performance to the performance they can experience when they use the services from a xed location.

Transcription

1 I the Proceedigs of The First Aual Iteratioal Coferece o Mobile Computig ad Networkig (MobiCom 9) November -, 99, Berkeley, Califoria USA Performace Compariso of Mobile Support Strategies Rieko Kadobayashi ATR Media Itegratio & Commuicatios Research Laboratories Seika-cho, Soraku-gu, Kyoto 9-, Japa rieko@mic.atr.co.jp Masahiko Tsukamoto Dept. of Iformatio Systems Egieerig Faculty of Egieerig, Osaka Uiversity Yamadaoka, Suita, Osaka, Japa tuka@ise.eg.osaka-u.ac.jp Abstract This paper presets performace compariso amog ve strategies for mobile support. The major facilities that are required for a etwork protocol to support mobile hosts are locatio maagemet ad packet forwardig. Based o this observatio, we cosider ve basic strategies which use distict methods to achieve these facilities ad compare their performace. These ve strategies are Broadcast Noticatio (), Broadcast Forwardig (), Broadcast Query (), Default Forwardig (), ad Default Query (). As a result of aalytical evaluatio ad compariso, it is show that uder dieret etwork coditios, such as umber of routers, etwork topology, migratio/commuicatio ratio, data/cotrol packet size ratio, dieret strategies produce miimum etwork trac. I short, ad show the best performace i scalability, while ad are eciet for frequet migratio. O the other had, is suitable for a small etwork which has hosts with rare migratio. Itroductio I order to realize mobile commuicatio i computer etworks, two kids of trasparecy are required: operatioal trasparecy ad performace trasparecy []. The operatioal trasparecy meas that mobile users ca cotiuously access to etwork services without beig forced to operate ay additioal procedures durig or after their migratio. The performace trasparecy, o the other had, meas that mobile users ca use the etwork services with similar performace to the performace they ca experiece whe they use the services from a xed locatio. Focusig o the operatioal trasparecy, a umber of mobile host protocols have bee proposed [], [], [], [], [], [9], [], [], whereas performace trasparecy has ot yet bee fully discussed. Performace trasparecy ca be achieved through eciet use of etwork resources such as etwork badwidth. Notice that there are two basic fuctios that are essetial to mobility support: locatio maagemet ad packet forwardig. The eciet use of etwork badwidth is sigicatly aected by these fuctios, sice cotrol packet to exchage the locatio iformatio ad data packet routed via ooptimal path produce large trac. Hece, performace evaluatio ca be ivestigated through the observatio o the etwork trac produced by these two fuctios. We ca cosider several distict strategies based o how to implemet these fuctios. For example, oe possible solutio for locatio maagemet is that the router seds a oticatio packet to all other routers whe the router detects a ew mobile host. Aother possible solutio is that the router seds the packet to a particular router isted of all routers. Cosequetly, wehave ve basic strategies for mobile support: Broadcast Noticatio (), Broadcast Forwardig (), Broadcast Query (), Default Forwardig () ad Default Query (). Although the existig proposals have dierece i details, they ca be categorized ito these basic strategies. Ulike the approach i [] which compares mobile host protocols directly, we compare these basic strategies. Therefore, the fudametal characteristics cocerig the performace ca be observed more clearly. As a result of aalytical evaluatio ad compariso, it is show that uder dieret etwork coditios, such as umber of routers, etwork topology,, data/cotrol packet size ratio, dieret strategies produce miimum et-

2 H H H H R R H move R R H H H move router host Figure : Example of etwork coguratio. work trac. I short, ad show thebest performace i scalability, while ad are ef- ciet for frequet migratio. O the other had, is suitable for a small etwork which has hosts with rare migratio. I sectio, the etwork model ad the ve strategies are briey described. I sectio, we rst aalyze the trac of each strategy, ad the compare them usig two example etwork topologies. We also discuss the performace compariso i geeral topology etworks. Fially, we coclude the paper ad state future work i sectio. Mobile Support Strategies Cosider a simple etwork model as show i Figure. Routers are coected to each other via wired liks. They may have wireless iterface as well as wired iterface. I this model, all hosts ca potetially be mobile hosts, because they ca move freely from oe subetwork to aother. For example, host H ca move to the subetwork o which router R resides, ad ito the wireless cell of router R if it has a wireless iterface. A mobile host is served by at least oe router which hadles the data packets from/to the mobile host. We refer the router as curret router. I some cases, there is aother router which has dieret role for servig the mobile host. We refer the router as default router, which is resposible for advertisig the locatio of the mobile host. Note that this locatio is ot always the curret locatio. The default router may advertise the xed locatio which will ot chage despite the migratio. Of course, i some cases, oe router acts as both default router ad curret router. The curret router may choose to sed a oticatio packet to all routers, the default router or eve o router, whe it detects a ew mobile host. The oticatio packet icludes the ew locatio iformatio of the mobile host. I the latter two cases, o receivig a data packet destied to the mobile host, the router must select the way of forwardig packets. Oe way is that the router forwards the packet to the default router, ad the alterative is that the router seds a query packet to the default router so that it ca get the curret locatio to be used for forwardig. Cosequetly, we have ve basic strategies as described below:. Broadcast Noticatio () I a lik state routig protocol like IS-IS protocol [], wheever a router detects a ew mobile host, it becomes the default router ad broadcasts a oticatio packet, which icludes the curret locatio of the the mobile host, to all the other routers i the same etwork. I this case, the default router is also the curret router at the same time. The previous default router also broadcasts a oticatio packet to all the other routers to let them kow that it is o loger the default router. Sice a router lears a ew locatio wheever a host moves, it ca forward data packets to the curret locatio usig the optimal path.. Default Forwardig () I, havig detected a ew mobile host, a router becomes the curret router ad seds a oticatio packet oly to the default router, which will be ackowledged with a cormatio packet from the default router. If a router receives a data packet to the mobile host, it forwards the packet to the default router, sice the default router always advertises the xed locatio of the mobile host. The data packets are the forwarded by the default router to the curret router.. Default Query () There is similarity betwee ad cocerig the way of migratio oticatio, though there is a little dierece i the way of forwardig packets. Sice the curret router seds a oticatio packet oly to the default router, a router receivig a data packet eeds to get the curret locatio before it forwards the packet. This is doe by sedig a query packet to the default router. After that the router forwards the packet usig the same optimal path as used i.. Broadcast Query () We have already discussed the cases i which the curret router seds a oticatio packet to either all routers or the default router whe a mobile host moves. We the cosider how a router 9

3 Table : Strategies used i mobile support protocols. Mobile Broadcast Broadcast Broadcast Default Default Protocols Noticatio Forwardig Query Forwardig Query Carlberg [] [ Ioaidis et al. [] [ IS-IS protocol [] [ Mobile IP [] [ Perkis ad Bhagwat [] [ Taaka ad Tsukamoto [], [] [ [ Teraoka et al. [9] [ Wada et al. [] [ ca forward a data packet whe it does ot kow either the curret locatio or the default router of the mobile host. I such case, oe choice the router ca select is to ask all routers where the mobile host is. It broadcasts a query packet to all routers ad waits a respose from the curret router. After learig the curret locatio of the mobile host, the router forwards the data packet.. Broadcast Forwardig () The alterative way is to forward the data packet to all routers istead of sedig a query packet. The curret router itercepts the packet ad passes it to the mobile host, while the other routers merely discard it. Table shows which strategy is used i the existig proposals. Almost all protocols use oly oe strategy, while our proposals use two strategies. They discuss the improvemet i performace by usig two strategies i a hybrid way []. Although is ot used i these protocols, it has bee widely used i packet radio etworks to support commuicatio betwee hosts whose locatios are ot kow beforehad []. To our kowledge, is ot used i mobile support protocols. Performace Evaluatio. Trac Aalysis Amog may factors that aect performace trasparecy, we use etwork trac as performace measure. The trac produced by each strategy ca be calculated by packet size hop cout. We dee several parameters relevat to the etwork coguratio: N : Total umber of routers. L : Total umber of liks amog routers. H : Average distace betwee routers, i umbers of hops. Note that H icludes the distace betwee a give router ad itself, which is equal to zero. d : Average size of data packets. c : Average size of cotrol packets. : Commuicatio ratio. This is a umber of messages a mobile host receives per secod. : Migratio ratio. This is a umber ofmi- gratio per secod. First, we aalyze the trac per migratio of oe mobile host. The trac of is Lc sice the default router ad the previous default router idividually broadcast a oticatio packet to all routers i the same etwork whe a mobile host moves. We assume that uses the oodig method as deed i IS-IS protocol to broadcast the oticatio packets. I the oodig method the cotrol packets are trasmitted oce o every lik. The trac of ad that of are sice oticatio packets are ot used. I ad, the trac costs Hc because the cotrol packets are exchaged betwee the curret router ad the default router for oticatio ad ackowledgmet. We the aalyze the trac per commuicatio. For simplicity, we ca omit the trac betwee a sedig host ad its curret router ad betwee a receivig host ad its curret router sice the trac is the same i every strategy. I, the data packet ca be forwarded alog the optimal path, hece the trac is Hd. The trac of costs Hd, which is as twice as that of sice the data packet is forwarded to the curret router via the default router. I, the data packet is forwarded to all routers ad the the trac is NHd. To query the locatio of the mobile host,

4 Table : Trac aalysis for ve strategies. per commuicatio Hd NHd (N + )Hc + Hd Hd Hc + Hd per migratio Lc Hc Hc total trac Hd+Lc NHd (N +)Hc + Hd Hd +Hc Hc+ Hd+Hc Table : Trac compariso i grid topology. strategy trac (a) Figure : Network topologies: (a) grid topology ( = ); (b) depth biary tree topology ( =). ad eed (N +)Hc ad Hc, respectively. I additio to the cotrol trac, they eed Hd to forward the data packet. We assume that i ad broadcast is achieved by uicast to all destiatio. These aalytic results are summarized i Table. (b). Compariso i Grid Topology Based o the fudametal aalysis discussed above, we the compare the trac usig two examples of etwork topology. First, we cosider a grid topology as show i Figure (a). Assume that a mobile host ca move to ay of the routers. Here, we have N = ; L =( ); ( )( +) H =. Let k be = ad l be d=c. We assume l = for simplicity. The total trac of each strategy is the give i Table. The trac of ad that of icrease as O(), while the trac of ad that of icrease as O( ). I other words, ad have scalability, whereas ad show the worst performace regardig scalability. O the other had, sice ad are idepedet of k, they are eciet for frequet migratio. Figure shows the graphical results. The performace dierece amog strategies is well represeted ( )(k + +) ( )( +) ( )( + )( +) (k + )( )( +) (k +)( )( +) O( ) O( ) O( ) O() O() i this gure. I additio to the above observatio, we ca see from this gure that is applicable to oly such a etwork i which a host rarely moves.. Compariso i Biary Tree Topology Let us cosider aother example, depth biary tree topology as show i Figure (b). Assume that mobile hosts ca move to oly those routers which are leaves of the topology. Here, we have N = ; L = ; H = +( ). We assume l = to simplify the compariso, ad the the total trac of each strategy is give as show i Table. From this table, we obtai the similar results as i the case of grid topology. That is, ad are much better tha the rest i terms of scalability, while ad are eciet for frequet migratio. We also show the illustrative results i Figure. The same tred as i the gird topology ca be see i this gure. Hece, we ca say that the fudametal

5 , ad Figure : Compariso of total trac i a grid topology etwork: deotes the umber of routers o the edge , ad Figure : Compariso of total trac i a biary tree topology etwork: deotes the depth of the tree.

6 Table : Trac compariso i biary tree topology. strategy trac + k (k +)+ + O( ) ( ) + O( ) ( ) + + O( ) (k + )( + ) O() (k +)( + ) O() (a) Figure : Network topologies represetig the cases where H ad L are miimum or maximum: (a) liear; (b) complete graph. characteristics of each strategy are idepedet of the etwork topology.. Compariso i Geeral Topology Network To ascertai that whether the performace characteristics obtaied via previous compariso is true i ay etwork or ot, we eed further examiatio. Now we compare ve strategies without assumptio o etwork topology ad the data/cotrol packet size ratio. For that purpose, we dee a ew parameter, p, ad let p be L=H. Clearly p will chage as etwork topology chages. Usig p, we have ew formulas for total trac as show i Table. From this table, we ca see that selectio of a strategy depeds o the parameters available. depeds o p, i.e., the etwork topology, however the others do ot. ad deped o the umber of routers, however they are idepedet of k, i.e., the migratio/commuicatio ratio. ad deped k like, though they are idepedet of p. (b) I order to grasp the dierece amog strategies, it will be greatly helpful to show these formulas graphically as a fuctio of k ad l at dieret N. Ulike the graphs show i Figure ad Figure, we will show the performace of ve strategies i oe graph from aother poit of view. I short, the graph shows the optimal strategy regardig k ad l. The boudary betwee ad is determied by k which varies accordig to p, hece we start from examiig the rage of p. Sice p ca be calculated for give H ad L, we must cosider the case where H ad L show the smallest/largest value whe the give umber of routers are equal. Figure depicts such cases: liear topology ad complete graph topology. L is the miimum ad H is the maximum i the liear topology, where L = N, (N )(N +) H =, N hece the miimum value of p is N N +. L is the maximum ad H is the miimum, o the other had, i the complete graph topology, where N(N ) L =, H = N N, hece the maximum value of p is N. As a result, k is miimum i complete graph topology ad the value is N, while k is maximum i liear topology ad the value is N + N. Figure shows the regio of which strategy is optimal regardig give k, l ad N i the complete graph topology. Similarly, Figure shows the optimal strategy i the liear topology. Note that the other topologies except the lier topology ad the complete graph topology exist betwee these two extreme cases. It is easily see from these gures that the same tred as i the grid topology ad the biary tree topology exists i geeral. That is, ad are eciet for frequet migratio, whereas is suitable for the opposite case. ad have scalability ad wide applicability. Additioally, we ca see that ad gai advatage as the umber of liks icreases as compared with. It meas ad ca be used i a dese etwork by which we mea the multi-liked topology etwork.

7 Table : Trac compariso cosiderig etwork topology ad data/cotrol packet size ratio. total trac /Hc pk + l Nl l + N + k +l k + l + umber of routers = umber of routers = umber of routers = data/cotrol packet ratio Figure : Regio of the optimal strategy for give k ad l whe p is maximum. umber of routers = umber of routers = umber of routers = data/cotrol packet ratio Figure : Regio of the optimal strategy for give k ad l whe p is miimum.

8 Coclusio For each of the mobile support strategies, we have aalyzed the trac per migratio ad per commuicatio, ad thus the total trac. We have rst discussed their performace i two typical etwork topologies: grid topology ad biary tree topology. From these basic compariso, the fudametal characteristics of each strategy have become clear. is useful for small ad rare migratio etwork. ad are suitable if the migratio ratio is relatively high i small etworks. ad have advatage of scalability ad are applicable for the etworks i which the migratio ratio is ot so high. I additio, we have discussed the performace dierece amog the ve strategies i geeral etworks. As a result of compariso from wide variety of viewpoit, we have show that uder dieret etwork coditios, such as umber of routers, etwork topology,, data/cotrol packet size ratio, dieret strategy produces miimum etwork trac. This result leads us to a ew idea that the best performace is obtaied if the strategies are chaged dyamically accordig to the etwork coditio. As metioed i sectio, there are few proposals usig two or more strategies, however we should further study about this issue i order to provide mobile users with real performace trasparecy. Ackowledgemet The authors would like to thak Dr. R. Nakatsu ad Dr. K. Mase of ATR Media Itegratio & Commuicatios Research Laboratories for their valuable commets ad support. [] ISO, \9 Iformatio techology - Telecommuicatios ad Iformatio exchage betwee systems - Itermediate system to Itermediate system Itra-Domai routeig iformatio exchage protocol for use i cojuctio with the Protocol for providig the Coectioless-mode Network Service (ISO )," 99. [] Perkis, C. E., \IP Mobility Support, Iteret Draft," draft-ietf-mobileip-protocol-.txt, 99 (workig draft). [] Myles, A. ad Skeller, D., \Compariso of Mobile Host Protocols for IP," Iteretworkig: Research ad Experiece, Vol., pp. {9, 99. [] Perkis, C. E. ad Bhagwat, P., \A Mobile Networkig System Based o Iteret Protocol," IEEE Persoal Commuicatios, Vol., pp. -, 99. [] Taaka, R. ad Tsukamoto, M., \A CLNPbased Protocol for Mobile Ed Systems withi a Area," Proc. IEEE Iteratioal Coferece o Network Protocols, pp. {, 99. [9] Teraoka, F., Yokote, Y. ad Tokoro, M., \A Network Architecture Providig Host Migratio Trasparecy," Proc. ACM SIGCOMM 9, pp. 9{, 99. [] Tsukamoto, M. ad Taaka, R., \A Protocol for Wide-Area Mobile Commuicatio i CLNP Networks," Trasactios of Iformatio Processig Society of Japa, Vol., No., pp. {, 99 (i Japaese). [] Wada, H., Yozawa, T., Ohishi, T. ad Taaka, Y., \Mobile Computig Eviromet Based o Iteret Packet Forwardig," Proc. Witer USENIX, pp. {, 99. Refereces [] Carlberg, K. G., \A Routig Architecture That Supports Mobile Ed Systems," Proc. IEEE MILCOM, pp. 9{, 99. [] Hah, J. J. ad Stolle, D. M., \Packet Radio Network Routig Algorithms: A Survey," IEEE Commuicatios Magazie, Vol., No., pp. {, 9. [] Ioaidis, J., Duchamp, D. ad Maguire Jr., G. Q., \IP-based Protocols for Mobile Iteretworkig," Proc. ACM SIGCOMM 9, pp. -, 99.