mở rộng wlan bằng kỹ thuật mạng hình lưới không dây

8/4/2019 M rng WLAN bng k thut mng hnh li khng dy

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M rng WLAN bng k thut mng hnh li khng dy

S pht trin nhanh ca cng ngh mng khngdy trong nhng nm gn y cho phpngi s dng ch ng trong vic la chn gii

php thch hp khi trin khai mng. Mi cngngh mng khng dy c thit k hotng mt phm vi nht nh v c phn loitheo kh nng ph sng ca tng cng ngh.Trong thc t thng c phn chia thnh cc

loi mng: Mng c nhn WPAN, mng ni b WLAN, mng thWMAN, mng din rng WWAN. Tnh cht ca mi loi mng ccu thnh thng qua mt tp cc tham s v bng thng, phm vi mng,nng lng tiu th, v tr ca ngi s dng...

TVN

S pht trin nhanh ca cng ngh mng khng dy trong nhng nmgn y cho php ngi s dng ch ng trong vic la chn gii

php thch hp khi trin khai mng. Mi cng ngh mng khng dyc thit k hot ng mt phm vi nht nh v c phn loitheo kh nng ph sng ca tng cng ngh. Trong thc t thng c

phn chia thnh cc loi mng: Mng c nhn WPAN, mng ni bWLAN, mng th WMAN, mng din rng WWAN. Tnh cht cami loi mng c cu thnh thng qua mt tpcc tham s v bngthng, phm vi mng, nng lng tiu th, v tr ca ngi s dng...Mi tng quan v phm vi ph sng v tc truyn d liu ca tngloi mng c minh ha trong Hnh 1 [3].
http://www.wirelessvn.com/wirelesslan/166-mo-rong-wlan-bang-ky-thuat-mang-hinh-luoi-khong-dayhttp://www.wirelessvn.com/wirelesslan/166-mo-rong-wlan-bang-ky-thuat-mang-hinh-luoi-khong-day


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Hnh 1.Cc cng ngh mng khng dy v phm vi ng dngu im v tc truyn cao v phm vi ph sng rng, WiMAX l la chn smt cho cc ng dng mng khng dy c s lng ngi s dng ln, cung cp

ng thi nhiu dch v khc nhau (thoi, video, Internet) trn cng mt ngtruyn khng dy[9]. Tuy nhin, vi cc ng dng mng c phm vi va v nh,cng ngh WiMAX khng phi l mt gii php ph hp do gi thnh thit b ucui cao, chi ph thit lp mng ln. Trong cc ng dng mng khng dy phm viva v nh, cng ngh WLAN (IEEE 802.11) vn l mt gii php hon ton phhp v c im k thut cng nh chi ph s dng. Tuy nhin, do hn ch v tm

ph sng, cng ngh WLAN truyn thng khng th p ng c cc ng dngcn m rng mng. V vy, trn c s cc yu t cng ngh c sn ca cng nghkhng dy chun, yu cu t ra l phi xy dng c gii php kt ni to ramng c phm vi ph sng cao hn nhng vn m bo c tnh cht ca mng.K thut mng hnh li khng dy WMN (Wireless Mesh Network) c th ccoi l mt gii php tt cho vn t ra, nhm m rng phm vi ph sng cho ccmng WLAN chun. Da trn cc thit b c sn ca WLAN cng vi mt s citin v c phn cng, phn mm; xy dng giao thc truyn thng mi, k thutmng hnh li khng dy c th ci thin ng k tm ph sng ca mng banu.


3/14

So snh WLAN v WiMAX

WiMAX

(802.16a)

WLAN

(802.11b) (802.11a/g)

ng dng c bn Mng khng dybng thng rng

Mng khng dyni b

Mng khng dyni b

Di tn 2GHz n 11GHz 2.4GHz ISM 2.4GHz ISM (g)

Bng thng knh C th iu chnhc trong khong1.25MHz-20MHz

25MHz 20MHz

Ch truyn dliu

Song cng Bn cng Bn cng

Cng ngh vtuyn

OFDM DSSS OFDM

hiu qu cabng thng

5 bps/Hz 0.44 bps/Hz 2.7 bps/Hz

Mt m 3DES (Bt buc)

AES (Ty chn)

RC4

(AES vi802.11i)

RC4

(AES vi802.11i)

Kh nng ding

(Mobility)

Mobile WiMAX

(802.16e)

ang c phttrin

ang c phttrin

Kt ni mngli

(Mesh Network)

C Tu thuc vohng sn xut

Tu thuc vohng sn xut

u im Tc truyn cao,phm vi ph sngrng

Tc truyncao, gi thnh r

Tc truyncao, gi thnh r


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K THUT MNG HNH LI KHNG DY WMN

Khi nim mng hnh li (Mesh Network) ni chung c s dngtrong mt s lnh vc ca ngnh cng ngh thng tin. K thut mng

hnh li l cch thc truyn ti d liu, m thanh v cu lnh gia ccnt x l, cho php truyn thng lin tc v t xc nh li cu hnhxung quanh ng i b che chn bng cch nhy t nt ny sang ntkhc cho n khi thit lp c kt ni. Mng li c kh nng t hngn v to ra mng c tin cy cao; c th hot ng khi c mt nt bli hoc cht lng kt ni mng km. Trong lnh vc mng khng dy,mng li c p dng ni rng phm vi ph sng ca mng khngdy truyn thng. Cc nt trong mng truyn thng trc tip vi cc nt

khc v tham gia trong mng li. Nu mt nt c th kt ni vi mtnt ln cn khc th s c kt ni vi ton mng [8].

Cc cu hnh mng

Cng ngh mng WLAN c pdng trin khai mng khng dydin rng thng qua mt s ci tin v phn cng v phn mm trn ccchun 802.11a, 802.11b c di tn khc nhau (Bng 1). Chun 802.11b

thng c dng khi ci t giao thc truyn thng gia cc nt do ct ca chun ny cho php phm vi truyn ln hn khi hot ng ditn 2.4GHz.Trong k thut mng hnh li, c cc khi nim:

-Nt (Node): Gm c router v/hoc cc client (my tnh, PDA,... ).

-Nt ng ln (Uplink node): Nt kt ni ti mng Internet thng quang truyn hu tuyn cung cp kt ni Internet cho ton mng.

-Nt ng xung (Downlink node): Nt kt ni ti mng v c khnng phc v c kt ni hu tuyn v v tuyn cho mng.

-Nt lp (Repeater node): Nt kt ni vo mng v khng dng phcv cc client ch ng vai tr l nt trung gian lp tn hiu.


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Cc cu hnh mng c bn [4],[6]

im im (Point-to-Point): L kiu kt ni n gin nht, hai nttruyn thng qua hai anten thu pht cng sut cao hng trc tip vinhau.

Hnh 2.Mng im-imim a im (Point-to-Multipoints):Kt ni c chia s gia nt

ng ln dng anten a hng vi cc nt ng xung (hoc nt lp)vi anten thu cng sut cao. Cu hnh mng ny d trin khai hn cuhnh imim v khi thm mt thu bao mi ch cn lp t thmthit b ti khu vc thu bao ch khng phi lp ti nt ng ln. Tuyvy, cc trm thu phi nm trong phm vi ph sng v c ng nhnthng vi trm pht sng gc. Cc vt cn nh cy ci, nh ca, i ni,


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... s gp phn lm cu hnh mng li im im hot ng khnghiu qu.

Hnh 3.Mng im a im


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a im a im: Mi nt c vai tr khng ch l im truy nhpcho cc trm m cn lm nhim v chuyn tip d liu.

Hnh 4.Mng a im-a imCu hnh ny c tin cy mng cao nht do cc nt c s lin thngvi nhau, mt nt ch cn c kt ni vi mt nt bt k m khng cn

phi c kt ni trc tip vi nt ng ln nh trong cu hnh im a im, l c thkt ni vi ton mng. Tuy nhin, i li giao thctm ng ca mng s c phc tp cao hn.


8/14

Giao thc truyn thng

Giao thc truyn thng gia cc nt l yu t k thut ct li ca mng.

Mng c kh nng t phc hi tt cng nh tm c ng iti uhay khng l nh vo giao thc truyn d liu gia cc nt x l trongmng. C mt s k thut ang c xut lm giao thc truyn thngcho mng li nh: AODV (Ad-hoc On Demand Distance Vector),PWRP (Predictive Wireless Routing Protocol), OLSR (Optimized Link

State Routing Protocol), TORA (Temporally-Ordered Routing

Algorithm),... Tuy nhin, s cha c giao thc no c chn chnh thccho n khi chun cho mng hnh li khng dy 802.11s ra i [1],[6].

Cc giao thc u c thit k datrn nguyn tc chung ging nhau,ch khc nhau v cch th hin ci t v x l thng tin. Trong phnny gii thiu Giao thc nh tuyn ng DSR (Dynamic SourceRouting Protocol). y l giao thc c nhiu u im v tnh n gin,hiu qu cao, c kh nng t t chc, t nh cu hnh tt.

Cc c im ca DSR

Giao thc c cu thnh t hai c ch: Pht hin ng truyn v Duytr ng truyn. Cc c ch ny cho php cc nt trong mng truynthng trc tip hoc gin tip vi tt c cc nt cn li trong mng li.

- Pht hin ng i RD (Route Discovery): L c ch tm ng khint gc S mun gi gi d liu ti nt ch D nhng cha bit ng i.

- Duy tr ng i RM (Route Maintenance): L c ch trong nt S

c kh nng tm ng mi khi ng truyn ang s dng b gin ondo cu hnh mng thay i hoc kt ni gia cc nt trong ngtruyn khng hot ng. Khi pht hin ra ng truyn c b t, Sc th tm mt ng truyn ti D khc m n bit hoc thc hin cch RD tm ra ng mi.


9/14

Cc c ch RD v RM hot ng hon ton da theo yu cu ca ccnt. Khng ging vi cc giao thc khc, DSR khng i hi phitruyn nh k cc gi d liu tm ng qung b, cc tn hiu kt nihoc cc gi d liu pht hin ntln cn. Vi l do ny, DSR lm gim

nghn mch mng do truyn nh k cc gi d liu v 0 khi tt c ccnt c v tr tng i n nh so vi cc nt khc v tt c cc ng icn thit cho vic truyn thng c pht hin.

C ch pht hin ng RD

Khi mt nt S cn gi mt gi tin ti nt ch D, S ghi th t cc bci trong c ng i ti D vo phn thng tin header ca gi tin. Thng

thng, S s ly thng tin v ng i thch hp ti D bng cch tmtrong b nh cc ng i c lu li t nhng ln i trc (RouteCache) ca nt. Nu khng tm thy, S khi to c ch RD tm ngi. Trong trng hp ny, S c gi l gc (initiator) v D l ch(target) ca c ch RD.

C ch duy tr ng (Route Maintenance)

Khi gi hoc chuyntip mt gi tin bng ng truyn xc nh c,mi nt c trch nhim kim chng vic nhn d liu ca nt tip theotrong ng i. Gi d liu s c tip tc truyn (vi mt s ln cxc nh trc) cho ti khi c xc nhn nhn c d liu.

Cc tham s nh hng n hiu sut mng

Mt trong nhng vn c quan tm hng u khi thit k, trin khaiv a mng vo hot ng l kho st c cc tham s nh hng n

hiu sut ca mng.

K thut v tuyn

Tham s nh hng ln n hiu sut mng l cng ngh v tuyn. Spht trin mnh m ca cng ngh bn dn, cng ngh tn s v tuyn


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v l thuyt truyn thng l cc yu t gp phn thc y cng nghmng khng dy pht trin. C nhiu phng php c xut tngdung lng v khnng mm do ca cc h thng v tuyn bao gmnh: anten c hng, h thng MIMO. Tuy nhin, c th nng cao

hn na hiu sut ca h thng khng dy cn phi c s ci tin trongcc giao thc lp cao hn, c bit l lp iu khin truy nhp (MAC)v giao thc nh tuyn.

Kh nng m rng

Kch thc mng ln c th lm cho giao thc nh tuyn hot ngkhng hiu qu, khng tm c ng i tin cy v lm gim hiu sut

mng. Mng li c kin trc ad-hoc nn kh ci t cc c ch a truynhp tp trung nh: a truy nhp phn chia theo thi gian TDMA v atruy nhp phn chia theo m CDMA do phc tp v cc yu cu vng b thi gian (vi TDMA) v qun l m (vi CDMA). V vy, cch truy nhp thng c dng l a truy nhp phn tn CSMA/CA.Tuy nhin, CSMA/CA c hiu qu s dng li tn s khng gian rtthp, gim kh nng m rng ca mng nn k thut ny cng khng

phi l ti u. V vy, vic to ra k thut lai ghp gia CSMA/CA vi

TDMA hoc CDMA c th l mt hng tip cn mi nng cao tnhnng ca mng.

Bng thng v cht lng dch v

Khc vi cc loi mng ad-hoc khc, hu ht cc ng dng mng likhng dy l cc dch v bng rng vi nhiu yu cu v cht lngdch v (QoS). Do vy cn c nhiu vn khc cn quan tm khi thitk giao thc truyn thng: tr truyn, t l mt mt d liu, bngthng ti tng nt,...

Bo mt mng


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Qua thc t s dng, cng ngh WLAN bc l nhiu yu im trongbo mt nn bi ton bo mt cho mng li khng dy vn cha thcs c li gii tha ng. C rt nhiu cc k thut bo mt c xutcho WLAN, tuy nhin cha c c ch hon chnh no c xut cho

mng li. Do kin trc ca phn tn ca h thng nn cha c c chphn phi kha cng khai trong WMN. Hu ht cc gii php bo mtcho mng ad hoc khng tin cy ci t do c ch bo mt camng khc vi cc mng ad hoc. V vy, bo mt mng vn cn l vn b ng, cc c ch bo mt nh: cc thut ton mt m, phn phikha bo mt, bo mt tng MAC, pht hin xm nhp v quan st mngcn c tip tc pht trin.

Tnh d s dng

Giao thc cn c thit k sao cho t c tnh t tr nhiu nht c th tng cng kh nng qun l nng lng, t t chc, kim sot thayi cu hnh ng, khc phc cc s c kt ni, xc thc ngi s dngnhanh. Ngoi ra, cc cng c qun l mng nh: theo di hiu sutmng, nh cu hnh cc tham s ca WMN cng cn c pht trintng ng. Cc cng c ny cng vi c ch t tr ca giao thc s gp

phn thc y s pht trin ca WMN.

Mt s ng dng tiu biu ca mng hnh li khng dy

Vi u im v m rng phm vi ph sng trn nn cc thit b c snca cng ngh mng WLAN, k thut mng li khng dy c th c


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ng dng trong cc ng cnh mkhng th s dng mng c dy thay th hoc nu thay th c th phi tr chi ph rt ln. Sau y lmt s ng dng tiu biu:

Giao thng cng cng

ng dng mng li trong giao thng cng cng cho php ngi sdng truy cp Internet trong khi ang di chuyn. H thng thng tin nyl s kt hp ca hai yu t: Kt ni di ng tc cao ti mngInternet v mng li trong tng phng tin giao thng (Hnh 5). Tuynhin, m hnh ny ch thc s c ng dng rng ri khi cng nghMobile WiMAX ra i. y cng l mt minh chng c th cho tnh

tng h gia hai cng ngh khng dy WLAN v WiMAX.

Hnh 5. ng dng WMN trong tu inDoanh nghip

L cc mng c va v nh trong phm vi mt vn phng ca cng mtn nguyn hoc mng phm vi rnglin kt cc vn phng khc nhaunm cc n nguyn khc nhau. Hin ti, cc mng IEEE 802.11 cs dng rt nhiu trong cc vn phng. Tuy nhin, y ch l cc mngc lp, cha c s kt ni vi nhau. Vic dng mng hu tuyn ktni l gii php khng mang li hiu qu kinh t do chi ph thit lpng truyn ln. Trong trng hp ny, mng hnh li khng dy lgii php ph hp v tit kim c chi ph.


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iu khin t ng

Thng thng tn hiu ca cc h thng iu khin ngun in v ccthit b in t (n chiu sng, thang my, iu ha nhit ,... ) trongcc khu nh ln c truyn qua mng hu tuyn. Tnh cht ca mnghn ch kh nng m rng ca h thng khi lp t thm cc thit b mi nhng a hnh phc tp. Vic trin khai mng hnh li thay th truyn tn hiu mang li hiu qu kinh t cao v kh nng linh ngtrong s dng mng.

Y t

D liu trong h thng y t nh hnh nh v thng tin chn on cnc x l v truyn kp thi t phng ny sang phng khc. D liuny thng cha hnh nh chn on phn gii cao nn vic truyni hi bng thng ln. Khc vi mng hu tuyn thng thng ch cth h tr truy nhp mng t nhng v tr nht nh, mng li khng

dy cung cp cho ngi s dng mt cch truy nhp mng c ngnhng vn m bo bng thng cn thit.

Quan st an ninh

Cc h thng quan st an ninh ni ng ngi i hi h tng mng ctc truyn cao truyn cc hnh nh ng lin tc. Cch tip cntheo mng li khng dy cung cp cho h thng kh nng linh hot

trong iu khin v thu nhn tn hiu ngay c khi cc thit b thay i vtr -iu ny khng c c vi mng hu tuyn. Thm vo , cngvic lp t thit b mi v bo tr thit b c cng d dng hn.


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KT LUN

Thc t chng minh vi s ra i ca cng ngh WiMAX, cng nghWLAN khng b thay th m song hnh vi WiMAX. Hai cng nghny b tr ln nhau: WiMAX cung cp kt ni khng dy din rng choWLAN; WLAN phn phi kt ni ca WiMAX n ngi s dng cuithng qua h tng mng c sn. Mc d cn nhiu vn k thut cnc khc phc, k thut mng li khng dy l mt gii php tt chocc ng dng mng c phm vi kt ni va v nh, c thit lp datrn h tng mng WLAN c sn. K thut ny gip tit kim c chi

ph nhng vn m bo c cc yu cu ti thiu ca mng khng dydin rng. Mng hnh li khng dy c th c ng dng trin khainhiu dch v thit thc phc v cuc sng. Tuy nhin, k thut ny

c pht trin thnh chun chnh thc v hot ng thc s c hiuqu, cn phi tin hnh nhiu nghin cu hon thin cc yu t quantrng, c bit l giao thc truyn thng v bo mt mng.

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