VI di gii sir ne tA bit diu truyen eft lieu cho nut B, mOt lit sau nu tD ding quy& djnh truyen de lieu cho nut B, boi vi D Ichang nhfui they nut A dang hoot dOng khi D
222 Bong 6¢ theri gltm trong mon° cam Min
Trong mang cam Bien c6 mOt so disc diem ma anh hutmg den you eau thiet ke cita cac thu$t toan dOng b0 then gian:
➢ Thuat tan phrli phit hop vOri pham vi mang mutilhop rang 16n, cac nut bi rang
buOc ve mat Wing luring. Yeu cau ve pham vi bao ham ca se, Wring cac nut trong mang va mat do cac nat.
➢ Yeu cau ve do chinh xac c6 the thay doi khitc nhau tir mili gily cho den hang
gily.
➢ !Chong sir di,mg them phan cling chi gianh cho muc dich &mg bo vi ton chi phi
va neng luqng them vao cho phan phu do.
➢ Muc dO di dOng la rat thip.
➢ Hau nhu khong c6 gidi han tren c6 dinh ve tre truyen g6i v1 phu thuOc 16p
MAC, 161 cac g6i, va truyen lai.
➢ Tri troy& gifts hai nut hang x6m la khong ding ke. MOt khoitng cach 30m can
10^-7s vi van thc anh sang la c =3.10^8m/s.
CO rat nhieu giao thirc ang b0 thtri gian truyen thiing c6 ging gift viec ding bei gift cac nut 6 moi thin diem nhung lai khong quan tar' n den !tang luqng va cau hinh
nal 1-Inr Thane I.nng Al 7776 -Rai Tign Tang
mang cho nen khong the ap citing vao mang cam bien. VI disc diem cita mang cam bien cho nen giao thirc eking b0 thei gian can cho y ve the yin de ve de chinh xac, chi phi rang Itroug va cac you eau ye be ruin.
Phuong phap co ban de d8ng b0 thei gian tong mang cam bien la cong the gitta cac nut trong town mang. Thiet lap moi lien he cop day (pair-wise) gifta cac nut trong mang sau de me rOng ra toan mang.
CO hai cach thiet lap so cong tic gifta hai nut trong mpg de la deng be* gift ben
gfri va ben nhen (Sender-Receiver) va gifts ben nhon va ben nhOn (Receiver-Receiver).
D6ng b0 gifta ben gfri va ben nhan yeu can lien ket hai chieu gitta hai nut lan can. Trong phucmg phap demg b0 gifta ben nhen va ben nhen, nhieu nut nhen cua the g6i c6 nhin thai gian nhu nhau d6ng b0 vei nhau ma khong you call thing be vOi ben gin (n& gfri goi tin broadcast den hai nut A va B, sau de A va B to deog 1)0 v6i nhau kitting an den Sc). Hai phuong phap nay duqc mieu to nhu hinh (2.10).
B
B
A 4‘
Ifinh 2.10.D ang ba ben phcit/ben *In vet ben nhdn/ben nhdn. 2.2.3 Giao that dong NI gift ben nh(ln vd ben phat
Trong giao thirc nay, mOt nut goi II ben nhan, trao dei gei du lieu vori net khic goi la ben phit, lam cho ben nhan d6ng be WA ding he cfut ben phat. Giao thee ding b0 gitta ben nhan va ben phat nbi chung la dei hen dtr?mg not 2 chieu gifta cac nut lan
cert.
Dien hinh cfut giao thirc clang b0 gift ben phat va ben nhOn la Lightweight time synchronization protocol (LTS). Giao thirc nay dua ra bOi VAN GREUNEN va RABAEY de deng b0 citing h6 cua mang voi ang h6 cfla cac nut tham chieu, vi do nhu c6 the c6 1)0 nhOn GPS. Trong kin heat dOng n6 dieu lchien cac nut de sir clortg Wing luqng hieu qua va dat duqc dO chinh xac cao, va dua ra nhang gioi hart tuang dui
chinh xac ye cac phin cfmg co se va the he thong. LTS kh8ng yeu au phai update ding he eve be va ne cling khong tree luqng t6c dO tr8i thvc so.
Dal Fine Thing Long Al 777h -RAI Tiln TAng
LTS chia qua trinh deing b0 lElm 2 giai down:
❖ Giao thirc d6ng b0 2 chieu de deng b0 2 nut Ian can.
+ De gitt cac nut hoc mOt tip hqp cac nut can quan tam Clang be theo met tham chieu chung, LTS xay di,mg mOt cly phin tan tir cac not tham chieu den tat ca cac nat. Neu Sic lei khi deng 1)0 single-hop la dOc lap, pit phei y het nhau va c6 trung binh la 0 thi cac nut la cna thy cling dirqc ding b0 vei lei bing 0 nhung syr thay dei la tong the thay d6i dqc theo dubng truyen tir nut tham chi& den nut la. VI vay su thay doi nay c6 the tai thieu hoa bang viec tim ra ciy phan
tan c6 chieu cao nhe that.
Ding b# 2 chau
Diu tien chung to se nghien cuv ye deng be hai chieu (hinh 2 1 1)
Sau khi qua trinh 6Mg b0 lei duqc Ichei dOng a not i, goi da lieu you &au dew b0 &nye djnh clang tai thbi diem tl voi thbi gian Li(t1). Nat i dieu lchien cac gei qua he thOng host dOng va cac nein xep. Tre dubng truyen c6 the bien thien rat nhieu. Khi nut i gel bit diu tien tai thbi diem t2, nut j nhon bit cuoi ding ciia gei t.i t 3 = t2 + T -F tp
,trong de T la tre debug truyen va tp la then gian truyen gei (chieu dai cua goi tinh theo bit).
Al 7776 Tan Wing f)ei 1-Tor Thing 1.nng
I
bong b¢ Igi xung to g6i bong be) djnh
g6i Ydri nh5n th&i gian Mt') ti chuyin giao g6i 68 truyen
h4 th8ng host bong, truy nthip kenh truyen
bat 68u truyin g6i
— &rang fruiter'
LAO thbi glen truyin g6i t3—
14— nwing nhin g6i ts— nh8n thbi giant(15)
g6i phoc &fp dang b6 djnh clang(
I
16— e—nhin thbi giant...1(t6) 4_chuy'in giao g6i d8 truyen OS, truy nhig kenh truyen
bat au truyen g6i
-Ow
mating nh$n g6i
L 06)
L 1 01)LJ 5)
—t 7
nhin thbi giant,(18) —ow —is
Hinh 2.11.Hogt dung ctia viec (long b0 ben phcit/ben nhan
Sau da met thin gian, tai thai diem t4, g6i dif lieu den duqc bio hieu den ling dung hoc he thOng host dOng cim nut j qua met qua trinh ngit, sau da duqc &nit du tai then diem t5 yeti thbi gian Lj(t5). Tsi t6, not j djnh dkuig g6i phitc dap vii thai gian Lj(t6), va dieu WU& gei do den he thong host dOng dm n6 va ngan xep numg. Goi nay bao gbm ca thin gian truttc d6 11 Lj(t5) va Li(t1). Nut i ngirng nhan g6i vio th&i diem t7 (t6 cOng vOi mao dau cim msng hotic he thOng host dOng) vi &nit deu tai thin diem t8 yeti then gian Li(t8). Bay gib ta se Olin tfch vi sao not i nhat' m str hieu chinh ciut no. De c6 , chting ta gia sir khang c6 bit 16 sir ten nil) gitta cac clang ha trong khoang thbi gian tir tl den t8, do d6 0 = * ) vii cac nut
va tren thtrc to nut i u6c dotin 0 bang viec vat dofin .
L i (t5 ) =
2
4(4) + r + tp + Li(t 8) — tp — (Li (t6) — Lj (ts))
Bei finr TWAng i.nng Al 777h Tien Tung
Tit hinh ye ta thity nhan thei gian Lj(t5) &Intl diu str quay lai cita nut i, cot the xay ra bat Id Inc nito trong khoang tir tl den t8. Tuy nhien chimg ta cd the lam giam su kh8ng xac djnh nay bang cac nh#n xet sau:
✓ Chi do mot dO tri &rang truyen r tong vOi then gian truyen gdi tp gifta tl va t5
✓ Chi c6 them mot khoing tp gifta t5 va t8 d8i yei g6i phitc clap.V6i cac mit
tinh chting ta c6 the gia thiet ring tre throng truyen la nhu nhau theo ca hai human.
Thtri gian gifts t5 va t6 ding duqc tInh beri hieu Li (t6) — Lj(ts).
Do v#y, co the giitin su Icheing chinh xac cita t5 den Ichoing
/ = ELL(t i) + r + tp ,L i (t8) — r — tp — (Lj(t 6 ) — Li (t5)) .1. Neu chting ta gia sir thtri gian sir chmg trong hg thing host dOng va ngiin xep mang, khoang ngit cling nhu lit tre gian sir chmg trong hg thing host dOng va ngiin xep mang, khoang ngit cling nhu lit tre &ging truyen la nhu nhau theo hai huong, thl tir not i se suy ra mit j se ce, Lj(t5) tai thei diem (xet so vdi nut i)
Vi the ,
0 = A(ts) = Li(ts)— 1,;(ts) — Li(ts) + 11(4) — 11(t5)
2
Bay gib mit i cd the dieu chinh d6ng 116 cac b0 bang viec gin them de loch 0 vao. Bing cach thy mit i se deg b0 veri th?ri gian cvc b0 cita mit j. !Chi mic dich ctia viec gin them nay la de cho nut j ye 0 thi phai can them gni thin 3, giri tir i den j va bao gem ca 0. Trong trtrtmg hqp nay thi toan be qua trinh cuing b0 can 3 g6i.
Sit s6 ding be cao nhit cita m8 hinh nay la nett r va tp co do chinh xac cao.Sai se d6ng b0 that su c6 the do cac khoang ngit khac nhau O i va j, den cac thtri diem khac nhau gifta gifta viec ngit de nhon met gdi va clanh clau thtri gian gni do, va cac th6i gian tray nh#p kenh khac nhau. Nhfing su kheong chinh xac nay co the gitim clang ke neu mit you ciu co the danh diu thin gian cac geti cint no tang ch(im tang tot, tot nhit la ngay truck khi truyen hoc ngay sau khi chiem duqc dutmg truyen.
Ding bp trong toitn negng
Nth co khi Wing ang b0 theo hai chieu, LTS giai quyet di:cc nhiem va dOng b0 tit ca cac mit trong town mang yeti mit thaw chieu. Neu met not i nito d6 each mit
I jai HQC ThAng I nng Al 777A -Rill Tign Wing thaw chieu mOt khoang la hi hop va neu 161 clang b0 thong thu&ng phi thuOc vao cac