I 1.1 v J \)v \J b) Tdn s(f
d) n)/lg e) mal 1I((li.
2. M(;mg hlllh sao (star) Iii. m<.tng dicu khitn liung Wm, cach sftp xep v~t 1y
giong ngoi sao- hinh 2.76 (b). T<.tl Uim la may Xlr Iy trung (j.m cua m~ng ho~c la mQt thiet bi t~p trung cac moi truyen thong; cac nut dUQ'c bo' Iff chung quanh va
noi tiep voi may trung tam (vi dl,l, m<.tng di9n Ihm.li). Neu trung tam hong se hong d. m';lng.
3. M(;mg phJn nip IIOi}C liinl! cd ..... · (hierarchy/tree) gam mQt 10<;1t cac nhanh hQi tl,l gian tiep t<;11 diem dinh cay (hlnh 2.76 c). Trong h~ lhong nay. giiIa hai tr<;1m bat ky chi co m¢t duang truyen. D<;1ng m~ng nay c6 the hinh thanh tiI m¢t
so cae hi; thong m<;lng buyt. M<!-ng hlnh cay thLIemg SlI dJ,lng eho khoiing each cae nut IOn hem 100m.
4. M(lIIg w)ng (rin;?) ia m~ng tapa khong co trung tam, tat d d.e nut dLIqe noi vong khcp kin (hlnh 2.76 d), khoang caeh gifra cae nut thlIl'mg nho hem i OOm. Dfrii~u trang h~ thong lien tJ,le hru thong quanh eho den khi co h~ thong
nao do nh~n no. Dfrli¢u co the dung dLIqe eho tat cii cae nut.
5. Mt;mg mat llltfi (mesh), khong co mQl hlnh mau nhat djnh - hlnh 2.76e. Truyen thong gifra de nut thong qua cae duemg dil li¢u phue.
Thu~t ngu m<;lng eJ,le be) (LAN) duqe Slr dl,lng khi mq.ng thiet l~p trong khu
vl!e dja Ii h~p ho~e chi 2, 3 may vai nhau ho:)c nhu tat cii. thiet bj trong eung toa nhit ho~e giua d.e toa nha trcn eung mQt dia dicm xay dtpIg. LAN thuang dung m<;lng buyt, vong ho~e sao.
M~ng di¢n rQog (WAN) ia m~ng noi lien cae may tfnh, thie't bj dau euoi va cae m<;lng el,le bQ tren to~m quoe ho:)e a cap quae gia thong qua oLICmg oay oi¢n tho~i ho~e de eong ey truyen thong khac.
M~ng toim cau (IN1ERNET) la h¢ thong gam cae m'.lng may tinh duqe lien ket voi nhau trcn ph<;lm vi toan the giai, t<;\o dieu ki¢n thu~n Iqi eho cae dieh VlJ twyen thong dilli¢u, nhLI dang nh~p tir xa, truyen d.c t¢p tin, thLI tin di¢n tlr va cae nh6m thong tin khae.
2.5.3. Giao thuc (protocol)
Dil li¢u truy6n ehua hai lo~i thong tin, mQt ia iO<;li du ii¢u may muon truyen sang may khae, io~i kia thu~t ngu gQi 1.1 dil lir;u giao "lIfC (data protocol) duqe
Slr dyng bai giao di¢n gifra may tinh va m'.lng d~ dieu khicn vi¢e ehuyen giao dfr Ji¢u VaG trong m<;lng ho~e tir mOt m<;lng VaG trong m')t may vi tfnh. Giao thue 1.1 Ji¢u VaG trong m<;lng ho~e tir mOt m<;lng VaG trong m')t may vi tfnh. Giao thue 1.1
t~p cae lieu ehurin chi phoi vi¢e ehuy~n tM thong tin, oieu khi~n thai gian,tuan tl!
truy e~p va ki~m soat I6i trong trao dbi thong tin. M9t giao thue c6 3 thanh phan IiI:
1. ell pJuip (syntax) xue dinh dC).ng thue dfr li¢u, cae mue tin hi¢u va rna hoa.
2. Ngttnghfa (semantics) giai quyct dong bQ hoa, diell khien va xLc Ii loi. 3. Djnh thiJi gian (timing) giai quyet van oe tuan tt! eho dfr li¢u va ehQn toe
oQ eua dfr li¢u.
(ISO) ua d~nh ra m9t h¢ thong giao thuc chulln 7 tOp g9i la mo hlnh lien ket cae h¢ thong md OSI (Open System lntercanection). Cae 16p nay ta:
1. Lap v¢11i (physical layer) mieu ta phan c(rug d.e m<;lch chuyen cha thong tin giua hai thiet b~ nhlI lo~i ca.p dung. cong xuat/nh~p, mue ui~n ap va cae chan d.m.
2. LOp kef no,' dtt lif}u (data link layer) HI. ldp xac d~nh giao thlrc gui va nh~n thong baa, phat hi~n va slra 16i. sap xep hqp If dl"r 1i~u duqc truycn. L&p
nay lien quan den vi¢c goi du li~u thanh cae g6i va d~t chung vao trang d.p. roi Hiy chung khoi cap t\li di~m nh~n cuoi.
3. LOp mqng (network layer) giai quyet ul1ang truyen thong, glli va giu thea
dlIong nhAt u~nh, dicu khitn cac thong haa HCn m\lng va dam b~l.O thong baa dung ndi.
4. LOp truyin tdi (transport layer) cung cap phlIoog phap rna thea d6 du
li~u duqc truyen di. No thiet l~p va gill m6i quan h¢ gilra may truyen va may nh~n.
5. Up thea phiell (session layer) lien quan t6i vi~c thiet l~p d6i tho<;li gilr3
d.c qua trinh lrng dlfng dU"qc noi v6i nhau bai m~ng. No co trach nhi¢m ljuyct
djnh thai gian b~t/tat truyen th6ng giua hai tr::tm .
6. LiJp trinh bay (Presenration lager) lien quan v6i vi¢c cho phcp tM hien di.i li~u da giai rna dllqc truyen thea hinh thlrC phu. hqp v6i che' Hie cua ngU"m sit
d\,lng.
7. LOp lIng d~ng (application layer) dam bao r~ng dl1 li~u truyen giiia hai (mg dl,lng bat ky dU"qc hieu va cung cap cho nguoi siJ dl,lng cac chuc nang Xlr Ii (mg dl,lng bat ky dU"qc hieu va cung cap cho nguoi siJ dl,lng cac chuc nang Xlr Ii thong tin va ca.c d~ch vl:\ (mg dQ.ng Cl:\ the nhu giao thuc truyen t¢p FfP ha~c thu
di~n ttl.
2.5.3.1. Cae chuilD ve m~Dg
Thu~t ngu truyen thong deli rQIIR dUQ"c dung cho m<;lng. trang do thong tin
duqc dieu bien tren tan s6 mang tan s6 va tuyeD. moi trlICmg truy€n 1ft cap dong tI1.).c. D~c trlffig cua ca.c m<;lng tapo Cl:\C bq dai rQng la mQt m~ng buyt voi cac
nMnh. Truyen dai r(mg cha phep mQt tUQ'ng s:6ng m<;lng uin so radio da dicu bien truy~n dbng thai (co the truyen tach ha~c truyen don (multiplex)). t'!-o Cd h9i cho cac dl1Cmg truyen thong da kenh.
Truy/n hallg ca sci chlqc su dl,lllg khi thong tin soluu thong tfl!c tiep trang m6i truem.g truycn. Truy~n bang co sa bi h(;ln chc ve clf Iy truyen dan va chi cho phcp thlfc hi~n m¢t kcnh lruycn thong trong mot hie.
Vi~n Ky thUi}t Di¢n tu va Di~n (Institute of Electrical and Electronic Engineers - IEEE) My dii phiit trien mot s6 lieu chuan cho m(;lng cl,lc b(l. Cae tieu chufln nay dllqc su dl,lng de xac dinh cac m~ng b~c thap hC1I1 duqc phat trieD cho nhfrng ml,lc dich Cl,l the sau:
IEEES02.1 (A) Tieu chufln m~ng cl,lc b¢ va m;:tng trung lam. Mieu ta chung