A Scheme Encouraging Mobile Nodes to Forward Packets via Multiple Wireless Links Aggregating System Between the Internet and Mobile Ad Hoc Networks

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We have proposed a system that achieves high-speed and high-quality communication between mobile nodes and the Internet by using multiple network interfaces of multiple mobile nodes. In this system, adjacent mobile nodes connect to each other with
  A scheme encouraging mobile nodes to forward packetsvia multiple wireless links aggregating system betweenthe Internet and mobile ad hoc networks Yosuke Ito 1 , Hiroshi Mineno 2 , and Susumu Ishihara 3 1 Graduate School of Science and Technology, Shizuoka University,3-5-1, Johoku, Hamamatsu, Shizuoka, 432-8561, Japan,Phone/ Fax:+81-53-478-1265, Email: ito@ishilab.net 2 Faculty of Information, Shizuoka University, Email: mineno@cs.inf.shizuoka.ac.jp 3 Faculty of Engineering, Shizuoka University, Email: ishihara@ishilab.net Abstract.  We have proposed a system that achieves high-speed and high-qualitycommunication between mobile nodes and the Internet by using multiple net-work interfaces of multiple mobile nodes. In this system, adjacent mobile nodesconnect to each other with short-range high-speed links and establish temporarynetworks. A mobile node in a temporary network simultaneously uses multiplelinks owned by the nodes in the network when it communicates with nodes out-side the network. In this system, a part of data packets for one node have to berelayed by the other nodes in the temporary network. However, other nodes mightnot relay data packets unless they receive some profit from their contribution. Inthis report, we introduce credits as an incentive to network nodes to relay packets.We propose a method that provides secure credit exchanges between nodes relay-ing packets and a node requesting the relays, and the method provides a trustedthird party that assists those nodes exchanging credits. Keywords.  mobile computing, multiple paths, mobile IP, cooperation, incentiveof forwarding, accounting, fairness, SHAKE, ad hoc network  1 Introduction In wireless communication environment, users demand to connect to the Internet com-fortably at any time and place. In a previous report [1], we proposed SHAKE (a pro-cedure for SHAring multiple paths to create a cluster networK Environment) to enablehigh-speed, reliable communication with multiple network interfaces for a temporalgroup of mobile devices. In SHAKE, mobile devices gathering in particular locationestablish a temporary network (we call this network an  alliance ) by establishing ashort-range high-speed wireless link (e.g., wireless LAN). When a mobile device inan alliance accesses the Internet under a situation where the node has to use a slow link (e.g., 2G, 3G cellular), it uses not only its link to the Internet but also the links betweenthe other mobile devices in that location and the Internet. This improves the data trans-mission speed, reliability and connectivity of the communication between the mobiledevices and the Internet.  Internetlong-range wireless link(2G, 3G, etc.) alliance short-range high-speed link(802.11, etc. )movemoveCNHA ALMNMNMNMN AM AM   Internet PayloadSrc: CNDst: AL Home Addr PayloadSrc: CNDst: AL Home Addr Src: HADst: AL CoAPayloadSrc: CNDst:AL Home Addr Src: HADst: AM CoAPayloadSrc: CNDst: AL Home Addr    CNHA AM ALshort-range high-speed link (b) mechanism CN: Correspondent NodeHA: Home AgentMN: Mobile Node AL: Alliance Leader  AM: Alliance Member  (a) use case Fig.1.  Mobile IP SHAKE In SHAKE, nodes must assist other nodes by using their own external link to relaytraffic. If nodes refuse a relay connection because they have to use their own CPUpower, memory, and battery to relay traffic for other nodes, communicating by usingthe SHAKE will be impossible. To solve this problem, we propose a scheme that usescredits as an incentive to encourage nodes to relay traffic for other nodes.The rest of the paper is organized as follows. In Section 2, we review the SHAKEarchitecture, the issues, and the related work. In Section 3, we present architecture formotivating mobile nodes to perform relays. In Section 4, we discuss robustness andoverhead of the proposed scheme. Section 5 summarizes this paper. 2 SHAKE In this section, we provide an overview of SHAKE. In SHAKE, mobile nodes establishan alliance to enhance communication speed between them and the Internet. A noderelaying data packets for another node in an alliance is described an Alliance Member(AM), and a node requesting the relay of data packets to AMs is described an AllianceLeader (AL). When an AL communicates outside of the alliance, it distributes trafficnot only to its own external link but also to those of the AMs. 2.1 Mobile IP SHAKE Mobile IP SHAKE [1] is an implementation of SHAKE on the IP layer. We assumethe use of Mobile IP SHAKE in this paper. To establish SHAKE on the IP layer, anode that distributes traffic on the path between the correspondent node (CN) of anAL and the alliance including that AL is necessary. If no node distributes packets sentfrom the CN to the destination node (AL), the CN has to know all the addresses of thenodes in the alliance (AM). This is not ideal because it is not functionally practical forordinaryhosts on the Internet to know the addresses of all AMs for a short time session.  Mobile IP SHAKE exploits a feature that assures that the packets from the CN to aMobile Node (MN) always go through the Home Agent (HA) of an MN on the MobileIPv4 mechanism unless route optimization is used, and introduces a traffic-dispersionmechanisms into the HA. For this reason, Mobile IP SHAKE does not require anyspecial mechanism for CNs.Figure1providesanoverviewofMobileIPSHAKE.AnALregistersanAM’scare-of address (CoA) as well as the AL’s own CoA to the HA of the AL in advance. Whenthe HA forwards packets sent from the CN, it encapsulates the packets and distributesthem not only to the AL but also to the AMs. The AMs decapsulate the transmittedpackets and forward them to the AL throughthe links in the alliance. When packets aretransmitted from the inside of an alliance to the external link, the AL encapsulates anddistributes packets to each AM. Then, each AM forwards the packets to the destinationnode or the AL’s HA as in the reverse tunneling technology used in Mobile IPv4.In the followingsection, we describe transmission from a node in an alliance to out-side the cluster as ‘ uplink  ’, and transmission from outside the alliance into the allianceas ‘ downlink  ’. 2.2 Issues in using SHAKE In SHAKE, AMs have to offer CPU resources, battery power, and link bandwidth tothe AL. For this reason, AMs may refuse to relay packets for the AL unless mutualtrust exists between the AL and the AMs or unless some reward is promised. There-fore, we introduce a mechanism for motivating AMs to relay packets for the AL bygranting rewards to the AMs. We deal with this issue in this paper. Adding to this, themanagement of heterogeneous mobile nodes in the alliance and traffic distribution areimportant issues. These issues have been discussed in [2]. 2.3 Related Work The issues of cooperationof mobile nodesforpacket forwardinghavebeen investigatedin ad hoc networks and multi-hop cellular networks. In [5,7], reputation mechanisms for ad hoc networks were proposed. In [10], Eidenbenz et al. proposed game theory ap-proach in ad hoc networks. Golle et al. analyzed the incentives in peer-to-peernetworks[9].OurapproachforourspecialarchitectureSHAKEiscredit-basedmechanism.Credit-basedmechanismisusedinadhocnetworks[3,6,4],andinmulti-hopcellularnetworks [11,8].In[3],ButtyanandHubauxproposedvirtualcurrencycalled nuglets .Thesenderof a packet loads  nuglets  on the packet, and the intermediate nodes acquire some  nu-glets  from that packet by forwarding it. In [6], they proposed an improved mechanism.In [3,6], to ensure the payment of the correct amount of   nuglets  to each node, tamper-proof hardware is used. Our system does not need any tamper-proof hardware at anynode. Zhong et al. proposed a method relying on a central authority that collects re-ceipts from the forwarding nodes [4]. In this method, intermediate nodes send receiptsafter forwarding data messages. Then, the central authority charges the source nodesand rewards the forwarding nodes based on the receipts.  The following are differences between these credit-based methods and our method.First, in [4,11], authors use cryptographic functions based on public key cryptography, whereas our solution is based on symmetric key cryptography requiring less computa-tionload.Secondly,someofabovecredit-basedapproachesdonotsolvea case inwhichthe destination of a packet pays the reward. When SHAKE is used, an AL has to grantAMs the rewards in both cases when the AL is the transmission source and the destina-tion, becausethe AL relies on AMs in bothcases. So we designeda mechanismadaptedto the both cases. Thirdly, these approaches assume only a rational malicious node thatattempts to cheat if the expected benefit of doing so is greater than the expected benefitof acting honestly. In other words, they do not take care of the offenders for pleasure.We suppose that the existence of such offenders is one of serious problems. In additionto the cases that malicious nodes attack the system intentionally, cracked computersmight attack other hosts unintentionally. This leads to collapse the systems and to lossservice provider’s confidence. The fourth difference is that above credit-based methodscan not distinguish unintentionalpacket losses from packet drop of malicious node,andcan not solve contradiction of charging arisen from packet losses. We also address thisproblem. 3 A scheme encouraging mobile nodes to forward packets onSHAKE To encourage Alliance Members (AMs) to relay packets for an Alliance Leader (AL)in SHAKE, we introduce an incentive for AMs. We propose a method of using creditas the incentive. Each AM receives credit in compensation for the relay. Therefore, if an AL wants to send packets via an AM, the AL needs to pay credit for the AM. Theamount of credit is proportional to the size of the packet. We assume that the credit canbe converted into real money or can grant privilege to users in provider services. If anode wants to get more credit, the node can get by paying its debit or buy them usingreal money, or be remunerated by forwarding others’ data traffic.We introduce a trusted third party to maintain users’ credit account, and we callthis party a Credit Server (CS). We assume that the CS and the Home Agent (HA) arecompletely reliable and do not coalesce with other hosts. From a practical standpoint,HAs will be managed by ISP or carrier if Mobile IP is used for mobile phone. Becauseof this, it is considered to be reasonable that the HAs are completely reliable. The CSis the authority for managing credit, and the CS rewards AMs that have forwardedpackets reliably and charges the ALs. The CS charges and rewards for the relay of packets forwarded successfully. We use Forward Reports (FRs) from an AM and a HAfor judging whether packets have been successfully forwarded. Between the HA andthe CS, and between the AM and the CS, the FRs are assumed not to be modified by athird party by using secure session like IPsec.In the following discussion, we deal with the following malicious attacks. –  Forgery of credit:Individual nodes may illegitimately try to increase their own credit.  InternetCNHA ALAMCS CN: Correspondent NodeHA: Home AgentCS: Credit Server  AL: Alliance Leader  AM: Alliance Member  ),,,(  MAC length seq payload   AL HA  K  ),,,(  length seq payload  )(  payload  (1)(2)(3)(FR)(1)(2)(3) Data flowrelay listrelay listControl message flow -  seID seID ,, relay list 30seID15002221500221 AM AL lengthseqrewardcharge (=Forward Report (FR) )  MAC   AM  HA  K   - ),,(  length seq payload  seID ,  MAC   AL HA  K -  ), ,(  length seq seID ,  AL AM30 Fig.2.  Uplink procedure –  Free riding (AL’s refusal to pay to CS):An AL may claim that it did not initiate some communicationdespite being helpedby AMs. The CS has to refuse these kinds of claims. –  AM’s false charge for rewards:An AM may charge credit by sending a false FR to the CS. The CS has to refusesuch kinds of charges. 3.1 Forwarding uplink packetsOverview  Figure 2 illustrates the flow of data packets and control messages for cred-iting procedures in uplink. In Section 2.1, in uplink on Mobile IP SHAKE, we pointedout that both the transitions of passing through HA and of not passing through HAcould be used. However in this paper, we assume that packets from an AL to a CN areforwarded by the HA. The purpose of this is that we intend to enable the HA to confirmthat AMs forward packets with certainty.In uplink, the packets from an AL are delivered to the CN via an AM and an HAexcept packets sent directly from that AL’s own external link. When the HA forwards acertain amount of packets via the AM, it generates a FR and sends it to the CS. We sup-pose that the HA sends the FRs to the CS via TCP for reliable transmission. When theCS receives the FRs from the HA, it judges whether each packet has been successfullyforwarded. After this operation, the CS pays the reward to the AM and charges it to theAL for the successfully forwarded packets. This CS’s payment is supposed to be leviedas ISP or other service charges. When no FR is received from the HA, the CS judgesthat forwarding has failed, and does not charge or reward credit. Protocolin detail  Inthis section,we presentdetails ofthe uplinkprotocol.The packetsfrom an AL to a CN are distributed to a communication path via an AM (AL    AM
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