1 Origins of Ad Hoc: Packet Radio Networks

1.1 Introdution Gi tr ca vic c mt mng li khng cn c s h tng c pht hin vo nhng nm 1970.

Vo thi im , my tnh cn cng knh. DARPA c mt d n c bit n nh i packet

radio, mt s thit b u cui khng dy c th giao tip vi nhau trn chin trng. Packet radio l

mt cng ngh m rng khi nim chuyn mch gi. Trong sut nhng nm 1970, ALOHA, D n ti

i hc Hawaii chng minh tnh kh thi ca vic s dng cc phng tin pht sng radio gi /

nhn cc gi d liu trong mt h thng radio duy nht.

Nhng ngi tin phong ng gp cho lnh vc PRNET bao gm Robert Khan, Barry Leiner, Leonard

Kleinrock, v John Jubin. Cc vn k thut cho PRNET l ng truyn, kim sot lung, kim sot

li, gn a ch, nh tuyn, khi to v kim sot. Mt trong nhng tnh nng hp dn nht ca

PRNET l trin khai nhanh chng. Sau khi ci t h thng t khi to v t chc. C ngha l cc nt

mng c th pht hin ra kt ni vi cc nt ln cn v a ra cc chin lc nh tuyn da trn cc

lien kt ny. PRNET khng cn phi qun tr.

1.2 Technical Challenges PRNET khc vi cc mng c dy. Chng c mt c s h tng backbone v cc nt nh l cc router

v switch nhm forward cc gi tin. PRNET cc thit b di ng bn thn hot ng nh cc router.

Vic s dng cc kt ni khng dy v cc kt qu tnh ton di ng l thc thc ln v k thut. Cc

thch thc l:

Kim sot lung trn cc lien kt khng dy a nh tuyn.

Kim sot li trn cc lien kt khng dy.

To v duy tr cc thng tin nh tuyn chnh xc.

C ch x l{ nh tuyn di ng.

Chia s knh truy cp bi nhiu ngi dung.

Kh nng x l ca thit b u cui

Yu cu v nng lng.

1.3 Architecture of PRNETs Nh m t trong hnh 2.1, PRNET bao gm mt s thit b lp radio, thit b u cui khng dy, v

cc trm di ng chuyn dng. Vai tr ca b lp l khuch i tn hiu t mt trm n trm khc,

cho n khi n ch. Cc trm di ng nhm ly tuyn ng nh tuyn gia cc host. Khi trng

thi mng thay i (do thit b u cui di chuyn, khng khuch i tn hiu, tc nghn, thay i

tin cy cc hop) tuyn ng c gn li bi cc trm nhm p ng yu cu tr ti thiu. Cc

thit b u cui khng bit n hot ng ca cc trm.

1.4 Components of Packet Radios Nh trong hnh 2.2, my tnh ngi dng mun giao tip vi mt i pht cn phi thng qua mt

terminal-network controller (TNC). My tnh ngi dng thng c gi l thit b di ng / thit

b u cui, trong khi cc i pht v TNC thng c gi l cc packet radio. Packet radio, do ,

thc hin cc chc nng lin quan ti giao thc lp 1, 2, v 3. PRNET l tp hp cc radio packet,

mt s packet kt ni vi thit b ngi dng, mt s khc th khng.

1.5 Routing in PRNETs

1.5.1 Point-to-Point Routing

PRNETs h tr giao tip point-to-point qua nh tuyn point-to-point. y, mt gi xut pht t

mt mng di chuyn qua mt lot cc repeater cho n khi ti ch. nh tuyn point-to-point y

l mt tp th t ca cc repeater c xc nh bi cc trm di ng. Trm ny l thnh phn duy

nht trong mng bit c ton b cc kt ni ca mng l topology mng. Vi thng tin

topology mng, trm di ng tnh ton ng nh tuyn point-to-point tt nht v phn phi thng

tin ny tt c cc repeater ng nh tuyn hoc trc tip n ngun tin. Kiu ny ph hp vi

cc thit b u cui di chuyn chm.

1.5.2 Broadcast Routing

Cng ngh radio cung cp cc tnh cht broadcast rt tt. Qung b thng tin cho tt c cc i pht

trong mt mng s gy ra flooding. m bo rng mi gi tin radio packet ch chuyn tip mt

packet mt ln, repeater duy tr mt danh sch nh danh cc gi tin gn y nhn c v

chuyn tip.

Trong broadcast routing, mt gi tin pht ra t cc ngun packet radio c dng sng. Mc d qung

b l rt mnh (do cc packet c nhn bi tt c cc nt trong mng khng phn vng), n khng

hiu qu cho vic giao tip gia 2 nt do tt c cc nt trong mng phi tham gia vic truyn

nhn cc gi tin khng dnh cho chng. Do , khi broadcast routing c s dng cho truyn thng

point-to-point, a ch ch c gn trong mi gi d liu. Khng c ng nh tuyn c th ly

trc cho vic truyn d liu, do , quyt nh nh tuyn khng tp trung. Cc gi tin cui cng s

n c host ch nu mng khng c phn vng. i vi cc thit b u cui di chuyn nhanh

broadcast routing l ph hp v n khng cn tnh ton cc tuyn ng.

1.5.3 Packet Forwarding

Connectionless mun chuyn cc gi tin cn mt s hot ng nn duy tr topology mng v cc

thng tin cc kt ni gia cc nt. iu ny lm cho khi thay i topology mng lu lng thng tin

cho nh tuyn l ng k. Phng php ny thng c kt hp vi broadcast routing, mi gi tin

mang y thng tin nh tuyn cho n i n ch.

Vi phng php chuyn tip gi tin hng kt ni, vic thnh lp mt ng nh tuyn trc khi

d liu c th vn chuyn l cn thit. Cch tip cn ny thng c kt hp vi nh tuyn point-

to-point, mi nt u c mt bng nh tuyn chuyn tip cc gi tin n cc lin kt tng

ng. Do , nu topology mng thay i, giai on ti thnh lp tuyn ng l cn thit.

1.5.4 Impact of Mobility

Trong PRNET, tt c cc thnh phn ca mng u c th l di ng. Mt s di chuyn tng i

chm (v d repeater) do , s thay i topo mng backbone khng phi l thng xuyn. Cc gi

nh c thc hin trong PRNET l thit b ngi dng bnh thng di chuyn chm point-to-

point routing c thi gian t nht mt vi giy trc khi tuyn ng khc phi c la chn.

Khi t l di ng ca ngi s dng c tng ln, nh tuyn im-im c th khng c thc

hin v hu ht thi gian s c chi tiu trong vic tnh ton point-to-point cc tuyn ng thay

th cc thay v chuyn tip cc gi tin ti cc im n ca chng. Trong nhng trng hp nh vy,

hiu sut truyn thng s rt thp. Broadcast routing t b nh hng bi tnh di ng ca ngi s

dng do cc gi d liu khng i theo mt tuyn ng im-im c th no. Thay vo , mi nt

c nhim v chuyn tip cc gi tin, v do , cc my ch ch s nhn c cc gi d liu cui

cng. Tuy nhin broadcast routing c nng lng khng hiu qu.

1.6 Route Calculation Mi packet radio hot ng theo cch phn phi y . Chng thu thp v duy tr cc thng tin v

topology mng hin ti nhm a ra cc quyt nh c lp lm th no a cc gi tin n ch.

Mi nt duy tr cc bng sau y:

Neighbor table

Tier table

Device table

Neighbor table

Khi radio packet c bt, n s qung b mt PROP(packet radio organization packet) mi 7,5 giy,

cng b s tn ti ca n v thng tin v topology mng di gc nhn ca n. Do tnh cht qung

b ca PROP cc hang xm ca n s nhn c gi tin ny v cp nht neighbor table ca chng

Hnh

Trong PRNET cht lng ng truyn c o bng s lng gi tin nhn c chia cho s lng

gi tin gi i trong khong thi gian PROP. Thng tin ny s c sau c s dng bi cc thut ton nh tuyn.

Tier Table

nh tuyn trong PRNET ph thuc vo vic cc packet radio duy tr c thng tin v packet radio

tt nht cho vic chuyn tip gi tin n cc ch. Thng tin tier c packet radio chuyn tip trung

bnh 3.75 giy cho mt hop v cui cng s n c tt c cc packet radio. Do , cui cng, tt c cc packet radio bit khong cch t n n tt c cc im v cc packet radio tip theo cn

chuyn gi tin (next-hop) (xem Bng 2.2)

Trong PRNETs, con ng tt nht c nh ngha l con ng ngn nht vi kt ni tt trn mi

hop. Tuy nhin, mt con ng tt nht c th thay i theo thi gian. Khi mt lin kt (v d, t nt A n B) ti mt packet radio ln cn l xu, tt c ng i (trong tier table) ca nt A m c

next-hop l nt B s nh du l xu. Cc nt xu mi cng c thng bo qua PROP

Device Table

Vi cu hnh mng ca packet radio c thit b u cui v thit b lp, cn phi duy tr bng mapping

gia thit b v packet radio. Do tnh di ng bng mapping phi c cp nht. Cc thit b nh kz

gi mt gi iu khin trn ng truyn c dy gn vi packet radio ca n. Cc packet radio theo di cc thit b c lin quan v tuyn truyn thng tin mapping ny thng qua mt PROP ti mt

packet radio khc trong mng vi mt tc trung bnh l 3.75 giy cho mi hop. Do , khi mt packet radio nhn c mt gi tin gi n mt thit b di ng c th, thit b ang gn vi packet

radio ny bit c v chn next-hop ph hp chuyn tip cc gi tin.

1.6.1 Principles of Packet Forwarding

Chuyn tip c thc hin bng thng tin c t device table v tier table, v t header gi tin.

ETE Header

Cc header end-to-end (ETE) c to ra bi cc thit b di ng / thit b u cui, khng phi

packet radio. N bao gm ID / a ch ca thit b ngun, c s dng cp nht thng tin

mapping device-packet radio, v ID / a ch ca thit b ch, c s dng trong chuyn tip gi

tin.

Routing Header

Tri ngc vi ETE header, routing header (xem Bng 2.3) c to ra bi packet radio ngun. Cc routing header ng gi cc ETE header, v n l routing header s s dng chuyn tip cc gi

tin. Lu rng packet radio ID ngun, sequence number, v packe radio ID ch vn cn nguyn vn trong sut ng i ca gi n packet radio ch.

1.7 Pacing Techniques Thi gian m mt gi tin c la chn truyn c xc nh bi mt giao thc ng gi ba

thnh phn.

Cc giao thc nhp cung cp iu khin lung v iu khin tc nghn trong khi m bo s dng

hp l cc knh. Mt k thut lung c s dng, trong yu cu rng mt gi tin truyn n mt packet radio nht nh c bo nhn (hoc loi b) trc khi gi khc c gi n cc packet

radio ny. Nh li trc bo nhn c cung cp mt cch th ng. Do bo nhn khng c truyn i n khi packet radio sn sang nhn gi tin tip theo t packet raido truyn trc.

Bi vy tc nghn gi tin c th hin nh nt tht c chai ca cc bo nhn quay tr li packet

radio. Ngoi ra, c mt b m cho mi packet radio.

c tnh thi gian cn thit ca s tr gia truyn gi, packet radio cn o tr chuyn tip ca

mi gi tin m n chuyn tip. Packet radio ghi li thi gian m ti n truyn gi tin thnh cng truyn v nhn c bo nhn. Vic tr chuyn tip, bao gm tt c thi gian x l, xp hng, v s tr truyn dn.

Hnh 2.3 cho thy ba packet radio tham gia trong chuyn tip gi tin. Packet radio L gi gi tin phi

cho php khong thi gian khng ch cho packet radio M nhn gi tin v bo nhn m cn

packet radio N nhn gi tin v bo nhn. Packet radio ngun phi m bo khng ch hang xm

trc tip nhn v chuyn tip gi tin thnh cng m cc hang xm theo sau cng phi nhn v

chuyn tip cng gi tin . Do , packet radio ngun phi ch mt khong thi gian ba frame. Nu ch i mt thi gian ch c hai khung, n khng c cch no bit c khi packet radio N

thnh cng trong vic nhn c cc gi tin t M. iu ny c ngha rng khng c packet radio c

th truyn ti ngn hn mt phn ba thi gian.

1.8 Media Access in PRNETs PRNET s dng CSMA. CSMA ngn chn packet radio truyn khi mt packet radio khc ang s dng

ng truyn.

1.9 Flow Acknowledgments in PRNETs Cc gi tin c chuyn tip qua mt ng duy nht thng qua PRNET. Mi packet radio kim tra

cc thng tin cha trong cc tiu gi tin v tier table, device table. Packet radio phi quyt nh

khi no l truyn ti cc gi tin, khi no phi cp nht cc routing header trc khi truyn, v khi

no cn cp nht cc bng ring ca mnh.

Packet radio khc trong phm vi pht cng s nhn c gi tin truyn. Nu cc neighbor ny khng

phi l mt phn ca ng i n s loi b gi tin. Do truyn dn khng ch chuyn tip gi n

packet radio tip theo m cn bo nhn n packet radio gi gi. Cc nt trung gian s gi passive

ACK, nt ch g active ACK bo qu trnh gi hon tt.

2 Ad Hoc Wireless Networks

2.1 What Is an Ad Hoc Network? Ad hoc wireless l mng vi 2 hay nhiu thit b c kh nng kt ni mng khng dy. Cc thit b

ny c th giao tip vi cc nt khc trong phm vi pht sng hoc ngoi phm vi pht sng ca n.

Vi vic giao tip vi nt ngoi phm vi pht sng cn nt trung gian chuyn tip cc gi tin.

Mng ad hoc t t chc v thch nghi. Ngha l mng c th thnh lp m khng cn h thng qun

tr. Cc thit b trong mng ad hoc c th pht hin s c mt ca cc thit b khc v thc hin cc

tn hiu bt tay bt u chia s.

Cc thit b ad hoc c th khc nhau v kh nng tnh ton, lu tr, giao tip. Cc thit b ad hoc

khng ch nhn ra s c mt ca cc thit b m cn xc nh loi, thuc tnh ca cc thit b .

Mng ad hoc khng cn c s h tng. Tuy nhin do tnh di ng thng tin nh tuyn phi thay i

phn nh nhng thay i trong lien kt.

Do mng ad hoc da vo chuyn tip cc gi d liu qua cc nt khc, in nng tiu th s tr

thnh mt vn quan trng.

2.2 Heterogeneity in Mobile Devices Nh th hin trong hnh 3.2, cc thit b di ng c th tn ti di nhiu hnh thc. C s khc bit

ln gia cc thit b ny, v tnh khng ng nht ny c th nh hng n hiu sut truyn thng

v thit k ca giao thc truyn thng.

Bng 3.1 cho thy mt s thng s k thut ca cc thit b di ng. R rng l c s khc bit trong

kch thc, sc mnh tnh ton, b nh, a, v dung lng pin. S hin din ca tnh khng ng nht ng rng mt s thit b mnh m hn nhng ci khc, v mt s c th l my ch trong khi

nhng ci khc ch c th l khch hng. Vic chuyn tip d liu n cc thit b khc cng gy tn

nng lng nn cn tnh ton nng lng trc khi chuyn tip.

Hnh 3.1 cho thy rng mc d s khc bit gia cc thit b di ng, chng vn c th c ni

mng vi nhau. Cc nhu cu thng tin v cu hnh c th khc nhau nhng mt thit b nh c th

hin th thng tin c ch bin t mt thit b ln

2.3 Wireless Sensor Networks Gn y c s quan tm cho cc cm bin khng dy. Chng c kch thc rt nh va c kh nng

giao tip v lu tr.

Cm bin khng dy l mt thit b ad hoc. Cm bin khng dy kt ni v vo cc thi im thch

hp n gi thng tin n mt s nt.

2.4 Traffic Profiles Ad hoc c th xy ra trong nhiu hnh thc khc nhau. Vi 2 nt, giao tip s din ra trong 1 khong

thi gian v kt thc khi phin kt thc hoc 1 trong 2 nt ri i, ging peer-to-peer.

Hnh thc khc xy ra khi hai hay nhiu thit b giao tip vi nhau v chng di chuyn trong cc

nhm. M hnh ny din ra trong mt thi gian di.

Mt hnh thc khc l cc thit b giao tip khng thng nht.

2.5 Types of Ad Hoc Mobile Communications Thit b di ng trong mng ad hoc c th giao tip host ngang hng vi n l peer-to-peer.

Nhng trong trng hp 3 hoc nhiu hn cc nt trong phm vi ca nhau l remote-to-remote.

Thng thng remote-to-remote dung kt ni gia cc nhm nt.

2.6 Types of Mobile Host Movements

2.6.1 Movements by Nodes in a Route

Mt tuyn ng trong mng ad hoc gm mt ch (DEST) v mt ngun (SRC) cng mt s nt

trung gian. Di chuyn bt c nt no trong cc nt ny cng nh hng n tnh ng ca tuyn

ng. Nt ngun c ng downstream v khi n ra khi phm vi ph sng ca cc hng xm di

ca n (di theo th t ng i) ng i tr thnh khng hp l, do cc nt di c th xa

b tuyn ng i. Tng t nh vy khi nt ch ra khi phm vi ph sng cc nt khc cng

c thong bo xa tuyn ng i. Vi cc nt trung gian cng tng t.

Vic thay i v tr lm vic phn phi li giao thc nh tuyn din ra thng xuyn. iu ny c

cp nht cho tt c cc nt nhm duy tr thng tin nh tuyn chnh xc. Tuy nhin vic cp nht

thng tin nh tuyn qu mng khng dy gy ra lng ph lu lng do vy cn cc giao thc nh

tuyn tt.

2.6.2 Movements by Subnet-Bridging Nodes

Trong kch bn ny nu mt nt c vai tr lm cu ni gia 2 subnet di chuyn c th s chia mng

thnh 2 mng nh. Vic di chuyn cc nt cng th th lm 2 mng hp thnh 1 mng ln.

Khi cc mng con hp nht hnh thnh cc mng ln hn, cc thut ton nh tuyn c th chp

nhn cc mng con mi bng cch cp nht tt c cc bng nh tuyn ca cc nt. iu ny, tuy

nhin, rt khng hiu qu. Mt chng trnh nh tuyn hiu qu nn t b qu trnh ny v chn

cp nht cc nt b nh hng.

2.6.3 Concurrent Node Movements

Trong thc t c trng hp cc nt di chuyn ng thi, do cn cc quy tc m bo tnh thng

nht khi cu hnh li hoc sa cha.

2.7 Challenges Facing Ad Hoc Mobile Networks

2.7.1 Spectrum Allocation and Purchase

Cc quy nh lin quan n vic s dng ca bng tn radio hin ang di s kim sot ca FCC.

Hu ht cc th nghim mng ad hoc u trn bang tn ISM. trnh nhiu ad hoc phi hot ng

trn cc bng tn cho php. L vi sng vi bng tn 2.4GHz c th gy nhiu cho wireless LAN.

2.7.2 Media Access

Khng ging nh cc mng di ng, khng c kim sot tp trung v ng b ha trong mng ad

hoc. Do TDMA v FDMA khng ph hp. Ngoi ra nhiu giao thc MAC khng tng thch vi

my di ng. Nn vic h tr QoS lp 2 l kh khan.

Trong mng ad hoc cc nt dng chung mt ng truyn nn vic truy cp vo cc knh phi thc

hin mt loi phn phi qua giao thc MAC. Do khng c nt tnh nn khng th da vo mt nt

phn phi tp trung. Giao thc MAC phi ginh quyn truy cp nhng cng phi trnh cc xung t.

2.7.3 Routing

S hin din ca di ng c ngha rng lin kt c thit lp v ph v thng xuyn. Thut ton

nh tuyn distance vector ch dng cho mng di ng vi tnh di ng thp (trong h thn mng

c). Tuy nhin hin ti thut ton nh tuyn link state hay distance vector khng th bt kp vi tc

thay i lin kt thng xuyn trong mng ad hoc. Do , cc giao thc nh tuyn mi l cn

thit.

2.7.4 Multicasting

Cc phng php truyn thng cc cuc hi ngh video hoc m thanh s dng cc giao thc nh

tuyn multicast. Cn phi xy dng mt cy multicast xc nh cc my s nhn bn tin. Tt c cc

phng php i vi mng dy da trn thc t rng cc router l tnh, v mt khi cc cy multicast

c hnh thnh, cc nt cy s khng di chuyn. Tuy nhin, y khng phi l trng hp ca mng

ad hoc.

2.7.5 Energy Efficiency

Hu ht cc giao thc mng hin ti khng xem tiu th in nng l mt vn bi v n cho rng

cc thit b c cung cp bi ngun in. Tuy nhin, cc thit b di ng ngy nay ch yu hot

ng bng pin. Cng ngh pin vn cn tt hu so vi cng ngh vi x l. i vi mng ad hoc cn ch

vn ny. Thit b di ng va ng vai tr ca thit b tng tc ngi dng v thit b trung

gian (chuyn tip cc gi tin). Chuyn tip cc gi tin cho ngi dng khc c th s tn kh nhiu

nng lng.

2.7.6 TCP Performance

TCP l mt giao thc end-to-end c thit k cung cp lu lng v kim sot tc nghn trong

mt mng. TCP l mt giao thc hng kt ni, do , c mt giai on thnh lp kt ni trc khi

truyn d liu. Kt ni c hy b khi truyn d liu c hon thnh. Tuy nhin, TCP gi nh

rng cc nt trong tuyn ng l tnh, v ch thc hin cc hot ng iu khin lung v tc nghn

ti SRC v cc nt DEST.

TCP da trn RTT v mt gi tin kt lun tc nghn xy ra trong mng. Tht khng may, TCP

khng th phn bit tnh di ng v tc nghn mng. Tnh di ng c th gy ra mt gi v RTT di.

Do , mt s ci tin hoc thay i l cn thit m bo rng cc giao thc vn chuyn thc

hin ng m khng nh hng n truyn thng end-to-end.

2.7.7 Service Location, Provision, and Access

M hnh client/server s khng ph hp vi mng ad hoc.

2.7.8 Security & Privacy

Cc mng ad hoc l cc mng c lp. Thng qua nh danh hng xm, ngi dng c th bit c

l ngi l hp l hay l khng hp l.

3 Ad Hoc Wireless Media Access Protocols

3.1 Introduction ng truyn khng dy c th c chia s v bt kz lc no cc nt c th truyn. iu ny c th

dn n tranh chp truyn qua cc knh. Trong mt mng ad hoc khng dy, mi nt c th c th

di chuyn, v do , khng c nt mng c nh hot ng nh b iu khin trung tm.

Mt giao thc MAC l mt tp hp cc quy tc hoc th tc cho php vic s dng hiu qu

ng truyn. Mt nt l mt my ch c gng truy cp vo cc ng truyn. Sender l mt nt

l c gng truyn ti trn ng truyn. Receiver l mt nt nhn thng tin.

3.1.1 Synchronous MAC Protocols

Trong giao thc MAC ng b tt c cc nt c ng b ha vi cng mt thi gian. iu ny nh

mt b m qung b tn hiu thng xuyn. Tt c cc nt lng nghe tn hiu ny v ng b thi

gian.

3.1.2 Asynchronous MAC Protocols

Trong giao thc MAC khng ng b, cc nt khng nht thit phi theo cng mt thi gian. Mt c ch kim sot phn phi hn c s dng phi hp truy cp knh. Nh vy, truy cp vo cc

knh c xu hng l contension-based.

3.2 Problems in Ad Hoc Channel Access

3.2.1 Hidden Terminal Problem

Hai nt ngoi phm ph sng ca nhau, khng pht hin c yu cu gi. Khi c 2 nt cng gi tin

n 1 nt, xung t xy ra.

trnh va chm, tt c cc nt ln cn ca receiver cn phi c thng bo rng knh ny s

c chim. iu ny c th t c bng cch dnh ring mt knh truyn thng ip iu

khin, bng cch s dng mt giao thc bt tay. Mt tin nhn RTS (Request To Send) c th c s

dng bi mt nt cho bit mun truyn d liu. Nt nhn s qung b CTS nhm chp nhn v

thng bo cho cc nt ln cn khc bit ng truyn bn.

3.2.2 Shortcomings of the RTS-CTS Solution

Phng php RTS-CTS khng phi l mt gii php hon ho cho vn thit b n. S c trng

hp khi va chm xy ra v RTS v CTS kim sot cc tin nhn c gi bi cc nt khc nhau. Trong

hnh nt B gi p ng CTS cho RTS t nt A. Tuy nhin n xung t vi RTS t nt D gi n nt C.

Nt D n vi nt B. Bi v D khng nhn c CTS t C n tip tc gi RTS. Khi nt A nhn c CTS

n khng bit c va chm nt C v bt u gi d liu n B. D liu ny s xung t vi CTS t

C p ng cho D.

Mt kch bn khc c vn khi nhiu tin nhn CTS c cp cho cc nt ln cn khc nhau, gy ra

va chm. Nh th hin trong hnh 4.4, hai nt gi RTS ti cc nt khc nhau ti cc thi im khc nhau. A gi RTS n B. Khi B p ng CTS cho A, C gi RTS n B (RTS ny cho D nhng B nhn c)

v c xung t. V C khng nhn c CTS t B trong khi n gi RTS n D, C khng bit lien lc gia

A v B. Nt D gi CTS cho C. C A v C u truyn d liu nn c xung t xy ra nt B.

3.2.3 Exposed Node Problem

hnh trn B l nt exposed, n mun truyn dn vi A nhng do n nm trong phm vi thu ca C

nn khng c thc hin truyn, gy lng ph lu lng.

3.3 Receiver-Initiated MAC Protocols Trc khi sender gi d liu phi tin hnh gi thng bo.

3.4 Existing Ad Hoc MAC Protocols

3.4.1 Multiple Access with Collision Avoidance (MACA)

MACA nhm gii quyt cc vn nt n v nt exposed.

Theo hnh MACA s dng bt tay 3 bc, RTS-CTS-d liu. u tin sender gi cho receiver mt RTS

n t ch knh truyn, iu ny chn cc truyn pht ca hng xm sender. Sau receiver

gi li CTS cp truyn dn, iu ny chn cc truyn dn ca hn xm receiver

4 Overview of Ad Hoc Routing Protocols C nhiu giao thc c pht trin cho mn ad hoc. Cc giao thc ny phi i ph vi nhng hn

ch in hnh ca cc mng ny, trong bao gm in nng tiu th cao, bng thng thp, v t l

li cao.

4.1 Bellman-Ford Nhiu lc nh tuyn trc y c xy dng cho mng khng dy Ad hoc da trn thut ton

Bellman-Ford. Cc lc ny cng c nghin cu gii quyt cc vn ca lc Distance

Vector (DV). Trong thut ton Bellman-Ford, mi nt i duy tr mt bng nh tuyn cha thng tin

khong cch v thng tin next-hop trn ng i ngn nht ti ch j bt kz, trong khong cch

chnh l chiu di ngn nht t i ti j. cp nht thng tin v ng i ngn nht mi nt s

thng xuyn trao i bng nh tuyn vi cc nt bn cnh n. Da trn bng nh tuyn t cc

nt ln cn , nt i bit c khong cch ngn nht t cc ln cn ca n ti nt ch bt kz. Do

, vi mi nt ch j, i s chn mt nt k cho chng k tip sao cho khong cch t i qua k ti j l

nh nht . Cc thng tin tnh ton mi ny s c lu tr vo bng nh tuyn ca i v c trao

i vng cp nht nh tuyn tip theo. nh tuyn ny c u im l n gin v tnh ton hiu

qu do c im phn b. Tuy nhin nhc im ca n l hi t chm khi topo mng thay i v c

xu hng to cc vng lp nh tuyn c bit l khi cc iu kin lin kt khng n nh.

4.2 LinkState nh tuyn ny cng l mt trong nhng thut ton c s dng rng ri trong nhiu giao thc,

chng hn nh OSPF. Mc d nh tuyn Link State him khi c s dng cho mng khng dy,

song n li cha nhiu tim nng cung cp cc gii php nh tuyn theo yu cu cho cc tiu chun

nh tuyn khc nhau. Trong nh tuyn Link State, khi c mt nt pht hin ra c thay i trong

vng kt ni vi n, nt lm trn trng thi kt ni mi bi gi cha thng tin kt ni c cp

nhp. Cc nt khc thng bo v s thay i ny khi gi trng thi lin kt ti, do thng tin v

topo mng thay i theo. nh tuyn Link State p li s thay i mng nhanh hn DBF. N tnh

ton ng i theo kiu tp trung d dng chng li cc vng lp nh tuyn. Tuy nhin do nh

tuyn Link State cng da vo c ch flooding qung b thng tin v s thay i kt ni ca nt,

thng tin iu khin lm cho nh tuyn Link State c cht lng km hn DBF v on-demand trong

mi trng khng dy bt chp chnh xc m n cung cp. Vn khc trong nh tuyn Link

State l mt nt c th khng tm ra nhng bin i v topo mng chnh xc nu ton b mng c

chia thnh hai phn v sau c khi phc li.

4.3 Table-Driven Approaches Giao thc nh tuyn table-driven c gng duy tr tnh nht qun, cp nht thng tin nh tuyn cho

tt c cc nt khc trong mng. Giao thc ny yu cu mi nt duy tr mt hoc nhiu bng lu tr thng tin nh tuyn, chng p ng cc yu cu thay i topo mng bng cch truyn i cc

tuyn ng mi cp nht.

4.4 Destination Sequenced Distance Vector (DSDV) Destination Sequenced Distance Vector (DSDV) l giao thc nh tuyn da trn thut ton nh

tuyn Bellman-Ford. Ci thin thc hin y l trnh cc vng lp nh tuyn trong mng in thoi di ng ca router. Mi nt trong mng di ng duy tr mt bng nh tuyn c cha tt c cc ch c th n v chi ph n ( ay l s hop). Do , thng tin nh tuyn lun lun c sn, bt

k cc nt ngun c yu cu mt ng i hay khng.

Mt h thng nh s th t c s dng cho php cc thit b di ng phn bit cc tuyn

ng c vi nhng tuyn ng mi. Cp nht bng nh tuyn c gi nh kz trn ton mng duy tr tnh thng nht bng. iu ny c thto ra rt nhiu bn tin iu khin trong mng, lm

cho vic s dng ti nguyn mng khng hiu qu. lm gim bt vn ny, DSDV s dng hai loi gi tin cp nht tuyn ng. u tin l full dump. Loi gi tin ny mang tt c cc thng tin

nh tuyn hin c v c th yu cu multiple network protocol data units (NPDUs). Trong lc

chuyn ng nhiu cc gi ny khng c truyn thng xuyn. Mt loi gi nh tuyn khc nh

hn dng cp nht nhng thay i so vi gi full dump.

Bn tin broadcast nh tuyn mi s cha a ch ca nt ch, s lng hop, sequence number ca

tin, v sequence number nh du phn bit cc bn tin broadcast. Cc tuyn ng mi c gn

nhn theo s mi nht (theo th t tang dn). Tuyn ng s th t ln hn s c dng. Nu

cng s th t s dng tuyn ng c s hop nh hn.

4.5 Wireless Routing Protocol (WRP) Trong WRP mi nt cha bng nh tuyn lu tr thng tin v khong cch v ng i (t nt th

2 n nt cui) n ch. WRP thuc kiu nh tuyn dng thut ton tm ng. N trnh cc vn m v tn bng cch buc mi nt thc hin kim tra tnh nht qun ca thng tin trc gi

n bi cc nt ln cn. iu ny loi b cc vic lp v cung cp cho hi t nh tuyn nhanh hn

khi xy ra mt lin kt li.

Trong WRP cc nt bit n cc nt ln cn bng ACK hoc cc tin khc. Nu mt nt khng gi cc

gi tin, n phi gi mt thng ip Hello trong mt khong thi gian quy nh m bo kt ni

c nhn bit. Nu khng, vic thiu cc tin nhn t nt c th ch ra s tht bi ca lin kt khng dy v iu ny c th gy ra mt bo ng gi. Khi mt nt nhn c bn tin Hello t nt mi,

thng tin nt mi c thm vo bng nh tuyn v nt ny gi bn copy bng nh tuyn ca n

cho nt mi.

WRP s phi duy tr bn bng l: bng khong cch, bng nh tuyn, bng chi ph v bng danh sch

cc tin truyn li (MRL). Bng khong cch ch ra s lng hop gia n v ch n ca n. Bng nh

tuyn cho bit next-hop. Bng chi ph ch ra tr ca lin kt c th. MRL cha s th t ca cc

tin cp nht, b m tin truyn li, bo nhn, v danh sch cc cp nht gi trong tin cp nht. Cp

nht MRL trong bn tin cp nht cn c truyn li v cc nt ln cn cn bo nhn cho cc bn tin

ny.

m bo rng thng tin nh tuyn chnh xc, thit b di ng gi tin nhn cp nht nh kz ti

cc lng ging ca n. Cc bn tin cp nht c cha mt danh sch cc bn cp nht (ch, khong

cch n ch, nt trc ch), v mt danh sch ch ra nt no nn gi li bo nhn cho bn tin

update. Nt gi bn tin cp nht sau khi x l vic vp nht ca mt nt ln cn hoc mt khi s

thay i lin kt c pht hin.Khi mt lin kt hng, cc nt pht hin ra s gi tin cp nht n

cc nt ln cn v nhng nt ln cn s sa i cc mc bng khong cch ca n v kim tra cc

ng dn mi qua cc nt khc.

4.6 Source-Initiated On-Demand Approaches y l loi nh tuyn to ra cc tuyn ng khi c yu cu ca nt ngun. Khi mt nt yu cu mt

ng i n ch, n khi to mt tin trnh nh tuyn trong mng. Qu trnh ny hoan thnh khi

mt tuyn ng c tm thy hoc tt c cc tuyn ng c th c kim tra. Mt khi tuyn ng c pht hin v thnh lp, n c duy tr bi mt s hnh thc cho n khi ch

tr nn khng th n c hoc khng cn tuyn ng na.

4.7 Ad Hoc On-Demand Distance Vector Routing (AODV) Giao thc nh tuyn Ad Hoc On-Demand Distance Vector (AODV) c xy dng da trn thut

ton DSDV m t trc. AODV l mt ci tin trn DSDV bi v n gim thiu s lng cc bn tin broadcast bng cch to ra cc tuyn ng trn da theo cc yu cu, tri ngc vi vic duy tr

mt danh sch y ca cc tuyn ng nh trong thut ton DSDV.

Khi mt nt mun gi mt thng ip ti mt s nt ch v khng c c mt con ng hp l

n ch , n khi to mt qu trnh tm ng xc nh v tr cc nt. N qung b gi tin route request (RREQ) n cc hng xm. Cc nt hng xm ny li chuyn tip yu cu n cc nt

hng xm cho n khi n nt ch hoc n mt nt trung gian c ng n nt ch (ng ny

phi vn s dng c). AODV s dng s th t ch (DestSeqNum) m bo rng tt c cc tuyn l loop-free v cha thng tin tuyn ng gn y nht. Mi nt duy tr s th t ring ca mnh v broadcast ID.Broadcast ID c tng ln cho mi bn tin RREQ khi nt khi to tm ng

v cng vi a ch IP ca nt, xc nh duy nht mt RREQ. Mi nt trong mng u c mt s th

t v s ny c tang ln mi khi c nh tuyn n n, s ny nhm xc nh mi ca ng di

n n cng nh trnh lp v hn. Khi bn tin RREQ gi i s th t ca ch c cha trong

(nu trc nt ny cha nh tuyn n ch th s ny = 0). Mt nt trung gian nu c ng i

n ch s p ng li bn tin RREQ nu s th t nt ch ca n ln hn hoc bng s th t

trong RREQ (tc l ng i khng c hn). Broadcast ID c tc dng khi mt nt x l RREQ ri,

khi gp li RREQ ny da vo broadcast ID ny bit n x l{ cha.

Trong sut qu trnh chuyn tip bn tin RREQ cc nt trung gian ghi trong bng nh tuyn ca n

a ch nt hng xm u tin gi RREQ cho n, qua thit lp mt con ng ngc li. Nu c

thm cc bn sao ca cng 1 RREQ n n s c loi b. Khi bn tin RREQ n ch hoc nt trung

gian c ng i hp l n ch, nt ny s gi mt bn tin unicast route reply (RREP) ngc li

hng xm u tin gi RREQ cho n. Khi RREP c gi ngc li cc nt dc ng ny ghi vo

bng nh tuyn cc nt gi RREP n n. Vi mi ng i c thi gian router nhm xc nh xem

nu qu thi gian ny n s b xa nu khng c s dng. Bi v RREP c chuyn tip dc theo

con ng c thnh lp bi RREQ, AODV ch h tr vic s dng cc lin kt i xng.

Trong AODV, cc tuyn ng c duy tr nh sau: Nu mt nt ngun chuyn ng, n khi to

li vic tm ng tm mt con ng mi n ch. Nu mt nt dc theo tuyn ng di

chuyn, hng xm trc (theo th t ng i t ngun n ch) ca n thng bo di chuyn v

truyn tin nhn thng bo lin kt tht bi (mt RREP vi chi ph v hn) cho lng ging trc n

n xa tuyn ng, cc nt ln lt thng bo cho lng ging trc n cho n nt ngun.

Mt kha cnh khc ca giao thc l vic s dng bn tin Hello c thc hin nh kz bi mt nt

thng bo cho cc nt khc trong vng pht sng ca n. Bn tin Hello nhm duy tr kt ni ca

nt. Tuy nhin, vic s dng tin Hello l khng cn thit. Cc nt nghe bn tin gi li m bo nt

k tip vn cn ti c. Nu khng lng nghe truyn li th c th s dng mt s k thut c th l

tip nhn tin hello.

4.8 Dynamic Source Routing (DSR) DSR l giao thc nh tuyn theo yu cu da trn cc khi nim v nh tuyn ngun. Cc nt cn

phi duy tr trong b m cache cc tuyn ng nh tuyn chng bit. Cc tuyn ng b nh

cache lu tr lin tc c cp nht nh cc tuyn ng mi c hc.

Giao thc gm 2 giai on chnh l tm ra tuyn ng v duy tr tuyn ng. Khi mt nt cn gi

d liu i trc tin n tm trong cache c tuyn ng n ch khng. Nu n c mt tuyn

ng cha qu hn n c ch, n s s dng tuyn ng ny gi cc gi tin. Nu cache

khng c tuyn ng nh vy n s khi to vic tm ng bng cch truyn mt gi tin yu cu

tuyn ng. Gi tin yu cu ny c cha a ch ca ch, a ch ngun v mt s nh danh duy

nht cho gi tin . Mi nt nhn tin ny kim tra xem n c bit tuyn ng n ch hay

khng. Nu khng n s thm a ch ca n vo danh sch cc nt trn ng i ca bn tin v

chuyn gi tin ny i theo cc con ng ca n. hn ch s lng bn tin request chuyn tip

trn mng cc nt ch chuyn tip cc bn tin nu n cha tng thy bn tin v nu a ch ca n

khng xut hin trong h s lu tr tuyn ng ca bn tin. Mt bn tin tr li c to ra khi bn

tin yu cu hoc n c ch hoc n mt nt trung gian m trong cache ca nt trung gian

cha mt ng i cha qu hn n ch. Khi gi tin request n ch hoc nt trung gian c

ng n ch n s c mt bn ghi cc nt n ch .

Hnh di minh ha s to thnh ca h s ng i v vic chuyn tip cc bn tin yu cu qua

mng. Nu nt to bn tin reply l nt ch n s t h s tuyn ng (route record) cha trong

bn tin request vo bn tin reply. Nu l nt trung gian n s ni tuyn ng lu tr ca n trong

cache vo h s tuyn ng v to bn tin reply. gi li bn tin reply nt p ng phi c

ng i n nt ngun. Nu n c tuyn ng n ngun trong cache n s dng tuyn ng

ny. Nu khng, nu lin kt i xng c h tr n c th o ngc chiu ca ng trong h

s tuyn ng bn tin reply. Nu lin kt i xng khng c h tr, nt c th bt u tm

ng n ngun v gi bn tin reply qua ng mi ny.

Bo tr tuyn ng thc hin thng qua s dng route error packets v bo nhn. Route error

packets c to ra mt khi tng lin kt d liu gp phi vn truyn. Ngun lun lun b gin

on khi mt tuyn ng c ct ngn. Khi nhn c mt gi tin tuyn ng li, nt li c

xa khi b nh cache, v tt c cc tuyn c cha cc nt li c ct ngn ti im . Ngoi

route error packets, bo nhn c s dng xc minh tnh chnh xc ca cc lin kt tuyn

ng. Khi mt nt gi mt gi tin n nt khc trn tuyn ng, nt phi nhn c mt bo

nhn. Nu khng c bo nhn th nt gi li tip tc yu cu, c th yu cu nhiu ln v n mt

khong thi gian nh trc m khng thy bo nhn th tuyn ng b loi khi b nh cache.

5 Kch bn m phng. M phng vi giao thc DSR vi 10 nt di chuyn ngu nhin trong phm vi 1000x1000. a hnh

phng. To mt kt ni TCP gia nt 0 v nt 1.

Khi to cc tham s

set val(chan) Channel/WirelessChannel ; #Loi ng truyn

set val(prop) Propagation/TwoRayGround ; #Phng php tryn s dng sng radio

set val(netif) Phy/WirelessPhy ; #Giao din mng

set val(mac) Mac/802_11 ; #Giao thc mac

#set val(ifq) Queue/DropTail/PriQueue ;

set val(ifq) CMUPriQueue #Loi hng i

set val(ll) LL ; #Giao thc link layer

set val(ant) Antenna/OmniAntenna ;

set val(ifqlen) 100 ; #S lng gi ti a trong hng i l 100

set val(nn) 10 ; #S nt l 10

set val(rp) DSR ; #S dng giao thc DSR

set val(x) 1000 ; #Chiu x l 1000m

set val(y) 1000 ; #Chiu y l 1000m

set val(stop) 300 ; #Thi gian m phng l 300s

M phng vi a hnh phng

set topo [new Topography]

$topo load_flatgrid $val(x) $val(y)

To 10 nt di chuyn ngu nhin

for {set i 0} {$i < $val(nn)} {incr i} {

set node_($i) [$ns node]

$node_($i) random-motion 1

$node_($i) start

}

To mt agent TCP gn vo nt 0.

set tcp [new Agent/TCP/Newreno]

$tcp set class_ 2

$ns attach-agent $node_(0)

To mt agent sink gn vo nt 1. Agent ny c gi bo nhn v agent TCP.

set sink [new Agent/TCPSink]

$ns attach-agent $node_(1) $sink

Kt ni 2 agent ny

$ns connect $tcp $sink

To ng dng FTP truyn qua lin kt TCP va to

set ftp [new Application/FTP]

$ftp attach-agent $tcp

$ftp set type_ FTP

Tin hnh o s lng gi tin truyn i / gi tin n ch nh gi cht lng ng truyn.