Support for Wireless LAN Design

Transcription

1 Assocaton for Informaton Systems AIS Electronc Lbrary (AISeL) AMCIS 2005 Proceedngs Amercas Conference on Informaton Systems (AMCIS) 2005 Support for Wreless LAN Desgn Abhjt Dutt Unversty of Wsconsn - Mlwaukee, adutt@uwm.edu Derek L. Nazareth Unversty of Wsconsn - Mlwaukee, derek@uwm.edu Follow ths and addtonal works at: Recommended Ctaton Dutt, Abhjt and Nazareth, Derek L., "Support for Wreless LAN Desgn" (2005). AMCIS 2005 Proceedngs Ths materal s brought to you by the Amercas Conference on Informaton Systems (AMCIS) at AIS Electronc Lbrary (AISeL). It has been accepted for ncluson n AMCIS 2005 Proceedngs by an authorzed admnstrator of AIS Electronc Lbrary (AISeL). For more nformaton, please contact elbrary@asnet.org.

2 Wreless LAN Desgn Support for Wreless LAN Desgn Abhjt Dutt Unversty of Wsconsn-Mlwaukee Derek L. Nazareth Unversty of Wsconsn-Mlwaukee ABSTRACT As moble devces become common n manstream computng, t becomes mperatve to effectvely desgn computng archtectures that seamlessly and effectvely ntegrate them. Rapd advancements n wreless technology has made t possble to buld effcent wreless local area networks (WLANs). Desgnng WLANs presents some unque challenges. Some heurstcs are avalable for WLAN desgn, but they represent pecemeal solutons, focusng on a lmted set of ssues. Ths paper provdes a more comprehensve approach to WLAN desgn, by provdng support for addtonal tasks n the desgn process, as well as by provdng the desgner the opton of examnng multple competng optons. The approach s developed n modular fashon, thereby permttng the easy substtuton of alternatve models n any phase of the process. We beleve the approach to be useful for WLAN desgners, and t provdes an apt llustraton of desgn scence n nformaton systems research. Keywords: WLAN desgn, Network nfrastructure, Wreless networkng, Moble computng. INTRODUCTION Wreless networkng has the potental to provde users unprecedented flexblty n accessng and modfyng nformaton. It s estmated that n near future, about 40% of the e-commerce transactons wll be ntated through a moble devce or nvolve some form of wreless networkng (Varshney and Vetter, 2002). Wreless networks come n many forms, though t s convenent to classfy them n terms of ther range (Agarwal et. al., 2003). These nclude personal area networks, wreless local area networks, wreless metropoltan area networks, and wreless wde area networks. Ths paper addresses wreless local area networks (WLANs) only. WLANs are the drvers behnd the wdespread avalablty of hotspots that offer wreless connectvty to the Internet. Wth a wde varety of hardware, software, securty, and protocol choces avalable, the desgn and mplementaton of WLANs could be challengng and confusng (Varshney, 2003). Several heurstc approaches to WLAN desgn are avalable. However, they represent pecemeal solutons. Ths paper attempts to provde a more comprehensve approach to WLAN desgn to assst and gude potental WLAN desgners through the multfaceted decsons that consttute the process. It presents a desgn framework that allows WLAN desgners to assemble alternatve desgns, evaluate these alternatves, and assst n the selecton of a preferred desgn. CURRENT APPROACHES TO WIRELESS LAN DESIGN A number of dfferent approaches have been proposed for WLAN desgn, ncludng vendor whtepapers, desgn gudelnes, and soluton technques for specfc ssues. Wreless network throughput represents an mportant aspect of WLAN desgn. The theoretcal maxmum throughput under alternatve securty protocols s dscussed n (Jun et al., 2003). A smlar analyss s provded n (Csco, 2003a). Placement of wreless access ponts s another aspect of WLAN desgn that has receved attenton. Lee et. al. (2003) develop a nteger programmng soluton strategy for optmal placement to acheve load balancng gven user traffc demands. Securty n WLANs s an area that has been the subject of desgn gudelnes. Convery et. al. (2003) provde a detaled dscusson on WLAN securty. Edney and Arbaugh (2004) provde detaled dscussons on securty protocols for WLAN desgn, and suggest the use of a securty archtecture. Performance modelng for networks s also relevant to WLAN desgn, wth models for resource utlzaton and response tme presented n (Menasce and Almeda, 2003). Several authors acknowledge the need for a more comprehensve approach. Gast (2002) proposes the ncorporaton of network topology, project plannng, and ste surveys as part of WLAN desgn, wthout addressng the core tasks n WLAN desgn. Roshan and Leary (2003) suggest the use of qualty of servce measures, deployment, and securty, though no clear soluton strategy s presented. Perhaps the most comprehensve approach s presented n (Csco, 2003b). It dscusses hardware selecton (pp ), securty consderatons (pp ), qualty of servce measures (pp ), and roamng consderatons (pp ), as fundamental ssues n WLAN desgn. Though the presentaton s slanted towards Csco products, the dscussons are useful and can be adapted for a more unversal treatment. Proceedngs of the Eleventh Amercas Conference on Informaton Systems, Omaha, NE, USA August 11 th -14 th

3 Wreless LAN Desgn However, none of these approaches provde a truly holstc soluton. Rather, they represent pecemeal attempts to address varous facets of WLAN desgn. Ths paper adopts the vew that WLAN desgners could beneft from a more comprehensve approach, that addresses these ssues, whle also factorng n cost and performance consderatons. WIRELESS LAN DESIGN FRAMEWORK For the purposes of ths paper, a WLAN s vewed as consstng of wreless devces, hotspots, hotspot controllers, and access ponts. Several dfferent topologes are possble. A number of protocols and standards for supportng dfferent forms of wreless communcaton are also avalable. The desgn approach advocated here assumes the followng: Wreless devces are not addressed. WLAN topologes are also not addressed. Only wreless networks that employ the IEEE techncal specfcaton are addressed. WLAN Desgn s a multdmensonal problem. It nvolves decsons that address very dfferent aspects, but are n some manner related. Ths paper adopts a modular approach to WLAN desgn. Ths permts workng on dfferent aspects of the desgn n ndependent manner, as well as the easy swap of one component, should the underlyng technologes change, or should alternatve desgner preferences dctate so. We have dentfed four related modules for WLAN desgn, vz. nfrastructure desgn, securty desgn, cost estmaton, and performance modelng. These components are nexorably lnked, but can be addressed n somewhat ndependent manner. It s not the ntent that the framework produces a sngle WLAN desgn recommendaton. Rather, t s expected that multple competng desgns are possble, characterzed by dfferent cost, performance, and securty measures. Allowng the desgner to trade off between these objects s a necessary part of the desgn framework. The basc structure of the proposed WLAN desgn framework s presented n Fgure 1. External nputs wll shape the desgn of ndvdual components. Relatonshps between varous desgn components are also hghlghted. Fgure 1. Wreless LAN Desgn Infrastructure Desgn Specfyng the archtectural components for a WLAN requres estmaton of network throughput, selecton of access ponts, and layout to meet specfc objectves. These are related decsons, and must be performed n tandem. Selecton of access pont devces wll affect the layout, and subsequent cost of the WLAN. Lkewse, throughput wll be affected by access pont selecton and layout, and wll n turn affect the performance. Proceedngs of the Eleventh Amercas Conference on Informaton Systems, Omaha, NE, USA August 11 th -14 th

4 Wreless LAN Desgn Network Throughput Analyss WLAN throughput requrements can be computed s several ways. One approach s based on users and ther ndvdual requrements. Ths s a data ntensve strategy that requres dentfcaton of all users, estmaton of ther requrements, ncludng frequency of access, and specfcaton of the resource requrements at the server for each requrement. Network throughput WT est s estmated as f pq Dq 8192 (1 + WT = OH ) est p q where f pq represents the frequency of access of applcaton q by user p, D q the data returned by applcaton q, 8192 converts bytes to Klobts, and OH represents the wreless protocol overhead (approxmately 0.8 to 1). Snce ths nvolves tedous data collecton, and potentally suspect data based on user perceptons of frequences, an analyss of server logs may yeld a more accurate pcture, based on the servce demand for dfferent types of requests. Usng ths approach, network throughput can be estmated as WT = sd R 8192 (1 OH ) est + where sd represents the servce demand for request type, and R the volume of data returned by request type. The desgner can select ether approach, or employ both to estmate throughput. Actual throughput s a functon of bandwdth, error performance, congeston, and other factors. Throughput s also moderated by qualty of servce guarantees. A smple estmate of network throughput s gven by WT B log + S N = 2 (1 ) 1 + dr lv where B s the bandwdth, S/N represents the sgnal to nose rato, d the dstance traversed, R the data transfer rate, l the frame length, and v the transmsson velocty. Accordngly, the sgnal strength S can be estmated, for a gven sgnal to nose rato. Access Pont Selecton The access pont characterstcs are specfed n terms of the type, power, and range of the antenna selected. Clearly, the larger the range, the fewer the number of devces needed. Ths also has mplcatons for throughput and costs. Antenna Layout The layout model of the access ponts wll depend on the grd pattern or the way the access ponts wll be placed (hexagonal versus tled), the percentage area of deadspots and the access pont characterstcs. Deadspots can be computed as 4d 4 r 2 2 π for a tled layout, or 1.5 3d 3 r 2 2 π for a hexagonal layout, where d represents the dstance between access ponts, and r s the range for the antenna. Based on ths, the percentage of deadspots for a non-overlappng regular layout s 21.5% for tled, and 9.3% for hexagonal patterns. Deadspots can be elmnated by shrnkng d, and ths condton s acheved for d=1.77r for a tled pattern, and d=1.90r for a hexagonal pattern. Selectng values of d less than ths provdes no addtonal beneft, and ncreases overlap. In the layout model, the desgner can select an approprate confguraton and dstance between antennae, tradng off overlap and deadspots. Securty Desgn Ths component enables a desgner to specfy securty requrements, ncludng specfcaton of securty protocols used, user authentcaton polcy, and user access polcy. At the WLAN layer, t s mportant to ensure that the ntegrty of the data s not compromsed, and protocols for encrypton need to be selected. Wred Equvalent Prvacy (WEP), W-F Protected Access (WPA) based on Temporal Key Integrty Protocol (TKIP), Robust Securty Networks (RSN) represent optons for the desgner to select. Proceedngs of the Eleventh Amercas Conference on Informaton Systems, Omaha, NE, USA August 11 th -14 th

5 Wreless LAN Desgn At the access control layer, the am s to ensure that only data from authorzed users enters the WLAN. Protocols that can be used to mplement access control n WPA and n RSN nclude IEEE 802.1X, Extensble Authentcaton Protocol (EAP), and Remote Authentcaton Dal-In User Servce. The authentcaton layer establshes user dentty, and the polcy decsons are made at ths layer. Protocols avalable at ths stage nclude Transport Layer Securty (TLS) [the default for WPA], Kerberos V5, and Protected Extensble Authentcaton Protocol (PEAP). Gven the multplcty of goals for securty desgn, no sngle soluton approach can be unversally recommended. Instead, a prescrptve system usng a rule-based strategy s recommended. Cost Estmaton The cost ncurred for nstallng and operatng a WLAN s easly computed. Intal setup costs nclude hardware, software, nstallaton and confguraton costs. Operatng and mantenance costs nclude personnel costs, and upgrade costs. In an effort to mantan comparablty between the ntal and ongong costs, the ongong costs wll be computed for a perod of two years, as rapd technology advancement would render the desgn obsolete. To facltate equal treatment of vendor costs, suggested lst prces wll be employed for all hardware, software, and upgrade costs. All cost nformaton wll be stored n a database for easy computaton and update Performance Modelng Several dfferent measures of network performance have been recommended, such as response tme, throughput, avalablty, and cost among others (Menasce and Almeda 2002). Ths approach to WLAN desgn wll focus on network utlzaton, response tme, and throughput, as performance relevant metrcs. Utlzaton can be easly estmated for each resource n the WLAN. Utlzaton for a resource j s smply estmated as U j = sd ST j j where sd j represents the servce demand for request type at resource j, and ST j s the servce tme for request type at resource j. Clearly, utlzaton cannot exceed 1. An average value of utlzaton across resources s not meanngful, and nstead, the maxmum value, representng the bottleneck resource, s suggested. Response tme s estmated usng a queung model where servce tme and wat tme at each resource needed by a request are estmated. Ths s estmated as: Average response tme = f = RT f ST * (1 U ) j j where f represents the relatve frequency of request type as a fracton, RT s the estmated response tme for request type, and U j s the utlzaton of resource j. Note that the computaton ncludes only those resources that are needed for ths request. Throughput can be estmated n a varety of ways. Whle t s temptng to examne t from a resource perspectve, e.g. number of requests servced by resource, t s more meanngful to estmate t from a user perspectve, partcularly n the case of lost connectons, dropped messages, and request tmeouts. Accordngly, throughput s estmated as: T est ( sd RT RT ) = max where RT max represents the response tmeout for requests. WLAN Desgn Evaluaton The desgn process outlned wll permt the WLAN desgner to generate several dfferent WLAN desgns, each of whch s characterzed by several dmensons, ncludng deadspot percentage, cost, securty consderatons met, network utlzaton, response tme, and throughput. These metrcs employ dfferent unts, makng comparablty dffcult. It s recommended that a multple crtera approach be adopted for alternatve desgn evaluaton, gven that the mportance accorded to dfferent crtera wll vary. An ntutvely appealng approach s the use of the Analytc Herarchy Process (Saaty, 1980). It permts j Proceedngs of the Eleventh Amercas Conference on Informaton Systems, Omaha, NE, USA August 11 th -14 th

6 Wreless LAN Desgn decson makers to trade off among dverse crtera wthout havng to perform explct tradeoffs. Addtonally, t provdes for a herarchcal analyss of the problem, permttng the desgner to examne related crtera when evaluatng solutons. Another alternatve s a neghborhood search of a promsng soluton. After generatng several alternatve desgns, the desgner can select a preferred soluton, and search n close proxmty of ths soluton. Yet another approach would nvolve the use of an deal soluton, and the use of multdmensonal scalng to select a soluton that s the closest to ths deal. Tradtonal multple crtera decson makng methods lke mult-objectve lnear programmng are not recommended gven the nature of the functons. FUTURE RESEARCH Implementaton of the desgn modules and ntegraton nto a cohesve system represents the next logcal step. The use of a varety of soluton approaches, e.g. algorthmc (nfrastructure desgn, cost estmaton), rule-based (securty desgn), probablstc (performance modelng), and nteractve teratve (desgn evaluaton), coupled wth the need for a separate database on product characterstcs, ntroduces the need for nteroperablty between modules, and the assembly of a robust physcal archtecture of the desgn components. Creaton, calbraton, and testng of the models wll ental some smulaton to valdate performance under a varety of desgn scenaros. Applcaton to real world desgn problems would then be undertaken. Ths ncludes applcaton to new desgn problems, as well as dentfcaton of alternatve desgns for currently wred facltes. CONCLUSIONS Ths paper dscusses an approach to WLAN desgn that s more comprehensve than the current heurstc approaches. Support s provded for nfrastructure desgn, securty desgn, and performance estmaton. Several mechansms are proposed for the evaluaton of competng desgns. The use of a modular approach permts easy replacement of one component of the desgn wth relatvely lttle effect on the rest of the desgn. Upgrades to the framework, to accommodate new technologes or alternatve consderatons, are also facltated. Clearly there are other consderatons that have not been ncluded n the desgn framework. Lkewse, some assumptons for the estmaton procedures can be challenged. Nonetheless, t represents a good startng pont for WLAN desgn. It provdes a desgner wth a set of meanngful measures to evaluate alternatve desgns, thereby leadng to a more nformed decson, and presumably a better desgn. REFERENCES 1. Agarwal, M., Char K., and Shankar, R. (2003) Demystfyng wreless technologes: Navgatng through the wreless technology maze, Communcatons of the Assocaton for Informaton Systems, 12, 12, Csco. (2003a) Capacty, coverage, and deployment consderatons for IEEE g, Csco Whte Paper, Csco Systems, Inc. 3. Csco. (2003b) Csco AVVID wreless LAN desgn, Csco Desgn Gude, Csco Systems, Inc. 4. Convery, S., Mller, D. and Sundaralngam, S. (2003) Csco SAFE: Wreless LAN securty n depth, Csco Whte Paper, Csco Systems, Inc. 5. Edney, J. and Arbaugh, W.A. (2004) Real Securty: W-F protected access and , Addson-Wesley, Boston. 6. Gast, M.S. (2002) wreless networks: The defntve gude, O Relly Meda, Sebastopol, CA. 7. Jun, J., Peddabachagar, P. and Schtu, M. (2003) Theoretcal maxmum throughput of IEEE and ts applcatons, Proceedngs of the Second IEEE Internatonal Symposum on Network Computng and Applcatons (NCA 03), Cambrdge, MA, Lee, Y., Km, K., and Cho, Y. (2002) Optmzaton of AP placement and channel assgnment n wreless LANs, Proceedngs of the 27 th. Annual IEEE Conference on Local Computer Networks (LCN 02), Tampa, FL, Menascé, D.A. and. Almeda, V.A.F. (2002) Capacty plannng for web servces: metrcs, models, and methods, Prentce Hall, Upper Saddle Rver, NJ. 10. Roshan, P. and Leary, J. (2003) Wreless local-area network fundamentals, Pearson Educaton. 11. Saaty, T.L. (1980) The analytc herarchy process, McGraw Hll Company, New York. 12. Varshney, U. and Vetter, R (2002) Moble Commerce: Framework, Applcatons and Networkng Support, Moble Networks and Applcatons, 7, 3, Varshney, U. (2003) Wreless I: Moble and Wreless Informaton Systems: Applcatons, Networks and Research Problems, Communcatons of the Assocaton for Informaton Systems, 12, 12, Proceedngs of the Eleventh Amercas Conference on Informaton Systems, Omaha, NE, USA August 11 th -14 th