Ki Hc Cng Ngh Thng Tin V Truyn Thng

BO CO : K THUT VIBA SNG DNG CA VIBA TRONG WIFI GVHD : HONG QUANG TRUNG Nhm thc hin :1. Hong Vn Thm2. Nguyn Th Thu3. Nng L Thy4. V Vn Thc5. inh Th Thy6. Bi Duy Tin7. Nghim Hu Ton8. L Trng Ton Thi Nguyn thng 11 nm 2011

Li ni uHin nay cc nhu cu v dch v di ng khng ch dng li dch v thoi truyn thng m cn c s pht trin nhanh v mnh cc nhu cu v dch v s liu di ng c bit l dch v truy cp Internet di ng, khin cho nh sn xut v khai thc mng phi tm kim cc kin trc mng mi trn c s kin trc h tng truyn thng gim gi thnh v n gin ho vic xy dng cc mng a dch v, a phng tin.Cc mng 2G phc v kh tt nhu cu thoi thng thng v mt s ng dng th h 2 nh SMS hay truy nhp Internet bng cng ngh WAP. Nhng khi ngi s dng i hi cc dch v nh in thoi video hay truy cp Internet tc cao th chng hon ton khng th p ng c. Bn cnh , cc h thng thng tin di ng hin nay l cc h thng bng hp ch cung cp c cht lng thng tin hn ch, nht l i vi nhu cu truyn s liu nhng gi cc cao.S pht trin ca cc thit b di ng cng ngh cao nh my tnh xch tay laptop, my tnh b ti palmtop, thit b h tr k thut s c nhn PDAcng thc y nhu cu truyn d liu di ng trong khi mng in thoi di ng th h th ba (3G) vn c coi l gii php ca tng lai cho cc dch v truyn thng a phng tin di ng li cha sn sng nhp cuc. Bi cnh ny dn n vic s dng rng ri mt lp mng di ng khng dy mi. l mng cc b v tuyn WLAN (Wireless Local Area Network). Mng WLAN s p ng kp thi nhu cu v truyn s liu khng dy tc cao vi gi thnh h v linh hot cao, trin khai nhanh chng. Cc cng ngh Wi-fi da trn chun IEEE 802.11b xy dng cho WLAN c l cha kho gip cc nc ang pht trin i tt n u, ui kp cc nc pht trin trong lnh vc cng ngh thng tin.Nhn thc r c s pht trin tt yu ca cng ngh Wi-fi, Vit Nam cng ty VDC ch ng trin khai im nng (hotspot) truy cp dch v Wi-fi ti nhng khu trung tm, phc v Seagames 22 v sp ti VDC s ng k c c tn trn bn Wi-fi th gii. S kin ny chng t Vit Nam ang thc s ho nhp v pht trin cng vi nhng tin b mang tnh t ph ca nn cng ngh cao th gii.

Mc lc1. Thut Ng Wi - Fi :31.1. S Lc V Gii Php Mng Khng Dy Wi-Fi :31.2. Mt S u im Va Nhc im Cua Mang Khng Dy :42. Wi Fi S Dung Chun Cng Ngh IEEE 802.11 :52.1. Chun Cng Ngh IEEE :52.2. Tim Hiu Cac Chun Cng Ngh IEEE 802.11x :62.3. C Ch Truy Cp ng Truyn Ca 802.11:73. Bng Tn S Dng Wi-Fi :84. Cc Thnh Phn Mng Khng Dy Wi-Fi:94.1. Access Point:94.2. Cc Thit B My Trm:124.3. Antenna:135. Cc M Hnh Mng Khng Dy:166. M hnh mng ca chun 802.11b187. Cu hnh h thng wifi218. ng dng wifi22

1. Thut Ng Wi - Fi :Trc y, chi co dn ky thut mi s dung mang khng dy, th ma chi trong mt thi gian ngn thi mang khng dy a tr nn ph bin khp moi ni. Thut ng Wi-Fi la mt t ghep vit tt cua Wireless-Fidelity (thng tin khng dy trung thc).iu nay a c khng inh cua Hip hi Wi-Fi quc t (Wi-Fi Alliance).

Logo WirelessSau khi sng to ra h thng truy cp khng dy vi tiu chun IEEE 802.11b Direct Sequence, hip hi Wi-Fi quc t c thnh lp nm 1999. Cc thnh vin sng lp hip hi sng to logo ngn gn thay th cho dng ch IEEE 802.11b Direct Sequence. Hip hi chn Wi-Fi lm logo cho mnh. Wi-Fi cn c gn km vi li gii thch l "The standard for Wireless Fidelity", t ny c ngha l chun cho khng dy trung thc v ngi ta hiu Wi-Fi c ghp bi cc ch u ca Wireless Fidelity.Vy Wi-Fi hay mng 802.11 l h thng mng khng dy s dng sng v tuyn, ging nh in thoi di ng, truyn hnh v radio.

1.1. S Lc V Gii Php Mng Khng Dy Wi-Fi :Mang khng dy cho phep chung ta giao tip, truy cp cac ng dung va thng tin ma khng cn cac thit bi cng knh nh trc y na. Chung ta co th t do di chuyn va kha nng m rng cac ng dung, thng tin cho cac toa nha, cng ty, va trng hoc nhng ni khac trn th gii giao tip vi nhau cach d dang. Chng han, mang khng dy cho phep chung ta co th xem E-mail va truy cp Internet bt c ni nao ma ho thich.Xu hng mang khng dy hin nay c ph bin rng rai trong kt ni mang may tinh. Hay hinh dung, trong cac cuc hi hp nu chung ta mun bao cao thng qua cac C s d liu cua mt cng ty, ma dung Wi-Fi thi tin li hn nhiu v nhiu mt nh: uy tin, trach nhim, thi gian va vt cht cua cng ty o. Tt ca cac yu cu trn u co th c giai quyt bng cac thit bi mang khng dy Wi-Fi.Cac thit bi mang khng dy ngay nay u kt ni bng song Radio va s dung chun IEEE 802.11X, trong iu kin mi trng (vn phong, nha xng) thich hp ma khoang cach truyn trong pham vi t 10m - 300m. Hoat ng bng tn 2.4GHz (chun IEEE 802.11b, IEEE 802.11g) va bng tn 5.8GHz (chun IEEE 802.11a). La mt giai phap ly tng cho vic kt ni mang ni b va truyn d liu bng thng rng trong vung phu song. iu kin nh vy se cho phep cac thit bi khng dy k ni vi nhau bt c ni u trong pham vi phu song. Cho php 256 thit b khc truy cp vo h thng khng dy, iu ny gip doanh nghip khng tn thm chi ph thit lp cho vic m rng mng sau ny.1.2. Mt S u im Va Nhc im Cua Mang Khng Dy :u im:- Khng phai khoan tng, bm va i dy.- Khng cn phai ngi nhng vi tri c inh.- Trong nhiu trng hp la giai phap c tit kim nhiu tin.- Co th m rng pham vi. Co th tin cy.- Cai t d dang.Nhc im:- Phc tap hn trong vic quan ly va vn hanh.- Co th bi nhiu.- Vn v an ninh thng tin truyn.- Tn s cang cao thi tc cang cao, co th bi suy giam nhiu.

2. Wi Fi S Dung Chun Cng Ngh IEEE 802.11 :2.1. Chun Cng Ngh IEEE :IEEE la mt t chc cua nc My chuyn phat trin nhiu loai tiu chun, trong o co cac tiu chun v truyn d liu. Bao gm mt s uy ban chiu trach nhim v vic phat trin nhng d thao v mang LAN chuyn sang cho ANSI (American National Standards Institute) tha nhn va c tiu chun hoa trn toan nc My. IEEE chuyn cac d thao cho ISO (International Organization of Standardazation).Chun IEEE 802.11- La tp hp cac tiu chun vin thng iu tit cac mang cuc b v cac chun giao din mang v mt vt ly chng han nh Card Interface, Bridge, Router, Switch, Access Point, WLAN Client Adapters, cable va tt ca nhng gi thuc linh vc truyn tinh hiu va phng phap truy cp co lien quan n vic ni mang v mt vt ly. - Tiu chun IEEE 802.11 inh nghia la mt b nhng chun giao tip may tinh trong WLAN. Dong ho 802.11 gm nhng ky thut truyn song trong khng khi dung giao thc c ban ging nhau. Cac chun ph bin nht la IEEE 802.11b, IEEE 802.11g, va chung c sa i t chun gc. IEEE 802.11a la chun trong mang khng dy ra i u tin, nhng IEEE 802.11b thi c chp nhn rng rai u tin, theo sau la IEEE 802.11b va ti IEEE 802.11n. Vn bao mt la khuyt im trong mang khng dy, t o IEEE a co nhng yu cu nng cp them nh IEEE 802.11i sau khi co nhng thay i cua c quan lut phap va chinh phu. Va cac chun IEEE 802.11x (c-f, h, j) la s m rng, va sa i dich vu ung n from cac chun trc.Di y la bang danh sach cac chun c s dung hin nay:

IEEE 802.11 IEEE 802.11d IEEE 802.11hIEEE 802.11pIEEE 802.11n

IEEE 802.11a IEEE 802.11e IEEE 802.11iIEEE 802.11r

IEEE 802.11b IEEE 802.11FIEEE 802.11jIEEE 802.11T

IEEE 802.11c IEEE 802.11gIEEE 802.11kIEEE 802.11u

2.2. Tim Hiu Cac Chun Cng Ngh IEEE 802.11x :IEEE 802.11 (Legacy mode): la phin ban gc cua chun IEEE 802.11, ra i nm 1997 va c cng b nm 1999, tc truyn d liu 1-2 Mbit/s, s dung bng tn 2.4GHz. Va sau o bt ng b sung la IEEE 802.11b.IEEE 802.11b: ra i 11/1999, tc 11Mbit/s, bng tn 2.4GHz, dung ph bin va c xem nh mt ky thut WLAN. IEEE 802.11b s dung mt ky thut truyn song bng DSSS nh mt chun gc.IEEE 802.11a: cung ra i 11/1999, tc 54MBit/s, bng tn 5GHz. Tuy nhin, bng tn cao thi rt mong manh, yu t. Tt ca cac hiu qua cua IEEE 802.11a u vt tri hn IEEE 802.11b/g nhng chi mong manh va yu t. Vi vy tin hiu IEEE 802.11.a khng th vt thm nhp xa hn IEEE 802.11b bi vi chung bi cac bc tng va vt th rn khac hp thu trn ng i. IEEE 802.11a s dung ky thut OFDM. IEEE 802.11c: c ph chun 11/1998, hoat ng nh mt cu ni cho mang khng dy.IEEE 802.11d: ra i 2001, la chun cho nhng cng ty phat trin cac san phm khng dy trn nhiu quc gia khac nhau.IEEE 802.11e: ra i 2005, nng cao 802.11 MAC cho QoS.IEEE 802.11F: Inter-Access Point Protocol, ra i 2003IEEE 802.11g: ra i nm 2003, la phin ban nng cp cua IEEE 802.11b, tc 54MBit/s, bng tn 2.4GHz.IEEE 802.11h: ra i 2004, la chun giai quyt cac vn nhiu vi v tinh va Radar dung bng tn 5GHz. Chun nay cung cp tinh nng DFS chon knh t ng va giam nhiu bng AP, va tinh nng TPC iu chinh cng xut truyn dn.IEEE 802.11i: ra i 2004, tng kha nng bao mt, s dung WEP bao mt nhng WEP thi bao mt kem, sau o ra i WPA va cai tin hn la WPA2 s dung ma hoa khi theo thut toan AES, con WEP va WPA s dung ma hoa theo thut toan RC4. Cui cung la phng phap bao mt tt nht hin nay la EAP dung chng thc trn may chu.IEEE 802.11j: ra i 2004, hoat ng bng tn 5GHz, s m rng cua ngi Nht dung cho cac ng dung Radio di ng bn trong va bn ngoai.IEEE 802.11k: ra i 2007, nng cp trong vic o lng tai nguyn Radio.IEEE 802.11p: d kin ph bin nm 2009, dung mang khng dy trn cac phng tin giao thng.IEEE 802.11r: ra i nm 2007, nng cp da trn IEEE 802.11d cho phep chuyn vung.IEEE 802.11T: lin quan n WPP s oan hoat ng cua mang khng dy.IEEE 802.11u: quy inh cach thc tng tac vi cac thit bi khng tng thich vi 802 nh mang in thoai di ng.IEEE 802.11n: nhanh hn va xa hn IEEE 802.11g.Tng quat hn, mang khng dy thng s dung chun IEEE 802.11a, IEEE 802.11b, IEEE 802.11g va hin nay mt s may Laptop dung IEEE 802.11n.2.3. C Ch Truy Cp ng Truyn Ca 802.11:Mng 802.11 s dng c ch Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) truyn d liu.CSMA/CA l c ch lng nghe trc khi truyn (Listen Before Talk = LBT). Trm truyn s kim tra tn hiu sng mang trn ng truyn v i cho n khi knh truyn ri trc khi thc s truyn.CSMA/CD s dng ACK xc nhn thay v ty s dng mi trng truyn khi c xung t xy ra. Vic s dng ACK rt n gin, khi mt thit b khng dy gi gi tin, u nhn s p li bng ACK nu nh gi tin c nhn ng v y . Nu u gi khng nhn c ACK th n xem nh l c xung t xy ra v truyn li gi tin.Giao thc CSMA/CA trnh kh nng xung t ga cc trm dng chung ng truyn bng cch s dng random back off time (khong thi gian bt k phi i trc khi c th ginh quyn s dng ng truyn). Khong thi gian ngay sau khi ng truyn bn l khong thi gian d xy ra xung t nht, c bit l trong mi trng c nhiu ngi s dng. Ti thi im ny, cc my trm phi i cho ng truyn rnhv s c truyn d liu ti cng mt thi im. Chnh v th, khi ng truyn rnh, random back of time s tr hon vic truyn d liu ca trm, hn ch ti a kh nng xy ra xung t gia cc trm.M t CSMA/CA:+ Trc khi mt my trm mun gi d liu, my phi thng bo cho bit my mun gi d liu trong bao lu. Li thng bo ny s cho my trm khc bit phi i bao lu trc khi my c th gi thng tin.+ Cc my trm khc khng c gi thng tin cho n khi khong thi gian phi ch kt thc.+ My trm truyn d liu s khng bit c d liu truyn n ni cn truyn hay cha cho n khi nhn c mt tn hiu bo nhn c d liu.+ Nu 2 my trm cng gi d liu, chng cng khng bit c mnh ang gy nhiu ln nhau. My trm ch nhn bit c ang c my trm khc cng truyn d liu khi khng nhn c tn hiu bo li t ni cn truyn d liu.+ Cc my trm phi i mt khong thi gian ngu nhin ri th truyn li ln na (khi nhn bit c c my ang ginh ng truyn, gy nhiu ).

3. Bng Tn S Dng Wi-Fi :Tn s s dng ph bin cc chun IEEE 802.11b, IEEE 802.11g l 2.4GHz.Cng sut l 1000mW. rng bng thng 22MHz.Cc sng v tuyn s dng cho Wi-Fi gn ging vi cc sng v tuyn s dng cho thit b cm tay nh in thoi di ng, radar, b m, v cc thit b khc. N c th chuyn v nhn sng v tuyn, chuyn i 1s, 0s sang sng v tuyn v ngc li. Nhng Wi-Fi c mt s khc bit so vi cc sng v tuyn khc ch:Chng pht v truyn tn hiu tn s 2.4GHz hoc 5GHz.Tn s ny cao hn so vi cc tn s s dng in thoi di ng, cc thit b cm tay, pht thanh v truyn hnh.Tn s cao hn cho php tn hiu mang theo nhiu d liu hn.Knh thng tin: bng thng ca chun IEEE 802.11b v IEEE 802.11g cho php xy dng 14 knh khc nhau truyn dn thng tin, nhng hin nay ngi ta thng dng mt trong cc knh nh s t 1 n 11, v trnh dng ln ln gia cc knh vi nhau, cho nn ngi ta thng dng cc knh 1,6, v 11, v n cng gip nng cao cht lng tn hiu sng ng k.4. Cc Thnh Phn Mng Khng Dy Wi-Fi:Gm c: Access Point, cc thit b my trm, Antenna,...4.1. Access Point:

Access PointAP cung cp cho cc my trm mt im truy cp vo trong mng. Mt AP l mt thit b haft-duplex vi kh nng hot ng thng minh tng ng vi kha chuyn mch Ethernet phc tp.V tr cc AP thng t ti trung tm cc thit b mun kt ni hay cc cng ty ln, va v nh. Ni c t nhiu x sng v tuyn l ni tt nht t mng khng dy.Mi trng bn trong, Access Point s ph sng ti a l 50m. Cc vt liu xy dng dng trong nh ca v c c th va chm vi khu vc ph sng.Khu vc bn ngoi, thit k v li ch ca cc antenna c th tng trong khu vc ph sng khong vi trm mt.

V tr Access PointAccess Point lin lc vi cc my trm khng dy, cc mng c dy, v cc thit b khc.C 3 ch m AP c th thit lp:+ Ch gc (Root mode)+ Ch lp (Repeater mode)+ Ch bridge (Bridge mode)Root mode:Ch gc c dng khi mt AP kt ni n mt mng c dy. Hu ht cc AP c h tr cc ch khc nhng vn c th c cu hnh vi ch Root mc nh. Khi mt AP kt ni vi mt phn on mng c dy thng qua cng Ethernet ca n th AP ny thng c cu hnh theo kiu Root. Khi ch Root th cc AP chung mt h thng phn on c dy s c th lin kt vi nhau. Cc AP lin lc vi nhau h tr chc nng chuyn vng cng nh chc nng ti lin kt. Cc my trm khng dy c th lin lc v trao i vi cc my trm khng khc thng qua cc AP kt ni vi nhau qua mng c dy hay khng dy.

Ch rootBridge Mode:Trong ch Bridge, cc Access Point hot ng chnh xc nh Bridge khng dy. Trn thc t chng m thnh cc Bridge khng dy khi c cu hnh theo ch ny. Ch mt s nh AP trn th trng c chc nng Bridge.

Ch BridgeNh hnh v, cc my trm khng dy khng lin kt vi cc bridge v cc bridge khng dy ny c dng ni hay nhiu phn on mng c dy li vi nhau qua mi trng khng dy.

Repeater Mode:Trong ch Repeater, cc Access Point n gin to ra mt tn hiu mng m rng dy mng Infrastructure. Mt Repeater khng kt ni vt l bng dy n tt c mng. Thay v, n nhn cc tn hiu radio t AP, thit b cui v cc repeater khc th n chuyn li cc khung m n nhn. Mt Repeater nm gia mt AP v cc user hot ng nh mt tip m cho cc khung i ti v i v gia cc ngi dung v AP trong mng khng dy.

Ch Repeater hnh trn, ta thy mt Access Point hot ng nh l mt AP Root v mt AP hot ng nh l Repeater khng dy. Access Point trong ch repeater kt ni n cc my trm khng dy vi vai tr v kt ni vi AP Root ngc dng vi vai tr l mt my trm. Vic s dng mt AP trong ch repeater s khng c ngh tr khi tht cn thit bi v cc xung quanh mi AP trong trng hp ny phi chng lp ln nhau t nht l 50%. Cch cu hnh ny lm gim thiu phm vi m cc client c th kt ni n AP repeater. Ngoi ra, do AP repeater truyn thng vi cc client nh l AP ngc dng trn ng ni khng dy nn lm gim dung lng trong mt phn on mng khng dy. Ngi ta dng kt ni AP repeater s gp phi vn v thng thng thp v thi gian tr cao.4.2. Cc Thit B My Trm:Cc thit b my trm l mt thut ng, bao hm mt s thit b mng WLAN v mt Access Point nhn dng nh l mt my trm trong mng. Cc thit b ny bao gm: PCMCIA (Personal Computer Memory Card International Association). B bin i loi ni tip v Ethernet. Card USB (USB Adapter). Card PCI v ISA.Cc my trm WLAN l nhng nt mng cui nh my tnh bn, my tnh xch tay, cc my tnh PDA m chng cn kt ni khng dy vo mng khng dy Infrastructure. Cc thit b my trm WLAN trn c lit k cung cp vic kt ni cho cc my trm.PCMCIA v Compact Flash Card:

PCMCIAThnh phn ph bin nht trong mt vi mng khng dy l card PCMCIA. Cc thit b ny c dng trong cc my tnh xch tay v my tnh c nhn PDA. Card PC l thnh phn cung cp vic kt ni gia my trm v mng. Card PC c ng dng nh l mt module radio trong AP, Bridge, Workgroup Bridge, USB Adapter, PCI, ISA, v ngay trong c my in.4.3. Antenna:Antenna l mt thit b dng bin i cc tn hiu radio tn s cao trn ng truyn thnh cc sng trong khng kh.Antenna chuyn i nng lng in sang sng RF i vi antenna truyn hay pht sng RF sang nng lng in i vi antenna nhn.Kch thc vt l ca antenna nh chiu di l lin tc, trc tip n tn s m antenna c th qung b sng hay nhn sng.C 3 loi ni chung:+ Antenna a hng.+ Antenna n hng.+ Antenna nh hng mnh.Antenna a hng:Hu ht cc loi antenna mng WLAN l loi antenna lng cc. Antenna lng cc l loi antenna a hng, bi v n pht ra nng lng nh nhau theo tt c mi hng xung quanh trc ca n. Cc hng ca antenna tp trung nng lng ca chng vo trong hnh nn, gi l beam. Antenna lng cc c mt yu t pht x di ch mt inch m n thc hin chc nng tng ng nh antenna rabit ears trong mt s ti vi. Cc antenna lng cc c s dng vi mng WLAN t hn v tn s ca mng WLAN nm trong vng tri ph vi sng 2.4GHz thay v 100GHz ca tri ph ti vi. Do cc tn s cao hn nn chiu di sng v cc antenna tr nn nh hn.Cc antenna a hng c s dng khi vic che ph theo cc hng xung quanh trc ngang ca antenna c yu cu. Antenna a hng c hiu qu nht ti ni c nhu cu bao ph mt vng rng ln xung quanh mt im trung tm. Cc antenna a hng thng c s dng cho vic thit k mng im-nhiu im theo dng cu trc mng hnh sao.

im-Nhiu imKhi s dng bn ngoi, mt antenna a hng s c t trn nh ca cu trc ti trung tm ca vng bao ph.Khi s dng bn trong, n c t gia to nh bao ph, gn trn nh c iu kin tt nht cho vic bao ph.Cc loi anten ng hng: Rubber Duck, Omni-directional, Celing Dome, Small Desktop, Mobile Vertical, Ceiling Dome...

Anten Omni-directional

Anten Rubber Duck

Antenna n hng:Antenna n hng xut hin ti mt vi kiu dng v hnh dng thit k khc nhau. Mt s loi antenna n hng thng xuyn c s dng vi mng WLAN l: Patch, Panel, Yagi. Tt c antenna ny thng phng v c thit k cho vic vt tng. Mi loi c c im bao ph khc nhau.

im - imAnten n hng c nhiu kiu dng v kch thc khc nhau, in hnh c cc loi anten: Yagi, Patch, Backfire, Dish...

Anten Yagi

Anten Patch

Antenna nh hng mnh:Antenna nh hng mnh pht tn hiu beam hp nht v c li ch nht trong s ba loi Antenna. Cc antenna nh hng mnh th c hnh lng cho, hnh a dng cho kt ni khng dy im ni im. Mt s loi a cp nh Parapol bi v chng tng t nh cc loi a v tinh nhn to thu nh. Mt s c gi l antenna khung li bi v chng c thit k cho vic gim sc cn ca gi.Antenna nh hng mnh khng c vng che ph cc my trm c th s dng. Cc antenna ny c s dng cho cc ng truyn thng im ni im. v c th truyn i theo mt khong cch ln 42Km. Kh nng s dng mnh m, cc antenna nh hng mnh c th kt ni hai to nh cch nhau vi trm dm nu khng c g cn tr chng. Thm vo , cc antenna ny c th nhm hng trc tip trong mt to nh thot khi s cn tr. Cch thit lp ny s c s dng kt ni mng n nhng ni m khng th dng dy v cc mng khng dy khc.

5. Cc M Hnh Mng Khng Dy:Nhng mng 802.11 bao gm 4 thnh phn vt l chnh. Cc thnh phn:Stations: cc my trmMng c xy dng trao i d liu gia cc my trm. Cc my trm l cc thit b my vi tnh s dng cc card mng khng dy. in hnh, cc my trm c th l my tnh xch tay, cc my tnh bn v cc thit b khng dy khc. Cc my trm khng nht thit phil cc thit b di ng m c th l cc my tnh bn c kt ni bng mng LAN khng dy. V trong mi trng LAN, ngi ta dng mng khng dy trnh vic ko dy mng trong LAN. Cc khu vc ln cng c th thun li t mng khng dy, chng hn nh mt tng sn xut s dng mng khng dy kt ni cc thnh phn vi nhau. 802.11 nhanh chng tr thnh mt chun cng nghip trong vic kt ni cc thit b tiu th in vi nhau. Chng hn nh Apples Airport Express kt ni cc my tnh n m thanh ni bng 802.11, TiVos kt ni mng khng dy. Cc thit b khc c th trao i thng truyn thng tc cao trn 802.11.Access Point:Cc khung trn mt mng 802.11 phi c chuyn i sang loi khung khc nhau. C chc nng lm cu ni cho cc mng c dy v mng khng dy.Wireless medium: di chuyn cc khung t my trm n my trm, chun ny s dng wireless medium. Mi tng vt l khc nhau c nh ngha; cc kin trc cho php nhiu tng vt l c trin khai h tr 802.11 MAC.Distribution sytem:Khi mt vi AP c kt ni t mt khu vc bao ph ln, chng phi giao tip vi nhau truy tm bc di chuyn ca cc my trm di ng. Distribution system l thnh phn lun l ca 802.11 thng xuyn a cc khung ti ch ca h. 802.11 khng ch ra bt c k thut c bit no cho distribution sytem.

M hnh mng: c 2 m hnhM hnh BSS:L mt nhm cc my trm giao tip vi nhau . Khi mt my trm nm trong BSS, th n c th giao tip vi cc my khc trong BSS.

M hnh Independent BSS (Ad - Hoc)Cc my trm trong mt IBSS giao tip vi nhau mt cch trc tip v phi l dy giao tip trc tip. Ti thiu ca mt mng 802.11 l IBSS vi hai my trm. Trong m hnh ny khng c AP. V vy, cc my trm mun lin lc trc tip vi nhau phi nm trong vng ph sng ca nhau. IBSS thnh thong cn c gi l Ad-Hoc BSS hay Ad Hoc Network.

M hnh Infrastructure BSSM hnh ny khng bao gi c gi l IBSS. M hnh mng ny c phn bit vi m hnh Ad-Hoc ch c s dng mt AP. Cc AP ny c s dng cho tt c cc giao tip trong mng BSS, bao gm cc thit b di ng trong khu vc phc v ging nhau. C hai thun li chnh:+ BSS c xc nh bi khong cch t AP. Cc my trm khng bt buc nm gn cc my trm khc, m ch cn nm trong vng ph sng ca AP.+ AP nm trong m hnh BSS ny nhm phc v cc my trm tit kim in nng. AP s ghi ch li khi no my trm vo ch tit kim in v a vo vng m cc khung cho n. Cc my trm hot ng c th tt ch wireless v khi ngun in bt ln th ch truyn v ly li cc khung trong vng m t AP.M hnh ESS:Cc m hnh BSS ch bao ph trong mng nh, nhng khng th bao ph trong mng ln hn. 802.11 cho php cc mng khng dy tu tin iu chnh kch thc ln to ra kt ni gia cc m hnh BSS vi nhau vo mt m hnh c gi l ESS. Mt ESS c to ra t dy chuyn cc BSS vi mt backbone network. Tt c AP trong ESS c gn mt SSID, ngha l tn ca mng phc v cho cc user.

M hnh ESS6. M hnh mng ca chun 802.11b

Tiu chun ph bin nht hin nay l IEEE 802.11b. Tiu chun 802.11b c Hip hi k s in v in t (IEEE) a ra vo thng 9 nm 1999. Mng WLAN IEEE 802.11b tc cao hot ng bng tn 2.4 GHz v c th cung cp tc truyn dn ln ti 11 Mbps. IEE 802.11b ch xc nh hai lp cui ca m hnh tham chiu OSI: lp vt l (PHY) v lp lin kt s liu (phn lp iu khin truy nhp MAC)

Quan h gia 802.11b v cc lp ca m hnh tham chiu OSI

CC THNH PHN CA MNG IEEE 802.11B

Mng IEEE 802.11b bao gm cc thnh phn sau y tng tc vi nhau (hnh 4):

- B dch v c s BSS: l khi kin trc c bn nht trong mng WLAN 802.11b. Hnh minh ha di y ch ra 2BSS, mi BSS c 2 trm STA thnh phn.- H thng phn phi DS: l thnh phn kin trc lin kt gia cc BSS.- im truy nhp AP: l mt trm STA ngoi vic hot ng nh mt trm bnh thng cn cung cp truy nhp ti h thng phn phi DS bng cch cung cp cc dch v h thng phn phi DSS.

- Kin trc mng IEEE 802.11b- B dch v m rng ESS: l mt b gm nhiu BSS lin kt vi nhau v c th tch hp vi mngLAN di dng mt BSS c lp.LP VT L ca IEEE802.11b

Lp vt l cp n giao din vt l gia cc thit b v vic truyn cc bit th trn knh truyn thng. IEEE 802.11b cung cp 3 loi tc : tc c bn (1 Mbit/s) s dng iu ch chuyn pha nh phn vi sai DBPSK, tc m rng (2 Mbit/s) s dng iu ch chuyn pha cu phng vi sai DQPSK v tc nng cao (5.5 Mbps v 11 Mbit/s) s dng iu ch kho m b sung CCK.

Cc loi tc truyn dn ca IEEE 802.11bTc di miu chTc Bit/K hiu1 Mbit/s11 (Barker Sequence)BPSK1 MSps12 Mbit/s11 (Barker Sequence)QPSK1 MSps25.5 Mbit/s8 (CCK)QPSK1.375 MSps411 Mbit/s8 (CCK)QPSK1.375 MSps8Ngoi ra IEEE 802.11b cn nh ngha vic dch chuyn tc t ng, cho php iu chnh t ng tc truyn trong cc iu kin c nhiu, tc l cc thit b s truyn cc tc thp hn (1, 2, 5.5 Mbps) trong iu kin c nhiu v thit b di chuyn sangvng truyn dn tc cao hn th kt ni s t ng nng tc ln.

Lp vt l ca IEEE 802.11b chia thnh 2 phn: giao thc hi t lp vt l (PLCP) v phn lp ph thuc mi trng vt l (PMD). PMD thc hin vic m ho v gii m v tuyn cong PLCP trnh by giao din chung phn lp MAC v cung cp vic cm ng sng mang v n nh knh ri (CCA).

PHN LP IU KHIN TRUY NHP MAC CA IEEE 802.11bPhn lp MAC (Medium Access Control) lm chc nng giao din gia lp vt l v thit b lp trn. Phn lp MAC xc nh mt c ch truy nhp c bn (da trn a truy nhp cm ng sng mang CSMA) cho cc nt di ng truy nhp vo mi trng v tuyn. Hai chc nng chnh ca lp MAC l kim tra d li chu trnh CRC v phn mnh gi (Packet Fragmentation). Mi gi tin s c tnh ton v c gn v mt gi tr CRC m bo rng gi tin s khng b sai khi trong qu trnh truyn dn. Vic phn mnh gi s ct cc gi tin ln thnh cc gi nh hn truyn trong khng gian. Vic ny s mang li hai li ch: th nht l gim yu cu pht li v gi cng ln th kh nng gi b sai cng ln, li ch th hai l trong trng hp gi b sai th cc nt ch cn truyn li mt gi nh, do vic truyn li s nhanh hn.

7. Cu hnh h thng wifi

Hnh sau ch ra cu hnh y h thng Wi-Fi. Vng ph sng ca cc AP to ra mt im nng hotspot, ngi dng vi cc thit b nh laptop c trang b card wi-fi c th truy nhp vo mng thng qua giao tip vi AP. Cc AP ti mt im nng c tp trung v switch v kt ni vi mng thng qua b nh tuyn (router). Cc router c ni vo mng hu tuyn bng mt phng thc truyn dn no tu thuc nh cung cp dch v.

RADIUS AAA ServerBilling System

RADIUS

Cng thu bao

INTERNET

SHDSL Router

SHDSL WAN Leased-Line

SHDSL Router

Switch

Hotspot

Switch

Hotspot

SECISCOWIRELESS

CISCO SE

CISCO SE

AP

CISCO SE

AP

CISCO

AP AP

CISCO SE AP AP

Cu hnh h thng

Trong phng n trin khai ca mnh, VDC la chn phng thc truyn dn SHDSL (Single- pair High-Speed Digital Subscriber Line). Gii php SHDSL s dng truyn d liu cn bng vi tc c th t t 192 Kbit/s ti 2.3 Mbit/s trn mt i cp n. Thm vo , tn hiu SHDSL c kh nng truyn dn xa hn so vi cc kt ni s dng cng ngh ADSL v SDSL, cho php cc nh cung cp dch v tho mn nhu cu cc khch hng xa. S dng cng ngh ny, ti mi im truy cp hotspot phi c mt b nh tuyn SHDSL, cung cp truyn dn bng thng rng ra Internet.

i vi h thng Wi-Fi: mi trng truyn dn l mi trng sng, truyn tin theo chun 802.11b. Thc cht y c th coi l mi trng pht qung b (broadcast), tt c cc my trm (client) ng vo vng ph sng u c th bt c tn hiu, cc AP t c kh nng iu khin c truy nhp. Gii php c a ra l s dng thit b cng thu bao. Thit b ny s ng chn ti ng ra ca cc AP i Internet, mi trng sng s lun c cc AP cung cp cho bt c mt my trm no ng trong mi trng truyn sng. Nhng khi ngi s dng truy nhp vo mi trng sng ca mt AP th ngay lp tc cng thu bao s tin hnh vic nhn thc thu bao.Ngi s dng s c iu khin t ng truy nhp vo mt trang Web nhn thc c xy dng tch hp trn cc cng thu bao. Ti y, username/password (tn ngi s dng/mt khu) s c yu cu nhp vo. Cng thu bao lin lc vi AAA Server tp trung ti trung tm qun l iu hnh mng theo giao thc RADIUS ly thng tin v khch hng trong h thng c s d liu.

8. ng dng wifi

Kha nng truy cp mang internet khng dy khng chi la tin ich duy nht cua wifi. Sau y la 10 ng dung khac cuacng ngh ny.

Bin in thoai tr thanh iu khin t xa

Mangwifi co kha nng kt ni tt ca cac thit bi in t trong cn h cua ban. Va thng qua may in thoai cm tay, ban co th iu khin moi vt dung.

Cac hang ch tao in thoai ln rt quan tm ti tinh nng hu ich nay. iTune controlling remove cua Apple, All Encompassing Gmote trn nn Android va XBMC remotes la nhng ng dung ph bin hin nay. Nu co mt chic in thoai thng minh, ban a nm gi ca th gii s trong tay.

iu khin may in t xa

iu khin may in lun la mt vn "au u" vi nhiu nhn vin vn phong, khi hu ht cac cng ty khng th trang bi may in cho mi ca nhn hoc phong ban.

Thay vi phai thao, cm dy ni vao laptop mi ln cn in n, ngi s dung co th kt ni may in trc tip vao mangwifi cua cng ty. Bng cach nay, ngi dung co kha nng iu khin may in t moi vi tri thng qua laptop.

Ngoai ra, vi phn mm Dropbox (thich hp vi ca my s dng h iu hnh Window va Mac), ngi s dung co th ra lnh cho may in bng in thoai di ng.

Thng bo c tin nhn in thoi trn my tnh

Android Notifier la mt ng dung hu ich danh ring cho in thoai chay h iu hanh cua Google, cho phep chuyn chung bao hiu cuc goi n, tin nhn, bao lch t in thoai ti may vi tinh.

Nh o, ngi s dung se khng con phai lo s ting chung bao hiu "v duyn" cua in thoai pha v s tp trung cua cc ng nghip. Android Notifier cung la mt minh chng cho s quan tm va sang tao cua Google trn nn tang cua mang wifi.

Bin in thoai tr thanh thit bi phat song wifi

S dung laptop nh mt b phat wifi tr nn quen thuc. Tuy nhin, khng nhiu ngi co th lam iu o vi mt chic in thoai.

s dung c chc nng nay, in thoai cn c be khoa va cai mt vai phn mm cn thit nh: PDAnet cua iPhone, Wireless Tether cua h iu hanh Android.

Nh vy, mang wifi giup ngi s dung co th truy cp internet "moi luc moi ni" qua song in thoai di ng.

Xem phim trn moi tivi trong gia inh

y la mt ng dung hu ich, c bit vi nhng ngi m phim anh.tng chinh la s dung mt thit bi nh may vi tinh, may chi game Playstation hay Xbox lam may chu trung tm kt ni cac in t trong gia inh. Nh vy, ban se co mt trung tm giai tri gia inh c kt ni qua mang wifi vi rt nhiu tinh nng a dang.

Phn mm iu khin la Windows Media Mentre, XBMC hay Google Media Serve danh cho Window. Mangwifi ni b cho phep ngi s dung trao i d liu, truy cp va trinh chiu kho phim tai nhiu tivi khac nhau.

Chia se d liu gia cac may tinh

Hin tai, co rt nhiu phng phap khac nhau chia se d liu gia cac may tinh t gn nhau nh mang ni b (LAN) hay internet. Mang wifi cung la mt cach hu hiu lam vic o.

u th ln cua mang khng dy chinh la...khng cn co dy ni. T o, mang wifi giai phongban khoi nhng m dy phin toai, bin vn phong cung nh cn h cua ban gon gang va hin ai hn.Nu ban a thich s dng phn mm Dropbox thi y cung la mt cach chia se d liu rt tin li.

Nghe nhac "moi luc moi ni"

Kha ging tin ich phat phim, thng qua mang wifi, ngi s dung co kha nng iu khin va phat nhac trn moi loa c kt ni vao mang giai tri khng dy cua cn h.

Tin ich nay a co t kha lu, c trang bi trn cac b phat th h cu va thit bi phat nhac khng dy. Tuy nhin, theo cac chuyn gia thi phn mm Airport Express cua Apple co tinh nng ni tri va giup ngi dung iu khin loa t in thoai iPhone hoc iPod.

Ti anh t may anh ky thut s

Thay vi phai ni the nh may anh nh thng thng, the nh SD Eye-Fi th h mi cho phep tai trc tip anh ti may vi tinh.

H iu hanh iOS cua Apple h tr rt tt th nh SD Eye-Fi. Ngoai ra, ngi s dung cung co th tai trc tip anh ln mang trc tuyn Facebook hoc trang web nh Flickr v Picasa.

Gip in thoi nhn bit a im

Nhiu in thoi thng minh cho php ngi dng t lch trnh v in thoi s t ng lm nhng vic nh: m tivi, iu ha nhit , bt n khi bn ti nh hoc c quan. Nhng mt trong nhng vn ln khi s dng in thoi nh mt thit b iu khin thng minh l s nhn bit a im.

GPS l mt cng c hu hiu v ph bin trong lnh vc nh v, tuy nhin xc nh chnh xc ta hay vn phng lm vic ca bn khng phi l mt cng vic n gin. Hn na, sai s cho php ca GPS kh ln, v vy nh v bng GPS kh c th xc nh bn ang ng pha trong hay pha ngoi cnh ca cn h ca mnh. GPS cng rt ngn pin khin nhiu ngi s dng phi pht s khi m ng dng ny.

Mng wifi chnh l mt gii php thng minh dnh cho in thoi. Khi ngi s dng v ti nh, chic in thoi s t ng nhn bit v kt ni vi mng wifi ti nh v thc hin nhng cng vic c nh sn. ng dng ny hin ch c trn cc my dng h iu hnh Android.

ng b ha d liu, nh v m nhc

Cc y vi nm, khi nhng thit b nghe nhc nh iPod mi ra i, phng tin duy nht kt ni v ng b ha cc thit b ny l thng qua cng USB.

Tuy nhin, cng vi s pht trin ca cc chun kt ni cng mng wifi, ngy nay ngi s dng c th ng b v kt ni thit b cm tay vi mi my tnh cng nh h iu hnh mt cch d dng.

Vic ng b ha in thoi Android vi iTune, Winamp hoc iPhone vi h iu hnh Linux c th hin mt cch trn tru, n gin.

Ngoi ra, bn c th s dng mt s phn mm chuyn dng nh: Photosync, Wi-Fi File Explorer, Dazzboard, Android Manager Wi-Fi v Awesome Drop gip cng vic ng b d liu thun tin hn.

Nu nhn thc thnh cng th ngi s dng mi c php thng qua Subscriber Gateway i ra Internet, v thng tin tnh cc s c cng thu bao gi v AAA Server. Cng thu bao cn c kh nng iu khin truy nhp theo thi gian thc, cho php cung cp cc loi dch v a dng.Da theo m hnh mng c xy dng v phng n k thut ca h thng RADIUS v tnh cc th yu cu i vi i ch IP u ni ti cc router SHDSL bt buc phi l a ch thuc di IP cng cng (Public_IP) v phi c cp tnh do h thng cc hotspot s c kt ni v trung tm qua Internet do cc a ch ny phi c hiu trn Internet. V cc cng thu bao phi tin hnh trao i thng tin AAA vi RADIUS server t ti trung tm qun l mng nn cc a ch u ni ti cc SHDSL router phi c cp tnh, khng thay i sau mi ln h thng khi ng li.Theo thit k, c 2 trung tm mng l 75 inh Tin Hong, H Ni v 125 Hai B Trng, TP. HCh Minh. (Trong trng hp cn trin khai nhanh nhng im s dng Wireless Bridge, VDC 292Ty Sn c th c s dng thnh mt trung tm).Theo k thut u ni SHDSL, ti trung tm s kt ni ti DSLAM bng mt ng Fast Ethernet, kt ni ny c thc hin trn Switch trung tm. Kt ni i Internet c iu khin bi hai cng thu bao chy song song phn ti. Do h thng wireless, c c im l bng thng ln, mi trng a truy nhp nn cn thit phi c phng php bo v hp l trnh cc hnh thc tn cng vo mng VNN. Phng php bo v thch hp nht l s dng bc tng la (firewall) ti hai im trung tm theo m hnh nh trn.