STATISTICAL PERFORMANCE ANALYSIS OF THE PREDICTIVE FAST AND SEAMLESS HANDOFF SCHEME FOR THE NESTED MOBILE NETWORK

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1 Pak. J. Statst. 011 Vol. 7(5), STATISTICAL PERFORMANCE ANALYSIS OF THE PREDICTIVE FAST AND SEAMLESS HANDOFF SCHEME FOR THE NESTED MOBILE NETWORK Ing-Chau Chang and Cou-Song Lu Departent of Coputer Scence and Inforaton Engneerng, Natonal Changhua Unversty of Educaton, Changhua, Tawan, R.O.C. Eal: and ABSTRACT In the past, our proposed HCoP-B has acheved route optzaton and resolved the RO-stor proble for handoffs of the nested oble network. However, because HCoP- B was a pure layer three,.e., network layer, approach whch handoff operatons were perfored after the layer two,.e., data lnk layer, lnk breaks, t stll suffered fro a long handoff latency and serous packet losses. In ths paper, by adoptng the handoff predcton concept of the fast oble IPv6 on HCoP-B, we proposed a cross-layer archtecture, whch was called the fast HCoP-B (FHCoP-B), to trgger layer three HCoP- B route optzaton flow by and lnk events before the actual Layer handoff occurs. In ths way, FHCoP-B further shortened both the handoff latency and packet losses of HCoP-B. We further adopted the analytcal odel to nvestgate handoff latences and total buffer szes of HCoP-B, FHCoP-B and two well-known NEMO schees wth the rado lnk protocol, whch could detect packet losses and perfors retransssons over the error-prone wreless lnk. Hence, FHCoP-B outperfored the other three schees by achevng shortest handoff latences, the sallest nubers of packet losses and the least total handoff costs durng handoff wth lttle extra buffers. Consequently, t exhbted sgnfcant benefts on supportng fast and sealess handoff n the nested oble network even over error-prone wreless lnks. KEY WORDS HCoP-B; FHCoP-B; Fast Handoff; Nested Moble Network; rado lnk protocol. INTRODUCTION NEtwork MOblty (NEMO) has been dentfed as an portant concept of collectve oblty of a set of oble nodes as n the vehcular network (Lach et al., 003). The IETF NEMO workng group extends MIPv6 (Johnson et al., 003) as NEMO Basc Support (NBS) (Devarapall and Wakkawa, 005) by creatng a b-drectonal tunnel between the oble router (MR) and ts hoe agent (MR-HA) to acheve perforance proveents over MIPv6 for network oblty. As the levels of nestng of the nested NEMO ncrease, packets destned to a oble network node (MNN) should pass through MR-HAs at each level. Ths knd of pnball routng (Thubert and Molten, 00) ntroduces large transsson delays and tunnelng overheads. Hence, there have been lots of researches workng on how to support route optzaton (RO) for NEMO (Thubert and Molten, 007; Calderón et al., 006; Chang and Chou, 009). In (Chang 011 Pakstan Journal of Statstcs 591

2 59 Statstcal perforance analyss of the predctve fast and sealess and Chou, 009), we have proposed the herarchcal care-of prefx (HCoP) wth a novel bndng update tree (BUT) schee,.e., HCoP-B, at the oblty anchor pont (MAP) to acheve an optal route between the correspondent node (CN) and MNN, reduce the handoff latency and avod duplcate global bndng update (GBU) essages for RO. For allevatng the qualty of servce (QoS) degradaton durng the handoff of the oble node (MN), IETF has proposed the Fast Handovers for Moble IPv6 (FMIPv6) protocol (Koodl et al. 008) to reduce the handoff latency of MIPv6 and thereby acheve sealess handoff of an MN. As the receved wreless lnk sgnal strength falls below a predefned threshold, the lnk layer,.e., layer two (L), of the oble node wll notfy ts network layer,.e., layer three (L3), to start ts L3 handoff operatons proactvely wth ts current and forthcong access routers, whch are called the prevous access router (PAR) and next access router (NAR) n FMIPv6 respectvely. Hence, the oble node edately resues ts connectons wth the CN as soon as t has re-attached to the NAR through the new wreless lnk. As the oble network s ore and ore popular n recent years, t s portant to support sealess handoff of the nested oble network and thereby antan the QoS of each ongong real-te applcaton. Hence, we wll propose the cross-layer FHCoP-B here for effcent oblty anageent of the nested oble network. FHCoP-B acheves the followng erts. Frst, t defnes a cross-layer archtecture and correspondng essage flows whch ntegrate the L fast handoff event notfcaton of FMIPv6 nto the L3 route optzaton flow of HCoP-B. Second, the FHCoP-B works over heterogeneous wreless networks, whch consst of two knds of prevalent wreless lnks,.e., the short-range one between each oble router (MR) and MNN nsde the oble network and the long-range one between the top-level MR of the oble network and the access router. Thrd, t classfes the oble network handoff nto two ajor categores and eght handoff scenaros. In ths way, FHCoP-B proactvely starts ts essage flow before the handoff occurs such that t can sgnfcantly reduce the handoff latency and packet loss of the real-te applcaton. The MIPv6 return routablty (RR) procedure, whch refers to the ethod for establshng the oble node s able to receve packets delvered to the IPv6 addresses that t clas to own (Koodl and Perkns, 007), s also ncluded n the proposed FHCoP-B for NEMO to avod vulnerabltes to denal-of-servce attacks and traffc stealng at the CN and MNN. In ths paper, we further adopt the analytcal odel proposed n (Mohanty and Akyldz, 007) to nvestgate perforances of HCoP-B, FHCoP-B and two well-known schees by consderng the frae error rate over error-prone wreless lnks, whch s rare n the NEMO lterature. Based on the rado lnk protocol (RLP) (Bao, 1996), whch s an autoatc repeat request (ARQ) fragentaton one, to detect packet losses and perfors retransssons on the wreless lnk, we frst atheatcally analyze handoff latences, total buffer szes and total handoff costs of FHCoP-B and then utlze nuercal data to exhbt sgnfcant benefts of FHCoP-B on supportng fast and sealess handoffs n the nested oble network. The reander of ths paper s organzed as follows. Secton descrbes related work on usng FMIPv6 for oble nodes and for oble networks. Secton 3 presents the proposed FHCoP-B archtecture and ts sgnalng flows for handoff. Secton 4 exhbts perforance evaluatons for three etrcs of FHCoP-B wth RLP and Secton 5 shows

3 Chang and Lu 593 nuercal results of HCoP-B, FHCoP-B and the other two well-known NEMO schees, respectvely. Secton 6 concludes ths paper. RELATED WORKS Reverse Routng Header (RRH) (Thubert and Molten, 007) uses a type 4 routng header to record the care-of address (CoA) of each nteredate MR n the nested NEMO when the MNN frst sends a packet to the CN. Whenever the CN sends a packet destned to the MNN, ths packet s routed to the HA of the MNN s servng MR frst and forwards to the MNN va an optal route, accordng to CoAs of all nteredate MRs recorded n a type routng header. In ths way, RRH resolves the pnball routng proble. However, RRH ntroduces extra packet and processng overhead for the routng header. The CN and MR-HA also need spaces to record routng nforaton for each MNN. Moble IPv6 route optzaton for NEMO (MIRON) (Calderón et al., 006) uses DHCPv6 n each MR to provde topologcally eanngful IPv6 addresses to every chld MR of the next lower layer and the vsted oble node (VMN) n the nested NEMO. The VMN sends a bndng update (BU) essage to ts HA and every CN to optze the path between the for RO. In HCoP-B (Chang and Chou, 009), the MAP nherts the concept of HMIPv6 (Solan et al., 005) to anage care-of prefx (CoP) allocaton and antan the bndng cache for all MNNs. HCoP-B also bulds a BUT on the MAP to record the NEMO topology and nforaton about all CNs of MNNs and all MR-HAs n the nested NEMO. HCoP-B frst acheves an optal route between the CN and MNN by copng wth the pnball routng for the nested NEMO. Second, t reduces the handoff latency by overlappng the duraton of the prefx delegaton and the local bndng update (LBU) to the MAP, and the global bndng update fro the MAP to MR-HAs and CNs for RO. Fnally, t avods duplcate GBU essages for RO fro an MNN to all connectng CNs and thereby reduces GBU bandwdth consupton. However, these NEMO schees ntroduce any extra L3 operatons to optze the route between the CN and MNN after the L handoff has been copleted, whch n turn sgnfcantly rases the handoff latency and deterorates QoS of actve real-te applcatons. FMIPv6 was proposed to reduce the sgnfcant MIPv6 handoff latency that was ntroduced by operatons lke lnk-layer procedures, oveent detecton, IP address confguraton and locaton update. It enables the MN to ssue the Router Solctaton for Proxy Advertseent (RtSolPr) essage to ts PAR and wat for the Proxy Router Advertseent (PrRtAdv) essage fro the PAR for quckly detectng that t wll ove to a new subnet of an NAR and confgurng an prospectve new CoA (NCoA) on the NAR when the MN s stll connected to ts PAR. In (Dopoulou et al., 005), the authors adopt three types of L events,.e., Lnk gong down, Lnk down and Lnk up to notfy L3 of the current wreless lnk status. Oppostely, as the IEEE 80.16e sute of specfcatons has been proposed n recent years, the work n (Jang et al., 008) descrbes how the MIPv6 fast handover can be pleented on 80.16e lnk layers. In essental, these schees only support the fast handoff of a sngle MN. They cannot be adopted as fast handoff schees of a NEMO. In (L et al., 008), an enhanced fast handover schee for MIPv6 was proposed to acheve low handover latency and packet delay by reducng latences of the duplcate address detecton (DAD) for verfyng unqueness of the new CoA at the NAR and

4 594 Statstcal perforance analyss of the predctve fast and sealess MIPv6 bndng update procedures before handoff. However, t cannot be easly ntegrated wth those non-mipv6-based route optzed NEMO schees lke MIRON and HCoP-B. There are few researches entoned about supportng fast handover n NEMO. In (Zhong et al., 007), a fast NEMO (FNEMO) schee was proposed. When the handover of an MR s trggered, the MR sends an FBU to ts HA for settng up a tunnel wth the NAR by exchangng the handover ntate (HI) and handover acknowledge (HAck) essages. Hence, FNEMO elnates the round trp and extra encapsulaton of the PAR by drectly tunnelng the packet va the NAR to the MR. However, t has not entoned how to forward packets receved by the PAR to the NAR durng the handover for avodng packet losses. FAST HCOP-B ARCHITECTURE AND HANDOFF FLOWS As shown n Fgure 1(a), the HCoP-B handoff procedure begns wth layer channel scannng, authentcaton and assocaton, and follows wth layer 3 prefx delegaton, bndng update and eda strea resupton. Hence, all MNNs n the ovng oble network wll stop recevng ongong eda streas between te t,.e., the te when the L lnk down event of the old lnk occurs, and t6,.e., the te to resue recevng packets that are forwarded fro the NAR, whch wll thereby sgnfcantly degrade QoS of real-te servces. Hence, as shown n Fgure 1(b), our FHCoP-B wll overlap the L3 prefx delegaton, L authentcaton and assocaton procedures wth the odfed L3 bndng update,.e., the predctve bndng update (PBU), by the L lnk gong down event of the old lnk at te t1, whch s notfcaton of the nent handoff. Hence, the MNN can resue ts eda strea as early as possble after t4. In ths way, the handoff latency of FHCoP-B wll be reduced to the value of (t4-t), nstead of that of (t6-t) n orgnal HCoP-B. Fg. 1: Tng dagras of HCoP-B and FHCoP-B handoffs Fgure shows the network archtecture where FHCoP-B works. Because IEEE supports long-dstance transsson, t s adopted as the wreless lnk to provde connectvty between the top-level MR of the NEMO and ts assocated AR on Internet. Oppostely, short-range IEEE wreless lnks are used to connect nternal MRs and underlyng MNNs. Notatons used are lsted n Table 1.

5 Chang and Lu 595 Notatons l MR l HA, S H D tbc tcc tn tout l HR trs, tra t HMRA, t URI Allocaton tl tdad Tf B Dp r A / ( r 1) K Table 1: Notatons and Ther Descrptons Descrptons The th MR at the lth layer of the nested NEMO Hoe agent and hoe regstrar of l MR Internet dstance n hop count fro the source node S to the destnaton one D n the nested NEMO The processng te, whch value s 5s, for the node to update the bndng cache when recevng the BU. The processng te, whch value s 5s, for the MR to confgure ts new CoA. The propagaton delay, whch value s 10s/hop, between any two adjacent nodes n the nested NEMO. The propagaton delay, whch value s 10s/hop, between any two adjacent nodes n Internet. The propagaton delay, whch value s 10s/hop, to transt the RS, RA, HMRA or SIP URI allocaton essage between two adjacent MRs n the nested NEMO. Layer handoff latency, whch value s 0s (Mohanty and Akyldz, 007) latences of the duplcate address detecton (DAD), whch value s 1000s (La and Chu, 005) The one-way frae transportaton delay through a wreless lnk wth RLP (Mohanty and Akyldz, 007) The end-to-end packet transportaton delay between two nodes wth RLP The average one-way sgnalng packet transportaton delay usng UDP between two nodes wth RLP The ntal value of the retranssson ter usng UDP, whch value s 150s (Mohanty and Akyldz, 007) The factor by whch the retranssson ter teout duraton s ncreased after each faled retranssson, whch value s (Mohanty and Akyldz, 007) The axal nuber of faled retransssons to freeze the teout value of the retranssson ter, whch value s 10 (Mohanty and Akyldz, 007) The nuber of lnk layer fraes per packet; the frae sze s 19 bytes (Mohanty and Akyldz, 007).

6 596 Notatons n p c Pc Pw Pf q, j Statstcal perforance analyss of the predctve fast and sealess Descrptons The axu nuber of RLP trals to transt a frae over the lnk layer before abortng transsson, whch s 3 for RLP (Mohanty and Akyldz, 007). The lnk layer nterfrae nterval, whch s 0s (Mohanty and Akyldz, 007) The probablty that the frst frae transtted by the MNN s receved correctly by the BS, beng the th retranstted frae at the jth retranssson tral (Bao, 1996). Packet loss probabltes of the wred lnk, whch value s equal to (Mohanty and Akyldz, 007). Packet loss probablty n the wreless lnk, Frae error rate of the lnk layer. End-to-end packet loss probablty between two nodes wth RLP 1e 5 Dependng on whether the ovng oble subnet leaves ts orgnal MAP, there are two types of handoffs n FHCoP-B. Frst s the ntra-map handoff and the other the nter-map one. Because the flow of the nter-map handoff s ore coplex than that of the ntra-map one, we descrbe t below. The nter-map handoff occurs when the oble subnet leaves ts old NEMO, whch s anaged by the prevous MAP (), and arrves at the new NEMO under the new MAP (NMAP). Based on the L type of the egress lnk used by the HLMR before and after handoff, the Inter-MAP handoff can be further classfed nto four L handoff scenaros. 1. The whole NEMO, whch connects drectly to the PAR under the, perfors ts handoff as a new NEMO to the NAR that s anaged by the NMAP. Because both the old and new L lnks are ones, we call ths knd of handoff as the to one.. The whole NEMO, whch connects drectly to the PAR, perfors ts handoff to a new prevous MR (PMR) nsde the new NEMO under the NAR anaged by the NMAP. Because the old and new L lnks are and ones respectvely, we call ths knd of handoff as the to one. 3. The oble subnet nsde the old NEMO under the PAR hands over to the NAR, whch s anaged by the NMAP, as a new NEMO. Because the old and new L lnks are and ones respectvely, we call ths knd of handoff as the to one. 4. The oble subnet nsde the old NEMO under the PAR hands over to a new PMR nsde the new NEMO under the NAR anaged by the NMAP. Because both the old and new L lnks are ones, ths handoff s called as the to one. Fgure shows a general exaple of the to nter-map handoff. The jhlmr HLMR,.e., MR, of the oble subnet, whch s the th MR at the jhlmr th layer of the old nested NEMO under the PAR before the handoff, wll connect to an MR under

7 Chang and Lu 597 the NAR as MR lhlmr at the lhlmr th layer of the new nested NEMO under the NAR anaged by the NMAP after the handoff. In the followng, we wll descrbe the nter- MAP handoff flow of FHCoP-B. Due to space ltaton, please refer to (Lu, 009) for those of RRH, MIRON and HCoP-B. HA L HLMR ( L j HLMR HA l ) j HLMR HLMR HA ( HA l ) 1 HA 0 HA MAP H CN hops MAP H HA hops l H NMAP hops 0 MR 1 l HLMR MR1 ( lhlmr 0) L MR 1 l MR PPMR (PPMR) j MR HLMR ( HLMR) L MR JH ( L j HLMR 1) levels A oble subnet hands over to a new NEMO as a subnet at the l HLMR th layer 3 MR l HLMR MR ( lhlmr 3) l HLMR MR ( lhlmr 6) 6 MR Fg. : The to nter-map handoff FHCoP-B nter-map Handoff The proposed flow of FHCoP-B to nter-map handoff s shown n Fgure 3. In ths secton, the te spent for each FHCoP-B stage s calculated for the deal case that assues no error occurs when the packet passes through the wreless and wred lnks, whch s far fro realty. Hence, perforance evaluatons of all FHCoP-B stages wth RLP wll be presented n next secton. (a) Whenever the L of HLMR,.e., MR jhlmr at the jhlmr layer n the old NEMO, receves a new MOB_NBR-ADV essage fro the PMR s L (S-BS) and observes an nent L handoff accordng to ts handoff decson algorth, t wll ssue the NEW_LINK_DETECTED (NLD) essage, whch needs the te of t e, to trgger the FHCoP-B L3 handoff procedure. Then the L3 of

8 598 Statstcal perforance analyss of the predctve fast and sealess j MR HLMR perfors the RtSolPr/PrRtAdv procedure wth the to acqure AP- IDs and MR-Infos of the nearby NMAP wth the deal te of tn jhlmr 1 tout. After that, jhlmr MR follows the prefx delegaton process for confgurng prospectve CoAs of underlyng MRs and MNNs layer by L layer wth the axal te of ( thmra tcc ) ( L jhlmr 1) for MR at layer L. Then each MR and MNN executes the LBU/LBA procedure to create the jhlmr teporary LBC and VBC at MR wth the axal te of t L j 1 t. n HLMR bc (a) Prefx Delegaton Handoff Preparaton Latency (b) Predctve Bndng Update FHCoP-B (c) Handoff Layer Latency Handoff Latency VMN MR MR ) MR j HLMR PAR NLD HMRA LBU LBA L j l MR L L3 lhlmr ( L Create teporary BC LSW LUP L3 L (S-BS) MOB_NBR-ADV RtSolPr PrRtAdv LBU Retreve BUT fro LBA FBU (BC) Buffer forwarded packet FBAck Network Entry UNA L3 NAR L (T-BS) Acqure AP-ID and MR-Info j NMAP HA Reattach BUT to NMAP and LBU(BUT) DAD LBA HI (BC) Modfy BC of NMAP HAck Frst forwarded packet Buffer forwarded packet Last forwarded packet l HA L j l HA L HA CN Frst forwarded packet GBU to HA GBAck HoT CoT HoT CoT GBU to CN GBAck Orgnal packet Last forwarded packet Frst subsequent packet Buffer subsequent packet bufferng te NMAP bufferng te for forwarded packets (d) Meda Strea Resupton... Send frst forwarded packet to MNN Send last forwarded packet to MNN NMAP Bufferng te for subsequent packets Send subsequent packet to MNN FHCoP-B essage orgnal packet sgnal forwarded packet L event subsequent packet Fg. 3: The flow of FHCoP-B to nter-map handoff (b) For odfyng prospectve BUT of the NMAP at the sae te of delegatng jhlmr prefx n the oble subnet, MR sultaneously ssues an LBU essage to the for retrevng BUT nforaton of the oble subnet such that the

9 Chang and Lu 599 can then forward ths LBU wth those BUT nforaton ebedded to the NMAP. Hence, the NMAP can perfor the te-wastng DAD process wth the te of tdad by detectng unqueness of prospectve CoAs at the NMAP before the nter- MAP handoff actually occurs. Consequently, these overlapped procedures spend the deal te forulated as Equaton 1 for the FHCoP-B nter-map handoff. t j 1 t ( H 1) t t ( thmra tcc ) ( L jhlmr 1) tn L jhlmr 1 tbc, MAX n HLMR out NMAP but DAD jhlmr After that, MR perfors the FBU/FBAck process to the. The further starts bufferng all packets, whch are denoted as the frst, nteredate and last forwarded ones n Fgure 3, sent to MNNs n the oble subnet to avod packet losses durng handoff as t receves the FBU. It converts the FBU nto the HI essage and forwards t to the NMAP for creatng a tunnel to redrect packets between the and odfyng the bndng cache of the NMAP wth new entres of the oble subnet. After that, the HAck essage s frst sent back to the and jhlmr fnally reached MR wth the forat of the FBAck. At the te when the receves the HAck, whch eans the tunnel s ready, t wll forward ts buffered packets to the NMAP for bufferng the agan. Hence, the bufferng te,.e., the duraton that each forwarded packet has been buffered n the, s equal to t t H. The round trp te of FBU/HI/HAck/FBAck n ths case s bc out NMAP equal to tn jhlmr 1 tout ( H NMAP 1) tbc. On the other hand, after the NMAP fnshes the DAD process, t wll frst send GBU essages and then wat for global bndng acknowledgeent (GBAck) wth all HAs of MRs n the oble subnet for odfyng appngs of correspondng bndng entres nto the NMAP s address, accordng to the herarchcal anageent concept of HMIPv6. As proposed n HCoP-B, the NMAP s responsble to securely update locaton nforaton wth the CN on behalf of the MNN n the oble subnet. Therefore, t perfors the RR echans to verfy the CN by copletng the HoT/HoT process through ts HA and the CoT/CoT one wth the CN before t sends non-duplcated GBUs to update bndng nforaton of the CN for optzng routes of subsequent packets fro the CN to the NMAP, nstead of to the for forwarded packets before the CN receves the GBU. Hence, the axal te of the RR process and the round-trp te of the GBU/GBAck process for route optzaton are forulated as the value of NMAP HA l HLMR NMAP tout MAX H l HLMR HCN, H HA CN and NMAP tout HCN respectvely. Subsequent packets have to be cached n the NMAP for antanng correct packet orderng untl all precedng forwarded ones have been redrected fro the to the NMAP, whch starts when the receves the HAck as descrbed above. We denote the te to buffer subsequent packets n the NMAP as the NMAP bufferng te for subsequent packets, whch s equal to the dfference of the followng two perods and forulated as Equaton. The frst one conssts of four (1)

10 600 Statstcal perforance analyss of the predctve fast and sealess epochs for the last forwarded packet to travel fro the CN to the CN ( t H ), buffer n the ( t t H ), redrect to the NMAP ( t out out H NMAP bc out NMAP ) and buffer agan n the NMAP untl all precedng forwarded packets have been forwarded to the MNN,.e., the NMAP bufferng te for forwarded packets, whch wll be descrbed later. The second perod s the te for the frst subsequent packet to travel fro the CN to the NMAP, whch s equal to t out H CN NMAP. Hence, wth ths knd of predctve bndng update procedure,.e., part b n Fgure 3, executed before or durng the nent L handoff actually occurs, FHCoP-B can update bndng entres, reattach BUT nforaton, and perfor DAD, GBU and RR processes n the NMAP such that the handoff latency of FHCoP-B nter-map handoff s sgnfcantly reduced. Further, wth aforeentoned packet bufferng and forwardng echanss, packet dsorderng and losses durng handoff are avoded altogether. CN CN bc e L n HLMR HLMR out NMAP NMAP t t t t j l t (H H H ) () (c) Whenever the handoff decson algorth of L of MR jhlmr MR jhlmr decdes to start the handoff, wll notfy ts L3 of the LINK_SWITCH (LSW) essage wth the te of te to begn the network entry procedure wth the NAR s L,.e., T-BS, whch also needs the te of t L. As a result, the L handoff procedure ntroduces latency of te tl. lhlmr (d) As soon as the L handoff procedure of the HLMR,.e., MR at the l HLMR layer of the new NEMO after handoff, has copleted, the L wll ssue the LINK_UP essage to ts L3, whch spends the te of te and n turn lets the L3 send the unsolcted neghbor advertseent (UNA) essage through the NAR to the NMAP to fnsh the L3 handoff process wth the te of te tn lhlmr 1 tout. Hence, packets buffered n the NMAP wll be forwarded to each MNN to contnue the eda strea va NAR, all upper MRs of the MNN n the new NEMO, whch wll ntroduce the latency of L jhlmr lhlmr tn ( L jhlmr lhlmr ) tout for the MNN under the deepest MR n the oble subnet after handoff. As a result, the total te for contnung the eda t L j l 3 + t t. Wth ths approach, strea s equal to n HLMR HLMR each forwarded packet has to be buffered n the NMAP wth the NMAP bufferng te for forwarded packets, whch s calculated as follows. Frst, the perod fro when the receves the HAck untl when the NMAP receves the UNA s t j l t t t. Second, the perod for equal to n HLMR HLMR e L out packets to be forwarded fro the to NMAP s tout H NMAP. Hence, the NMAP bufferng te for forwarded packets s equal to the dfference of these two perods, as shown wth Equaton 3. t j l t t t ( H ) (3) n HLMR HLMR e L out NMAP e out

11 Chang and Lu 601 L jhlmr lhlmr Ideal Handoff Latency: At the worst case, the deepest MNN under MR stops recevng packets durng the perod fro the te when the last packet followng the orgnal path s receved to that when the frst forwarded packet has arrved at ths MNN. Hence, the deal nter-map handoff latency of FHCoP-B can be forulated as Equaton 4, whch s the dfference of the followng two perods. One s the perod fro the te when the receves the last orgnal packet and the FBU before handoff to that when the frst forwarded packet arrves at the MNN; the other s the perod to convey the last orgnal packet fro the to the MNN. t t t t H 3 t j l 4 (4) e L bc out NMAP n HLMR HLMR Ideal Total Bufferng Te: The deal total bufferng te for ths handoff scenaro s the su of these three bufferng tes,.e., that of, that of NMAP for forwarded packets and that of NMAP for subsequent packets, whch s forulated as Equaton 5. t 4t t t j l bc e L n HLMR HLMR CN CN t ( H H H 4) (5) out NMAP NMAP Ideal Packet Loss Te: because all packets durng handoff are buffered by the and NMAP, there s no packet loss for the nter-map handoff of FHCoP-B. Ideal Total Handoff Cost: Though FHCoP-B spends the handoff latency forulated by Equaton 4 to resue recevng packets fro the CN, t has no packet losses durng the handoff due to ts packet bufferng and forwardng echanss n the and NMAP wth the cost of total bufferng tes forulated by Equaton 5, as entoned above. Conversely, wthout any bufferng echans, RRH, MIRON and HCoP-B all suffer packet losses for the duraton equal to ther handoff latences. Hence, we defne the total handoff cost (n the unt of te) for each schee as the su of ts packet loss te and total bufferng te n ths paper to express the cost to handle the nter-map handoff, whch s equal to the value calculated by Equaton 5 for FHCoP-B. PERFORMANCE EVALUATIONS WITH RLP In the followng, we analyze real handoff latences and total buffer szes for storng real-te VOIP essages ssued by the CN durng handoff for FHCoP-B wth RLP. Due to the space ltaton of ths paper, please also refer to (Lu, 009) for atheatcal analyses of RRH, MIRON and HCoP-B. The handoff latency s defned as the te requred for the deepest MNN to resue packet transssons of VOIP sessons when the handoff occurs. In ths paper, we extend the analytcal odel, whch contans only one wreless lnk connectng the MN and the BS, for MIP n (Mohanty and Akyldz, 007) to that for FHCoP-B, whose councaton path between the CN n the Internet and the L MNN attached to the deepest MR n the nested oble network conssts of (L+) wreless lnks between ths MNN and PAR n Fgure, and W wred lnks between PAR and the CN. Then the end-to-end packet loss probablty P between the CN and ths MNN before handoff s forulated by Equaton 6, where Pw and Pc denote packet loss probabltes of a wreless lnk and a wred lnk, respectvely.

12 60 Statstcal perforance analyss of the predctve fast and sealess L W P 1 1 P 1 P (6) w c Consder RLP s used for error recovery n the lnk layer. The packet loss probablty n a sngle wreless lnk, P w, s gven n (Mohanty and Akyldz, 007) and s forulated as Equaton 7, where Pf s the frae error rate of the lnk layer, K s the nuber of lnk layer fraes per packet and n s the axu nuber of RLP trals to transt a frae over the lnk layer before abortng transsson. Hence, the end-to-end packet loss probablty q wth RLP between two nodes, whch conssts of W wreless lnks and W wred lnks, n NEMO s forulated by Equaton 8. P 1 1 p p p w n n f f f / K (7) / q 1 1 p f p f p f (1 pc ) n n KW Accordng to (Mohanty and Akyldz, 007), the one-way frae transportaton delay, T f, through a wreless lnk wth RLP s forulated by Equaton 9, where t n s the propagaton delay through a wreless lnk and s the lnk layer nterfrae nterval. Further, p c, j W, whch s gven by (Bao, 1996) and forulated by Equaton 10, denotes the probablty that the frst frae transtted by the sendng node s receved correctly by the recevng node, beng the th retranstted frae at the jth retranssson tral for =1,,, n and j=1,,,. n 1, 1 (9) T t p p c t j f n f j n 1 j1, 1 j f f f f j 1 p c p p p p (10) Thus, passng through W wreless lnks and W wred lnks between two nodes n NEMO wth RLP, the end-to-end packet transportaton delay, B, s forulated by Equaton 11, where ( K 1) s the total nterfrae nterval over a wreless lnk. B W T K 1 W t (11) f out Because FHCoP-B sgnalng essages are transported by UDP, the average one-way sgnalng packet transportaton delay, D, usng UDP between two nodes through W p wreless lnks and W wred lnks s forulated by Equaton 1 (Mohanty and Akyldz, 007), where r s the factor by whch the retranssson ter teout duraton s ncreased after each faled retranssson, s the ntal value of the retranssson ter, denotes the axal nuber of faled retransssons to freeze the teout (8)

13 Chang and Lu 603 value of the retranssson ter, and A s / ( r 1), respectvely. Values of these paraeters are lsted n Table 1. Dp q B A q r q A r r (1) 4.1 Handoff Latency of FHCoP-B wth RLP As descrbed n Secton 3, the nter-map handoff latency of FHCoP-B s the dfference of the followng two perods. One s the perod fro the te when the receves the last orgnal packet and the FBU before handoff to that when the frst forwarded packet arrves at the MNN after handoff; the other s the perod to convey the last orgnal packet fro the to the MNN before handoff. The frst perod can be further dvded nto four stages. Frst, as the receves the FBU, t converts the FBU nto the HI essage and forwards t to the NMAP through H NMAP wred lnks on Internet for creatng a tunnel to redrect packets between the and odfyng the bndng cache of the NMAP wth new entres of the oble subnet. After that, the HAck essage s sent back to the along the sae H wred lnks but n reverse drecton of NMAP HLMR L j 1 HI. The essage lengths of HI and HAck, whch contans CoAs of all MRs n L jhlmr 1 the oble subnet, are equal to (56+16* ) bytes. Hence, the one-way duraton for the HI/HAck stage can be forulated by Equaton 13. Second, the converts the HLMR HAck to the FBAck, whch s 88bytes, and forwards t to MR j through ( jhlmr 1) wreless lnks wth the duraton calculated by Equaton 17. Thrd, after the L handoff lhlmr procedure of MR at the l HLMR layer of the new NEMO after handoff has copleted, the L ssues the LINK_UP essage to ts L3, whch then sends the 40-byte UNA essage through the NAR to the NMAP va ( lhlmr 1) wreless lnks and one wred lnk to fnsh the L3 handoff process, whch duraton s calculated by Equaton 18. Fnally, as the NMAP receves the UNA, packets buffered n the NMAP wll be forwarded to each MNN to contnue the VOIP eda strea va NAR, all upper MRs of the MNN n the L jhlmr lhlmr new NEMO. Hence, the latency for the MNN under the deepest MR n the oble subnet after handoff to receve the frst forwarded VoIP packet, whch s 93 bytes (.e., the su of 40 bytes of IPv6 header, 8 bytes of UDP header and 45 bytes of RTP essage), through L jhlmr lhlmr wreless lnks and one wred lnk s forulated by Equaton 19. On the other hand, the second perod spends the te to convey the last orgnal 93-byte VoIP packet fro the to the MNN through L wreless lnks and one wred lnk before handoff so that the duraton of the second perod s expressed by Equaton 16. Consequently, the handoff latency of FHCoP-B wth RLP s equal to t t t (13) (16) (17) (18) (19) and forulated as Equaton 0. e L bc q 13 B13 Aq13 r 1 q 13 A r 1 r (13) where 1 H NMAP q p c, B13 H NMAP T out

14 604 Statstcal perforance analyss of the predctve fast and sealess q 14 B14 Aq14 r 1 q 14 A r 1 r (14) where 1 CN H CN q p c, B14 H T out q 15 B15 Aq15 r 1 q 15 A r 1 r (15) where where where where 1 CN H NMAP CN q p c, B15 H NMAP T out q 16 B16 Aq16 r 1 q 16 A r 1 r (16) 1 n n / K ( L) q p p p 1 p B16 L Tf K 1 tout f f f c q 17 B17 Aq17 r 1 q 17 A r 1 r (17) 1 n n / K ( jhlmr 1) q p p p 1 p B17 ( jhlmr 1) Tf K 1 tout f f f c q 18 B18 Aq18 r 1 q 18 A r 1 r (18) 1 n n / K ( lhlmr 1) q p p p 1 p B18 ( lhlmr 1) Tf K 1 tout f f f c,,, where q 19 B19 Aq19 r 1 q 19 A r 1 r (19) 1

15 Chang and Lu 605 K ( L jhlmr lhlmr ) q p p p 1 p B19 L jhlmr lhlmr Tf K 1 tout n n / f f f c, t t t (13) (16) (17) (18) (19) e L bc t t t e L bc q13 B13 Aq13 r 1 q 13 Ar 1 r q16 B16 Aq16 r 1 q 16 Ar 1 r qx Bx A qx r 1 q x Ar 1 r x17,18,19 1 (0) 4. Bufferng Tes of FHCoP-B wth RLP bufferng te: As entoned n Secton 3, the bufferng te,.e., the duraton that each forwarded packet has to be buffered n the, s equal to the te to update the bndng cache,.e., t bc, added by the round trp te of HI/HAck between the and NMAP, whch s equal to (13). Hence, the bufferng te of FHCoP-B wth RLP s expressed by Equaton 1. t bc (13) tbc 1q13 B13 Aq13 r 1 q 13 Ar 1 r 1 (1) NMAP bufferng te for forwarded packets: The NMAP bufferng te for forwarded packets s equal to the dfference of the followng two perods. The frst perod s fro the te when the receves the HAck untl when the NMAP receves the UNA, whch s equal to the su of te tl, the duraton for transttng the FBAck, whch s calculated by Equaton 17, and that for conveyng the UNA essage, whch s calculated by Equaton 18. The second perod s spent for packets to be forwarded fro the to NMAP, whch s expressed by Equaton 13. Hence, the NMAP bufferng te for forwarded packets of FHCoP-B wth RLP s expressed by Equaton.

16 606 Statstcal perforance analyss of the predctve fast and sealess t t (17) (18) (13) e L t t e L q13 B13 Aq13 r 1 q 13 Ar 1 r qx Bx Aqx r 1 q x Ar 1 r x17,18 1 () NMAP bufferng te for subsequent packets: The NMAP bufferng te for subsequent packets s equal to the dfference of the followng two perods, as entoned above. The frst one conssts of four epochs for the last forwarded packet to travel fro the CN to the wth the te forulated by Equaton 14, to be buffered n the wth the bufferng te, to redrect fro the to the NMAP wth the te forulated by Equaton 13 and to be buffered agan n the NMAP wth the NMAP bufferng te for forwarded packets. The second perod s the te for the frst subsequent packet to travel fro the CN to the NMAP, whch s forulated by Equaton 15. Consequently, the NMAP bufferng te for subsequent packets s equal to Equaton 3. (13) (14) bufferng te + NMAP bufferng te for forwarded packets (15) (3) Total bufferng te: As entoned above, the total bufferng te for the nter-map handoff scenaro s the su of three bufferng tes,.e., that of, that of NMAP for forwarded packets and that of NMAP for subsequent packets, whch s expressed as Equaton 4. bufferng te + NMAP bufferng te for forwarded packets NMAP bufferng te for subsequent packets = bufferng te + NMAP bufferng te for forwarded packets (13) (14) bufferng te + NMAP bufferng te for forwarded packets (15) ( bufferng te + NMAP bufferng te for forwarded packets) (13) (14) (15)

17 Chang and Lu 607 t (13) t t (13) (17) (18) (13) (14) (15) bc e L t 4t t 3 (13) (14) (17) (18) (15) bc e L t 4t t bc e L q13 B13 Aq13 r 1 q 13 Ar 1 r q14 B14 A q14 r 1 q 14 Ar 1 r q15 B15 Aq15 r 1 q 15 Ar 1 r x17, qx Bx A qx r 1 (4) 1 1 q x A r r Total Handoff Cost of FHCoP-B wth RLP Because the total handoff cost (n the unt of te) for each schee s defned as the su of ts packet loss te and total bufferng te, t can be calculated by Equaton 4 for FHCoP-B wth RLP. PERFORMANCE COMPARISONS In the followng, we present average handoff latences, total bufferng tes and total handoff costs for four NEMO schees,.e., RRH, MIRON, HCoP-B and FHCoP-B by applyng aforeentoned equatons for nuercal results wth RLP two hundred tes. As shown n Fgure for the topology of the nested NEMO, hop counts between any two nodes, except the and NMAP, n Internet are assued to be unforly dstrbuted aong 1 to 30 hops but that between the and NMAP s aong 1 to 10 hops. j MR HLMR at the jhlmr th layer and ts underlyng oble subnet n the old NEMO wll perfor an nter-map handoff to the l HLMR th layer of the new NEMO. Default values of L, jhlmr and Pf are set as 6, 3 and 0.1, respectvely. We use three dfferent values,.e., 0, 3 and 6, of l HLMR, to observe nfluences of dfferent nter-map handoff destnatons on these three perforance etrcs. 5.1 Handoff Latences wth RLP We llustrate average values of the handoff latency for these four schees n Fgure 4. Frst, nter-map handoff latences of MIRON, RRH and HCoP-B wth RLP decrease as the value of jhlmr rases, whch s because the nuber of layers,.e., L j l, for control packets and VoIP essages to pass n the new NEMO HLMR HLMR decreases accordngly, as shown n Fgure 4. RRH wth RLP suffers hgher handoff latences than MIRON wth RLP because t appends the extra routng header wth (16* ( L j l 1) ) bytes nto each GBU and VoIP packet to the deepest MNN HLMR HLMR

18 608 Statstcal perforance analyss of the predctve fast and sealess for recordng CoAs of all parent ( L jhlmr lhlmr 1) MRs n the new NEMO, whch therefore enlarges ts GBU and VoIP packet length and ther correspondng nubers,.e., K, of wreless fraes. However, GBU and VoIP packet length of MIRON are 88 bytes and 93 bytes respectvely, whch are fxed no atter the value of jhlmr s. Please note that the decreasng rate of HCoP-B handoff latency s sgnfcant when applyng RLP. L jhlmr 1 The reason of ths s due to the packet sze,.e., (1+16* ) bytes, of ts LBU, L jhlmr 1 whch contans CoAs of all MRs n the oble subnet and s conveyed fro the l MR HLMR to the NMAP, s decreased exponentally. Hence, no atter the value of l HLMR s, HCoP-B wth RLP acheves saller handoff latences than MIRON and RRH wth RLP do as jhlmr 3. Conversely, because HCoP-B has to perfor ts L3 prefx delegaton, DAD and bndng update processes after ts L handoff, handoff latences of t wth RLP are uch larger than those of FHCoP-B wth RLP that executes ts L3 and DAD processes trggered by L events before the old lnk breaks, whch behaves the sae as they are n the deal case. On the other hand, as the value of P grows fro 0 to 0., the end-to-end packet loss probablty q, the end-to-end packet transportaton delay B, the average one-way sgnalng packet transportaton delay, D p, usng UDP grow slghtly. Hence, handoff latences of all four schees wth RLP rase accordngly. f l HLMR =0 l HLMR =3 l HLMR =6 Fg. 4: Coparsons of nter-map handoff latency ( l HLMR = 0, 3 and 6) 5. Total Bufferng Tes wth RLP As shown n Fgure 5, because no packet bufferng echanss are proposed for MIRON, RRH and HCoP-B, all ther total bufferng tes are equal to zero. Conversely, the total bufferng te of FHCoP-B wth RLP for the nter-map handoff s the su of

19 Chang and Lu 609 bufferng tes of the, the NMAP for forwarded packets and the NMAP for subsequent packets. Therefore, ts value grows as values of lhlmr or jhlmr rase, accordng to Equaton 17 or 18, whch s a coponent of Equaton 4 respectvely. Slar to the trend of handoff latences entoned above, as the value of P grows fro 0 to 0., total bufferng tes of all four schees wth RLP grow slghtly. f l HLMR =0 l HLMR =3 l HLMR =6 Fg. 5: Coparsons of nter-map total bufferng te ( l HLMR = 0, 3 and 6) 5.3 Packet Loss Tes and Total Handoff Costs wth RLP As entoned above, because all forwarded and subsequent packets durng handoff are buffered by the and NMAP, the packet loss te for the nter-map handoff of FHCoP-B wth RLP s zero. Oppostely, wth MIRON, RRH and HCoP-B, those packets ssued fro the CN durng nter-map handoff are copletely lost because these three schees have no packet bufferng and forwardng echanss at all. Hence, values of ther packet loss tes are equal to those of ther handoff latences, whch decrease as the value of jhlmr rases, as shown n Fgure 6. Furtherore, FHCoP-B wth RLP acheves the lowest total handoff cost (n the unt of te) aong all four schees because t executes the proposed predctve bndng update process to avod packet losses wth lttle extra total buffers.

20 610 Statstcal perforance analyss of the predctve fast and sealess l HLMR =0 l HLMR =3 l HLMR =6 Fg. 6: Coparsons of nter-map packet loss te ( l HLMR = 0, 3 and 6) l HLMR =0 l HLMR =3 l HLMR =6 Fg. 7: Coparsons of nter-map total handoff cost ( l HLMR = 0, 3 and 6)

21 Chang and Lu 611 CONCLUSION In ths paper, we have proposed an effcent FHCoP-B schee to support fast and sealess handoff for the nested NEMO. We have also derved atheatcal equatons to denote perforance etrcs of FHCoP-B wth RLP over error-prone wreless lnks. As copared to HCoP-B and two tradtonal NEMO schees,.e., RRH and MIRON, FHCoP-B acheves the lowest handoff latences, the sallest nubers of packet losses and the least total handoff costs wth lttle extra buffers when a oble subnet hands over to a new NEMO. In the future, we wll further propose the reactve FHCoP-B process to handle stuatons such as fast or erroneous oveents for the nter-map handoff of the oble subnet. ACKNOWLEDGMENTS Ths work was supported by Natonal Scence Councl (NCS), Tawan, under Grant Nuber NSC98-1-E REFERENCES 1. Bao, G. (1996). Perforance evaluaton of TCP/RLP protocol stack over CDMA wreless lnks. ACM WINET, 3, Calderón M., et al. (006). Desgn and experental evaluaton of a route optzaton soluton for NEMO. IEEE Journal on Selected Areas n Councatons, 4(9), Chang, I.C. and Chou, C.H. (009). HCoP-B: a herarchcal care-of prefx wth BUT schee for nested oble networks. IEEE Trans. on Vehcular Technology, 58(6), Devarapall, V. and Wakkawa, R (005). NEMO basc support protocol. IETF RFC Dopoulou, L., Leoles, G. and Veners, I.O. (005). Fast handover support n a WLAN envronent: challenges and perspectves. IEEE Network, 19(3), Jang, H., et al. (008). Moble IPv6 fast handovers over IEEE e networks. IETF RFC Johnson, D., Perkns, C. and Arkko, J. (003). Moblty support n IPv6. IETF RFC Koodl, R. and Perkns, C.E. (007). Moble nter-networkng wth IPv6: concepts, prncples, and practces. Hoboken, New Jersey, John Wley & Sons. 9. Koodl, R., et al. (008). Moble IPv6 fast handover. IETF RFC Lach, H.Y., Janneteau, C. and Petrescu, A. (003). Network oblty n beyond-3g systes. IEEE Councatons Magazne, 41(7), La, W.K. and Chu, J.C. (005). Iprovng handoff perforance n wreless overlay networks by swtchng between two-layer IPv6 and one-layer IPv6 addressng. IEEE Journal on Selected Areas n Councatons, 3(11), L, R., et al. (008). An enhanced fast handover wth low latency for Moble IPv6. IEEE Transactons on Wreless Councatons, 7(1),

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