(Old)

Information Server

MAC 2

MIH NewAR/DHCP

SIP SIP Proxy

New Link Available

Attach the new Link

PANA pre-authentication and pre-configuration to obtain IP address

Bi-Directional Tunnel

Link Up

MIH_Resource.Query

MIH_Resource.Response

Handover

Initiation

Existing Data

SIP Binding Update/Registration

Interface SwitchRequest

New Data from Network Y

Disconnect

old AR/link

Handover Selection

Link Down

NetworkSelection

Information Response

1MAC MAC MAC

1

Tunnel Delete

Handover Evaluation

(New)Network Y

Proxy

Fig. 3 802.21 assisted SIP-based mobility management for heterogeneous handover

with a correspondent host. The mobile queries aninformation server to learn about available net-works that are of type Y. The mobile makes anMIH query to verify that the required resources tosustain the session are available. It then selects anappropriate network and retrieves more informa-tion about that network, such as the address andthe type of security servers, DHCP server address,MAC address of the access point, etc. With thisinformation, the mobile initiates MPA proceduresto pre-authenticate with network Y and configuresitself for operation in that network. These opera-tions could include layer 3 pre-configuration, layer-2 pre-authentication by pre-establishing the keysin the neighboring access points, proactive bindingupdate (e.g., SIP ReINVITE), etc. At this pointthe mobile is ready to switch layer-2 connectionswhen appropriate by using IEEE 802.21 commandprimitives such as “Initiate Handover.” Once the“Link up” event is received from the MIES indicat-ing that the target layer 2 connection is ready, the

mobile starts using the new interface. The “Linkdown” command can delete the proactive tunnel.At this time, traffic to the mobile flows through thenew interface and the handover is complete. In thecase of handover involving single interface the se-quence of events will take a different order, sincethe same physical interface participates in commu-nication both before and after the handover. Thephysical interface gets configured with two logicaladdresses, one from the current network and onefrom the next network during the handover pro-cess.

5 Implementation and experimental results

This section describes an implementation based onthe 802.21 framework and MPA scheme, and pro-vides performance results and compares these withnon-optimized mobility management. Figure 4ashows the experimental test-bed with four networks

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defined. We have experimented with two kindsof handover scenarios: one between two 802.11networks belonging to different administrativedomains; the other between 802.11 and CDMA1x-EVDO access networks. For both the cases, wedemonstrate how the 802.21 information discovery,event service and MPA framework help to improveperformance during handover. Case I deals withterminals equipped with a single 802.11 interface,and case II deals with terminals with two differ-ent types of interfaces. The event services Link Upand Link Down act as triggers to help the hand-over. We apply Link Up event notification for thehandover involving 802.11 access networks, and weapply Link Down event notification for the hand-over involving EVDO and 802.11 networks. How-ever, events such as Link Going Down and LinkGoing Up maybe more appropriate for dual-modedevices. Figure 4b, c illustrate the mechanism asso-ciated with both of these cases, respectively. Addi-tionally, we also describe experimental results ofMPA-assisted layer 2 pre-authentication appliedto intra-technology and inter-domain handovers inSect. 5.3. We describe the details in the followingsections.

5.1 Intra-technology, inter-domain handoff

In Figure 4a, Network 1 is the current point ofattachment (cPoA), Networks 2 and 3 are possiblenew points of attachment (nPoA), and network 4is where the correspondent node (CN) resides. Themobile is initially in Network 1 and starts commu-nicating with the correspondent node.

Media-independent Pre-Authentication is inde-pendent of the underlying mobility managementprotocol and we have demonstrated MPA usingboth SIP Mobility (SIP-M) [31] and MIPv6 [16] asmobility management protocols. The configurationprotocol is DHCP, the authentication agent (AA)is a PANA [24] server with a backend Diameterserver to carry out EAP-TLS (Extensible Authen-tication Protocol) [1]. The configuration agent (CA)is a DHCP Relay Agent and the NextAccess Router (NAR) is an edge router runningthe Linux operating system. We have used IP-IP tunneling functions for SIP-based mobility andhave taken advantage of IPSEC tunnel for MIPv6.After a successful connection setup using SIP, voicetraffic flows between the MN and the CN. Thisvoice traffic is carried over RTP/UDP. We have

AP1 Coverage Area AP 2 & 3 Coverage Area

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INTERNETInformation

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AP 3AP 2AP 1

CTN – Candate Target NetworksTN – Target Network

AA CAAA CA

AA CAAA CA

Tunnel deletion signaling

Packets that could belost

CT N

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CT N

Tunnetled Data

domainData in new

a

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Fig. 4 Experimental setup for MPA and 802.21 assisted handover. (a) Logical test bed scenaria, (b) Intra-technology. Inter-domain, (c) Inter-technology, Inter-domain

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used RAT (Robust Audio Tool) as the media agentand the streaming traffic is generated using acodec with a spacing of 20 ms between packets.

For non-optimized handovers (those that do notemploy 802.21 and MPA mechanisms, the hand-over delay and packet loss take place during themobile’s layer 2 movement, IP address assignment,post-authentication, and mobility binding update.The DHCP interaction takes a long time to com-plete the detection of duplicate IP addresses andthe binding updates can be delayed if the corre-spondent node is too far from the mobile node.The experimental results show that 4 s of delayare attributed to the above factors. We observedapproximately 200 packets were lost due to thisdelay. The situation is worse in case II, where itmay take up to 15 s to authenticate and establishconnectivity with CDMA network.

These delays can be reduced by taking advan-tage of the network discovery mechanisms of 802.21and the pre-authentication technique of MPA. The802.21 framework provides details of neighbor-ing networks that may include channel numbers,addresses of APs, DHCP servers, PANA servers,etc. Such information helps the mobile commu-nicate with network elements ahead of time andperform a proactive handover. We have used anRDF/XML-based query and response mechanismsto obtain the required information from the inf-ormation server. We briefly describe the relatedsoftware modules that were used to obtain the rel-evant neighborhood information from the infor-mation server. Details of the mechanism includingthe RDF schema can be found in reference [10]. Inour testbed, at the information server we use Jos-eki to interpret the RDQL [29] and send appro-priate responses to the client. We use Jena [15],which is a Java framework for building semanticWeb applications, for forming RDQL. It providesa programmatic environment for RDF, RDFS andOWL, including a rule-based inference engine.

We have used the Joseki server for publishingRDF models on the web. These models are rep-resented by URLs and can be accessed by queryusing HTTP GET. These queries and responsescan also be implemented using the Media Indepen-dent Handover protocol currently being definedby IEEE 802.21 working group. We implementedHTTP as the transport since the MIH protocol

transport mechanisms were not complete at thetime of experimentation.

We provide sample results of queries and re-sponses and timing break downs for some typicalqueries in Table 1. The queries shown in Table 1can primarily be divided into meta queries and sec-ondary queries. A meta query provides general in-formation about the neighboring networks, whilea secondary query provides detailed informationabout that network’s elements. Query–responsetimes can vary depending upon the network ac-cess delays and processing times. For example, APIdelay represents the delay incurred during interac-tion with the query application at the mobile andserver. Processing delay at the client and serverincludes the time spent for HTTP processing. Net-work delay is the delay to transmit the TCP pack-ets between the mobile and server. However, sincethese queries are carried out prior to the handoverevent, they do not contribute to handover delayand also do not result in packet loss. Successfulhandovers require that the information query andresponse are completed before the layer-2 hand-over, therefore these query and response delays arecritical. We ran experiments with Mobile IPv6, withand without Route Optimization (RO), as well aswith SIP as the underlying mobility managementprotocol. In addition, we also examined the effectsof buffering at the edge router that helps to reducethe packet loss during handover.

Figure 5a compares the results of the audio out-put with the non-proactive scheme, where as Fig. 5bshows several handoff statistics such as packet loss,delay, and jitter values with and without buffer-ing mechanism. Handover delays are dramaticallyreduced from those reported earlier; reducing thetime from seconds to milliseconds. Proactive dis-covery of the target AP also helped reduce thelayer 2 delay since it avoided scanning and theEAP-TLS procedure needed for full EAP authen-tication. Details of layer 2 pre-authentication aredescribed in Sect. 5.3. Packet losses were also red-uced due to handoff optimization at all layers. Asexpected, no packets were lost with buffering ena-bled. The Dynamic buffering scheme on the edgerouter helps to maintain a tradeoff between thepacket loss and additional delay. The highlightednumbers show that we were able to achieve zeropacket loss while keeping the delay between last

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Table 1 Sample query response for 802.21 MIIS

Query Response Processing delay (ms)

Current PoA: AP, Neighbor 0 PoA:ID:00:20:A6:53:B2:5E,Tariff: 20

Total 2,292

Query: Provide list of802.11-type neighboringnetworks and their withassociated tariff values

Neighbor 1 PoA :ID:01:23:45:67:89:AB,Tariff:50

API 1,291

Network 919Server 18Client 64

Neighbor 0 selected Target network channel: 10SSID: ITSUMO newpoa1

Total 1,473

Query: Provide list ofnetwork elements forNeighbor 0

Router address: 10.10.10.52 API 991

Router MACID:00:00:39:e6:8b:ee

Network 451

Subnet: 255.255.255.0 Server 13DHCP Server: 10.10.10.52 Client 18

pre-handoff packet and first in-handoff packet toa value within the threshold limit during the hand-over.

It is worthwhile to discuss the techniques thatwere used to optimize the layer 2 handoff delayin the experiment. In general, 802.11 layer 2 hand-off delay consists of many phases such as scanning,association, and authentication. In general, as theSNR (Signal-to-Noise Radio) of the mobile withthe current AP goes below certain threshold, themobile starts the scanning procedure by issuinga MLME-SCAN.request primitive [2] to discoverthe characteristics of the neighboring APs. Refer-ence [21] shows that scanning (discovery phase)takes the maximum amount of time during layer2 handover, since the mobile needs to scan all thechannels before associating with a specific chan-nel. There are related works [7] that reduce thelayer 2 scanning time by using different scanningalgorithms. In this proposed scheme, network dis-covery and selection are done proactively. By usi-ng IEEE 802.21 information discovery service andthe current location of the mobile node, we canobtain information such as the channel numberand ESSID of the access point in the neighboringnetworks which are needed by MLME-ASSOCI-ATE.request primitive. Based on this knowledge,the mobile can associate with the desired channel

number in the target network directly without per-forming the regular channel scanning operation.As a consequence, it is not required that targetAPs operate in the same channel. This mechanismis useful independent of whether the target AP isworking on the same channel or has the same ESS-ID as the current one. Since the mobile knows theAP’s channel number and ESSID it can changechannel and engage the target AP without incur-ring the delays associated with scanning. To real-ize this capability, we modified the IEEE 802.11MADWIFI driver [22] on the mobile device to usethe neighboring access point information from theIEEE 802.21 information service and to issue “As-sociation Request” commands to connect to neigh-boring APs. This modification eliminates the needfor the regular channel scanning procedure duringhandover.

5.2 Inter-technology, inter-domain handoff

Handover involving heterogeneous access can takeplace in many different ways depending upon theactivity of the second interface. In one scenario,the second interface comes up when the link tothe first interface goes down. This scenario usuallygives rise to undesirable packet loss and handoff

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Non-802.21 assisted SIP-based mobility

Handoff4 s

802.21 assisted SIP-based mobility – Optimized handoff

Non-802.21 ass d - i

Handoff4 s

802.21 assisted SIP-based mobility – Optimized handoff

Buffering

Enabled

Bu ffering

Disable d

Buffering

Enabled

+ RO

Enabled

BufferingDisabled

+ RO

Enabled

Buffering

Enabled

+ RO

Disabled

BufferingDisabled

+ RODisabled

Hand offParameters

3.00n/a3.00n/a2.00 n/aAvg. Buffered Packets

20 .00n/a50 .00n/a50.00n/aBuffering period (ms)

13 .00n/a50 .60n/a29.33 n/aAvg. packet jitter (ms)

29 .00n/a66 .60n/a45.33n/aAvg. inter-packet arrival time duringhandover (ms)

16 .0016 .0016 .0016.0016.0016.00Avg. inter-packet interval (ms)

01.5000.660 1.33Avg. packet loss

5.004.004.004.004.334.00L2 hand off(ms)

MIPv6 SIP MobilityMobility Type

a

b

Fig. 5 (a) Recorded signal activity: Non-optimized versus optimized. (b) Delay and packet loss statistics optimized

delay. In a second scenario, the second interface isprepared proactively while the mobile still commu-nicates using the first interface, and at some pointthe mobile decides to use the second interfaceas the active interface. This results in less packetloss as it uses make-before-break techniques. Inthe third scenario, all the required state and secu-rity associations (e.g., PPP state, LCP, CHAP incase of CDMA networks) are established aheadof time thus reducing the time taken for the sec-ondary interface to be attached to the network.This third scenario may be beneficial from a bat-tery management standpoint. Devices that operatetwo interfaces simultaneously can rapidly deplete

their batteries otherwise. However, by activatingthe second interface only after an appropriate net-work has been selected battery power may be usedmore efficiently. This third scenario demonstratesthe usefulness of 802.21’s Event Service (ES), In-formation Service (IS) and MPA.

Information discovery and MPA remain thesame as in Sect. 5.1 with intra-technology hand-over. In this experiment we also add a faster linkdown detection mechanism and a copy-forwardingtechnique at the access router to help reduce tran-sient packet loss during handover. We briefly dis-cuss these two procedures. The fast link down de-tection method is used to provide fast “link down”

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event indication and helps in quickly assisting layer-3 protocols to take necessary actions. The quick“link down” event indication uses a combined schemeof passive monitoring of 802.11 frames as well asactive probing of the AP at certain conditions. Aquick indication can provide better handoff per-formance to L3 handoff procedures. The copy for-warding scheme takes advantage of the bufferingin the edge routers, in addition, it also forwardsthe duplicate packets that it buffers. An MN thatrequests the copy-forward service from the (Cur-rent Point of Attachment) network will signal theCPFW (Copy-and-Forward) node of its intent touse the said service prior to handoff. This signal isreferred to as a copy request. Upon receiving therequest, the CPFW node will start to classify andcopy packets destined for the MN on the CPA. Thisprocess does not stop the original packets from be-ing forwarded to the MN in the CPA. The limit forthe amount of packets copied will be based on theestimated time it takes for the MN to complete thehandover. As a result the mobile may end up get-ting duplicate packets, but packet loss is reduced.In this scenario, the mobile is initially communi-cating using its first interface over technology X(e.g., 802.11). It then uses 802.21 and MPA to dis-cover a new access network of technology Y (e.g.,CDMA), learn the addresses of configuration ele-ments in that network, and then proactively pre-pare the required state information for its secondinterface to use technology Y. It then sets up proac-tive tunnels with the required access routers in thetarget network and establishes the security asso-ciation. Next, the device uses Link Down eventnotification triggers to the upper layers to initi-ate the handover process to the newly availableinterface. Since most of the required events suchas IP address acquisition, authentication, securityassociation, and binding update have already beentaken care of, the handover completes in less time.

We present results showing the usefulness of fastlink detection, copy-forwarding and MPA in Fig. 6.Figure 6c shows the results of optimized handoverthat uses MPA and IEEE 802.21. As compared tonon-optimized handover as shown in Fig. 6a and bthat may result in delays up to 18 s and packet lossesof 1,000 packets during handover from WLAN toCDMA, we were able to achieve zero packet loss,and 50 ms handoff delay between the last pre-hand-

off packet and first in-handoff packet. This handoffdelay includes the time due to “link down detec-tion” event and the time needed to delete the tun-nel after the mobile has moved. Thus, the handoffdelay in the experiment partly depends upon theRTT (Round Trip Time) in the CDMA network.However we observed about 10 duplicate packetsbecause of the copy-forwarding mechanism at theaccess routers. These duplicate packets are usu-ally handled easily by the upper layer application.These experimental results were taken using SIP-based mobility over IPv4 networks because of theunavailability of IPv6 deployment over the car-rier’s CDMA2000 network. But we expect similarresults if these sets of experiments are carried outusing MIPv6.

5.3 MPA-assisted layer 2 pre-authentication

In Sect. 5.1 and 5.2 we described how MPA in con-junction with 802.21 can help to optimize upperlayer operations during heterogeneous handover.In this section, we describe how a combination ofIEEE 802.21’s information service and MPA canassist in reducing the layer 2 delay during inter-domain handover. Mishra et al. describe severalcomponents that contribute to the layer 2 handoffdelay in Refs. [21,33]. References [3,12,32,33] de-scribe mechanisms to reduce several componentsof layer 2 delay. The IEEE 802.11ipre-authentication provides a mechanism tooptimize handover between APs by reducing theauthentication process delay. Primarily, this mech-anism consists of starting an EAP authenticationwith a target AP through the current associatedAP. In fact, IEEE 802.11i specification providesthe possibility to skip EAP authentication whenthere is a key (named PMK Pairwise Master Key),in the PMK Security Association cache or whenPre-Shared Key (PSK) mode is used. It is alsoimportant to mention that [33] provides a solutionbased on PMK pre-installation. The pre-installa-tion is carried out by the MN’s home AAA server.However this creates some deployment issues inroaming scenarios since visited domains may notalways allow other domains to install cryptographicmaterial in their own access points. In our app-roach, however, an entity in the visited domain

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Fig. 6 Recorded signalactivity MPA and IEEE802.21 assistedhandoff—CaseII—Inter-technology,Inter-domain handoff. (a)MIP-based non-optimizedhandoff, (b) SIP-basednon-optimized handoff.(c) MPA 802.21 assistedoptimized handoff

Handoff Delay~ 18s

802.11 CDMA

Handoff Delay16 s

802.11 CDMA

a MIP-based Non-optimized handoff

b SIP-based Non-optimized handoff

c MPA and 802.21 assisted optimizedhandoff

802.11 CDMA

(PAA) is in charge of doing this task without involv-ing the home domain.

One important limitation of the IEEE 802.11ipre-authentication is the fact it can only work whenAPs are connected to the same distribution sys-tem (DS) and can exchange layer 2 frames. Asa consequence, IEEE 802.11i pre-authenticationbetween APs that belong to different administr-ative domains (inter-domain handoff) is notpossible. Additionally, as another limitation, thismechanism involves a full EAP authentication witheach candidate AP and thus the home AAA serveris contacted every time the mobile moves. Thus,for the cases when IEEE 802.11i pre-authentica-tion cannot be run, the MN has to run a full EAPauthentication just after association with the newAP because it cannot be done through the currentAP. This considerably increases the handover timeas we have observed in our experiments. This lim-itation of 802.11i pre-authentication warrants analternative solution to deal with layer 2 handoffwhere IEEE 802.11i pre-authentication cannot beapplicable.

MPA in conjunction with 802.21 Information Ser-vice can help overcome the limitations associatedwith IEEE 802.11i pre-authentication.It does so byproactively installing the needed cryptographicmaterial to create a security association at layer 2that reduces the layer 2 handover delay and even-

tually the overall handoff time. We describe twoexperiments to illustrate the benefit of MPA-basedlayer 2 pre-authentication: non-MPA assisted hand-off and MPA assisted handoff. We have consideredIEEE 802.11 layer 2 technology as the candidatefor this experiment although the MPA mechanismis access independent.

In the non-MPA case, the MN is initially att-ached to an open AP (current AP) and it movesto an IEEE 802.11i enabled AP in a new domain.As in the normal handover case, after disassocia-tion with the open AP, the MN scans and discoversthe target AP. After the association process, theMN needs to authenticate with the target AP byrunning a full EAP authentication. We have usedEAP-TLS because it is a common authenticationmethod and it has been used in other related workssuch as [12,33]. EAP-TLS authentication methodis also used between MN and a backend authenti-cation server.

In the second scenario, we have used MPA and802.21-based information service. In this case, bef-ore the movement, the MN obtains the informa-tion about possible candidate target APs and alsoabout the PANA Authentication Agent (PAA).Then, just after establishing a security associationwith the Candidate Target Network (CTN) via itscurrent associated AP, the authentication agent(PANA server) derives a key for the mobile and

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each possible candidate AP controlled by thatPANA server. Each specific key is installed at eachcandidate target AP by using SNMPv3. Note thatafter PANA authentication, the MN is also ableto derive the same keys for each candidate targetAP that can potentially be used for running 802.11i4-way handshake. Because PAA installs these keysand MN has the same keys, EAP does not needto be executed at the target APs after the MNmoves. As the final step, the MN needs to asso-ciate with the selected candidate target AP andcomplete the needed 4-way handshake. Scanningoperation during the discovery phase is avoidedand EAP-TLS authentication is no longer neededto establish an 802.11i security association. Fur-thermore, when the MN moves between APs underthe same PAA, the MN can just run the associationand 4-way handshake procedures. It is importantto note that the precise location of the mobile withrespect to the target network access point ensuresthat the mobile is within the AP’s reach before itassociates with the AP without doing any scanning.IEEE 802.21 information service and single probe-request response message by the mobile can helpachieve this. Fig. 7a, b illustrate the signal flowsand the results of non-optimized L2 handoff andMPA-assisted optimized handoff, respectively.

As observed in Fig. 7b, scanning and EAP-TLSauthentication operations are totally skipped

during the MPA-assisted handoff. Scanning wasavoided because 802.21-based Information Serviceprovided the details of the access point and EAP-TLS was not necessary as the keys were distributedprior to the handoff. These two operations basicallycontribute to 97% of the overall layer 2 hand-off delay in our experiments. Specified scanningtimes have been measured in an environment withmany surrounding active APs operating at differ-ent channels. As per [21] it leads to higher scanningtime because there are active APs in each scannedchannel and the mobile spends more time waitingfor probe responses in every channel. Addition-ally, the AAA server is placed only two hops awayfrom the APs and certification validation is per-formed locally. As a consequence, the time takenfor EAP-TLS (∼94 ms) may be shorter than inother network architectures, Note that typicallythe AAA server is placed far from APs and somekind of additional certificate validation steps arenormally carried out increasing the overall EAP-TLS authentication process. In fact, as other exper-imental results [12,33] show, an EAP-TLS can costeven seconds (1.1 s and 5.1 s, respectively). Thesetimes are unacceptable for suitable handoff perfor-mance. As evident from Fig. 7a and b, the MPA-based solution reduces the layer 2 handoff delay toonly three main factors: authentication, associationand 4-way handshake time. MPA can achieve layer

AssociatedProbe Request

Probe Request

ScanningDelay

(460 ms)

Authentication Request

Authentication Response

Association Request

Association Request

Association Response

Association Response

Authentication+Association

(3.9 ms)

EAP-Req/ID

EAP-Response/ID

EAP-TLS/Start

EAP-TLS C-Hello

EAP-TLS S-Hello,S-Certll

EAP-TLS Cert,Change Cipherp

EAP-TLS ChangeCipher

EAP-TLS Empty

EAP-TLS

(93.8 ms)

EAP-TLS Success

4 Way Handshake

(8.8 ms)

EAP-oLKey: Message 1 EAP-oLKey: Message 2

EAP-oLKey: Message 3

EAP-oLKey: Message 4

Mobile AuthenticationServer

Data Traffic

OpenAP(Current AP)

802.11i AP(Target AP)

Authentication

Server

Associated

Authentication Request

802.11i AP

(Target AP)

EAP-oLKey: Message 1

EAP-oLKey: Message 2

EAP-oLKey: Message 3EAP-oLKey: Message 4

Mobile

Authentication

+Association

(5.12 ms)

4 Way

Handshakes

(9.49 ms).

Data Traffic

OpenAP(Current AP)

Authentication Response

Scanning skipped

EAP-TLSskipped

Probe Response

Probe Response

a b

New AP discovered, EAP performed proadively, Keys distributed to AP

Fig. 7 (a) Non-optimized L2 handoff delay. (b) MPA-assisted optimized L2 handoff

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2 delays of roughly 14.7 ms compared to ∼600 msin the non-MPA case. The results shown in Fig.7b show the effectiveness of MPA in reducing thelayer 2 related configuration during handoff. Thereduction of configuration time due to layer 2 pre-authentication is comparable with IEEE 802.11i-based pre-authetication. The MPA scheme looksmore attractive for inter-domain movement, since802.11i-based pre-authentication scheme cannot beapplied to situations where the neighboring APsbelong to two different domains. Authors have pro-vided a complete analysis of MPA-assisted layer 2optimization involving inter-domain handover in[19].

A careful breakdown of the handoff timingshows that layer 2 association, authentication and802.11i 4-way handshake take more or less an equalamount of time in both the cases, but the non-optimized case (Fig. 7a) contributes to more del-ay because of the additional delay introduced dueto layer 2 scanning and EAP-TLS procedure. Wealso observed that overall layer 2 scanning time isdependent upon MaxChannelTime and MinChan-nelTime parameters. In our specific experiment,we set the variables “ss_mindwell” and “ss_max-dwell” of MADWIFI driver to 10 ms and 50 ms,respectively and obtained a layer 2 scanning timeof 460 ms. These variables correlate with MinChan-nelTime and MaxChannelTime defined in the802.11 standard. Probe-Wait latency (amount oftime a station waits on a particular channel aftersending a probe request) depends on these set-tings. For example, when we changed these val-ues to 20 ms and 200 ms, respectively, total layer2 scanning time increased to 930 ms. Velayos andKarlsson [35] describe the factors that affect thescanning time and ways of optimizing the scanningtime.

We have used “madwifi-ng” drivers with Netgearwireless cards in both the MN and the APs. Hos-tapd and wpa_supplicant were used in the APs andMN respectively to deploy IEEE 802.11i.Net-snmp was used because it implementsSNMPv3 and its security extensions, and finally wehave used OpenDiameter to deploy the AAA ser-ver functionality that works as a backend serverfor the PANA Authentication Agent.

The set of three experimental resultsdescribed in Sects. 5.1, 5.2 and 5.3 highlight the

effectiveness of MPA and 802.21 for heterogeneoushandover. These results also validate that bothMPA and 802.21 can help optimize the handoverdelay at all layers by optimizing different handoveroperations such as discovery, network detection,configuration, authentication and binding update.

6 Performance comparison of MPA

In this section we highlight certain added featuresof MPA that are different than the existing make-before-break techniques. In particular, wecompare MPA with FMIPv6 and highlight thefunctional differences. MPA provides a make-before-break mechanism and takes care of manyupper-layer handover related functions leavingonly layer 2 handover operation to execute dur-ing the move. There are several other proactiveschemes, such as MITH [13], FMIPv6 [17] thatutilize make-before-break techniques and providecomparable performance.

The distinct features of MPA relative to otherrelated make-before-break schemes are as follows:(1) MPA can work over multiple types of mobilityprotocols; (2) MPA provides pre-authenticationsupport for both layer 3 and layer 2 thereby reducingthe delay due to authentication; (3) MPA pro-vides flexible ways of performing pre-configura-tion operation such as stateless auto-configurationand stateful pre-configuration using DHCP relayagent; (4) When assisted by IEEE 802.21 infor-mation discovery scheme, MPA can optimize thelayer 2 handoff by avoiding scanning and IEEE802.11i authentication; (5) MPA framework can beapplied to different types of handover such as inter-domain, intra-domain, inter-technology and intra-technology; (6) MPA provides a flexible bufferingmechanism at different parts of the network thatcan reduce the packet loss during the handover.

Now, we briefly compare MPA with FMIPv6.The IETF has defined two fast-handover protocolsfor MIPv6, such as hierarchical MIPv6 [34] and FastMIPv6 [17]. Both of these protocols try to reducethe packet loss and handover delay experiencedby the base version of MIPv6. There is a very fun-damental difference between MPA and FMIPv6.While FMIPv6 is limited to the use of MIPv6 as abinding protocol for fast-handover, MPA defines a

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mobility framework that can work independent ofthe mobility protocol, and can work with a numberof protocols including MIPv4 [27], MIPv6 [16], andSIP-based mobility [31]. However in the context ofMIPv6, we provide a brief functional comparisonbetween FMIPv6 and MPA over IPv6.

FMIPv6 provides two ways of providing fast-handoff: predictive mode and reactive mode. TheFMIPv6 predictive mode and MPA-based optimi-zation over MIPv6 exhibit some similarities forcertain operations such as pre-configuration andproactive binding update. Authors provide a com-plete overview of MPA operation and the imple-mentation results in the IETF MPA drafts [8] and[23] respectively. Reference [5] provides some exper-imental results of FMIPv6 that show that delaydue to proactive FMIPv6 is bounded by non-opti-mized layer 2 delay. Similarly MPA over IPv6 isalso bounded by non-optimized layer 2 delay inthe absence of any assistance from IEEE 802.21’sinformation discovery scheme. According to [5],handover latency for proactive FMIPv6 is equalto layer 2 IEEE 802.11 handover latency and iscomputed to be 320 ms. On the other hand, MPAassisted by IEEE 802.21 information discovery lim-its the layer-2 delay to 4 ms by avoiding scanning.FMIPv6 when assisted by IEEE 802.21 informa-tion discovery can also help to reduce the layer 2delay to a comparable value as obtained in the caseof MPA.

However there are a few functional differencesbetween MPA over IPv6 and predictive mode ofFMIPv6. Below, we list certain functional differ-ences between MPA over IPv6 and FMIPv6.

6.1 Pre-authentication

A key component of MPA over IPv6 is its pre-authentication mechanism. Pre-authentication is aprocess of authenticating a mobile with the tar-get network from the currently connected networkbefore the mobile moves to the new network [25].This pre-authentication can take place both in layer2 and layer 3. Studies [12] show that it takes up to5 s to complete layer-3 based EAP-AAA authenti-cation. Similarly layer 2 authentication takes up to600 ms [30] to support IEEE 802.11i in a roam-ing environment. Although IEEE 802.11i’s pre-

authentication mechanism can be used to optimizelayer 2 pre-authentication it is limited to use withinone DS (Distribution System) only. On the otherhand, MPA assisted handoff can bootstrap bothlayer 3 and layer 2 authentication while the mobileis still in the previous network thus optimizingthe time taken due to these operations during thehandover. This pre-authentication mechanism withthe assistance from IEEE 802.21’s Information Ser-vice helps to bootstrap layer 2 security such as802.11i and thus optimize the layer 2 delay also.Although FMIPv6 does provide proactive configu-ration and binding update, FMIPv6 itself does nothave any specific pre-authentication mechanismdefined as part of RFC 4068. However, recentlythere has been efforts to add pre-authenticationsupport to FMIPv6 [25], but this support has beenremoved from the next revised version of the draft.Thus, FMIPv6 when assisted by 802.21 informationdiscovery mechanism can help reduce the hand-over delay to layer 2 delay but without any securityoptimization.

6.2 Pre-configuration and binding update

The process of pre-configuration and binding upd-ate are also different between MPA over IPv6 andFMIPv6. In the case of FMIPv6, the router of theprevious access network and the router of the nextaccess network exchange information to facilitatepre-configuration and fast binding updates beforethe handover. In MPA,the protocol exchange takesplace between the mobile node and the authentica-tion agent, access router (AR) and configurationagent (CA) of the target network. The FMIPv6protocol exchange between the routers will re-quire some administrative agreement between theneighboring domains and thus FMIPv6 may bemore suited for intra-domain case where the rou-ters belong to the same administrative domain.Whereas MPA over IPv6 can work for both intra-domain and inter-domain since the pre-authenti-cation mechanism helps to complete the requiredpre-configuration and proactive binding updateswithout any need to have specific protocol ex-change between the previous access router (PAR)and next access router (NAR). This alleviates thedependence on the access routers and inter-

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communication between the access routers duringthe handover.

RFC 4068 [17] discusses the mobile’s pre-configuration operation. Through RtSolPr andPrRtAdv messages the mobile can formulate aperspective new CoA (nCoA) when it is still inthe previous access network. It does not howeverdiscuss the use of DHCPv6 to help the config-uration process. Whereas MPA over IPv6 doessupport both modes of pre-configuration, such asstateful configuration using DHCP relay agent andstateless auto-configuration where it can pass therouter’s prefix over the transient tunnel betweenthe NAR and PAR.

6.3 Auxiliary handoff operations

Additionally, many of the auxiliary handoff oper-ations such as buffering and tunneling are tightlycoupled with FMIPv6 signaling, whereas theseoperations in MPA are not tightly coupled withthe signaling of specific mobility protocols suchas MIPV6. MPA can make use of binding updatemechanisms that come with MIPv6 or any othermobility protocol, whereas pre-authentication,pre-configuration, tunneling and buffering func-tionalities could be dealt with by separate protocolsof choice. For example, in our implementation wehave used PANA for pre-authentication and tun-nel management and used a newly designed dy-namic buffering protocol [9] for buffering packetsand reducing the packet loss during handover.

6.4 Support for heterogeneous access handover

Unlike MPA, FMIPv6 in its current form does notprovide seamless handover support between het-erogeneous access technologies such as CDMAand 802.11. However there is a recent draft [28]that describes the support for handover with het-erogeneous access technologies by adding bi-cast-ing with buffering and selective packet deliverytechnique. MPA does enhance the support for het-erogeneous handover by providing a dynamicbuffering mechanism and copy and forwardingtechnique. Details of these techniques are describedin [9]. While newly added support for bi-casting

and buffering techniques for FMIPv6 are limitedto access routers, MPA’s buffering mechanism thatsupports heterogeneous handover is quite flexibleas it can be both time-limited and explicit bufferingand its placement is not limited to access routeronly. The newly designed buffering protocol canbe used independent of the mobility protocol used.Additionally, MPA can also be used for situationswhere the mobile does not need to execute anymobility protocol to support network controlledlocalized handover [28]. In this situation MPA al-lows the mobile to use tunnel management proto-col to communicate with Next Access Router andprovide seamless handoff support between 802.11and CDMA networks.

Deployment considerations

Besides the operational differences with FMIPv6for fast-handover, MPA also takes into consider-ation several deployment scenarios such as failedswitch over, ping-pong effect and QOS reservationin the target network during a mobile’s movement.More details of MPA can be found in Ref. [8].

Despite certain functional differences betweenMPA and FMIPv6, MPA’s pre-authentication mech-anism and stateful pre-configuration mechanismcan be used to augment FMIPv6’s functionalityand further optimize the handover performance.

7 Conclusions

In this paper we have presented a mobility optimi-zation framework that takes advantage of IEEE802.21 as well as a media independent pre-aut-hentication (MPA) framework to provide securedand seamless convergence and support heteroge-neous handover. We have discussed severalfunctional components of the IEEE 802.21 frame-work and their respective roles in providing theoptimization. We explain a laboratory experimentalsetup where we have implemented several func-tional components of 802.21 such as the EventService and Information Service functions, and theMPA technique. The implementation demonstr-ates network discovery, network selection,pre-configuration, pre-authentication, and proac-tive handover operations that are part of a mobility

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event. We presented the results of two types of het-erogeneous handover scenarios: intra-technology,inter-domain; and inter-technology, inter-domainand also demonstrated the effectiveness of MPA-assisted layer 2 pre-authentication. Results obtainedfrom these experiments validate how an MPA as-sisted IEEE 802.21 framework can provide securedseamless convergence and support different typesof heterogeneous handover scenarios by reducinghandover delays and packet losses to a level thatis acceptable for interactive VoIP and streamingtraffic. We also highlight additional features thatIEEE 802.21 assisted MPA framework providescompared to other make-before-break techniquesincluding FMIPv6.

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3. Bargh, M. S., Hulsebosch, R. J., Eertink, E. H., Prasad,A., Wang, H. et al. Fast authentication methods forhandovers between IEEE 802.11 wireless LANs. In:Proceedings of ACM WMASH 2004. Philadelphia.

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Ashutosh Dutta (Se-nior Member of IEEEand ACM) is currentlya Senior Scientist inTelcordia Technology’sInternet Network Re-search Laboratory withan emphasis on mobilenetworking and mid-dleware applications forthe wireless Internet.Prior to joining Tel-cordia Technologies,Ashutosh was the Direc-tor of Central Research

Facilities in Columbia University, from 1989 to 1997. His re-search interests include Session control protocols, Stream-ing multi-media, wireless multicast, and Mobile wireless In-ternet. Ashutosh has a BS in EE (1985) from India, MSin Computer Science (1989) from NJIT, and ProfessionalEngineering degree in EE from Columbia University. Heis also pursuing his part-time Ph.D at Columbia University.Ashutosh is currently serving as the Vice-chair of IEEEPrinceton and Central Jersey section.

Dr. Subir Das is aSenior Scientist inMobile NetworkingDepartment, AppliedResearch, TelcordiaTechnologies Inc. Priorto joining TelcordiaTechnologies, Dr. Daswas a faculty mem-ber in the E & ECEDepartment, Indian Ins-titute of Technology,Kharagpur, India. Dr.Das has more thanforty publications and

three US patents to his credit. He is very active in Stan-dards Organizations and a leading contributor to variousStandards. Dr. Das is a TPC member and a tutorial speakerin IEEE and ACM sponsored international conferences.His research interests include mobility management, net-work security, IP Multimedia Sub-Systems, and ad hoc net-working. He is a member of IEEE and a reviewer of IEEEand ACM journals and magazines.

David Famolari is aSenior Scientist and Pro-gram Manager within theApplied Research depart-ment of Telcordia Tech-nologies. David currentlymanages operations fora joint-research collabo-ration, called ITSUMO,between Telcordia andToshibaAmerica Research Inc(TARI) that is deliveringinnovative mobility, QoS,configuration and securitytechnologies for the next

generation of wireless IP networks. He holds B.S. and M.S.degrees in electrical engineering from Rutgers Universityand completed Ph.D. coursework at Columbia University.

Yoshihiro Ohba rec-eived a B.E., M.E.and Ph.D. degrees onInformation and Com-puter Sciences fromOsaka University,Japan, in 1989, 1991and 1994, respectively.From 1991 to 2000,he worked in Cor-porate Research andDevelopment Center,Toshiba Corporation,Kawasaki, Japan. Since

2000, he has been working as a Research Director in ToshibaAmerica Research, Inc., New Jersey, U.S.A.

Kenichi Taniuchi (kta-niuchi@tari.toshiba.com) is working asa researcher in Toshi-ba America Research,Inc, New Jersey, wherehe is involved in secu-rity and mobility areaof Internet wirelesscommunication. He hasa Master’s degree inInformation Sciencefrom Waseda Univer-

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Seamless proactive handover across heterogeneous access networks

sity, Tokyo, Japan in 2000. His research interest includeslocation based application service for mobility.

Victor Fajardo is cur-rently a researcher forToshiba America Re-search Inc in New Jer-sey. His main focusof research is mobilityand security. He is in-volved is standardiza-tion work particularlyIETF. Prior to thathe was a senior engi-neer for Xebeo com-munications workingon protocol develop-

ment for core networks specifically traffic engineering. Hehas also worked in startup companies where he devel-oped IP stacks and related protocols. Victor has completedhis Masters degree in Computer Engineering at CaliforniaPolytechnic University, Pomona.

Rafael Marin Lopezreceived the M. S.degree in ComputerScience from Univer-sity of Murcia, Mur-cia, Spain in 2000.In the same year hestarted as researchstaff in the Depart-ment of Informationand CommunicationsEngineering of theUniversity of Murciaon a national e-com-

merce project named PISCIS. In the end of this project,he followed as researcher in European IST Euro6IX pro-ject related with IPv6 from 2001 to 2003. During 2004 he hasalso worked on European FP6 IST Daidalos project basedon Mobility and IPv6. During the end of 2004 until now,he is a full time assistant lecturer in Department of Infor-mation and Communications Engineering. Additionally heis collaborating actively in IETF above all PANA WG andHOKEY WG. His main research interests include networkaccess authentication and authorization and related tech-nologies besides of mobility.

Toshikazu Kodama rec-eived the B.E., M.E.and Dr.E. degrees inelectrical engineeringfrom Tokyo Instituteof Technology, TokyoJapan in 1971, 1973and 1987, respectively.In 1973, he joined Tos-hiba Corporation, Ka-wasaki, Japan, wherehe has been engagedin the research anddevelopment of sur-face acoustic wave de-vices, ATM switching

systems and mobile communication systems. He is cur-rently the president of Toshiba America Research, Inc.He received the Excellent Paper Award of the IEICE, theAchievement Award of the IEICE, Japan Invention Award,Research Achievement Award from Director General ofthe Science Technology Agency Japan and IEEE Region 1Award in 1988, 1995, 1996, 1997 and 2005 respectively. Dr.Kodama is a member of the IEICE and IEEE.

Prof. Henning Schulz-rinne received hisPh.D. from theUniversity of Massa-chusetts in Amherst,Massachusetts. He wasa member of techni-cal staff at AT&T BellLaboratories, MurrayHill and an associ-ate department headat GMD-Fokus (Ber-lin), before joining theComputer Science andElectrical Engineeringdepartments at Colum-

bia University, New York. He is currently chair of theDepartment of Computer Science. Protocols co-developedby him, such as RTP, RTSP and SIP, are now Internet stan-dards, used by almost all Internet telephony and multimediaapplications. His research interests include Internet multi-media systems, ubiquitous computing, mobile systems, qual-ity of service, and performance evaluation. He is a Fellowof the IEEE.