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
c. Thu tyc them nh3p mai truang trong myn cam biin
Trong mang cam bien khang day yeu ciu diu tien va quan trong nhAt la can bing nang lucmg glita cac nut mang, sir dung nang lacing hieu qua trong thiet ke, lva chip thit tic them nh3p tad twang va kha nang thiet lap lii tuyen khi topo ming thay en.
Nhu da tim hieu a nhUng phin trtrac rang lacing cita nit tieu thu cha yen do truyen hooc nhOn dit lieu. th8ng thueng quit trinh truyen th8ng gam 4 trang thai: truyen, nlan, rai va the dO ngi. Trong d6 the dO truyen va nhOn la Mn nhieu rang ltrong nhAt, dva vao hog dOng ciut giao thirc them nh$p men throng to c6 the nhOn Only mat so van de va mic tieu thiet ke cita giao thirc MAC:
+ Xung dot: khi /ay ra xung dOt thi vita ton rang luqng tai ca nth Win va nai thu va nang lam ding de phat lai g6i tin d6, bei v#y can phai loci be xung dOt, tuy nhien nau c6 the dam bao luu luqng ctia mpg cam bien du thip thi xung dOt gin nhu duqc be qua.
+ Nghe taping: mac du khung Unicast gui tir mot nguan tai met dich, tuy nhien vi kenh vo tuyen la mai tnrbng chung cho tit ca cac nit hang xim ciia no boi v3y chimg deu nhen duqc tin hieu tir cac nit di va be qua tau chung lchong phai la dich tai, viec nay cling ten kha nhieu rang luqng. Tuy nhien d8i khi viec My la het sic can thiet khi thu thap thong tin ve hang xi:5m de xac djnh luu lacmg Men tai h8 trq cho rime dich quitn
+ Nghe ngOng a the de rai: khi mot nit 6 trang thai rai n6 sin sang nh$n dO tuy nhien trong nfrang ming luu lucmg it thi thai gian cher nhOn do lieu ton kha nhieu nang luong.
+ MOt th8ng s6 quan tong nem ngoiti nang lacing ra la you eau chuang trinh Ichong phirc taw, xir ding it tai nguyen nhu b0 nha, vi xir 15r ...
flan H9r Th5ng 1.nng Al 777A -RAI TiOn 'fling
Thu tic than nhap m8i throng mia mang cam bien thuemg duqc chia vio 2 nhem thu tic chinh la: thu tic cash tranh, va thir tic 1#p lich.
2.1.3 Tha tyc cynh tranh
Trong thu tic conk tranh, cc( hei truyen de lieu chia deu cho tat ca cic nut hang x6m. Neu chi c6 mot nut hang x6m an truyen du lieu thi khong van de gi, tuy nhien neu c6 2 ho(ic nhieu nut mu6n truyen khi de chang phai cash tranh veri nhau de gianh quy&I truyEn dtt lieu, 2 giao thirc quan tryng coa nh6m giao thirc nay la ALOHA va CSMA ma ta da c6 dip de cep 6 phan truck.
* Thit tic CSMA: Trong thu tic da truy cap cam bien song mang Wirth xung dot CSMA — CA(Carrier Sense Multiple Access with Collision Avoidance) MOt van de
gip phai v6i d6i turyng lam sit theo si kien, binh thutmg thi nut mpg 6 trang thai r6i trong met then gian dal, n6 chi bit diu host dOng khi c6 sir kien ben ngoii tic dOng, khi sir kien d6 xay ra gas nhu tat ca cac nut deu mu6n truy&I dft lieu met cich ding then, do vOy se do ra nhieu xung dot, au nut c6 gang giri dft lieu theo chu kjr thi Icha nang lap lai xung dOt la rat cao neu Wong c6 qui trinh them de xay ra. Sau day ta se
tim hieu nguyen ljr lam viec ca ban cua giao thirc da truy cap cam bien song mang nay. Ban dau khi met nut nh#n gdi da lieu mei de truyen di, ne eh& met then gian tre new nhien, mix dich cua viec lam nay nhim lim gam tinh d6ng be cim cac nut khi phit hien sir kien say ra (vi neu khi 2 nut xay ra xung dot ma trong lan thir titp theo neu c6 ding then gian cher thi van khong trinh khdi xung dot), trong then gian chtr nem nhien d6 nut c6 the at 6 hang thai neu, trong thbi gian nghe ng6ng nut se thirc hien cam bien sting mang. Neu nhu m8i truling truyen dang bin, sau met s6 lean thir ma van khong thinh ding n6 se dung lai va cher met then gian ngeu nhien, phi thuOc vio sot lan thu va thai gian ngit ells nut, sau d6 ne lai titp tic nghe ngeng m8i trutmg, car nhu vay khi ten met gi6i his ntio d6 ma van lch8ng thinh ding thi g6i se bj be qua. Trong mem hqp m8i twang rei, nut se gin bin tin RTS va chuyen sang trang thai cher, trong
throng hqp khong nh#n duce bin tin CTS, hoci c6 ban tin CTS cho nut 'chic thi n6
se quay lai qui trinh cher mot thin gian ngiu nhien va thu lai. Con neu nh#ri duqc bin tin CTS, ne se giri &Et lieu di vi cho ban tin ACK.
Tay tang trutmg hqp ma CSMA c6 the thay don then gian cher, thai gian nghe ng6ng la ngiu nhien hay c6 djnh. MOt dieu can luu y la can phan biet thu tic CSMA —
CA trong mang khong day va thu tic CSMA — trong mpg c6 day, ve cc bin thi 2 thi
tic nay gi6ng nhau la deu dua vio viec aim bien sang mang, tuy nhien thu tic truy cap CSMA — CA chi duqc gqi la trinh xung dot, do neo 'thong the phat hien khi ceo xung dot xay ra, do the dO truyen la bin song c8ng, nut mang tai met then diem chi c6
Dei 1-inr Th5ng i.nng Al 7778 -Rid Tin Thng the thu ho#c phit di? lieu. Do v#y trong lop trinh djnh tuyen sir dung thin Ate thim nhop mOi tru?mg nay thutmg sir dung mOt then gian trg ngau nhien de giam tinh thing WO giita cac nut, shim tang hieu qua tranh xung dOt.
Thiet bj duy tri ba thong so NB, CW va BE, trong d6 NB dem s6 thou diem rat lui, CW chi ra kich thuerc elm cira s6 xung dOt hien tai, BE la so mil cua theri diem nit lui hien tai. Khi c6 met gen du lieu de truyen di, cac th8ng so nay duce kheri tao Wong img von: NB=O, CW=2 va BE=macMinBE (trong d6 macMinBE la thong so curt giao thirc). Thiet bj se cher ngau nhien trong r th6i diem nit lui tiep theo trong khoing [0, 2 1' — 1] , khi de n6 thuc hien cam bier song mang, tau moi trtrerng rOi n6 se giam CW, va cher teri thai diem rot lui tiep theo va xem xet lei men trutmg truyen met lin nfta, neu mai throng yin r6i thi thiet 1)] se bit Mu truyen du lieu cos no. Trong twang hqp phit hien ra m8i truerng dang ban thl so then diem roi NB va so mu BE tang len va CW duqc $t lui CW=2, neu NB vuqt qui ngtrCrng thl khung der lieu duqc be qua, qui trinh truyen that bai. Cu nhu v#y cac bare duce lap lui.
2.1.4 The tyc xfp gch
Yu diem cita thit We nay la xip xep qui trinh truyen tai cac nut hang thorn di lchong thy ra xung dOt tai dau thu. Tuy nhien no cfmg c6 mOt vai nhuqc diem d6 la phirc tap tong thiet d(it va bio tri viec sip xep, lap ljch. (ki thuftt da truy cop phin chia theo then gian TDMA thubng dugc sir dung veil loci thu tuc them nh#p m8i tniemg nay)