Mang May Tinh

MNG MY TNH (COMPUTER NETWORKS) 1

MC LC

Phn loi mng my tnh theo phm vi a l ................................................ 3 H iu hnh mng NOS (Network Operating System)........................................ 16


MNG MY TNH (COMPUTER NETWORKS)

V c bn, mt mng my tnh l mt s cc my tnh c ni kt vi nhau theo mt cch no . Khc vi cc trm truyn hnh ch gi thng tin i, cc mng my tnh lun hai chiu, sao cho khi my tnh A gi thng tin ti my tnh B th B c th tr li li cho A.

Ni mt cch khc, mt s my tnh c kt ni vi nhau v c th trao i thng tin cho nhau gi l mng my tnh.

T nhiu my tnh ring r, c lp vi nhau, nu ta kt ni chng li thnh mng my tnh th chng c thm nhng u im sau:

Nhiu ngi c th dng chung mt phn mm tin ch.

Mt nhm ngi cng thc hin mt n nu ni mng h s dng chung d liu ca n, dng chung tp tin chnh (master file) ca n, h trao i thng tin vi nhau d dng.

D liu c qun l tp trung nn an ton hn, trao i gia nhng ngi s dng thun li hn, nhanh chng hn.

C th dng chung thit b ngoi vi him, t tin (my in, my v,...).

Ngi s dng trao i vi nhau th tn d dng (E-Mail) v c th s dng h mng nh l mt cng c ph bin tin tc, thng bo v mt chnh sch mi, v ni dung bui hp, v cc thng tin kinh t khc nh gi c th trng, tin rao vt (mun bn hoc mun mua mt ci g ), hoc sp xp thi kho biu ca mnh chen ln vi thi kho biu ca nhng ngi khc,...

Mt s ngi s dng khng cn phi trang b my tnh t tin (chi ph thp m chc nng li mnh).

Mng my tnh cho php ngi lp trnh mt trung tm my tnh ny c th s dng cc chng trnh tin ch ca mt trung tm my tnh khc ang ri, s lm tng hiu qu kinh t ca h thng.

Rt an ton cho d liu v phn mm v phn mm mng s kho cc tp tin (files) khi c nhng ngi khng quyn hn truy xut cc tp tin v th mc .


PHN LOI MNG MY TNH THEO PHM VI A L

Mng my tnh c th phn b trn mt vng lnh th nht nh v c th phn b trong phm vi mt quc gia hay quc t.

Da vo phm vi phn b ca mng ngi ta c th phn ra cc loi mng nh sau:

GAN (Global Area Network) kt ni my tnh t cc chu lc khc nhau. Thng thng kt ni ny c thc hin thng qua mng vin thng v v tinh.

WAN (Wide Area Network) - Mng din rng, kt ni my tnh trong ni b cc quc gia hay gia cc quc gia trong cng mt chu lc. Thng thng kt ni ny c thc hin thng qua mng vin thng. Cc WAN c th c kt ni vi nhau thnh GAN hay t n l GAN.

MAN (Metropolitan Area Network) kt ni cc my tnh trong phm vi mt thnh ph. Kt ni ny c thc hin thng qua cc mi trng truyn thng tc cao (50-100 Mbit/s).

LAN (Local Area Network) - Mng cc b, kt ni cc my tnh trong mt khu vc bn knh hp thng thng khong vi trm mt. Kt ni c thc hin thng qua cc mi trng truyn thng tc cao v d cp ng trc thay cp quang. LAN thng c s dng trong ni b mt c quan/t chc...Cc LAN c th c kt ni vi nhau thnh WAN.

Trong cc khi nim ni trn, WAN v LAN l hai khi nim hay c s dng nht.

Mng cc b - LAN

Mng cc b (LAN) l h truyn thng tc cao c thit k kt ni cc my tnh v cc thit b x l d liu khc cng hot ng vi nhau trong mt khu vc a l nh nh mt tng ca to nh, hoc trong mt to nh.... Mt s mng LAN c th kt ni li vi nhau trong mt khu lm vic.

Cc mng LAN tr nn thng dng v n cho php nhng ngi s dng (users) dng chung nhng ti nguyn quan trng nh my in mu, a CD-ROM, cc phn mm ng dng v nhng thng tin cn thit khc. Trc khi pht trin cng ngh LAN cc my tnh l c lp vi nhau, b hn ch bi


s lng cc chng trnh tin ch, sau khi kt ni mng r rng hiu qu ca chng tng ln gp bi. tn dng ht nhng u im ca mng LAN ngi ta kt ni cc LAN ring bit vo mng chnh yu din rng (WAN).

Cc thit b gn vi mng LAN u dng chung mt phng tin truyn tin l dy cp, cp thng dng hin nay l: Cp ng trc (Coaxial cable), Cp dy xon (shielded twisted pair), cp quang (Fiber optic),....

Mi loi dy cp u c tnh nng khc nhau.

Dy cp ng trc c ch to gm mt dy ng gia cht cch in, chung quanh cht cch in c qun bng dy bn kim loi dng lm dy t. Gia dy ng dn in v dy t c mt lp cch ly, ngoi cng l mt v bc bo v. Dy ng trc c hai loi, loi nh (Thin) v loi to (Thick). Dy cp ng trc c thit k truyn tin cho bng tn c bn (Base Band) hoc bng tn rng (broadband). Dy cp loi to dng cho ng xa, dy cp nh dng cho ng gn, tc truyn tin qua cp ng trc c th t ti 35 Mbit/s.

Dy cp xon c ch to bng hai si dy ng (c v bc) xon vo nhau, ngoi cng c hoc khng c lp v bc bo v chng nhiu.

Dy cp quang lm bng cc si quang hc, truyn d liu xa, an ton v khng b nhiu v chng c han r. Tc truyn tin qua cp quang c th t 100 Mbit/s.

Nhn chung, yu t quyt nh s dng loi cp no l ph thuc vo yu cu tc truyn tin, khong cch t cc thit b, yu cu an ton thng tin v cu hnh ca mng,....V d mng Ethernet 10 Base-T l mng dng knh truyn gii tn c bn vi thng lng 10 Mbit/s theo tiu chun quc t ISO/IEC 8802.3 ni bng i dy cp xon khng bc kim (UTP) trong Topology hnh sao.

Vic kt ni cc my tnh vi mt dy cp c dng nh mt phng tin truyn tin chung cho tt c cc my tnh. Cng vic kt ni vt l vo mng c thc hin bng cch cm mt card giao tip mng NIC (Network Interface Card) vo trong my tnh v ni n vi cp mng. Sau khi kt ni vt l hon tt, qun l vic truyn tin gia cc trm trn mng tu thuc vo phn mm mng.

u ni ca NIC vi dy cp c nhiu loi (ph thuc vo cp mng), hin nay c mt s NIC c hai hoc ba loi u ni. Chun dng cho NIC l


NE2000 do hng Novell v Eagle dng ch to cc loi NIC ca mnh. Nu mt NIC tng thch vi chun NE2000 th ta c th dng n cho nhiu loi mng. NIC cng c cc loi khc nhau m bo s tng thch vi my tnh 8-bit v 16-bit.

Mng LAN thng bao gm mt hoc mt s my ch (file server, host), cn gi l my phc v) v mt s my tnh khc gi l trm lm vic (Workstations) hoc cn gi l nt mng (Network node) - mt hoc mt s my tnh cng ni vo mt thit b nt.

My ch thng l my c b x l (CPU) tc cao, b nh (RAM) v a cng (HD) ln.

Trong mt trm m cc phng tin c dng chung, th khi mt trm mun gi thng ip cho trm khc, n dng mt phn mm trong trm lm vic t thng ip vo "phong b", phong b ny gi l gi (packet), bao gm d liu thng ip c bao bc gia tn hiu u v tn hiu cui ( l nhng thng tin c bit) v s dng phn mm mng chuyn gi n trm ch.

NIC s chuyn gi tn hiu vo mng LAN, gi tn hiu c truyn i nh mt dng cc bit d liu th hin bng cc bin thin tn hiu in. Khi n chy trong cp dng chung, mi trm gn vi cp u nhn c tn hiu ny, NIC mi trm s kim tra a ch ch trong tn hiu u ca gi xc nh ng a ch n, khi gi tn hiu i ti trm c a ch cn n, ch trm s sao gi tn hiu ri ly d liu ra khi phong b v a vo my tnh.

Cc kiu (Topology) ca mng LAN

Topology ca mng l cu trc hnh hc khng gian m thc cht l cch b tr phn t ca mng cng nh cch ni gia chng vi nhau. Thng thng mng c 3 dng cu trc l: Mng dng hnh sao (Star Topology), mng


dng vng (Ring Topology) v mng dng tuyn (Linear Bus Topology). Ngoi 3 dng cu hnh k trn cn c mt s dng khc bin tng t 3 dng ny nh mng dng cy, mng dng hnh sao - vng, mng hn hp,v.v....

Mng dng hnh sao (Star topology)

Mng dng hnh sao bao gm mt trung tm v cc nt thng tin. Cc nt thng tin l cc trm u cui, cc my tnh v cc thit b khc ca mng. Trung tm ca mng iu phi mi hot ng trong mng vi cc chc nng c bn l:

Xc nh cp a ch gi v nhn c php chim tuyn thng tin v lin lc vi nhau.

Cho php theo di v s l sai trong qu trnh trao i thng tin.

Thng bo cc trng thi ca mng...

Cc u im ca mng hnh sao:

Hot ng theo nguyn l ni song song nn nu c mt thit b no mt nt thng tin b hng th mng vn hot ng bnh thng.

Cu trc mng n gin v cc thut ton iu khin n nh.

Mng c th m rng hoc thu hp tu theo yu cu ca ngi s dng.

Nhc im ca mng hnh sao:

Kh nng m rng mng hon ton ph thuc vo kh nng ca trung tm . Khi trung tm c s c th ton mng ngng hot ng.

Mng yu cu ni c lp ring r tng thit b cc nt thng tin n trung tm. Khong cch t my n trung tm rt hn ch (100 m).

Nhn chung, mng dng hnh sao cho php ni cc my tnh vo mt b tp trung (HUB) bng cp xon, gii php ny cho php ni trc tip my tnh vi HUB khng cn thng qua trc BUS, trnh c cc yu t gy ngng tr mng. Gn y, cng vi s pht trin switching hub, m hnh ny ngy cng tr nn ph bin v chim a s cc mng mi lp.


Mng hnh tuyn (Bus Topology)

Theo cch b tr hnh lang cc ng nh hnh v th my ch (host) cng nh tt c cc my tnh khc (workstation) hoc cc nt (node) u c ni v vi nhau trn mt trc ng dy cp chnh chuyn ti tn hiu.

Tt c cc nt u s dng chung ng dy cp chnh ny. Pha hai u dy cp c bt bi mt thit b gi l terminator. Cc tn hiu v gi d liu (packet) khi di chuyn ln hoc xung trong dy cp u mang theo i ch ca ni n.

Loi hnh mng ny dng dy cp t nht, d lp t. Tuy vy cng c nhng bt li l s c s n tc giao thng khi di chuyn d liu vi lu lng ln v khi c s hng hc on no th rt kh pht hin, mt s ngng trn ng dy sa cha s ngng ton b h thng.

Mng dng vng (Ring Topology)

Mng dng ny, b tr theo dng xoay vng, ng dy cp c thit k lm thnh mt vng khp kn, tn hiu chy quanh theo mt chiu no . Cc nt truyn tn hiu cho nhau mi thi im ch c mt nt m thi. D liu truyn i phi c km theo a ch c th ca mi trm tip nhn.

Mng dng vng c thun li l c th ni rng ra xa, tng ng dy cn thit t hn so vi hai kiu trn. Nhc im l ng dy phi khp kn, nu b ngt mt ni no th ton b h thng cng b ngng.

Mng dng kt hp

Kt hp hnh sao v tuyn (star/Bus Topology)


Cu hnh mng dng ny c b phn tch tn hiu (spitter) gi vai tr thit b trung tm, h thng dy cp mng c th chn hoc Ring Topology hoc Linear Bus Topology.

Li im ca cu hnh ny l mng c th gm nhiu nhm lm vic cch xa nhau, ARCNET l mng dng kt hp Star/Bus Topology. Cu hnh dng ny a li s uyn chuyn trong vic b tr ng dy tng thch d dng i vi bt c to nh no.

Kt hp hnh sao v vng (Star/Ring Topology) Cu hnh dng kt hp Star/Ring Topology, c mt "th bi" lin lc (Token) c chuyn vng quanh mt ci HUB trung tm. Mi trm lm vic (workstation) c ni vi HUB - l cu ni gia cc trm lm vic v tng khong cch cn thit.

Cc giao thc (Protocol)

Mt tp cc tiu chun trao i thng tin gia hai h thng my tnh hoc hai thit b my tnh vi nhau c gi l giao thc (Protocol).

Cc giao thc (Protocol) cn c gi l nghi thc hoc nh c ca mng my tnh.

nh gi kh nng ca mt mng c phn chia bi cc trm nh th no. H s ny c quyt nh ch yu bi hiu qu s dng mi trng


truy xut (medium access) ca giao thc, mi trng ny dng tuyn tnh hoc vng.... Mt trong cc giao thc c s dng nhiu trong cc LAN l:

1. Giao thc tranh chp (Contention Protocol) CSMA/CD

CSMA l vit tt t ting Anh: Carrier Sense Multiple Access, cn CD l vit tt t: Conllision Detect.

S dng giao thc ny cc trm hon ton c quyn truyn d liu trn mng vi s lng nhiu hay t v mt cch ngu nhin hoc bt k khi no c nhu cu truyn d liu mi trm. Mi trm s kim tra tuyn v ch khi no tuyn khng bn mi bt u truyn cc gi d liu.

CSMA/CD c ngun gc t h thng radio pht trin trng i hc Hawai vo khong nm 1970, gi l ALOHANET.

Vi phng php CSMA, thnh thong s c hn mt trm ng thi truyn d liu v to ra s xung t (collision) lm cho d liu thu c cc trm b sai lch. trnh s tranh chp ny mi trm u phi pht hin c s xung t d liu. Trm pht phi kim tra Bus trong khi gi d liu xc nhn rng tn hiu trn Bus tht s ng, nh vy mi c th pht hin c bt k xung t no c th xy ra. Khi pht hin c mt s xung t, lp tc trm pht s gi i mt mu lm nhiu (Jamming) nh trc bo cho tt c cc trm l c s xung t xy ra v chng s b qua gi d liu ny. Sau trm pht s tr hon mt khong thi gian ngu nhin trc khi pht li d liu. u im ca CSMA/CD l n gin, mm do, hiu qu truyn thng tin cao khi lu lng thng tin ca mng thp v c tnh t bin. Vic thm vo hay dch chuyn cc trm trn tuyn khng nh hng n cc th tc ca giao thc. im bt li ca CSMA/CD l hiu sut ca tuyn gim xung nhanh chng khi phi ti qu nhiu thng tin.

2. Giao thc truyn token (Token passing protocol)

y l giao thc thng dng sau CSMA/CD c dng trong cc LAN c cu trc vng (Ring). Trong phng php ny, khi iu khin mng hoc token c truyn ln lt t trm ny n trm khc. Token l mt khi d liu c bit. Khi mt trm ang chim token th n c th pht i mt gi d liu. Khi pht ht gi d liu cho php hoc khng cn g pht na th trm li gi token sang trm k tip.


Trong token c cha mt a ch ch v c lun chuyn ti cc trm theo mt trt t nh trc. i vi cu hnh mng dng xoay vng th trt t ca s truyn token tng ng vi trt t vt l ca cc trm xung quanh vng. Giao thc truyn token c trt t hn nhng cng phc tp hn CSMA/CD, c u im l vn hot ng tt khi lu lng truyn thng ln. Giao thc truyn token tun th ng s phn chia ca mi trng mng, hot ng da vo s xoay vng ti cc trm. Vic truyn token s khng thc hin c nu vic xoay vng b t on. Giao thc phi cha cc th tc kim tra token cho php khi phc li token b mt hoc thay th trng thi ca token v cung cp cc phng tin sa i logic (thm vo, bt i hoc nh li trt t ca cc trm).

Cc chun ca mng my tnh

mng t kh nng ti a, cc tiu chun c chn phi cho php m rng mng c th phc v nhng ng dng khng d kin trc trong tng lai ti lc lp t h thng v iu cng cho php mng lm vic vi nhng thit b c sn xut t nhiu hng khc nhau.

Hi ng tiu chun quc t l ISO (International Standards Organization), do cc nc thnh vin lp nn. Cng vic Bc M chu s iu hnh ca ANSI (American National Standards Institude) Hoa K. ANSI u thc cho IEEE (Institude of Electrical and Electronics Engineers) pht trin v ra nhng tiu chun k thut cho LAN.

ISO a ra m hnh 7 mc (layers, cn gi l lp hay tng) cho mng, gi l kiu h thng kt ni m hoc m hnh OSI (Open System Interconnection).

Chc nng ca mc thp bao gm c vic chun b cho mc cao hn hon thnh chc nng ca mnh. Mt mng hon chnh hot ng vi mi chc nng ca mnh phi m bo c 7 mc cu trc t thp n cao.

Mc 1: Mc vt l (Physical layer)

Thc cht ca mc ny l thc hin ni lin cc phn t ca mng thnh mt h thng bng cc phng php vt l, mc ny s c cc th tc


m bo cho cc yu cu v chuyn mch hot ng nhm to ra cc ng truyn thc cho cc chui bit thng tin.

Mc 2: Mc mc ni d liu (Data Link Layer)

Nhim v ca mc ny l tin hnh chuyn i thng tin di dng chui cc bit mc mng thnh tng on thng tin gi l frame. Sau m bo truyn lin tip cc frame ti mc vt l, ng thi x l cc thng bo t trm thu gi tr li.

Ni tm li, nhim v chnh ca mc 2 ny l khi to v t chc cc frame cng nh x l cc thng tin lin quan ti n.

Mc 3: Mc mng (Network Layer)

Mc mng nhm bo m trao i thng tin gia cc mng con trong mt mng ln, mc ny cn c gi l mc thng tin gia cc mng con vi nhau. Trong mc mng cc gi d liu c th truyn i theo tng ng khc nhau ti ch. Do vy, mc ny phi ch ra c con ng no d liu c th i v con ng no b cm ti thi im . Thng mc mng c s dng trong trng hp mng c nhiu mng con hoc cc mng ln v phn b trn mt khng gian rng vi nhiu nt thng tin khc nhau.

Mc 4: Mc truyn (Transport Layer)

Nhim v ca mc ny l x l cc thng tin chuyn tip cc chc nng t mc trn n (mc tip xc) n mc di n (mc mng) v ngc li. Thc cht mc truyn l m bo thng tin gia cc my ch vi nhau. Mc ny nhn cc thng tin t mc tip xc, phn chia thnh cc n v d liu nh hn v chuyn chng ti mc mng.

Mc 5: Mc tip xc (Session Layer)

Mc ny cho php ngi s dng tip xc vi nhau qua mng. Nh mc tip xc nhng ngi s dng lp c cc ng ni vi nhau, khi cuc hi thoi c thnh lp th mc ny c th qun l cuc hi thoi theo yu cu ca ngi s dng. Mt ng ni gia nhng ngi s dng c gi l mt cuc tip xc. Cuc tip xc cho php ngi s dng c ng k vo mt h thng phn chia thi gian t xa hoc chuyn mt file gia 2 my.


Mc 6: Mc tip nhn (Presentation Layer)

Mc ny gii quyt cc th tc tip nhn d liu mt cch chnh quy vo mng, nhim v ca mc ny l la chn cch tip nhn d liu, bin i cc k t, ch s ca m ASCII hay cc m khc v cc k t iu khin thnh mt kiu m nh phn thng nht cc loi my khc nhau u c th thm nhp vo h thng mng.

Mc 7: Mc ng dng (Application Layer)

Mc ny c nhim v phc v trc tip cho ngi s dng, cung cp tt c cc yu cu phi ghp cn thit cho ngi s dng, yu cu phc v chung nh chuyn cc file, s dng cc terminal ca h thng,.... Mc s dng bo m t ng ho qu trnh thng tin, gip cho ngi s dng khai thc mng tt nht.

H thng kt ni m OSI l h thng cho php truyn thng tin vi cc h thng khc, trong cc mng khc nhau, s dng nhng giao thc khc nhau, c th thng bo cho nhau thng qua chng trnh Pastren chuyn t mt giao thc ny sang mt giao thc khc.

Chun IEEE

Tiu chun IEEE LAN c pht trin da vo u ban IEEE 802. Tiu chun IEEE 802.3 lin quan ti mng CSMA/CD bao gm c 2 version bng


tn c bn v bng tn m rng. Tiu chun IEEE 802.4 lin quan ti s sp xp tuyn token v IEEE 802.5 gm cc vng truyn token.

Theo chun 802 th mc ni d liu c chia thnh 2 mc con: mc con iu khin logic LLC (Logical Link Control Sublayer) v mc con iu khin xm nhp mng MAC (Media Access Control Sublayer). Mc con LLC gi vai tr t chc d liu, t chc thng tin truyn v nhn. Mc con MAC ch lm nhim v iu khin vic xm nhp mng. Th tc mc con LLC khng b nh hng khi s dng cc ng truyn dn khc nhau, nh vy m linh hot hn trong khai thc.

Chun 802.2 mc con LLC tng ng vi chun HDLC ca ISO hoc X.25 ca CCITT.

Chun 802.3 xc nh phng php thm nhp mng tc thi c kh nng pht hin li chng cho thng tin CSMA/CD. Phng php CSMA/CD c a ra t nm 1993 nhm mc ch nng cao hiu qu mng. Theo chun ny cc mc c ghp ni vi nhau thng qua cc b ghp ni.

Chun 802.4 thc cht l phng php thm nhp mng theo kiu pht tn hiu thm d token qua cc trm v ng truyn bus.

Chun 802.5 dng cho mng dng xoay vng v trn c s dng tn hiu thm d token. Mi trm khi nhn c tn hiu thm d token th tip nhn token v bt u qu trnh truyn thng tin di dng cc frame. Cc frame c cu trc tng t nh ca chun 802.4. Phng php xm nhp mng ny quy nh nhiu mc u tin khc nhau cho ton mng v cho mi trm, vic quy nh ny va cho ngi thit k va do ngi s dng t quy nh.

Mng ETHERNET

Ethernet l mng cc b do cc cng ty Xerox, Intel v Digital equipment xy dng v pht trin. Ethernet l mng thng dng nht i vi cc mng nh hin nay. Ethernet LAN c xy dng theo chun 7 lp trong cu trc mng ca ISO, mng truyn s liu Ethernet cho php a vo mng cc loi my tnh khc nhau k c my tnh mini. Ethernet c cc c tnh k thut ch yu sau y:

C cu trc dng tuyn phn on, ng truyn dng cp ng trc, tn hiu truyn trn mng c m ho theo kiu ng b (Manchester), tc truyn d liu l 10 Mb/s.


Chiu di ti a ca mt on cp tuyn l 500m, cc on tuyn ny c th c kt ni li bng cch dng cc b chuyn tip v khong cch ln nht cho php gia 2 nt l 2,8 km.

S dng tn hiu bng tn c bn, truy xut tuyn (bus access) hoc tuyn token (token bus), giao thc l CSMA/CD, d liu chuyn i trong cc gi. Gi (packet) thng tin dng trong mng c di t 64 n 1518 byte.

Mng TOKEN RING

Ngoi Ethernet LAN mt cng ngh LAN ch yu khc ang c dng hin nay l Token Ring. Nguyn tc ca mng Token Ring c nh ngha trong tiu chun IEEE 802.5. Mng Token Ring c th chy tc 4Mbps hoc 16Mbps. Phng php truy cp dng trong mng Token Ring gi l Token passing . Token passing l phng php truy nhp xc nh, trong cc xung t c ngn nga bng cch mi thi im ch mt trm c th c truyn tn hiu. iu ny c thc hin bng vic truyn mt b tn hiu c bit gi l Token (m thng bo) xoay vng t trm ny qua trm khc. Mt trm ch c th gi i b d liu khi n nhn c m khng bn.

Cc thit b kt ni chnh ca LAN

Hub

Hub l mt trong nhng yu t quan trng nht ca LAN, y l im kt ni dy trung tm ca mng, tt c cc trm trn mng LAN c kt ni thng qua HUB. Mt hub thng thng c nhiu cng ni vi ngi s dng gn my tnh v cc thit b ngoi vi. Mi cng h tr mt b kt ni dng cp dy xon 10BASET t mi trm ca mng. Khi b tn hiu Ethernet c truyn t mt trm ti hub, n c lp li trn khp cc cng khc ca hub. Cc hub thng minh c th nh dng, kim tra, cho php hoc khng cho php bi ngi iu hnh mng t trung tm qun l hub.

C ba loi hub:

Hub n (stand alone hub)

Hub phn tng (stackable hub, c ti liu gi l HUB sp xp)

Hub modun (modular hub)


Modular hub rt ph bin cho cc h thng mng v n c th d dng m rng v lun c chc nng qun l, modular c t 4 n 14 khe cm, c th lp thm cc modun Ethernet 10BASET.

Stackable hub l l tng cho nhng c quan mun u t ti thiu ban u nhng li c k hoch pht trin LAN sau ny.

Ch : U ban k thut in t (IEEE) ngh dng cc tn sau y ch 3 loi dy cp dng vi mng Ethernet chun 802.3.

Dy cp ng trc si to (thick coax) th gi l 10BASE5 (Tc 10 Mbps, tn s c s, khong cch ti a 500m).

Dy cp ng trc si nh (thin coax) gi l 10BASE2 (Tc 10 Mbps, tn s c s, khong cch ti a 200m).

Dy cp i xon khng v bc (twisted pair) gi l 10BASET (Tc 10 Mbps, tn s c s, s dng cp si xon).

Dy cp quang (Fiber Optic Inter-Repeater Link) gi l FOIRL

Lin mng (internetworking)

Vic kt ni cc LAN ring l thnh mt lin mng chung c gi l Internetworking. Internetworking s dng ba cng c chnh l: bridge, router v switch.

Cu ni (bridge):

L cu ni hai hoc nhiu on (segment) ca mt mng. Theo m hnh OSI th bridge thuc mc 2. Bridge s lc nhng gi d liu gi i (hay khng gi) cho on ni, hoc gi tr li ni xut pht. Cc bridge cng thng c dng phn chia mt mng ln thnh hai mng nh nhm lm tng tc . Mc du t chc nng hn router, nhng bridge cng c dng ph bin.

B dn ng (router)

Chc nng c bn ca router l gi i cc gi d liu da trn a ch phn lp ca mng v cung cp cc dch v nh bo mt, qun l lu thng...

Ging nh bridge, router l mt thit b siu thng minh i vi cc mng thc s ln. router bit a ch ca tt c cc my tnh tng pha


v c th chuyn cc thng ip cho ph hp. Chng cn phn ng-nh truyn gi tng thng ip c hiu qu.

Theo m hnh OSI th chc nng ca router thuc mc 3, cung cp thit b vi thng tin cha trong cc header ca giao thc, gip cho vic x l cc gi d liu thng minh.

Da trn nhng giao thc, router cung cp dch v m trong mi packet d liu c c v chuyn n ch mt cch c lp.

Khi s kt ni tng thm, mng theo dng router tr nn km hiu qu v cn suy ngh n s thay i.

B chuyn mch (switch)

Chc nng chnh ca switch l cng mt lc duy tr nhiu cu ni gia cc thit b mng bng cch da vo mt loi ng truyn xng sng (backbone) ni ti tc cao. Switch c nhiu cng, mi cng c th h tr ton b Ethernet LAN hoc Token Ring.

B chuyn mch kt ni mt s LAN ring bit v cung cp kh nng lc gi d liu gia chng.

Cc switch l loi thit b mng mi, nhiu ngi cho rng, n s tr nn ph bin nht v n l bc u tin trn con ng chuyn sang ch truyn khng ng b ATM.

H IU HNH MNG NOS (NETWORK OPERATING SYSTEM)

Cng vi s nghin cu v pht trin mng my tnh, h iu hnh mng c nhiu cng ty u t nghin cu v cng b nhiu phn mm qun l v iu hnh mng c hiu qu nh: NetWare ca cng ty NOVELL, LAN Manager ca Microsoft dng cho cc my server chy h iu hnh OS/2, LAN server ca IBM (gn nh ng nht vi LAN Manager), Vines ca Banyan Systems l h iu hnh mng dng cho server chy h iu hnh UNIX, Promise LAN ca Mises Computer chy trn card iu hp mng c quyn, Widows for Workgroups ca Microsoft, LANtastic ca Artisoft, NetWare Lite ca Novell,....


Mt trong nhng s la chn c bn m ta phi quyt nh trc l h iu hnh mng no s lm nn tng cho mng ca ta, vic la chn tu thuc vo kch c ca mng hin ti v s pht trin trong tng lai, cn tu thuc vo nhng u im v nhc im ca tng h iu hnh.

Mt s h iu hnh mng ph bin hin nay:

H iu hnh mng UNIX: y l h iu hnh do cc nh khoa hc xy dng v c dng rt ph bin trong gii khoa hc, gio dc. H iu hnh mng UNIX l h iu hnh a nhim, a ngi s dng, phc v cho truyn thng tt. Nhc im ca n l hin nay c nhiu Version khc nhau, khng thng nht gy kh khn cho ngi s dng. Ngoi ra h iu hnh ny kh phc tp li i hi cu hnh my mnh (trc y chy trn my mini, gn y c SCO UNIX chy trn my vi tnh vi cu hnh mnh).

H iu hnh mng Windows NT: y l h iu hnh ca hng Microsoft, cng l h iu hnh a nhim, a ngi s dng. c im ca n l tng i d s dng, h tr mnh cho phn mm WINDOWS. Do hng Microsoft l hng phn mm ln nht th gii hin nay, h iu hnh ny c kh nng s c ngy cng ph bin rng ri. Ngoi ra, Windows NT c th lin kt tt vi my ch Novell Netware. Tuy nhin, chy c hiu qu, Windows NT cng i hi cu hnh my tng i mnh.

H iu hnh mng Windows for Worrkgroup: y l h iu hnh mng ngang hng nh, cho php mt nhm ngi lm vic (khong 3-4 ngi) dng chung a trn my ca nhau, dng chung my in nhng khng cho php chy chung mt ng dng. H d dng ci t v cng kh ph bin.

H iu hnh mng NetWare ca Novell: y l h iu hnh ph bin nht hin nay nc ta v trn th gii trong thi gian cui, n c th dng cho cc mng nh (khong t 5-25 my tnh) v cng c th dng cho cc mng ln gm hng trm my tnh. Trong nhng nm qua, Novell cho ra nhiu phin bn ca Netware: Netware 2.2, 3.11. 4.0 v hin c 4.1. Netware l mt h iu hnh mng cc b dng cho cc my vi tnh theo chun ca IBM hay cc my tnh Apple Macintosh, chy h iu hnh MS-DOS hoc OS/2. H iu hnh ny tng i gn nh, d ci t (my ch ch cn thm ch


AT386) do ph hp vi hon cnh trang thit b hin ti ca nc ta. Ngoi ra, v l mt phn mm ph bin nn Novell Netware c cc nh sn xut phn mm khc h tr (theo ngha cc phn mm do cc hng phn mm ln trn th gii lm u c th chy tt trn h iu hnh mng ny).

Cc Phng tin Kt ni mng lin khu vc (WAN)

Bn cnh phng php s dng ng in thoi thu bao kt ni cc mng cc b hoc mng khu vc vi nhau hoc kt ni vo Internet, c mt s phng php khc:

ng thu bao (leased line). y l phng php c nht, l phng php truyn thng nht cho s ni kt vnh cu. Bn thu ng dy t cng ty in thoi (trc tip hoc qua nh cung cp dch v). Bn cn phi ci t mt "Chanel Service Unit" (CSU) ni n mng T, v mt "Digital Service Unit" (DSU) ni n mng ch (primary) hoc giao din mng.

ISDN (Integrated Service Digital Nework). S dng ng in thoi s thay v ng tng t. Do ISDN l mng dng tn hiu s, bn khng phi dng mt modem ni vi ng dy m thay vo bn phi dng mt thit b gi l "codec" vi modem c kh nng chy 14.4 kbit/s. ISDN thch hp cho c hai trng hp c nhn v t chc. Cc t chc c th quan tm hn n ISDN c kh nng cao hn ("primary" ISDN) vi tc tng cng bng tc 1.544 Mbit/s ca ng T1. Cc ph khi s dng ISDN c tnh theo thi gian, mt s trng hp tnh theo lng d liu c truyn i v mt s th tnh theo c hai.

CATV link. Cng ty dn cp trong khu vc ca bn c th cho bn thu mt "ch" trn ng cp ca h vi gi hp dn hn vi ng in thoi. Cn phi bit nhng thit b g cn cho h thng ca mnh v rng ca di m bn s c cung cp l bao nhiu. Cng nh vic ng gp chi ph vi nhng khch hng khc cho knh lin lc l nh th no. Mt dng k l hn c a ra vi tn gi l mng "lai" ("hybrid" Network), vi mt knh CATV c s dng lu thng theo mt hng v mt ng ISDN hoc gi s s dng cho ng tr li. Nu mun cung cp thng tin trn Internet, bn phi xc nh chc chn rng "knh ngc" ca bn kh nng phc v cho nhu cu thng tin ca khch hng ca bn.


Frame relay. Frame relay "uyn chuyn" hn ng thu bao. Khch hng thu ng Frame relay c th mua mt dch v c mc xc nh - mt "tc thng tin u thc" ("Committed Information Rale" - CIR). Nu nh nhu cu ca bn trn mng l rt "bt pht" (burty), hay ngi s dng ca bn c nhu cu cao trn ng lin lc trong sut mt khong thi gian xc nh trong ngy, v c t hoc khng c nhu cu vo ban m - Frame relay c th s kinh t hn l thu hon ton mt ng T1 (hoc T3). Nh cung cp dch v ca bn c th a ra mt phng php tng t nh l phng php thay th l Switched Multimegabit Data Service.

Ch truyn khng ng b (Asynchoronous Trangfer Mode - ATM). ATM l mt phng php tng i mi u tin bo hiu cng mt k thut cho mng cc b v lin khu vc. ATM thch hp cho real-time multimedia song song vi truyn d liu truyn thng. ATM ha hn s tr thnh mt phn ln ca mng tng lai.

ng vi sng (Microware links). Nu cn kt ni vnh vin n nh cung cp dch v nhng li thy rng ng thu bao hay nhng la chn khc l qu t, bn s thy microware nh l mt la chn thch hp. Bn khng cn tr qu t cho cch ny ca microware, tuy nhin bn cn phi u t nhiu tin hn vo lc u, v bn s gp mt s ri ro nh tc truyn n mng ca bn qu nhanh.

ng v tinh (satellite links). Nu bn mun c chuyn mt lng ln d liu c bit l t nhng a im t xa th ng v tinh l cu tr li. Tm hot ng ca nhng v tinh cng v tr a l vi tri t cng to ra mt s chm tr (hoc "b che du") m nhng ngi s dng Telnet c th cm nhn c.

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Mang May Tinh