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S lc v cng ngh WIFI & WIMAX

HC VIN CNG NGH BU CHNH VIN THNGKHOA CNG NGH THNG TIN

ti tiu lun


Lp cao hc CH10CNK1

Ging vinPhm Th Qu.

Nhm thc hin:-

ng Tuyt Chinh. Nguyn L Phng. V Th Mai. Phm Th Trang. ng c Dng Nguyn H Nguyt.

H Ni 10/2010

Hc vin cng ngh Bu chnh Vin Thng

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Mc lcTNG QUAN V MNG KHNG DY Mng khng dy l g u im: Nhc im: Phn loi mng khng dy A. B. Da trn vng ph sng, mng khng dy c chia thnh 5 nhm: Da trn cc cng ngh mng, mng khng dy c chia thnh 3 loi: 4 4 4 5 6 6 8 8 8 9 11 11 12 13 13 13 14 14 15 16 16 16 19 19 20 21 21 22 23 25

Cc m hnh mng khng dy A. B. WIFI Khi nim wifi Dng chun 802.11 A. B. C. D. E. Original IEEE 802.11 LAN Standard IEEE 802.11b IEEE 802.11a IEEE 802.11g IEEE 802.11n M hnh mng AD-HOC: M hnh mng INFRASTRUCTURE

Hot ng ca mng wifi A. B. C. D. E. F. Tn s hot ng Gii hn v mnh tn hiu Tc d liu bng thng Knh Cc tham s cu hnh im truy cp khng dy v nh tuyn

Bo mt trong mng wifi Gii thiu Bo mt bng WEP (Wired Equivalent Privacy) Bo mt bng WPA (Wifi Protected Access ) Tng cng bo mt vi chun 802.11i


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S lc v cng ngh WIFI & WIMAXPhng php ti u v mt s bin php gi mng Wifi an ton Kt lun WiMax Tng quan v WiMax c im. Cc chun WiMAX Chun 802.16 Cu trc mng (Network Topology) Chng giao thc (Protocol stack) Cng ngh iu ch Cng ngh song cng. Cng ngh ghp knh Cht lng dch vu Cc chun b sung ca WiMAX 802.16a 802.16b 802.16c 802.16d 802.16e Vn bo mt Cc im yu trong bo mt ca WiMAX Bin php tng cng bo mt cho WiMAX Kt lun u im v ng dng


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TNG QUAN V MNG KHNG DYMng khng dy l gMng khng dy l mt h thng cc thit b c nhm li vi nhau, c kh nng giao tip thng qua sng v tuyn thay v cc ng truyn dn bng dy. Ni mt cch n gin mng khng dy l mng s dng cng ngh m cho php hai hay nhiu thit b kt ni vi nhau bng cch s dng mt giao thc chun, nhng khng cn kt ni vt l hay chnh xc l khng cn s dng dy mng (cable). V y l mng da trn cng ngh 802.11 nn i khi cn c gi l 802.11 mng Ethernet, nhn mnh rng mng ny c gc t mng Ethernet 802.3 truyn thng. V hin ti cn c gi l mng Wireless Ethernet hoc Wi-Fi (Wireless Fidelity).

u im:Tnh d dng kt ni v thun tin trong s dng lm cho mng Wireless nhanh chng ngy cng ph bin trong cuc sng chng ta, h tr tch cc trong cng vic ca chng ta. - Gi thnh gim nhiu i vi mi thnh phn ngi s dng. - Cng ngh khng dy c tch hp rng ri trong b vi x l dnh cho my tnh xch tay ca INTEL v AMD, do tt c ngi dng my tnh xch tay u c sn tnh nng kt ni mng khng dy. - Mng Wireless cung cp tt c cc tnh nng ca cng ngh mng LAN nh Ethernet v Token Ring m khng b gii hn v kt ni vt l (gii hn v cable). - Tnh linh ng: to ra s thoi mi trong vic truyn ti d liu gia cc thit b c h tr m khng c s rng but v khong cch v khng gian nh mng c dy thng thng. Ngi dng mng Wireless c th kt ni vo mng trong khi di chuyn bt c ni no trong phm vi ph sng ca thit b tp trung (Access Point). - Mng WLAN s dng sng hng ngoi (Infrared Light) v sng Radio (Radio Frequency) truyn nhn d liu thay v dng Twist-Pair v Fiber Optic Cable. Thng thng th sng Radio c dung ph bin hn v n truyn xa hn, lu hn, rng hn, bng thng cao hn. - Cng ngh Wireless bao gm cc thit b v h thng phc tp nh h thng WLAN, in thoi di ng (Mobile Phone) cho n cc thit b n gin nh tay nghe khng dy, microphone khng dy v nhiu thit b khc c kh nng truyn


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S lc v cng ngh WIFI & WIMAX nhn v lu tr thng tin t mng. Ngoi ra cng bao gm c nhng thit b h tr hng ngoi nh Remote, in thoi truyn d liu trc din gia 2 thit b.

Nhc im:Bn cnh nhng u im ca mng Wireless nh l tnh linh ng, tin li, thoi mith mng Wireless vn khng th thay th c mng c dy truyn thng. Thun li chnh ca s linh ng l ngi dng c th di chuyn. Cc Server v my ch c s d liu phi truy xut d liu, v v tr vt l th khng ph hp (v my ch khng di chuyn thng xuyn c). - Tc mng Wireless b ph thuc vo bng thng. Tc ca mng Wireless thp hn mng c nh, v mng Wireless chun phi xc nhn cn thn nhng frame nhn trnh tnh trng mt d liu. - Trong mng c nh truyn thng th tn hiu truyn trong dy dn nn c th c bo mt an ton hn. Cn trn mng Wireless th vic nh hi rt d dng bi v mng Wireless s dng sng Radio th c th b bt v x l c bi bt k thit b nhn no nm trong phm vi cho php, ngoi ra mng Wireless th c ranh gii khng r rng cho nn rt kh qun l. - Bo mt trn mng Wireless l mi quan tm hng u hin nay. Mng Wireless lun l mi bn tm v s giao tip trong mng u cho bt k ai trong phm vi cho php vi thit b ph hp. Trong mng c nh truyn thng th tn hiu truyn trong dy dn nn c th c bo mt an ton hn. Cn trn mng Wireless th vic nh hi rt d dng bi v mng Wireless s dng sng Radio th c th b bt v x l c bi bt k thit b nhn no nm trong phm vi cho php, ngoi ra mng Wireless th c ranh gii khng r rng cho nn rt kh qun l. Bng so snh h thng Mng Khng dy v Mng C dy H thng Tc Mng Khng dy 11/54/108Mbps Bo mt khng m bo bng c dy do pht sng thng tin ra mi pha Thi cng trin khai nhanh Mng C dy 10/100/1000Mbps Bo mt m bo ch b l thng tin nu can thip thng vo v tr dy dn Thi cng phc tp do phi thit k

Bo mt

Thi cng v


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S lc v cng ngh WIFI & WIMAX trin khai Kh nng m rng v d dng Kh nng m rng khong cch tt vi chi ph hp l Cc v tr kt ni mng c th thay i m khng cn phi thit k li i dy cho ton b h thng i hi chi ph cao khi mun m rng h thng mng c bit l m rng bng cp quang Cc v tr thit k khng c ng phi thit k li nu thay i cc v tr kt ni mng

Tnh mm do

Phn loi mng khng dyC nhiu cch phn loi: A. Da trn vng ph sng, mng khng dy c chia thnh 5 nhm:

Hnh 1: Phn loi mng v tuyn WPAN: mng v tuyn c nhn. Nhm ny bao gm cc cng ngh v tuyn c vng ph nh tm vi mt n hng chc mt ti a. Cc cng ngh ny phc v mc ch ni kt cc thit b ngoi vi nh my in, bn phm, chut, a cng, kha USB,Hc vin cng ngh Bu chnh Vin Thng 6

S lc v cng ngh WIFI & WIMAX ng h,...vi in thoi di ng, my tnh. Cc cng ngh trong nhm ny bao gm: Bluetooth, Wibree, ZigBee, UWB, Wireless USB, EnOcean,... a phn cc cng ngh ny c chun ha bi IEEE, c th l nhm lm vic (Working Group) 802.15. Do vy cc chun cn c bit n vi tn nh IEEE 802.15.4 hay IEEE 802.15.3 ... WLAN : mng v tuyn cc b. Nhm ny bao gm cc cng ngh c vng ph tm vi trm mt. Ni bt l cng ngh Wifi vi nhiu chun m rng khc nhau thuc gia nh 802.11 a/b/g/h/i/... Cng ngh Wifi gt hi c nhng thnh cng to ln trong nhng nm qua. Bn cnh WiFi th cn mt ci tn t nghe n l HiperLAN v HiperLAN2, i th cnh tranh ca Wifi c chun ha bi ETSI. WMAN: mng v tuyn th. i din tiu biu ca nhm ny chnh l WiMAX. Ngoi ra cn c cng ngh bng rng BWMA 802.20. Vng ph sng ca n s tm vi km (tm 4-5km ti a). WWAN: Mng v tuyn din rng: Nhm ny bao gm cc cng ngh mng thng tin di ng nh UMTS/GSM/CDMA2000... Vng ph ca n cng tm vi km n tm chc km. WRAN: Mng v tuyn khu vc. Nhm ny i din l cng ngh 802.22 ang c nghin cu v pht trin bi IEEE. Vng ph c n s ln tm 40-100km. Mc ch l mang cng ngh truyn thng n cc vng xa xi ho lnh, kh trin khai cc cng ngh khc. So snh cc nhm mng: Cng ngh Mng Chun Tc 110-480 Mbps Trn Kbps Trn Mbps 720 Vng ph sng Trn 30 feet Bng tn 7.5 GHz

UWB (Ultra WPAN wideband) Bluetooth WPAN

802.15.3a

802.15.1

Trn 30 feet 300

2.4 GHz

Wi-Fi

WLAN

802.11a

54 Trn feet

5 GHz


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S lc v cng ngh WIFI & WIMAX Trn Mbps Trn Kbps Trn Mbps Trn Mbps 11 Trn feet 384 4-5 dm 300

Wi- Fi Edge/GPRS (TDMA- GMS)

WLAN

802.11b

2.4 GHz 1900 MHz 400-2100 MHz 18002100 MHz

WWAN

2.5 G

CDMA 2000/1x WWAN EV-DO WCDMA/ UMTS

3G

2.4

1-5 dm

WWAN

3G

2

1-5 dm

Tt c cc cng ngh ny u ging nhau ch chng nhn v chuyn tin bng cch s dng sng in t (EM). B. Da trn cc cng ngh mng, mng khng dy c chia thnh 3 loi: - Kt ni s dng tia hng ngoi. - S dng cng ngh Bluetooth. - Kt ni bng chun Wi-fi.

Cc m hnh mng khng dyA. M hnh mng AD-HOC: a. Khi nim: o L mng gm hai hay nhiu my tnh c trang b card khng dy. o Tng t m hnh peer to peer trong mng c dy. o Cc my tnh c vai tr ngang nhau. o Khong cch lin lc 30-100m. o S dng thut ton Spokesman Election Algorithm(SEA).


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S lc v cng ngh WIFI & WIMAX b. M hnh vt l:

c. Cch thit lp: o Thit b: Card khng dy. o Driver. o Tin ch. d. Cu hnh o Cc Staion phi cng BSSID. o Cc Staion phi cng knh. o Cc Station phi cng tc truyn. B. M hnh mng INFRASTRUCTURE a. Khi nim:Hc vin cng ngh Bu chnh Vin Thng 9

S lc v cng ngh WIFI & WIMAX L mng gm mt hay nhiu AP(Access Point) m rng phm vi hot ng ca cc Station c th kt ni vi nhau vi mt phm vi gp i. AP ng vai tr l im truy cp cho cc trm khch trao i d liuvi nhau v ruy xut ti nguyn ca my ch. Mi AP c th lm im truy cp cho 10-15 my khch (ty sn phm v hng sn xut) ng thi ti mt thi im. b. M hnh vt l:

c. Cch thit lp o Thit b: o Card mng khng dy. o Access Point. o Driver. o Tin ch. d. Cu hnh o Cc Station phi cng BSSID vi AP.

Hc vin cng ngh Bu chnh Vin Thng 10

S lc v cng ngh WIFI & WIMAX o Cc Station phi cng knh vi AP. o Cc Ap phi cng mt ESID nu mun h tr roaming.

WIFIKhi nim wifiWi-Fi vit tt t Wireless Fidelity 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. H thng ny hot ng mt s sn bay, qun caf, th vin hoc khch sn. H thng cho php truy cp Internet ti nhng khu vc c sng ca h thng ny, hon ton khng cn n cp ni. Ngoi cc im kt ni cng cng (hotspots), WiFi c th c thit lp ngay ti nh ring. Tn gi 802.11 bt ngun t vin IEEE (Institute of Electrical and Electronics Engineers) Vin k thut in v in t M. Vin ny a ra nhiu chun cho nhiu giao thc k thut khc nhau, v n s dng mt h thng s nhm phn loi chng; 3 chun thng dng ca WiFi hin nay l 802.11a/b/g. Trong mt mng Wi-Fi, my tnh v card mng wifi kt ni khng dy n mt b nh tuyn khng dy (router). Router c kt ni vi Internet bng mt modem, thng l mt cp hoc modem DSL. Bt k ngi dng trong vng 200 feet hoc hn (khong 61 mt) ca cc im truy cp sau c th kt ni vi Internet, d cho tc truyn ti tt, khong cch 100 feet (30,5 m), hoc t c ph bin hn. Cc tn hiu khng dy c th m rng phm vi ca mt mng khng dy. Mng wifi c th c "m", nh vy m ai cng c th s dng, hoc "ng" trong trng hp s dng mt mt khu. Mt khu vc bao ph truy cp khng dy thng c gi l mt im nng khng dy. C nhng n lc tin hnh chuyn ton b thnh ph, nh San Francisco, Portland, v Philadelphia, thnh im nng khng dy ln. Nhiu ngi trong s cc k hoch ny s cung cp min ph, dch v h tr qung co, dch v qung co min ph cho mt khon ph nh. San Francisco gn y chn Google cung cp cho n vi mt mng khng dy. Wifi s dng cng ngh v tuyn lin lc, thng thng hot ng tn s 2.4GHz. Wifi l cng ngh c thit k phc v cho cc h thng my tnh nh ca tng lai,Hc vin cng ngh Bu chnh Vin Thng 11

S lc v cng ngh WIFI & WIMAX l in thoi di ng v thit k tiu th in nng ti thiu. PDA, my tnh xch tay, v cc ph kin khc nhau c thit k tng thch vi wifi. Thm ch cn c in thoi c pht trin m c th chuyn i lin mch t cc mng di ng vo mng wifi m khng cn b mt cuc gi. Li ch ca wifi - Wireless Ethernet. Wi-Fi l mt thay th Ethernet. Wi-Fi v Ethernet, c hai mng IEEE 802 chia s mt s yu t ct li. - Extended Access. S vng mt ca dy v cp m rng truy cp vo nhng ni c dy v cp in khng th i hoc ni m n l qu t i vi h i. - Chi ph gim. Nh cp trn, s vng mt ca dy v cp in mang li xung gi. iu ny c thc hin bi s kt hp ca cc yu t, chi ph tng i thp ca cc b nh tuyn khng dy, khng cn o ho, khoan v cc phng php khc c th l cn thit lm cho cc kt ni vt l. - Vn ng. C dy buc bn c nh mt a im. Vi khng dy bn c th t do thay i v tr ca bn m khng b mt kt ni ca bn. - Tnh linh hot. M rng truy cp, gim chi ph, v tnh di ng to c hi cho cc ng dng mi cng nh kh nng ca gii php sng to mi cho cc ng dng di sn.

Dng chun 802.11Mng WLANs hot ng da trn chun 802.11 (802.11 c pht trin t nm 1997 bi nhm Institute of Electrical and Electronics Engineers), chun ny c xem l chun dng cho cc thit b di ng c h tr Wireless, phc v cho cc thit b c phm vi hot ng tm trung bnh. Cho n hin ti IEEE 802.11 gm c 4 chun trong h 802.11 v 1 chun ang th nghim: - 802.11 - l chun IEEE gc ca mng khng dy (hot ng tng s 2.4GHz, tc 1 Mbps 2Mbps). - 802.11b - (pht trin vo nm 1999, hot ng tng s 2.4-2.48GHz, tc t 1Mpbs - 11Mbps). - 802.11a - (pht trin vo nm 1999, hot ng tng s 5GHz 6GHz, tcHc vin cng ngh Bu chnh Vin Thng 12

S lc v cng ngh WIFI & WIMAX 54Mbps). - 802.11g - (mt chun tng t nh chun b nhng c tc cao hn t 20Mbps - 54Mbps, hin ang ph bin nht). - 802.11e - l 1 chun ang th nghim: y ch mi l phin bn th nghim cung cp c tnh QoS (Quality of Service) v h tr Multimedia cho gia nh v doanh nghip c mi trng mng khng dy. - Thc t cn mt vi chun khc thuc h 802.11 l: 802.11F, IEEE 802.11h, IEEE 802.11j, IEEE 802.11d, IEEE 802.11s. Mi chun c b sung nhiu tnh nng khc nhau. A. Original IEEE 802.11 LAN Standard Nm 1997, IEEE (Institute of Electrical and Electronics Engineers )to ra chun u tin ca WLAN, gi l 802.11 sau tn ca nhm pht trin (IEEE 802.11). Tuy nhin, 802.11 ch h tr mng bng thng ti a l 2Mbps (hot ng 2.4GHz vi tc l 1Mpbs hoc 2Mpbs)- qu chm cho hu ht cc ng dng. Do , cc sn phm 802.11 khng cn c sn xut. B. IEEE 802.11b IEEE m rng chun 802.11 ban u vo thng 7 nm 1999, to ra chun 802.11b. 802.11b cung cp bng thng ln ti 11Mbps (hot ng tng s 2.4GHz v tc tng dn 1Mpbs, 2Mpbs, 5,5Mpbs v 11Mpbs. 802.11b s dng tn s sng radio khng cn ng k 2.4GHz nh l chun 802.11. Nh sn xut thng thch s dng tn s ny lm gim gi thnh sn phm. Bi v s dng tn s khng ng k, cc thit b 802.11b c th xy ra nhiu t nhng sn phm cng s dng tn s nh l l vi sng, in thoi m bng con (cordless phones) v rt nhiu sn phm ng dng cng s dng di tn 2.4. Tuy nhin, ch cn lp t thit b 802.11b xa nhng thit b khc, nhng vn nhiu d dng c gii quyt. - u im: gi thnh r, di tn hiu tt v khng d dng b tc nghn. - Nhc im: Tc thp nht, lp t nh d b nhiu bi cc thit b cng di tn khng ng k. C. IEEE 802.11a Song hnh vi 802.11b, IEEE tip tc a ra chun m rng th hai cng da vo 802.11 u tin - 802.11a. Chun 802.11a s dng tn s 5GHz, tc 54Mbps trnhHc vin cng ngh Bu chnh Vin Thng 13

S lc v cng ngh WIFI & WIMAX c can nhiu t cc thit b dn dng. ng thi, chun 802.11a cng s dng k thut tri ph khc vi chun 802.11b - k thut tri ph theo phng php a phn chia tn s trc giao (Orthogonal Frequency Division Multiplexing-OFDM). y c coi l k thut tri hn so vi tri ph trc tip (DSSS). Do chi ph cao hn, 802.11a thng ch c s dng trong cc mng doanh nghip, ngc li, 802.11b thch hp hn cho nhu cu gia nh. Tuy nhin, do tn s cao hn tn s ca chun 802.11b nn tn hin ca 802.11a gp nhiu kh khn hn khi xuyn tng v cc vt cn khc. Do 802.11a v 802.11b s dng tn s khc nhau, hai cng ngh ny khng tng thch vi nhau. Mt vi hng sn xut bt u cho ra i sn phm "lai" 802.11a/b, nhng cc sn phm ny ch n thun l cung cp 2 chun sng Wi-Fi cng lc (my trm dng chun no th kt ni theo chun ). u im: tc nhanh, khng b nhiu vi nhng thit b khc. Nhc: gi thnh cao, bc sng ngn nn d b cn.

D. IEEE 802.11g Vo nm 2002 - 2003, sn phm WLAN c cung cp mt chun mi c tn gi l 802.11g. 802.11g l kt hp u im ca hai chun 802.11a v 802.11b: cung cp bng thng ln ti 54mbps v s dng di tn 2.4 cho cc thit b pht sng. V 802.11g hot ng cng tn s vi 802.11b, ngha l cc im truy cp (access point AP) 802.11g s lm vic vi card mng Wi-Fi chun 802.11b... Thng 7/2003, IEEE ph chun 802.11g. Chun ny cng s dng phng thc iu ch OFDM tng t 802.11a nhng li dng tn s 2,4GHz ging vi chun 802.11b. iu th v l chun ny vn t tc 54Mbps v c kh nng tng thch ngc vi chun 802.11b ang ph bin. - u im: Tc nhanh, tn hiu tt v khng d b cn. - Nhc im: gi thnh cao hn 802.11b, nhng c th b nhiu bi di tn khng cn ng k. E. IEEE 802.11n Chun Wi-Fi mi nht trong danh mc Wi-Fi l 802.11n. 802.11n c thit k ci thin tnh nng ca 802.11g v tng bng thng c h tr bng cch tn dng nhiu tn hiu khng dy v anten (gi l cng ngh MIMO-multiple-input and multipleoutput). Khi chun ny hon thnh, 802.11n s h tr tc ln n 300Mbps. 802.11n cng cho tm ph sng tt hn cc chun Wi-Fi trc nh tng cng Hc vin cng ngh Bu chnh Vin Thng 14

S lc v cng ngh WIFI & WIMAX tn hiu. Cc thit b 802.11n s tng thch ngc vi 802.11g. - u im: l tc nhanh nht, vng ph sng tt nht; tr khng ln hn chng nhiu t cc tc ng ca mi trng. - Nhc im: gi cao hn 802.11g; s dng nhiu lung tn hiu c th gy nhiu vi cc thit b 802.11b/g k cn. Cc c im k thut ca IEEE 802.11 802.11a Nm chun ph Thng 7/1999 802.11b Thng 7/1999 802.11g Thng 6/2003 802.11n Thng 9/2009 300Mbps hay cao hn hay DSSS hay CCK OFDM 2,4GHz 5GHz hay hay

Tc ti a

54Mbps

11Mbps

54Mbps DSSS CCK OFDM 2,4GHZ 1 20MHz

iu ch

OFDM

DSSS CCK

hay

Di tn s 5GHz trung tn (RF) Spatial Stream 1 rng bng 20MHz thng

2,4GHZ 1 20MHz

hay

1, 2, 3 hay 4 20 MHz hay 40 MHz

Hot ng ca mng wifiTruyn thng qua mng khng dy l truyn thng v tuyn hai chiu. C th: - Thit b adapter khng dy (hay b chuyn tn hiu khng dy) ca my tnh chuyn i d liu sang tn hiu v tuyn v pht nhng tn hiu ny i bng mt ng-ten. - Thit b router khng dy nhn nhng tn hiu ny v gii m chng. N gi thng tin ti Internet thng qua kt ni hu tuyn Ethernet.Hc vin cng ngh Bu chnh Vin Thng 15

S lc v cng ngh WIFI & WIMAX Qui trnh ny vn hot ng vi chiu ngc li, router nhn thng tin t Internet, chuyn chng thnh tn hiu v tuyn v gi n adapter khng dy ca my tnh. A. Tn s hot ng C hai tn hiu tn s hin ang c s dng bi cc mng Wi-Fi: 2.4 GHz - Bao gm 14 knh, mi ln vi mt bng thng ca MHz hot ng khong 2022 trong bng ISM. 802.11b / g mng li hot ng trong bng tn 2,4 GHz. N l mt tn s ng ngi v nhiu thit b khc hn 802,11 thit b hot ng trong . V d, Bluetooth cng nh nhiu sn phm tiu dng nh l vi ba, in thoi 5 GHz - Bao gm 13 knh, mi ln vi mt bng thng ca cc hot ng khong 20 MHz trong bng U-NII. mng 802.11a hot ng trong di tn 5. Hin nay, ban nhc ny t ng c hn 2,4 GHz, nhng iu ny c th thay i khi th trng khng dy tip tc pht trin. Cc tn hiu tn s cao c suy gim cao hn qua thng qua nhng tr ngi hn so vi tn hiu tn s thp hn. y l bi v mt s nng lng ca trng in t chuyn vo cc ti liu ca chng ngi vt (bc tng xi mng, tn l,) lm gim sc mnh ca tn hiu. B. Gii hn v mnh tn hiua. Top of Form

B qua cc ch ca RF can thip cho mt thi im, n c th ni rng cng tn hiu nhn c l mt chc nng ca sn lng in ca my pht, tn s s dng, khong cch truyn i bng tn hiu, v xy ra trc khi tn hiu nhn c. Nhn c tn hiu sc mnh, v do phm vi c th s dng, c th thay i t nay n thi im ny bi v c im tuyn truyn c nng ng v khng th on trc. iu ny c ngha rng nhng thay i nh trong mi trng c th dn n nhng thay i ln cho cng tn hiu Rx. iu quan trng l nhn c tn hiu ting n. Ting n l mt chc nng can thip vo ngun sc mnh, khong cch v bng thng. Ngoi ra, cc ngun vn c ting n gy ra bi qu trnh vt l c bn nh chuyn ng nhit ngu nhin ca khng kh. Trong thc t, Rx tn hiu-nhiu (SNR) l cn thit cho tc truyn dn cao hn. SNR l quan trng hn sc mnh tuyt i tn hiu Rx. C. Tc d liu bng thngHc vin cng ngh Bu chnh Vin Thng 16

S lc v cng ngh WIFI & WIMAX Cc iu khon tc d liu v thng i khi c s dng thay th cho nhau. T l d liu s lin quan tc d liu, trong khi thng qua s c s dng m t s thc t ca cc bit d liu truyn / giy thng qua cc phng tin khng dy. Thng lng l gim bt bng giao thc, cnh tranh khch hng /va chm, v truyn li. 802,11 i hi phi tch cc v kp thi ghi nhn ca mi khung truyn. Khng ging nh Ethernet c dy, ni m cc c hi can thip l tng i nh, 802,11 d on mt xc sut can thip, chi ph do nhiu hn l cn thit i ph vi thch thc ny. Ngoi ra, khng ging nh Ethernet c dy, 802,11 cho php la chn tc truyn dn t SNRs thun li c th c khc phc bng cch s dng tc d liu chm hn (nh chm nht l 1 Mbit / giy). Chn chm hn tc d liu ph hp c th dn n mt thng lng tng th c ci thin vi tc d liu cao hn m l b hng v truyn li. IEEE 802.11 ban u c xc nh c im k thut 802,11 hai tc d liu: 1 v 2 Mbps. Nhng mc gi thp l khng cho mt s ng dng, trong thc y s pht trin ca tiu chun vi mc gi 802,11 d liu nhanh hn. Nhng, hy nh rng khng phi lc no nhanh hn l tt hn. Cc 1 Mbps tc d liu l nhiu hn cn thit cho nhiu ng dng, n c cho l d liu tc mnh m nht cho cc ng dng cng nghip ni chung. Cc chun ca mng khng dy c to v cp bi IEEE.- 802.11 : y l chun u tin ca h thng mng khng dy. Chun ny cha

tt c cng ngh truyn hin hnh bao gm Direct Sequence Spectrum (DSSS), Frequence Hopping Spread Spectrum (FHSS) v tia hng ngoi. 802.11 l mt trong hai chun miu t nhng thao tc ca sng truyn (FHSS) trong h thng mng khng dy. Nu ngi qun tr mng khng dy s dng h thng sng truyn ny, phi chn ng phn cng thch hp cho cc chun 802.11. - 802.11b : Hin l la chn ph bin nht cho vic ni mng khng dy; cc sn phm bt u c xut xng vo cui nm 1999 v khong 40 triu thit b 802.11b ang c s dng trn ton cu. Cc chun 802.11b hot ng ph v tuyn 2,4GHz. Ph ny b chia s bi cc thit b khng c cp php, chng hn nh cc in thoi khng dy v cc l vi sng- l nhng ngun gy nhiu n mng khng dy dng chun 802.11b. Cc thit b 802.11b c mt phm vi hot ng t 100 n 150 feet (1 feet = 0,3048m) v hot ng tc d liu l thuyt ti a l 11 Mbit/s. Nhng trn thc t, chng ch t mt thng lng ti a t 4Hc vin cng ngh Bu chnh Vin Thng 17

S lc v cng ngh WIFI & WIMAX n 6 Mbit/s. (Thng lng cn li thng b chim bi qu trnh x l thng tin giao thc mng v kim sot tn hiu v tuyn). Trong khi tc ny vn nhanh hn mt kt ni bng rng DSL hoc cp v cho m thanh lin tc (streaming audio), 802.11b li khng nhanh truyn nhng hnh nh c nt cao. Li th chnh ca 802.11b l ch ph phn cng thp. - 802.11a : Vo cui nm 2001, cc sn phm da trn mt chun th hai, 802.11a, bt u c xut xng. Khng ging nh 802.11b, 802.11a hot ng ph v tuyn 5 GHz (tri vi ph 2,4GHz). Thng lng l thuyt ti a ca n l 54 Mbit/s, vi tc ti a thc t t 21 n 22 Mbit/s. Mc d tc ti a ny vn cao hn ng k so vi thng lng ca chun 802.11b, phm vi pht huy hiu lc trong nh t 25 n 75 feet ca n li ngn hn phm vi ca cc sn phm theo chun 802.11b. Nhng chun 802.11a hot ng tt trong nhng khu vc ng c: Vi mt s lng cc knh khng gi ln nhau tng ln trong di 5 GHz, bn c th trin khai nhiu im truy nhp hn cung cp thm nng lc tng cng trong cng din bao ph. Mt li ch khc m chun 802.11a mang li l bng thng cao hn ca n gip cho vic truyn nhiu lung hnh nh v truyn nhng tp tin ln tr nn l tng. - 802.11g : 802.11g l chun ni mng khng dy c IEEE ph duyt gn y nht (thng 6 nm 2003). Cc sn phm gn lin vi chun ny hot ng trong cng ph 2,4GHz nh nhng sn phm theo chun 802.11b nhng vi tc d liu cao hn nhiu - ln ti cng tc ti a l thuyt ca cc sn phm theo chun 802.11a, 54 Mbit/s, vi mt thng lng thc t t 15 n 20 Mbit/s. V ging nh cc sn phm theo chun 802.11b, cc thit b theo chun 802.11g c mt phm vi pht huy hiu lc trong nh t 100 n 150 feet. Tc cao hn ca chun 802.11g cng gip cho vic truyn hnh nh v m thanh, li Web tr nn l tng. 802.11g thit k tng thch ngc vi 802.11b v chng chia s cng ph 2,4GHz. Vic ny lm cho cc sn phm ca 2 chun 802.11b v 802.11g c th hot ng tng thch vi nhau. Chng hn, mt my tnh s tay vi mt PC card khng dy 802.11b c th kt ni vi mt im truy nhp 802.11g. Tuy nhin, cc sn phm 802.11g khi c s hin din ca cc sn phm 802.11b s b gim xung tc 802.11b. Trong khi cc mng 802.11a khng tng thch vi cc mng 802.11b hay 802.11g, cc sn phm bao gm mt s kt hp ca ph v tuyn 802.11a v 802.11g s cung cp nhng th tt nht. y l mt tin tt lnh cho chun 802.11a; trong mi trng gia nh, ni m tn hiu v tuyn cn phiHc vin cng ngh Bu chnh Vin Thng 18

S lc v cng ngh WIFI & WIMAX xuyn qua nhiu bc tng v vt cn, ch mt mnh tnh nng 802.11g c th s t c la chn bi v phm vi hot ng ngn hn ca n. D. Knh Truyn thng trc tip gia cc trm khng dy, cho d l trong mt mng li qung co c bit hoc mng c s h tng, xy ra trn mt knh: mt bng tn s quy nh cho vic i li ca cc tn hiu in t. Knh c t trong cu hnh ca im truy cp hoc router khng dy. Trn trm khng dy, knh c chn trong qu trnh qut ca cc mng c sn.

E. Cc tham s cu hnh Mt im truy cp, hoc router khng dy hot ng nh mt im truy cp, thng c cu hnh vi mt chng trnh tin ch c cung cp bi cc nh sn xut ca thit b. Mi trm khng dy, c khch hng v cc im truy cp, phi c cu hnh theo cc cch sau: Ch hot ng - c hai ty chn cho ch hot ng: c s v c bit. Bt k Wi-Fi c kh nng thit b c th to ra hoc tham gia mt mng Wi-Fi trong ch c bit. Ch c mt im truy cp hoc router c th to ra mt hot ng mng WiFi ch c s, cc thit b nhng nh RCM4400W khng to ra mng li nh vy.


S lc v cng ngh WIFI & WIMAX Knh iu khin- phn m rng 802,11 s dng (a, b, g, n. ..) v cc thnh phn qun l xc nh cc knh c sn cho mng. Nhng knh nn c s dng? i vi cc im truy cp c trong phm vi ca nhau, thit lp n mt knh khc nhau trnh s can thip khc. Vi chun 802.11b / g mng, in hnh l cc knh 1, 6, v 11 c chn v khng chng cho, m bo tch tn s trnh va chm, tuy nhin, cc knh khc c th c s dng bi cc mng ln cn trong cng phm vi. Mt s im truy cp cho php t ng thit lp cc knh.

- Tn mng - Dch v nh danh (SSID) thc cht l tn ca mt mng Wi-Fi. Mt s mng qung b SSID vi cc thit b khng dy trong phm vi. V hiu ha cc mng khc pht sng ca 1 SSID ca mng. Mt v d v mt s SSID l "WiFiRabbit". Hu ht cc im truy cp v b nh tuyn khng dy c mt SSID mc nh, chng hn nh l "Linksys" hoc "admin". SSID c ln n 32 byte, v c th dng bt k k t nh phn, tuy nhin, bn nn s dng m ASCII. F. im truy cp khng dy v nh tuyn Phn ny a ra mt s thng tin v cc im truy cp v b nh tuyn c s dng trong cc mng Wi-Fi. Cc c t 802,11 xc nh mt im truy cp (hoc, AP,) nh mt trm khng dy (STA) nhm cung cp truy cp vo cc dch v phn phi (DS). Mt nh tuyn khng dy l 802,11 ph hp cng cung cp truy cp vo cc dch v phn phi bi v c chc nng AP. S khc bit chnh gia mt im truy cp v nh tuyn l b nh tuyn khng dy cho php khch hng truy cp vo nhiu mng v thc hin ng cc AP cho php truy cp vo mt mng n. Tuy nhin, ti cc im truy cp nhiu AP trong nhng ngy ny c kh nng nh tuyn. nh tuyn khng dy thng c chc nng nhiu hn mt im truy cp ngoi vic c th nh tuyn trn mng con. Di y l danh sch cc tnh nng c th c mt nh tuyn khng dy c th thc hin:o o o DHCP my ch NAT / tng la VPN Pass-Through


S lc v cng ngh WIFI & WIMAXo o o RIP1 H tr DMZ Tch hp DSL hoc cp modem

C nhng im truy cp khng dy trn th trng c mt s cc tnh nng b sung thng kt hp vi cc b nh tuyn, chng hn nh my ch DHCP. Mng khng dy l trin khai tt nht trong mt vai tr truy cp lp, ngha l chng s dng nh l mt im i vo mng hu tuyn. Trong qu kh, vic truy cp thng l bng quay s, ADSL, cp, ethernet, mng hnh sao, b tip sng khung (frame relay), ATM, v.v.. Mng khng dy l mt phng php n gin khc truy cp internet. Mng khng dy l d liu trong tng NetWork ging nh tt c cc phng php trong danh sch. Tt c nhng iu dn ti s thiu ht tc v s phc hi, mng khng dy khng iu chnh nhng phng tin trong s phn b hoc vai tr ca li trong mng. Tt nhin, trong nhng mng nh, s khng c s khc bit gia li, phn phi hoc lp truy xut ca mng. Lp li ca mng phi rt nhanh v vng chc, c th gi mt lng ln lu lng vi mt cht kh khn v kinh nghim thi gian khng gim. S phn phi ca lp trong mng nn nhanh, mm do v ng tin cy.

Bo mt trong mng wifi Gii thiuS pht trin khng ngng ca mng WiFi trong vi nm gn y gn ging nh s bng n ca Internet trong nhng thp k qua. Tuy nhin mng WiFi vn l mt mng rt d b tn cng. T nm 1997 n by gi, rt nhiu nghin cu nhm tng cng tnh bo mt ca mng WiFi c thc hin. Mi trng khng dy l mt mi trng chia s (shared medium) trong thng tin truyn i c th d dng b thu li (intercepted). Do , bo v thng tin truyn trn knh khng dy l mt yu cu cp thit. Ti thi im hin ti. Wifi ang chim u th rt cao trong h thng mng khng dy trong phm vi nh. T mt thit b Router c tch hp b pht sng Wifi hay mt AccessPoint (AP) thu tn hiu v pht ra sng Wifi, chic Laptop hay chic Iphone ca bn d dng to kt ni truy cp mng Ethernet hay mng internet. Cc thit b Router , AccessPoint, c c ch bo mt khc nhau, cc chun bo mt gm c :Hc vin cng ngh Bu chnh Vin Thng 21

S lc v cng ngh WIFI & WIMAX - Wired Equivalency Privacy (WEP) s dng cng ngh m ha 64 bit hoc 128 bit. M ha 128 bit an ton hn. Nhng ai mun s dng mng c kch hot WEP u phi bit kha WEP, kha ny thng l mt khu dng dy s. - WiFi Protected Access (WPA) l mt bc tin ca WEP v hin gi l mt phn ca giao thc mng bo mt khng dy 802.11i. N s dng giao thc m ha ton b bng mt kha tm thi. Ging nh WEP, bo mt WPA cng phi ng nhp bng mt mt khu. Hu ht cc im truy cp khng dy cng cng hoc l m hon ton hoc bo mt bng WPA hay WEP 128 bit. - Media Access Control (MAC) bo mt bng cch lc a ch ca my tnh. N khng dng mt khu i vi ngi s dng, n cn c vo phn cng vt l ca my tnh. Mi mt my tnh u c ring mt a ch MAC c nht. Vic lc a ch MAC ch cho php nhng my ng k mi c quyn truy cp mng. Cn ng k a ch ca my tnh khi thit lp trong router.

Bo mt bng WEP (Wired Equivalent Privacy)WEP l mt thut ton bo nhm bo v s trao i thng tin chng li s nghe trm, chng li nhng ni kt mng khng c cho php cng nh chng li vic thay i hoc lm nhiu thng tin truyn. WEP s dng stream cipher RC4 cng vi mt m 40 bit v mt s ngu nhin 24 bit (initialization vector - IV) m ha thng tin. Thng tin m ha c to ra bng cch thc hin operation XOR gia keystream v plain text. Thng tin m ha v IV s c gi n ngi nhn. Ngi nhn s gii m thng tin da vo IV v kha WEP bit trc. S m ha c miu t bi hnh4.

Hnh 4: S m ha bng WEPHc vin cng ngh Bu chnh Vin Thng 22

S lc v cng ngh WIFI & WIMAX Nhng im yu v bo mt ca WEP - WEP s dng kha c nh c chia s gia mt Access Point (AP) v nhiu ngi dng (users) cng vi mt IV ngu nhin 24 bit. Do , cng mt IV s c s dng li nhiu ln. Bng cch thu thp thng tin truyn i, k tn cng c th c thng tin cn thit c th b kha WEP ang dng. - Mt khi kha WEP c bit, k tn cng c th gii m thng tin truyn i v c th thay i ni dung ca thng tin truyn. Do vy WEP khng m bo c confidentiality v integrity. - Vic s dng mt kha c nh c chn bi ngi s dng v t khi c thay i (tc c ngha l kha WEP khng c t ng thay i) lm cho WEP rt d b tn cng. - WEP cho php ngi dng (supplicant) xc minh (authenticate) AP trong khi AP khng th xc minh tnh xc thc ca ngi dng. Ni mt cch khc, WEP khng cung ng mutual authentication.

Bo mt bng WPA (Wifi Protected Access )WPA l mt gii php bo mt c ngh bi WiFi Alliance nhm khc phc nhng hn ch ca WEP. WPA c nng cp ch bng mt update phn mm SP2 ca microsoft.

WPA ci tin 3 im yu ni bt ca WEP :WPA cng m ha thng tin bng RC4 nhng chiu di ca kha l 128 bit v IV c chiu di l 48 bit. Mt ci tin ca WPA i vi WEP l WPA s dng giao thc TKIP (Temporal Key Integrity Protocol) nhm thay i kha dng AP v user mt cch t ng trong qu trnh trao i thng tin. C th l TKIP dng mt kha nht thi 128 bit kt hp vi a ch MAC ca user host v IV to ra m kha. M kha ny s c thay i sau khi 10 000 gi thng tin c trao i.

- WPA s dng 802.1x/EAP m bo mutual authentication nhm chng li man-in-middle attack. Qu trnh authentication ca WPA da trn mt authentication server, cn c bit n vi tn gi RADIUS/ DIAMETER. Server RADIUS cho php xc thc user trong mng cng nh nh ngha nhng quyn ni kt ca user. Tuy nhin trong mt mng WiFi nh (caHc vin cng ngh Bu chnh Vin Thng 23

S lc v cng ngh WIFI & WIMAX cng ty hoc trng hc), i khi khng cn thit phi ci t mt server m c th dng mt phin bn WPA-PSK (pre-shared key). tng ca WPAPSK l s dng mt password (Master Key) chung cho AP v client devices. Thng tin authentication gia user v server s c trao i thng qua giao thc EAP (Extensible Authentication Protocol). EAP session s c to ra gia user v server r chuyn i thng tin lin quan n identity ca user cng nh ca mng. Trong qu trnh ny AP ng vai tr l mt EAP proxy, lm nhim v chuyn giao thng tin gia server v user. Nhng authentication messages chuyn i c miu t trong hnh 5.

Hnh 5: Messages trao i trong qu trnh authentication.


S lc v cng ngh WIFI & WIMAX - WPA s dng MIC (Michael Message Integrity Check ) tng cng integrity ca thng tin truyn. MIC l mt message 64 bit c tnh da trn thut tan Michael. MIC s c gi trong gi TKIP v gip ngi nhn kim tra xem thng tin nhn c c b li trn ng truyn hoc b thay i bi k ph hoi hay khng. Tm li, WPA c xy dng nhm ci thin nhng hn ch ca WEP nn n cha ng nhng c im vt tri so vi WEP. u tin, n s dng mt kha ng m c thay i mt cch t ng nh vo giao thc TKIP. Kha s thay i da trn ngi dng, session trao i nht thi v s lng gi thng tin truyn. c im th 2 l WPA cho php kim tra xem thng tin c b thay i trn ng truyn hay khng nh vo MIC message. V c im ni bt th cui l n cho php multual authentication bng cch s dng giao thc 802.1x.

Nhng im yu ca WPA.im yu u tin ca WPA l n vn khng gii quyt c denial-of-service (DoS) attack. K ph hoi c th lm nhiu mng WPA WiFi bng cch gi t nht 2 gi thng tin vi mt kha sai (wrong encryption key) mi giy. Trong trng hp , AP s cho rng mt k ph hoi ang tn cng mng v AP s ct tt c cc ni kt trong vng mt pht trch hao tn ti nguyn mng. Do , s tip din ca thng tin khng c php s lm xo trn hot ng ca mng v ngn cn s ni kt ca nhng ngi dng c cho php (authorized users). Ngoi ra WPA vn s dng thut tan RC4 m c th d dng b b v bi FMS attack ngh bi nhng nh nghin cu trng i hc Berkeley. H thng m ha RC4 cha ng nhng kha yu (weak keys). Nhng kha yu ny cho php truy ra kha encryption. c th tm ra kha yu ca RC4, ch cn thu thp mt s lng thng tin truyn trn knh truyn khng dy. WPA-PSK l mt bin bn yu ca WPA m n gp vn v qun l password hoc shared secret gia nhiu ngi dng. Khi mt ngi trong nhm (trong cng ty) ri nhm, mt password/secret mi cn phi c thit lp.

Tng cng bo mt vi chun 802.11iChun 802.11i c ph chun vo ngy 24 thng 6 nm 2004 nhm tng cng tnh mt cho mng WiFi. 802.11i mang y cc c im ca WPA. Tp hp nhng giao thc ca 802.11i cn c bit n vi tn gi WPA 2. Tuy nhin, 802.11i s dng thut tonHc vin cng ngh Bu chnh Vin Thng 25

S lc v cng ngh WIFI & WIMAX m ha AES (Advanced Encryption Standard) thay v RC4 nh trong WPA. M kha ca AES c kch thc l 128, 192 hoc 256 bit. Tuy nhin thut ton ny i hi mt kh nng tnh ton cao (high computation power). Do , 802.11i khng th update n gin bng software m phi c mt dedicated chip. Tuy nhin iu ny c c tnh trc bi nhiu nh sn xut nn hu nh cc chip cho card mng Wifi t u nm 2004 u thch ng vi tnh nng ca 802.11i.

Phng php ti u v mt s bin php gi mng Wifi an ton Mt phng php ti u v gi cho mng Wifi an ton:Ngy cng c nhiu mng Wifi c cung cp min ph. y va l tin tt va l tin xu. Tt bi bn c nhiu la chn; xu bi kh nng hacker t nhp t xa vo my tnh cao hn. Di y l mt phng php ti u v gi cho mng Wifi ca bn lun c an ton. Ti u Wifi cho VoIP, video, v game. Kch hot cc ng dng QoS u tin gi d liu Tt Wifi khi khng s dng Kch hot Wifi trong Windows XP Kch hot/v hiu ho Wifi trong Windows Vista Truy tm k t nhp vo mng Wifi Nhn cnh bo khi thit b mi kt ni Truy tm "k mi n" Chia s hotspot S dng Wifi chia s Wifi An ton kt ni hotspot Mng VPN c qung co V hiu ho mng Wifi ngang hngHc vin cng ngh Bu chnh Vin Thng 26

S lc v cng ngh WIFI & WIMAX Cu hnh Windows XP v hiu ho cc mng Ad-Hoc Tt mng Ad-Hoc

Nhng bin php bo mt n gin:Hin nay mng khng dy dn tr nn ph bin vn phng, cc qun c ph...Tuy nhin, my tnh kt ni Wifi l i tng rt d b hacker li dng. Di y l nhng bin php bo mt d lm. 1. S dng mng ca cng ty 2. Lun gi mt danh sch kt ni "sch" 3. Kch hot chc nng bo mt trn router 4. t mt khu 5. Kch hot chc nng bo mt web-mail Thng thng khi ng nhp vo mng Wifi va mi thit lp ch cn nhp chn SSID v nhp ng mt khu m ha WPA-PSK t v nhn nt Connect. Kt ni thnh cng c th "v t" lt web, chia s tp tin... vi cc my ngang hng trong mng LAN. Mt vn c bn trong bo mt mng Wifi cn quan tm l vic thit lp m ha, chng trng hp truy cp mng Wifi bt hp php. Tht vy, nu mng Wifi ca hng xm l Open Network (khng ci t mt khu m ha) th bn c th ng nhp vo mng d dng dng Internet min ph, thm ch khai thc ti nguyn...

Kt lunTrn con ng i t WEP n 802.11i, rt nhiu concept v bo mt ra i. C 6 concept c bn v bo mt ca mt mng vin thng, l : Identification, authentication, authorization, confidentiality, integrity & non-repudiation . WEP tht bi v mt bo mt v n c xy dng m khng tnh n nhng concept ny. Tuy nhin phi nhn nhn rng lc WEP ra i ngi ta khng lng c s pht trin bng n ca mng khng dy nn bo mt ca WEP lc rt n gin. By gi 802.11i ra i tng cng bo mt cho mng khng dy Wifi. Tuy nhin 802.11i (WPA2) ch c th software upgrade nu hardware c th p ng AES. Nu khng th phi cn hardware upgrade c th s dng 802.11i. V ngoi ra nhng sn phm thch ng vi 802.11i li khng th thch ng vi WEP.



WiMaxTng quan v WiMaxWiMax (Worldwide Interoperability for Microwave Access) l mt mng khng dy bng thng rng. WiMax c thit k da vo tiu chun IEEE 802.16. WiMax gii quyt tt nht nhng vn kh khn trong vic qun l u cui. WiMax s dng k thut sng v tuyn kt ni cc my tnh trong mng Internet thay v dng dy kt ni nh ADSL hay cp modem. WiMax nh mt tng i trong vng ln cn hp l n mt trm ch m n c yu cu thit lp mt ng d liu n Internet. Ngi s dng trong phm vi t 3 n 5 dm so vi trm ch s c thit lp mt ng dn cng ngh NLOS (Non-Line-Of-Sight) vi tc truyn d liu rt cao l 75Mbps. Cn nu ngi s dng trong phm vi ln hn 30 dm so vi trm ch th s c anten s dng cng ngh LOS (Line-Of-Sight) vi tc truyn d liu gn bng 280Mbps. WiMax l mt chun khng dy ang pht trin rt nhanh, ha hn to ra kh nng kt ni bng thng rng tc cao cho c mng c nh ln mng khng dy di ng, phm vi ph sng c m rng.

Theo nhu cu ca cc dch v bng thng rng ang pht trin mnh m, cc gii php truyn thng cung truy cp bng thng rng tc cao s dng dy cp nh DSL,Hc vin cng ngh Bu chnh Vin Thng 28

S lc v cng ngh WIFI & WIMAX Ethenet, v truyn dn quang. Tuy nhin, vic xy dng v bo tr h thng cp rt kh v t , cha k n vic hn ch v phm vi v tnh linh hot ca cc thit b cui vi cng ngh c dy l rt hn ch. Cng ngh truy cp khng dy (BWA) rt mm do, hiu qu, gi c hp l ang l gii php cho nhiu bi ton. S ni rng qui nh v tn s v tuyn cng y mn s pht trin ca cng ngh BWA . WiMAX l mt trong nhiu cng ngh khng dy ph bin hin nay, n cung cu truy cp khng dy tc cao cho cc WMAN (Wireless metropolitan area network, mng khng dy th). Chun IEEE 802.16 thng c gi l WiMAX, l mt c t cho chun lin lc khng dy bng thng rng. pht trin cho WMAN. So vi mt mng c dy phc tp, mt h thng WiMAX ch gm 2 phn: trm c s WiMAX (base station - BS) v trm thu bao (subscriber - SS). V vy, n c th xy dng nhanh chng vi mc gi thp. Khng dng li , WiMAX cn xem l bc tip theo ca cng ngh thng tin di ng. Sc mnh thng hp ca chun WiMAX v CDMA c so snh vi 4G.

c im.WiMax c pht trin vi nhiu c im nh: Cu trc mm do: WiMax h tr cc cu trc h thng bao gm im a im, cng ngh li (mesh) v ph sng khp mi ni. iu khin truy nhp MAC) phng tin truyn dn h tr im a im v dch v rng khp bi lp lch mt khe thi gian cho mi trm di ng (MS). Nu c duy nht mt MS trong mng, trm gc (BS) s lin lc vi MS trn c s im im. Mt BS trong mt cu hnh im im c th s dng anten chm hp hn bao ph cc khong cch xa hn. Cht lng dch v QoS : WiMax c th c ti u ng i vi hn hp lu lng s c mang. C 4 loi dch v c h tr: dch v cp pht t nguyn (UGS), dch v hi vng thi gian thc (rtPS), dch v hi vng khng thi gian thc (nrtPS), n lc tt nht (BE). Trin khai nhanh: So snh vi trin khai cc gii php c dy, WiMAX yu cu t hoc khng c bt c s xy dng thit lp bn ngoi. V d, o h to rnh cc ng cp th khng yu cu. Cc nh vn hnh m c c cc ng k s dng mt trong cc di tn ng k, hoc d kin s dng mt trong cc di tn khng ng k, khng cn trnh cc ng dng hn na cho chnh ph. Dch v a mc: Cch thc ni m QoS c phn pht ni chung da vo s tha thun mc dch v (SLA) gia nh cung cp dch v v ngi s dng cuiHc vin cng ngh Bu chnh Vin Thng 29

S lc v cng ngh WIFI & WIMAX cng. Chi tit hn, mt nh cung cp dch v c th cung cp cc SLA khc nhau ti cc thu bao khc nhau, thm ch ti nhng ngi dng khc nhau s dng cng MS. Cung cp truy nhp bng rng c nh trong nhng khu vc th v ngoi , ni cht lng cp ng th km hoc a vo kh khn, khc phc thit b s trong nhng vng mt thp ni m cc nhn t cng ngh v kinh t thc hin pht trin bng rng rt thch thc. Tnh tng thch: WiMax da vo quc t, cc chun khng c tnh cht r rt nh cung cp, to ra s d dng i vi ngi dng cui cng truyn ti v s dng MS ca h cc v tr khc nhau, hoc vi cc nh cung cp dch v khc nhau. Tnh tng thch bo v s u t ca mt nh vn hnh ban u v n c th chn la thit b t cc nh i l thit b, v n s tip tc a chi ph thit b xung khi c mt s chp nhn a s. Di ng: IEEE 802.16e b sung thm cc c im chnh h tr kh nng di ng. Nhng ci tin lp vt l OFDM (ghp knh phn chia tn s trc giao) v OFDMA (a truy nhp phn chia tn s trc giao) h tr cc thit b v cc dch v trong mt mi trng di ng. Nhng ci tin ny, bao gm OFDMA m rng c, MIMO (nhiu u ra nhiu u vo), v h tr i vi ch idle/sleep v hand off, s cho php kh nng di ng y tc ti 160 km/h. Mng WiMax di ng cho php ngi s dng c th truy cp Internet khng dy bng thng rng ti bt c trong thnh ph no. Li nhun: WiMax da vo mt chuN n quc t m. S chp nhn a s ca chun v s dng chi ph thp, cc chip c sn xut hng lot, s a chi ph gim t ngt v gi cnh tranh xy ra s cung cp s tit kim chi ph ng k cho cc nh cung cp dch v v ngi s dng cui cng. Mi trng khng dy c s dng bi WiMax cho php cc nh cung cp dch v ph v nhng chi ph gn vi trin khai c dy, nh thi gian v cng sc. Hot ng NLOS: Kh nng hat ng ca mng WiMax m khng i hi tm nhn thng gia BS v MS. Kh nng ny ca n gip cc sn phm WiMAX phn pht di thng rng trong mt mi trng NLOS. Ph sng rng hn: WiMAX h tr ng nhiu mc iu ch, bao gm BPSK, QPSK, 16QAM, 64QAM. Khi yu cu vi b khuch i cng sut cao v hot ng vi iu ch mc thp (v d BPSK hoc QPSK). Cc h thng WiMAX c th ph sng mt vng a l rng khi ng truyn gia BS v MS khng b cnHc vin cng ngh Bu chnh Vin Thng 30

S lc v cng ngh WIFI & WIMAX tr. M rng phm vi b gii hn hin ti ca WLAN cng cng (hotspot) n phm vi rng (hotzone) cng cng ngh th c th s dng nh v di chuyn. nhng iu kin tt nht c th t c phm vi ph sng 50 km vi tc d liu b h thp (mt vi Mbit/s), phm vi ph sng in hnh l gn 5 km vi CPE (NLOS) trong nh v gn 15km vi mt CPE c ni vi mt anten bn ngoi (LOS). Dung lng cao: C th t c dung lng 75 Mbit/s cho cc trm gc vi mt knh 20 MHz trong cc iu kin truyn sng tt nht. Tnh m rng. Chun 802.16 -2004 h tr cc di thng knh tn s v tuyn (RF) mm do v s dng li cc knh tn s ny nh l mt cch tng dung lng mng. Chun cng nh r h tr i vi TPC (iu khin cng sut pht) v cc php o cht lng knh nh cc cng c thm vo h tr s dng ph hiu qu. Chun c thit k t t l ln ti hng trm thm ch hng nghn ngi s dng trong mt knh RF. Cc nh vn hnh c th cp pht li ph qua hnh qut nh s thu bao gia tng. H tr nhiu knh cho php cc nh ch to thit b cung cp mt phng tin ch trng vo phm vi s dng ph v nhng quy nh cp pht c ni r bi cc nh vn hnh trong cc th trng quc t thay i khc nhau.

Cc chun WiMAXMc ch ca vic pht trin cc chun 802.16 l gip cho nn cng nghip cung cp cc gii php tng thch v tng tc c khng ph thuc nh cung cp v tng hiu qu kinh t ca cc sn phm WiMAX. HIn ti, WiMAX c 2 bin th: mt l ng dng khng dy c nh (Fixed wireless application) (qui nh trong chun IEEE 802.162004) v dch v khng dy cho di ng(mobile wireless service) (qui nh trong chun IEEE 802.16e). C hai chun c pht trin t IEEE 802.16 v IEEE 802.16a. Chun 802.16 chi xc nh tng vt l (PHY) v tng iu khin truy cp m trng(Media access control - MAC).



Chun 802.16Chun 802.16 c gi l h thng truy cp khng dy c nh (FBWA) l phin bn u tin ca dng chun 802.16 (cng b vo April 2002). N xc nh cc h thng khng dy bng thng rng hot ng trn di tn c cp php 10-66GHz, vic p ng di tn ny l kh t nhng n lm gim thiu nhiu t cc bng cao tn v rng bng ln. Bi v sng radio l rt ngn nn chng khng th xuyn qua cc ta nh, chun 802.16 ch s dng cho cc kt ni (tm nhn thng) line of sight (LOS). So vi kt ni nonline of sight (NLOS), LOS khng c mm d nhng mnh m v n nh hn. IEEE 802.16 c th tng tc vi cc mng khng dy khc nh h thng cellular v Wireless local area network (WLAN).

Cu trc mng (Network Topology)802.16 nh ngha 2 cu trc mng: point to point v point to multipoint. Kt ni PTP tc l s kt ni gia 2 thnh phn: BS v thu bao u cui. N s dng ti nguyn mt cch khng hiu qu v lng ph dn ti chi ph thc thi cao, N thng ch c s dng phc v cc khch hng cao cp (vd cc t chc nghin cu). Trong trng hp ny, cc kt ni n cha tt c bng thng c th to ra ng truyn tc cao. Mc d PTP c th p dng cho nhiu trng hp c bit song n qu t vi i b phn khch hng. Vi m hnh PMP, n s nhm mt s thu bao u cui kt ni ti mt BS c lp, n l gii php tt cho cc ngi dng khng cn ht bng thng. Bng thng khng s dng n trong mt thi im s c chia s gia cc ngi dng trong nhm, qua lm gim chi ph.



Chng giao thc (Protocol stack)Chun 802.16 nh ngha 2 lp thp nht ca m hnh OSI: MAC v PHY.

Lp chu trch nhim xc nh SS no n th c truyc p vo mng v c chia thnh 3 phn con: Service-specific convergence (hi t) sublayer, MAC common part sublayer (CPS), Security sublayer. CS chuyn i d liu u vo nhn c t CS service Access point (SAP) t cc gi d liu MAC. S chuyn i nh x thng tin t mng ngaoif vo thnh thng tin IEEE 802.16 MAC, v d nh lung dch v v nh danh kt ni. Chun hin ti c 2 c t CS: ATM CS v Packet CS. CS cn chu trch nhim chun b v khi to Q v cho php cp pht bng thng.Hc vin cng ngh Bu chnh Vin Thng 33

S lc v cng ngh WIFI & WIMAX CPS chu trch nhim iu khin chc nng truy cp, cp pht bng thng, m bo kt ni v bo tr. D liu, iu khin PHY, v cc thng tin qun l khc c chuyn i gia MAC CPS v PHY thng qua cc PHY SAP. Tng bo mt chu trch nhim cng thc, chuyn i kha v m ha. IEEE 802.16 PHY chu trch nhim truyn dn v tip nhn d liu. N nh ngha di tn 10-66Ghx vi LOS ba BS v SS. IEEE 802.16 h tr nhiu kn bng rng nh 20, 25, 28 MHz.

Cng ngh iu chIEEE 802.16 s dng m hnh iu ch n chuyn (single-carrier). Vi n, tt c cc gi tin c truyn dn tun t qua mt di tn n. N h tr 3 m hnh iu ch: QPSK (quadrature (gc vung) phase shift keying), 16QAM(quadrature amplitude modulation), 64QAM. Th t iu ch cng cao cho php nhiu bt m ha cho mt t th thu ddowwcj cng nhiu t l d liu. Tuy nhin th t t iu ch thp s lm chm tc truyn dn.

Cng ngh song cng.802.16 h tr c ghp knh phn tn (FDD) v ghp knh phn thi (TDD). FDD yu cu 2 knh: mt truyn dn v mt tip nhn trong khi TDD l mt knh n c chia s cho c ng ti ln v xung nhng c phn cch bi cc time slots khc nhau. FDD c thit k cho cc truyn dn i xng (symmetrical traffic) vi di tn thp hn v gi cao nhng tr ngn. Ngc li TDD h tr c i xng v bt xng (asymmetrical) truyn dn nn vic s dng tn s tt hn, nhng n khng th truyn v nhn cng mt thi im.

Cng ngh ghp knhCng ngh ghp knh c s dng trong 802.16 l ghp knh phn thi (TDM time division multiplexing) cho knh down v TDMA (time division multiple access) cho knh up. Trong TDM, cc thu bao cha s bng tn nhng c cp pht cc time slotsHc vin cng ngh Bu chnh Vin Thng 34

S lc v cng ngh WIFI & WIMAX khc nhau. TDMA l mt m hnh a truy cp mm do vi cc time slot c th c cp pht cho cc thu bao try thuc vo ch c nh hay ch phn tranh (contentions).

Cht lng dch vu cho php cc dch v cht lng khc nhau, truyn up cho php c nhm thnh 4 nhm ng dng ca 802.16 MAC: Unsolicited grant services (UGS): UGS c thit k h tr cc dch v vi tc bt c nh nh T1/E1 emulation v voice over IP (VoIP) m khng c im lng. Real-time polling services (rtPS): c s dng h trwoj cc dch v thi gian thc tc bit thay i nh MPEG v VoIP c im lng. Nonreal-time polling services (nrtPS): c s dng h trwoj cc dch v khng cn thi gian thc vi tc bit thay i nh FTP. Best-effort (BE) services: Vi cc dch v BE, cc gi c y i theo c ch rst-in-rst-out. Web browsing l mt v d.

Cc chun b sung ca WiMAX 802.16aChun ny s dng bng tng c bn quyn t 2 11 Ghz. y l bng tng thu ht c nhiu quan tm nht v tn hiu truyn c th vt c cc chng ngi trn ng truyn. 802.16a cn thch ng cho vic trin khai mng Mesh m trong mt thit b cui (terminal) c th lin lc vi BS thng qua mt thit b cui khc. Vi c tnh ny, vng ph sng ca 802.16a BS s c ni rng.

802.16bChun ny hot ng trn bng tng t 5 6 Ghz vi mc ch cung ng dnh v vi cht lng cao (QoS). C th chun u tin truyn thng tin ca nhng ng dng video, thoi, real-time thng qua nhng lp dch v khc nhau (class of service). Chun ny sau c kt hp vo chun 802.16a.

802.16cChun ny nh ngha thm cc profile mi cho di bng tng t 10-66GHz vi mc ch ci tin interoperability.

802.16dC mt s ci tin nh so vi chun 802.16a. Chun ny c chun ha 2004. Cc thit b pre-WiMAX c trn th trng l da trn chun ny.Hc vin cng ngh Bu chnh Vin Thng 35


802.16eang trong giai on hon thin v chun ha. c im ni bt ca chun ny l kh nng cung cp cc dch v di ng (vn tc di chuyn ln nht m vn c th dng tt dch v ny l 100km/h). Ngoi ra cn c nhiu chun b sung khc ang c trin khai hoc ang trong giai on chun ha nh 802.16g, 802.16f, 802.16h...

Vn bo mt Cc im yu trong bo mt ca WiMAXLp vt l v lp con bo mt

Hnh 1 Lp giao thc trong IEEE 802.16

Trong chun IEEE 802.16, cc mi e da an ninh bo mt c th xy ra i vi c lp MAC v lp vt l. Lp vt l ca mng 802.16 d b tn cng bi cc phng thc tn cng Jamming v Scrambling. Trong phng thc tn cng Jamming (tn cng theo kiu chn p), k tn cng to ra mt ngun nhiu mnh nhm lm gim dung lng ca knh, v th dn n tnh trng t chi yu cu dch v. Scrambling tng t nh tn cng Jamming, nhng c thc hin trong mt khong thi gian ngn hng vo mt khung c bit, v d nh lm xo trn cc bn tin iu khin v cc bn tin qun l. Tn cng Jamming c th pht hin bng cc thit b phn tch ph v tuyn. Trong khi tn cng Scrambling kh pht hin hn do tnh khng lin tc ca n, nhng vn c th pht hin bng cch gim st hiu sut mng. Hin nay, cc nghin cu v cc phng thc tn cng Jamming v Scrambling i vi mng IEEE 802.16 c cng b rng ri trn cc tp ch chuyn ngnh trn th gii. Trong chun IEEE 802.16, lp con bo mt c mc ch chnh l bo v cc nh cungHc vin cng ngh Bu chnh Vin Thng 36

S lc v cng ngh WIFI & WIMAX cp dch v ngn chn vic n cp dch v, ch khng phi l bo v nhng ngi s dng (NSD) dch v. Rt d nhn thy l lp con bo mt ch bo v d liu lp 2 trong m hnh 7 lp OSI, n khng m bo m ha d liu NSD u cui u cui. V li, n khng bo v lp vt l, do y cn phi b sung thm cc gii php m bo an ton cho lp vt l v bo mt cho cc lp cao hn trong mng. n cp ID cng l mt mi e da ng quan tm, k tn cng s dng phng thc ny nhm n cp a ch phn cng ca mt thu bao no ri s dng cho thit b ca mnh. a ch ny c th b nh cp qua giao din khng gian bng cch thu li cc bn tin qun l. S dng phng thc ny, k tn cng c th to ra mt BS gi mo hot ng nh mt BS tht. Mt him ha in hnh khc na c th xy ra xut pht t cch thc tn cng Water Torture Attack (tn cng thc l), trong phng php ny mt k tn cng gi mt lot cc khung lm tiu hao nng lng pin ca my thu. Thm vo , k tn cng vi mt b thu RF ti mt v tr thun li c th thu li d liu gi qua mi trng khng dy, do yu cu phi b sung thm k thut bo m tnh tin cy cho mng. Mng da trn chun 802.16a b sung thm hot ng theo cu hnh Mesh, iu ny dn ti mt mi e da bo mt mi khc, v d nh tin cy ca nt nhy tip theo trong mng Mesh do cc k thut bo mt hin nay cha th gii quyt tt c vn ny. Vic b sung h tr tnh di ng trong chun IEEE 802.16e cng s to nhiu c hi cho cc k tn cng, khi m v tr vt l ca k tn cng gi y khng cn b gii hn, cc bn tin qun l lc ny s phi i mt vi nhiu ri ro hn so vi trong mng IEEE 802.11. Do , cn phi a ra mt gii php duy tr mt kt ni tin cy khi mt SS di chuyn qua li gia cc cell phc v. Ngoi ra, vi mt b thu pht RF c cu hnh hp l, mt k tn cng c th thit lp mt knh v tuyn RF, gi mo khung mi v bt gi, thay i v truyn li cc khung t mt kha cnh c cho php. Thit k ny phi m bo chc chn mt cng ngh nhn thc d liu. N cng c th gi li mt khung khng b thay i mt cch hp l. Trong trng hp khong cch truyn ti l ln, giao din v tuyn v khong cch c th cho php mt k tn cng sp xp li v la chn cn thn cc khung chuyn tip. Do thit k phi tm c cc khung c dng li.Vn nhn thc ln nhauHc vin cng ngh Bu chnh Vin Thng 37

S lc v cng ngh WIFI & WIMAX Hai loi chng nhn c phn loi bi chun IEEE 802.16: mt l cc chng nhn cho cc nh sn xut v loi th hai l cho cc chng nhn SS. Khng c chng nhn cho BS. Mt chng nhn nh sn xut xc nhn nh sn xut ca mt thit b IEEE 802.16. N c th t chng nhn hoc c xc nhn bi bn th 3. Mt chng nhn SS xc nhn mt SS ring bit v tnh n c a ch MAC ca n. Cc nh sn xut to v xc nhn nhng chng nhn SS. Nhn chung BS s dng kha cng khai ca chng nhn nh sn xut xc minh chng nhn SS v t y vic nhn dng thit b l c cng nhn. Thit k ny tha nhn rng SS duy tr kha ring tng ng ti kha cng khai ca n trong mt kho lu tr kn, chng li k tn cng t tha hip d dng n. Khe h ln ca thit k bo mt IEEE 802.16 l thiu mt chng nhn BS. N ch bo v cc my trm client chng li tn cng lp li hay tn cng gi mo nh cung cp mt k hoch cho nhn thc ln nhau. iu ny c h tr bi Wongthavarawat (2005) khng c nhn thc ln nhau no c cung cp, chng c th lm tn hi bng cc tn cng lp li v xen gia v chng nhn SS l mt phng php nhn thc gii hn. Trong 802.16e, EAP c th thc hin nhng phng php nhn thc c bit ging nh EAPTLS (chng nhn da trn X.509).Cc nh ngha khng r rng

Thit k IEEE 802.16 tht bi trong vic nh ngha mt cch r rng s SA c cp php, cho mt v d, trng thi ca SA khng bao gi phn bit mt SA c cp php t mt ci khc, v do c th b tn hi t kiu tn cng lp li. iu ny s tr thnh vn c bit khi IEEE 802.16e thc s di ng v chuyn vng. Ngoi ra SS khng th xc nhn s dn li d liu cc SA. Do k hoch m ha c th b tn hi bi cc kiu tn cng s dng li kha m ha. Thm vo cc BS khng c cp php khng cha s nhn dng BS, t y SS khng th phn bit trao quyn t cc BS khng c trao quyn. n y chng ta c th tha nhn rng s ln trnh n t SS chng li vic qun l kha v m ha, t s bo v SS trc cc tn cng lp li v gi mo. Mt gii php chng li nhng tn hi t tn cng lp li l s dng b to gi tr ngu nhin t BS v SS ti cc SA trao quyn. Theo th cp kha ring v cng khai c s dng xc nhn cc a ch MAC ging nhau vi iu kin l phi nh ngha mt cch r rng tt c cc xc nhn a ch MAC m bo a ch MAC l duy nht nhm trnh vn gi mo.D liu ringHc vin cng ngh Bu chnh Vin Thng 38

S lc v cng ngh WIFI & WIMAX Trong IEEE 802.16, s dng m ha DES trong ch CBC cho d liu c nhn. DES trong ch CBC s dng 56 bit kha DES (TEK) v CBCIV (Initialization Vector). Ch CBC yu cu mt vector khi ti IV ngu nhin m bo k hoch (RSA, 2004). Quay tr li tho lun trc ca Wongthavarawat (2005) th CBCIV l c th on trc c, VD: CBCIV = [IV Parameter from TEK exchange] XOR [PHY Synchronization field] v 56 bit kha l khng m bo an ton vi kh nng tnh ton ngy nay, t n c th b tn hi trc cc tn cng c c vn bn ban u. Thm vo khng cung cp vic tm kim tnh ton vn ca bn tin s lm tng kh nng ca cc tn cng ch ng. Ngoi ra th theo Johnston and Walker,(2004) th bi v vector khi to SA l khng i v l cng khai cho TEK ca n v trng ng b PHY (synchronization field) l lp li v c th on trc nn vector khi to MPDU l c th on trc. IEEE 802.16e chn AES CCM s dng kha 128 bt ging nh mt phng php mt m d liu mi m bo kim tra tnh ton vn ca bn tin v bo v trc tn cng lp li bng cch s dng s gi (PN-Packet Number). Ln ny b pht c xy dng duy nht ging nh b m ha ngu nhin trn gi, m bo tnh duy nht v thm vo c ch nhn thc.Qun l kha

Chun IEEE 802.16 cng gp phi vn v giao thc qun l kha, l vic s dng khng gian tun t kha TEK ca n, n s dng ch s phn bit cc bn tin. Giao thc nhn dng mi TEK bng 2 bit ch s, s xoay vng ch s t 3 v 0 trn mi ln ti to kha th 4 to c hi cho cc tn cng replay, v vy gi thit cuc tn cng replay xy ra, SS cha chc pht hin ra iu ny. Johnston v Waker khng nh Chnh phng thc ti s dng mt m TEK v vc t khi to trong mt m, s dn n lm l c TEK v d liu.Cc im yu khc

Trong d liu nh ngha SA, mt AK c th ko di ti 70 ngy, trong khi th thi gian sng ca TEK ch c 30 pht, iu ny cho php mt k tn cng xen vo s dng li ccs TEK. Mt SA d liu c th tiu th ti 3.360 TEK trong khong thi gian sng ca AK ang i hi khng gian SAID phi m rng t 2 ln mc ti thiu l 12 bits. IEEE 802.11 c ngha l SS phi tin tng rng BS lun lun to ra AK mi, v v vy cn mt b to s ngu nhin ca BS phi hon ho nu khng AK v TEKs s d b tnHc vin cng ngh Bu chnh Vin Thng 39

S lc v cng ngh WIFI & WIMAX hi. Trong IEEE 802.16, khng cp n vn nhn thc BS ti SS iu ny to iu kin cho kiu tn cng gi mo c th lm tn hi n giao thc PKM. Mt v d, SS khng th xc minh bt c quyn hn bn tin no n t BS c php. BS phn hi li SS s dung thng tin cng khai v vy bt c BS gi mo no c th to ra mt phn hi nh vy.

Bin php tng cng bo mt cho WiMAXNhn thc ln nhau

Hu ht mi im yu v bo mt ca WiMAX u tp trung vo vn thiu mt chng nhn cho BS. Ch mt cch SS chng li s gi mo l thay th k hoch nhn thc bng mt k hoch khc h tr kh nng nhn thc ln nhau.Cc li bo v d liu

Chun 802.16 s dng DES-CBC cho m ha d liu. DES-CBC yu cu mt IV bo vn ny. Tuy nhin iu ng ngi y l 802.16 li s dng mt IV c th an trc c. gii quyt vn ny, mt xut mi l c th to ra ngy nhin mt IV trn mi khung, v sau n c th c chn vo trong phn ti trng. Vi cch lm nh vy mt k tn cng s khng th bit c IV gii m d liu i qua mng.Ci thin bo mt tch hp trong 802.16e

Nhiu ci tin trong sut qu trnh nghin cu nhng hu ht trong s h s c tch hp trong phin bn tip theo ca giao thc IEEE 802.16e c ph chun trong thng 1/2006. C th k n mt s ci tin nh: PKMv2 s c s dng thay th cho PKM. PKMv2 nh ngha mt cch t dng giao thc nhn thc m rng EAP (Extensible Authentication Protocol). Hn th na PKMv2 ch r mt phng thc bt tay ba bc thit lp mt kha nhn thc AK gia BS v SS. y l cch truyn AK gia BS v SS an ton hn. Hai phng php nhn thc ln nhau da trn RSA v EAP s c cung cp. C hai hoc mt trong hai phng php c th c s dng ring r. Chng s cng to ra kha ri sau c x l bi h thng phn cp kha. Trong nhn thc ln nhau da trn RSA,Hc vin cng ngh Bu chnh Vin Thng 40

S lc v cng ngh WIFI & WIMAX chng nhn X.509 c s dng c bi BS v SS v gii quyt rt nhiu vn thiu st bo mt lin quan n gi mo. Trong nhn thc EAP th da trn m hnh ba bn (threeparty). Chun 2001 nh ngha cc loi HMAC cho cc bn tin qun l. Trong PKMv2, vn ny c th c thng lng gia HMAC hoc CMAC. CMAC l mt AES da trn MAC c nh ngha bi NIST nh mt tiu chun ca chnh ph M. Ch chui cc bn tin c th c bo v vi mt m HMAC/CMAC c m rng. Cc m lun kt thc TLV trong mt bn tin gm nhiu TLVs. Bng cch ny n m bo bn tin c truyn qua mng m khng b tn cng. Nu mt ai c gng chn mt bn tin vo lu lng th gn nh chc chn pha thu s nhn ra rng bn tin khng gi bi ngi gi hp l bi v digest cha trong mi bn tin s khng khp vi digest c xy dng bi bn thu. Mt s phng php mt m s c tch hp li vi nhau. u tin l AES-CCM (trong 802.16-2004) c nhp vo thnh 802.11i 802.16e vi vic thm AES-CTR v AESCBC. AES-CCM c s dng kim tra tnh ton vn, nhn thc v bo v lu lng d liu. AES-CMC th li hu dng trong trng hp cn m bo lu lng thp vi mc bo mt khng cao trong cng mt thi im. AES-CTR l mt phng php c bit s c s dng mt m ha lu lng MBS. Cui cng th vi mi nhm khc nhau c th s c cc m hnh bo mt khc nhau. Vic kt hp cc phng php bo mt cn tnh n s cn bng gia cc phng php thnh phn m bo ph hp nht vi mc ch bo mt d liu .

Kt lunChun IEEE 802.16e c mt s thay i trong ch ch bo mt, n to ra trn mi khung mt IV ngu nhin, chng tn cng lp li bng cch s dng PN (packet number). N s s dng AES nh mt phng php m ha chnh v gii thiu mt phng php nhn thc d trn giao thc nhn thc m rng nh EAPTLS, EAPTTLS, PEAP, EAPSIM, m rng nhn thc ti server AAA. Ch AESCCM l mt mt m lin kt d liu mi cho c ch nhn thc d liu, c nh ngha bi NIST. Chun ny cng thay th kha TripleDES ang th nghim trong giao thc PKM bng ch AESECB v linh ng h thp gi thnh nhn thc li trong qu trnh chuyn vng (roaming).


S lc v cng ngh WIFI & WIMAX C ch bo mt l mt qu trnh x l phc tp, n yu cu nhng nghin cu chuyn su cng nh s c lng thng s v cc kt qu thc hin. IEEE 802.16e s m c cho di ng khng dy tuy nhin n cng c th b tn hi bi v cha c mt rng buc no i vi k tn cng. S cn nhiu vn phi tng cng nghin cu nh vn qun l kha t BS n SS, nhn thc ngi s dng chuyn vng v nng cp thoi. IEEE 802.16 (WiMAX) c th s ginh c thnh cng trong lnh vc truyn thng v tuyn. Cc nh cung cp thit b sn sng cung cp thit b WiMAX ca h. Tuy nhin cng ngh ny vn ang trong giai on pht trin v cn nhin hn na nhng nghin cu trong thi gian ti.

u im v ng dngWiMAX c thit k ch trng vo nhng thch thc gn vi cc loi trin khai truy nhp c dy truyn thng nh: Backhaul. S dng cc anten im im ni nhiu hotspot vi nhau v n cc trm gc qua nhng khong cc di (ng kt ni gia im truy nhp WLAN v mng bng rng c nh). Last mile. S dng cc anten im a im ni cc thu bao thuc nh ring hoc doanh nghip ti trm gc. WiMAX c pht trin vi nhiu mc tiu quan tm nh: Cu trc mm do : WiMAX h tr cc cu trc h thng bao gm im a im, cng ngh li (mesh) v ph sng khp mi ni. iu khin truy nhp MAC) phng tin truyn dn h tr im a im v dch v rng khp bi lp lch mt khe thi gian cho mi trm di ng (MS). Nu c duy nht mt MS trong mng, trm gc (BS) s lin lc vi MS trn c s im im. Mt BS trong mt cu hnh im im c th s dng anten chm hp hn bao ph cc khong cch xa hn. Cht lng dch v QoS : WiMAX c th c ti u ng i vi hn hp lu lng s c mang. C 4 loi dch v c h tr: dch v cp pht t nguyn (UGS), dch v hi vng thi gian thc (rtPS), dch v hi vng khng thi gian thc (nrtPS), n lc tt nht (BE). Trin khai nhanh: So snh vi trin khai cc gii php c dy, WiMAX yu cu t hoc khng c bt c s xy dng thit lp bn ngoi. V d, o h to rnh cc ng cp th khng yu cu. Cc nh vn hnh m c c cc ng k s dng mt trong cc di tn ng k, hoc d kin s dng mt trong cc di tnHc vin cng ngh Bu chnh Vin Thng 42

S lc v cng ngh WIFI & WIMAX khng ng k, khng cn trnh cc ng dng hn na cho chnh ph. Dch v a mc: Cch thc ni m QoS c phn pht ni chung da vo s tha thun mc dch v (SLA) gia nh cung cp dch v v ngi s dng cui cng. Chi tit hn, mt nh cung cp dch v c th cung cp cc SLA khc nhau ti cc thu bao khc nhau, thm ch ti nhng ngi dng khc nhau s dng cng MS. Cung cp truy nhp bng rng c nh trong nhng khu vc th v ngoi , ni cht lng cp ng th km hoc a vo kh khn, khc phc thit b s trong nhng vng mt thp ni m cc nhn t cng ngh v kinh t thc hin pht trin bng rng rt thch thc. Tnh tng thch: WiMAX da vo quc t, cc chuN n khng c tnh cht r rt nh cung cp, to ra s d dng i vi ngi dng cui cng truyn ti v s dng MS ca h cc v tr khc nhau, hoc vi cc nh cung cp dch v khc nhau. Tnh tng thch bo v s u t ca mt nh vn hnh ban u v n c th chn la thit b t cc nh i l thit b, v n s tip tc a chi ph thit b xung khi c mt s chp nhn a s. Di ng: IEEE 802.16e b sung thm cc c im chnh h tr kh nng di ng. Nhng ci tin lp vt l OFDM (ghp knh phn chia tn s trc giao) v OFDMA (a truy nhp phn chia tn s trc giao) h tr cc thit b v cc dch v trong mt mi trng di ng. Nhng ci tin ny, bao gm OFDMA m rng c, MIMO (nhiu u ra nhiu u vo), v h tr i vi ch idle/ sleep v hand off, s cho php kh nng di ng y tc ti 160 km/h. Mng WiMax di ng cho php ngi s dng c th truy cp Internet khng dy bng thng rng ti bt c trong thnh ph no. Li nhun: WiMAX da vo mt chuN n quc t m. S chp nhn a s ca chuN n v s dng chi ph thp, cc chip c sn xut hng lot, s a chi ph gim t ngt v gi cnh tranh xy ra s cung cp s tit kim chi ph ng k cho cc nh cung cp dch v v ngi s dng cui cng. Mi trng khng dy c s dng bi WiMAX cho php cc nh cung cp dch v ph v nhng chi ph gn vi trin khai c dy, nh thi gian v cng sc. Hot ng NLOS: Kh nng hat ng ca mng WiMAX m khng i hi tm nhn thng gia BS v MS. Kh nng ny ca n gip cc sn phN m WiMAX phn pht di thng rng trong mt mi trng NLOS. Ph sng rng hn: WiMAX h tr ng nhiu mc iu ch, bao gm BPSK, QPSK, 16QAM, 64QAM. Khi yu cu vi b khuch i cng sut cao v hot ng vi iu ch mc thp (v d BPSK hoc QPSK). Cc h thng WiMAX c th ph sng mt vng a l rng khi ng truyn gia BS v MS khng b cn tr. M rng phm vi b gii hn hin ti ca WLAN cng cng (hotspot) nHc vin cng ngh Bu chnh Vin Thng 43

S lc v cng ngh WIFI & WIMAX phm vi rng (hotzone) cng cng ngh th c th s dng nh v di chuyn. nhng iu kin tt nht c th t c phm vi ph sng 50 km vi tc d liu b h thp (mt vi Mbit/s), phm vi ph sng in hnh l gn 5 km vi CPE (NLOS) trong nh v gn 15km vi mt CPE c ni vi mt anten bn ngoi (LOS). Dung lng cao: C th t c dung lng 75 Mbit/s cho cc trm gc vi mt knh 20 MHz trong cc iu kin truyn sng tt nht. Tnh m rng. ChuN n 802.16 -2004 h tr cc di thng knh tn s v tuyn (RF) mm do v s dng li cc knh tn s ny nh l mt cch tng dung lng mng. ChuN n cng nh r h tr i vi TPC (iu khin cng sut pht) v cc php o cht lng knh nh cc cng c thm vo h tr s dng ph hiu qu. ChuN n c thit k t t l ln ti hng trm thm ch hng nghn ngi s dng trong mt knh RF. Cc nh vn hnh c th cp pht li ph qua hnh qut nh s thu bao gia tng. H tr nhiu knh cho php cc nh ch to thit b cung cp mt phng tin ch trng vo phm vi s dng ph v nhng quy nh cp pht c ni r bi cc nh vn hnh trong cc th trng quc t thay i khc nhau. Bo mt: Bng cch mt ha cc lin kt v tuyn gia BS v MS, s dng mt ha tin tin AES ch CCM, m bo s ton vn ca d liu trao i qua giao din v tuyn. Cung cp cho cc nh vn hnh vi s bo v mnh chng li nhng hnh vi nh cp dch v.
