M rng mng Wi-FiBn mun t do di chuyn gia cc phng ban m h!ng ph"i m#t th$i gian ch$ %&imy t'nh (t ni )i *o mng W+,-. c/ng nh0 h!ng )o )1ng *i2c m#t )i3n (t d )i2uhi di chuyn gia cc %im truy c4p h!ng d5y 6,789 Bi *i(t ny :; gic ti(n hnh m rng c/ng nh0 h0?ng d@n c#u h=nh cho ,79Bn mun t do di chuyn gia cc phng ban m khng phi mt thi gian ch i my tnhkt ni li vo mng Wi-Fi (WLAN), cng nhu khng lo lng vic mt lin kt d liu khi dichuyn gia cc im truy cp khng dy (Access Point - AP). Bi vit ny s gip bn tmhiu cch thc tin hnh m rng cng nhu hung dn cu hnh cho AP.Truc y, trong ta nh, vn phng thung lp t nhiu AP vi nhiu tn (SSD) khc nhau, p ng nhu cu di chuyn ca nhn vin s dung my tnh xch tay (client). Tuy nhincch lp t AP ny thung to ra hin tung can nhiu hoc nhng vng khng c sng,thm ch lm mt kt ni khi bn di chuyn gia cc tng trong vn phng. V sau gii phptrn uc ci tin bng vic s dung mt AP vi nhiu b khuych itn hiu (repeater)xung quanh. Uu im ca gii php ny l khng gy nhiu nhung lm nghn bng thng tiAP v tt c kt ni client u v mt im. Gn y, cc AP uc thit k thm tnh nngWDS (Wireless Distribution System) gip gii quyt bi ton m rng vng ph sng v khcphuc tnh trng nhiu .Tuy nhin, nu bn ang s hu nhng AP khng h tr WDS m vn mun m rng vngph sng v khng xy ra hin tung nhiu, bn hy roaming cc AP ny li vi nhau. Bngcch ny, bn s tit kim mt khong chi ph ng k. Mi AP vn chju trch nhim x l tnhiu trong vng pht sng ca mnh, chi khc l cc client c th "t do" di chuyn gia ccAP m khng phi lo mt kt ni, d tm AP v cc hin tung can nhiu nhu truc.Chc nng chnh ca AP l pht tn hiu khng dy (Wi-Fi). kt ni vi WLAN, client phi"bt tay" vi AP (hot ng ch m ha hoc khng). ch khng m ha, client cth kt ni ngay vi AP nhung nu AP uc thit lp m ha th client phi c mt khu ngnhp.ABng phC :Dng ,7AP chic th cung cpktniWLANtrong vngph sng ca mnh. Khi thit lp AP, cn luu vj trt AP m bo kh nng ph sng. AP c loilp ngoitri v trong nh phuc vu theo tng mucch s dung, ja hnh, mi trung nhung bn cnnhrngAPluncjnhcnclient th lundichuyn. Vi cc my trm di ng th vic di chuynra ngoi vng ph sng ca AP rt thung xy ra,chng hn, ngui dng c th ln tng trn, ra saumt bc tung, di chuyn t phng ny qua phngkhc...Khibn cn dichuyn khp phng hoc gia cctngth vicsdungduynht mtAPskhngm bo vng ph sng cng nhu kh nng phucvu kt ni lin tuc. m rng vng ph sng, bn cn lp t thm nhiu AP. Mi AP s ph sng mt khu vc.Cc AP nn lp t sao cho hn ch ti a vng khng c sng hoc rt yu.Hnh 1: vng ph sng APKhi client kt ni vi AP, bn c th thoi mi dichuyn gia cc AP; d nhin cc AP phi uc btr phhpvi yucuvmngkhngdycabn.Eoaming * cc ti(n tr=nh (t niRoaming l qu trnh x l, m bo kt ni Wi-Fi ca client khi di chuyn t AP ny sang APkhc. Khi bn di chuyn gia cc AP, kt ni phi uc thit lp trn AP mi. V vy bt ky dliu no ca bn ang gi truc khi roaming s uc gi li t AP c n AP mi. iu nygip vic gi nhn d liu trong v sau roaming khng bj mt. Khong thi gian tr hon lkhng ng k.Khi thit k, cnmbovngphsngva , khng nn s dung qu nhiu APtrong cng khu vc s to nn ph dyc lm client phi lin tuc thay i kt nivi cc AP. Nhiu AP s gip tng vng phsng nhung n phi uc cu hnh ng bn cthroaming tAPny sangAPkhc.Nhu Hnh 3, 2 AP uc thit k giao thaosngvi nhauvcuhnhcngknh1.Nhn trn hnh bn c th cho rng hp l,nhung thc t cu trc ny khng ng v client s khng bit uc tn hiu no ca AP1 hayAP2 v khng th quyt jnh khi no th tin hnh roaming t AP1 sang AP2. Tn hiu t APlun lan ta trong khng gian, ty theo gn hay xa AP m bn s nhn uc cung tnhiu mnh hay yu hoc vut ra ngoi vng ph sng hon ton.Trn hnh 3, client kt ni vi AP1 ti im A, nhung vn c th nhn tn hiu rt yu t AP2.Khi client di chuyn n im B, lc ny client s tin hnh roaming, thay i giao kt t AP1sang AP2. Tuy nhin do 2 AP cng knh gy nhiu ln nhau nn my tnh ca bn khng throaming cng nhu khng th gi nhn tn hiu n jnh nhu truc uc na. Lc ny c thxy ra tnh trng kt ni Wi-Fi chp chn.Fi(n tr=nh Eoaming c th tin hnh roaming, cc AP cn phi cng chun, SSD, ch m ha/ xc thcnhung khng uc trng knh.u tin, AP1 phi uc cu hnh khng trng knh vi AP2. iu ny gip my tnh ca bnphn bit uc tn hiu ca AP1 v AP2. Chng hn, 2 AP cng h tr chun 802.11g, bn cth cu hnh AP1 s dung knh s 1 v AP2 knh 6. Vic x l roaming s do trnh iu khin card Wi-Fi ca client m nhn (AP khng tham giavo qu trnh ny). Client c th thc hin mt trong hai cch chun bj tin hnh roaming:Cch 1: khi client nhn thy tn hiu t AP1 gim i, n s thc hin tm kim AP gn nht.Cch 2: khi client di chuyn ra cn vng ph sng AP1, tn hiu yu, khng m bo kt ni,n s tin hnh tm kim AP gn nht.Trnh iu khin card Wi-Fi ca client s quyt jnh lc no cn thc hin roaming. Gii thutroaming l cc gii thut b mt ca nh sn xut card Wi-Fi, bn khng th nhn thy thiim chnh xckhi no din ra tin trnhroaming.Giithut roaming thung cn c vocung tn hiu, cht lung tn hiu...Hnh 2: Vng sng cc AP "giao thoa" nhau.Hnh 3: can nhiu hai AP cng knhVi mi thit bj di ng khc nhau s c thi im roaming khc nhau. Mt s th tin hnhroaming ngay khi vo vng tn hiu mi; mt s th li roaming khi nhn thy tn hiu AP mitt hon. Khi client quyt jnh tin hnh roaming th buc tip theo l n phitm kim, dknh AP mi. C 02 cch.Dtmthung: client vadknh, valng nghe bo hiu 802.11 t AP mi.Dtm ch ng: client va dknh, vagiframe thm d 802.11 tm kim APmi.Khi client d tm thu ng, n chi ch nhnbo hiu t AP. D tm ch ng, client phigi thm d v ch nhn tn hiu tr li caAP.Dtmchngshiuquhonvclient trctiptmkim AP,giprt ngnthi gian tr hon vic gi nhn d liu.Trong Hnh 4, 2 AP dng 2 knh khc nhau. Client vj tr A s s dung AP1, khi di chuynn B, client nhn thy tn hiu AP1 khng cn m bo, n tin hnh d tm tn hiu AP2 tthon. V client khng th kt ni vi 2 AP cng lc nn sau khi tin hnh roaming, d tm knh, clients ngt kt ni vi AP1 v chuyn qua vi AP2. Kt ni thnh cng, client s s dung AP2lm im truy cp mi.GhHn 3nh phB h&pAP 2,4GHz (chun 802.11b/g) ucchia thnh 14 knh, mi knh c rngbngthngl22MHzv vyhu ht cc knh s chng lnnhau. Nuhai APcng knh, tnhiusbj cannhiu, phvlnnhau. Gii php s dung nhiu knhkhcnhautrnhchnglntnhiu. Trnhnh 5tathy, tns2,4GHzchi ccc knh1, 6, 11khng bj chng ln nhau.Fhc hi2n roamingHnh : !"i#nt $oa%ing gi&a hai AP Hnh ': !c knh 1( )( 11 kh*ng ch+ng ",n nhauM hnh: Ta nh ba tng, khong cch gia cc tngkh cao, tng mt c nhiu vt cn.Giiphp:bncnmi tng mt AP, lp t AP anxennhaumbovngphsngvtinhnhroaming cba tng. Ring tng mt s thmmtRepeater tng cung tn hiu. Trong m hnh ny,Test Lab sdung APD-Link DWL-7100AP thnghim.Truc tin, thit lp cu hnh cho AP, bn nidymng t my tnh trc tip vo AP1. Thit lp ja chi Ptnh cho my tnh l 192.168.0.x (c th t x t 1-254,tr 50 l jachi P mcjnh ca DWL-7100AP). Mtrnhduyt web, gjachi 192.168.0.50. Bnngnhp vi D l admin v password trng. Sau khi ng nhp thnh cng, bn s thy giaodin nhu hnh 7.Thc hin tng buc thit lp sau:Chon th Home, muc Wireless.- Wireless band: 802.11g- Mode: Access Point- SSD: aproaming (tn do bn t t)- SSD Broadcast: nable (ty chon nablehay Disable. y chon nable d kimtra).- Channel: 1- Authentication: pen System (bn c th chon cc ch bo mt khc WP, WPA...). Sau thit lp mt khu m ha.Bn chon th Status, ghi li ja chi MAC, s dng khi cu hnh Repeater.Cu hnh AP2 tuong t AP1. Luu channel lc ny l 6, mt khu m ha phi ging AP1.Cu hnh AP3 tuong t AP1, AP2. Luu channel l 11, mt khu m ha phi ging AP1.Hnh ): -* hnh v. t$/ 01t AP( 2#p#at#$ v3 s4 giao thoasngHnh 5: c,u hnh AP1 Hinh 6: c,u hnh AP2Tip theo,bn cu hnh Repeater kt niAP1.DoRepeater s tip nhn gitin t clientchuyn v cho AP1, nn cu hnh Repeater cng knh, cng ch bo mt nhu AP1.Wireless band: 802.11gMode: AP RepeaterSSDBroadcast: nable(AccessPoint vRepeater thit lp ging nhau).Channel: 1(vkt ni viAP1)Root APMACAddress: bng ja chiMACca AP1hoc nhn ntscan, Repeater s t ng tm kim cc AP ang hot ng, bnchon AP1 t danh sch. Luu , scan uc AP1 phianghot ng.Authentication: pen System. Sau xc lp mt khu bo mtging AP1.Khi thit lp xong cc AP v Repeater. Bn tin hnh lp tchng vo vj tr. AP gn trc tip vo dy mng, Repeater khngcn dy mng.Bn s dung my tnh xch tay tin hnh d tm v kt ni voAP vi SSD l aproaming. Bn c th th ping lin tuc ja chi P gateway v di chuyn giacc tng. Kt qu tht s bt ng phi khng bn, khng gi tin no bj "rt". Vic lp t AP,Repeater nhiu hay t phu thuc vo vj tr lp t, chung ngi vt, kh nng ph sng cathit bj...Vi gii php Roaming AP, bn c th t do di chuyn gia cc phng ban m khng phi lomt kt ni d liu. c bit, gii php ny gip bn tit kim chi ph khi c th s dung ccAP khng c tnh nng WDS.Iuc J/ng -----------------------------------------------Tham khoCCNP BCMSN Official Exam Certification Guide - Davide uca!"htt#$%%&&&'&irele((-net('com%re(ource(%tutorial(%ho&)roamin*)&ork('htmlHnh 7: c,u hnh AP3 Hnh 18: c,u hnh 2#p#at#$ k9t n:i v;i AP1