Cc giao thc nh tuyn trong mng MANET

Mng ty bin di ng MANET (Mobile Adhoc Network) c cu trc t cc node mng khng dy c c tnh t cu hnh v truyn thng a bc. Cc c tnh ring bit ca kin trc MANET t ra mt lot cc thch thc i vi bi ton nh tuyn. Bi bo tm tt c tnh c bn ca giao thc nh tuyn trong mng MANET, kho st cc so snh gia mt s giao thc nh tuyn in hnh.

1. GII THIU CHUNG Vi hng lot cc u im ca cng ngh truyn thng khng dy, cc mng di ng khng dy c pht trin rt mnh trong thi gian gn y. Mng di ng khng dy c th chia thnh hai kiu mng: mng h tng v mng khng h tng. Trong mng h tng, truyn thng gia cc phn t mng ph thuc vo s h tr ca h tng mng, cc thit b u cui di ng truyn thng n bc khng dy qua cc im truy nhp (cc trm c s) ti h tng mng c nh. Kiu mng khng ph thuc h tng cn c gi chung l cc mng ty bin di ng MANET (Mobile Adhoc Networks) [1,2], MANET l mt tp ca cc node khng dy c th t thit lp cu hnh ng trao i thng tin m khng ph thuc vo h tng c nh, cc kt ni truyn thng trong MANET c thit lp qua cc lin kt khng dy a bc. Do c tnh ty bin nn MANET c th cung cp mt min rng cc ng dng dch v cho cc vng mng cc b v th nh: Mng cng ng, mng h tr khn cp, cc im truy nhp cng cng, cc ng dng cho qun i, cc ng dng tnh ton nhng v phn tn, cc dch v theo khu vc v mng cm bin, v..v [3]. Bn cnh cc u im, MANET phi i mt vi mt lot cc thch thc do chnh cu trc mng to ra v d nh: tnh t tr ca cc node, iu hnh phn tn, nh tuyn a bc, cu hnh mng ng, cng sut tiu th v s khng n nh ca mi trng, lin kt khng dy, v..v [4]. vt qua cc thch thc v hon thin cc gii php cho mng MANET, rt nhiu nh nghin cu xut cc phng php mi nhm ci thin cc vn cn tn ti ca MANET trn mt lot cc kha cnh, v d nh: iu khin truy nhp phng tin, nh tuyn, qun l ti nguyn, iu khin cng sut v bo mt, v..v. Trong cc hng , vn ci thin k thut nh tuyn lun c t ra hng u, do k thut nh tuyn lun c coi l yu t then cht nh hng ti hiu nng mng truyn thng ni chung v mng MANET ni ring. Thm vo , do tnh phc tp v c tnh truyn thng a bc trong mi trng truyn dn khng dy nn hng lot cc vn phc tp lin quan ti k thut nh tuyn vn cha c gii quyt trit v ang c tip tc ci thin.
2. CC GIAO THC NH TUYN MANET

Vn lun c t ra i vi cc mng MANET chnh l phng php gi thng tin gia cc node khng c lin kt trc tip, khi m cc node trong mng di chuyn khng theo cc d on v dn ti cu hnh mng thng xuyn thay i. V vy, cc tip cn nh tuyn trong cc mng c nh truyn thng khng th p dng c i vi cc mng ty bin di ng khng dy. Mt phng php ph bin phn bit cc giao thc nh tuyn trong mng MANET da trn cch thc trao i thng tin nh tuyn gia cc node theo phng php ny, cc giao thc nh tuyn c chia

thnh: nh tuyn theo bng, nh tuyn theo yu cu v nh tuyn lai ghp (hnh 1). S khc bit ca cc giao thc ny xut pht t tnh chuyn bit i vi cc kha cnh nh tuyn nh phng php tm ng ngn nht, thng tin tiu nh tuyn hay c tnh cn bng ti, v..v.

Hnh 1: Phn loi cc giao thc trong MANET

2.1 Cc giao thc nh tuyn theo bng Trong phng php nh tuyn theo bng, cc node trong mng MANET lin tc nh gi cc tuyn ti cc node duy tr tnh tng thch, cp nht ca thng tin nh tuyn. V vy, mt node ngun c th a ra mt ng dn nh tuyn ngay lp tc khi cn. Trong cc giao thc nh tuyn theo bng, tt c cc node cn duy tr thng tin v cu hnh mng. Khi cu hnh mng thay i, cc cp nht c truyn lan trong mng nhm thng bo s thay i. Hu ht cc giao thc nh tuyn theo bng u k tha v sa i c tnh tng thch t cc thut ton chn ng dn ngn nht trong cc mng hu tuyn truyn thng. Cc thut ton nh tuyn theo bng c s dng cho cc node cp nht trng thi mng v duy tr tuyn bt k c lu lng hay khng. V vy, tiu thng tin duy tr cu hnh mng i vi cc giao thc ny thng l ln. Mt s giao thc nh tuyn in hnh theo bng trong MANET gm: Giao thc nh tuyn khng dy WRP (Wireless Routing Protocol), nh tuyn vector khong cch tun t ch DSDV (Destination Sequence Distance Vector), nh tuyn trng thi ti u lin kt OLSR (Optimized Link State Routing), nh tuyn trng thi gc rng (fisheye (Fisheye State Routing), v.v. 2.2 Cc giao thc nh tuyn theo yu cu Trong phng php nh tuyn theo yu cu, cc ng dn c tm kim ch khi cn thit, hot ng tm tuyn bao gm c th tc xc nh tuyn. Th tc tm tuyn kt thc khi mt tuyn khng c tm thy hoc khng c tuyn kh dng sau khi xc minh ton b tp hon v tuyn. Trong mng MANET, cc tuyn hot ng c th ngng do tnh di ng ca node. V vy, thng tin duy tr tuyn l ti quan trong i vi cc giao thc nh tuyn theo yu cu. So vi cc giao thc nh tuyn theo bng, cc giao thc nh tuyn theo yu cu thng c tiu trao i thng tin nh tuyn nh hn. V vy, v mt nguyn tc, cc giao thc ny c kh nng m rng tt hn i vi cc giao thc nh tuyn theo bng. Tuy nhin, vn ln nht ca cc giao thc nh tuyn theo yu cu l tr do tm kim tuyn trc khi chuyn tip thng tin d liu. V d v mt s giao thc nh tuyn theo yu cu gm: giao thc nh tuyn ngun ng DSR (Dynamic Source Routing), giao thc nh tuyn vector khong cch theo yu cu AODV (Ad hoc On- demand Distance Vector routing) v giao thc nh tuyn theo th t tm thi TORA (Temporally Ordered Routing Algorithm). 2.3 Giao thc nh tuyn lai ghp

Cc giao thc nh tuyn lai ghp c xut kt hp cc c tnh u im ca cc giao thc nh tuyn theo bng v theo yu cu. Thng thng, cc giao thc nh tuyn lai ghp MANET c s dng trong kin trc phn cp. Cc giao thc nh tuyn theo bng v theo yu cu c trin khai trong cc cp thch hp. Mt s v d v giao thc nh tuyn lai ghp: giao thc nh tuyn vng ZRP (Zone Routing Protocol), giao thc nh tuyn trng thi lin kt da trn vng ZHLS (Zone-based Hierarchical Link State routing) v giao thc nh tuyn mng ty bin lai HARP (Hybrid Ad hoc Routing Protocol), v.v...
3. SO SNH CC GIAO THC NH TUYN MANET

Do tnh phc tp v quan trng ca giao thc nh tuyn trong mng MANET nn vn so snh v nh gi giao thc nh tuyn c s quan tm ca rt nhiu nh nghin cu. Vic so snh v nh gi tt c cc giao thc vi tt c cc kha cnh c coi l khng c tnh kh thi. V vy, mt s hng nh gi giao thc c hnh thnh trong nhng nm gn y v c chia thnh hai hng so snh: cc giao thc trong cng mt kiu nh tuyn v khc kiu. 3.1 So snh cc giao thc nh tuyn cng kiu i vi tip cn ny, cc tiu ch nh gi thng c a ra l: phc tp giao thc gm phc tp thi gian, truyn thng v lu tr thng tin; cc c tnh k thut nh tham s nh tuyn, cch thc tnh ton tuyn, cp nht v ch ca cp nht; cc c tnh c th s dng xc nh kch bn ng dng, kh nng multicast v kiu cu trc mng. Tuy nhin, i vi mt s kiu giao thc nh tuyn c th, cc tiu ch trn thng c c th ha trong cc tham s ti hn. V d nh, i vi cc giao thc nh tuyn theo bng, tiu iu khin v c tnh khng lp vng l hai vn quan trng nht. Trong khi , cc giao thc nh tuyn theo yu cu li tp trung vo cc vn tr x l tuyn v lng ti nguyn tiu th. i. So snh cc giao thc nh tuyn theo bng Cc giao thc nh tuyn WRP, DSDV v FSR l cc dng in hnh ca kiu giao thc nh tuyn theo bng. Cc so snh, nh gi c thc hin theo cc tiu ch trn cc kha cnh c bn nh: phng php cp nht thng tin nh tuyn, k thut chng lp vng v phc tp giao thc. Phng php cp nht thng tin nh tuyn: Cc giao thc nh tuyn WRP, DSDV v FSR u l giao thc nh tuyn theo bng nhng c cc c tnh cp nht khc nhau. Giao thc WRP v DSDV s dng phng php cp nht theo s kin duy tr thng tin nh tuyn, trong khi FSR ch trao i thng tin gia cc node ln cn v tn sut ph thuc vo khong cch cc node. V vy, FSR c lng thng tin cp nht t hn hai giao thc trn. K thut chng lp vng: K thut chng lp ca cc giao thc in thoi theo bng WRP, DSDV v FSR l khc nhau. WRP ghi li thng tin cc node lin k dc ng dn nh tuyn trong bng nh tuyn ca cc node. V vy, WRP trnh c lp vng nhng phi b sung thng tin trong tiu . DSDV s dng chui tun t ch trnh lp vng v FSR s dng c tnh trnh lp vng k tha t thut ton nh tuyn trng thi lin kt. phc tp giao thc: phc tp thng tin v thi gian ca ba giao thc WRP, DSDV v FSR l tng t nhau. WRP c phc tp lu tr ln hn DSDV do b

sung thng tin chng lp vng. C hai phng php cp nht theo chu k v cp nht theo s kin u c ng dng trong WRP v DSDV. V vy, hiu nng ca giao thc ph thuc rt cht vo kch c mng v m hnh di chuyn ca node. FSR l giao thc nh tuyn trng thi lin kt nn phc tp lu tr ln nhng FSR c li th h tr nh tuyn a ng v cht lng dch v. ii. So snh cc giao thc nh tuyn theo yu cu DSR, AODV v TORA l cc giao thc nh tuyn theo yu cu c xut cho mng MANET nhm gim thng tin tiu v ci thin kh nng m rng. Cc tiu ch t ra so snh gm: Lng thng tin tiu nh tuyn, cp nht thng tin li ng dn, chng lp vng v hiu nng nh tuyn. Lng thng tin tiu nh tuyn: DSR thc hin phng php nh tuyn ngun v lu tr tm thi thng tin nh tuyn, cng nh s dng k thut trn lt gi tm tuyn. AODV s dng k thut tm kim tuyn tng t nh DSR nhng ch lu tr thng tin nh tuyn cho bc nhy k tip ti cc node ca tuyn hot ng. V vy, AODV c lng tiu thng tin nh tuyn nh hn v em li kh nng m rng tt hn khi kch thc cc bn ghi tuyn b gii hn. Cp nht thng tin li ng dn: Trong hai giao thc nh tuyn AODV v DSR, mt node thng bo ti ngun khi to li hot ng tm tuyn mi khi li ng dn xy ra. TORA s dng thut ton o ngc lin kt ti cu trc bng nh tuyn khi mt node pht hin li lin kt ti hng i. C AODV v DSR u s dng phng php trn lt thng tin ti tt c cc node khc v li lin kt, trong khi TORA ch trn lt thng tin ti cc node ln cn lin kt li. K thut chng lp vng: Giao thc nh tuyn AODV s dng cc s th t trnh lp vng, DSR s dng a ch trong trng ghi tuyn ca cc gi tin d liu v TORA s dng trng s n nht ca cc node trong tuyn hot ng chng vng lp. Tuy nhin, TORA yu cu thm s ng b ca cc node lin quan, v vy hin tng dao ng c th xy ra khi phi hp gia cc node cng thc hin mt tc v. Hiu nng giao thc: Hiu nng ca cc giao thc DSR v AODV c so snh trong [5] da trn m hnh m phng. Kt qu m phng ch ra trng hp kch bn c s lng node ln, hiu nng ca giao thc DSR tt hn AODV do tiu nh tuyn tn t ti nguyn hn. i vi m hnh c s lng node nh, ti v tc di chuyn thp, DSR cng c c hiu nng tt hn AODV. Nhng khi lng ti tng ln, hiu nng DSR suy gim r rt v thp hn so vi giao thc AODV. 3.2 So snh cc giao thc nh tuyn khc kiu. Cc kha cnh c a ra so snh cc giao thc khc kiu trong cc kho st gn y gm: cht lng dch v, hiu nng nh tuyn v kh nng m rng ca giao thc nh tuyn. Cht lng dch v: Cc giao thc kho st gm giao thc nh tuyn AODV, OLSR v TORA c thc hin trong mi trng m phng c mc tc nghn thp v s lng node c nh [6]. m bo mt s c tnh cht lng dch v, kt qu m phng cho thy hai giao thc OLSR v AODV thch hp hn TORA v c hiu nng tt hn trong mi trng gi nh xut.

Kh nng m rng: c tnh di ng ca cc node v s nh hng ti kh nng m rng ca cc giao thc nh tuyn trong mng MANET c nh gi trong [7]. Vi m hnh lu lng ti cao, giao thc AODV c hiu nng tt hn OLSR v TORA. Thm vo , khi s lng node tng v mc nghn mng ln th t l chuyn pht thnh cng cc gi tin ca AODV tt hn OLSR v TORA. Kha cnh hiu nng: Trn kha cnh phn tch hiu nng ca cc giao thc nh tuyn MANET, bi bo [8] so snh cc giao thc OLSR, DSR v AODV trong mi trng lu lng t tng ng gm: tc bit c nh CBR (Constant Bit Rate), theo phn b Pareto v hm m. Kt qu m phng cho thy hiu nng DSR tng ln i vi t s chuyn pht gi tin, hiu nng ca OLSR gim xung khi ti cao v tnh ng ca cc node tng. Ni cch khc, giao thc AODV cung cp gi tr hiu nng trung bnh tt nht trong ba giao thc trn. Trn m hnh xut bi [7] chng ti xy dng m hnh m phng tng t vi cc b sung v m hnh di chuyn ca cc node. Cc kt qu m phng v thng lng, ti, tr ca cc giao thc nh tuyn t c kt qu tng t [7]. Vi cc m hnh di chuyn b sung (ng ngu nhin, bc ngu nhin v hng ngu nhin), kt qu m phng u cho thy AODV c hiu nng tt hn so vi DSR v TORA ngay c khi h thng c lng ti cao. 4. KT LUN Cc giao thc nh tuyn MANET hin vn ang c tip tc nghin cu v ci thin. Trn c s cc giao thc nh tuyn xut, mt lot cc kha cnh lin quan ti vn nh tuyn nh: cht lng dch v, hiu nng mng, kch bn ng dng vn ang l cc vn m. V vy, xc nh tnh tng thch v kh nng trin khai ca giao thc nh tuyn, vic so snh v nh gi giao thc cn c thm cc m hnh v kch bn ng dng tip cn c cc iu kin thc tin.