Sm Hub/Switch cho mng LANVit bi: anhQpro

Nu chic Router ADSL ca bn c cng cc my tnh trong mng ni b ni vo, ngha l n ang c sn mt Switch nh, th bn c th m dng. Nhng khi s lng ngi dng vt qua s cng trn Router, th cng l lc bn cn quan tm n vic chn mua mt chic Hub hay Switch ri y. bit rng bn chic Hub hay Switch, v nn chn la chng theo nhng thng s no khi mua, chng ta cng tm hiu mt vi cng ngh dnh cho thit b chuyn dng cho mng LAN ny. GIAO DIN PHN CNG

Khng h c s khc bit v mt giao din phn cng gia Hub v Switch. Hai thit b ny cng u c cng RJ45 xp thnh mt hoc hai hng c nh s th t hoc khng. c im chung ca cc Hub v Switch l bn thng khng tm thy cng tc ngun ca chng. PHN LP THEO M HNH OSI

Hub ch kt ni v mt tn hiu in gia cc card mng my tnh, nn n nm lp 1 (Physical) ca m hnh OSI. Cn Switch c phn mm iu khin, n qun l v chuyn cc gi tin dng Frame, nn n l thit b nm lp 2 (Data Link) ca m hnh OSI. -C CH HOT NG Khi mt tn hiu in t card mng my tnh c gi n Hub, n c gi n ton b cc cng cn li ca thit b. Nhng thit b Hub khng dng ngun in ch lan truyn tn hiu, cn mt s Hub khc c ngun s khuch i tn hiu in ln trc khi y n ra cc cng ca mnh. Cn thit b Switch lu mt bng danh sch lin kt gia cc a ch MAC ca cc my tnh vi cng giao tip m n gn vo trn thit b. Bng bng danh sch ny, Switch c th nh hng gi tin lp 2 i t cng kt ni vi my tnh nhn.

- -- HIU SUT H THNG Do hot ng theo cng ngh CDMA/CD (Carrier Detect Multiple Access, Collision Detection), ngha l ti mt thi im ch c mt cp my tnh trao i vi nhau trong Hub, v chim ton b bng thng nn. Nu c hai my tnh do khng pht hin c nhau m gi c hai tn hiu u b hng, gi l s va chm (Collision). Khi c va chm xy ra, hai my tnh phi ngng qu trnh truyn d liu v i mt khong thi gian ngu nhin trc khi tin hnh truyn thng tin tr li. Nu c qu nhiu my tnh gn vo Hub cn truyn d liu cho nhau ti mt thi im, xc sut xy ra va chm rt cao, n mt ngng no th trong Hub ch ton cc gi tin b va chm v khng c my tnh no c th truyn d liu cho nhau na. Cc Switch c bng thng ln hn nhiu so vi Hub, v n c chia thnh nhiu knh nh. Mt khc, khi truyn d liu gia hai my tnh gn vo Switch, d liu s ch chim mt knh bng thng, v i t cng giao tip my tnh gi sang mt cng giao tip my tnh nhn. Do , cc my tnh khc cn li trong mng LAN gn vo Switch vn c th tip tc truyn d liu vi nhau m khng lo xy ra va chm tn hiu.

- -- -- -- -- -- -- BO MT Do tn hiu gi t mt my tnh gn vo Hub s i n tt c mi my tnh cn li, nn kh nng bo mt ca Hub l cc k yu km. Mt k tn cng ch vic truy cp c mt my tnh gn vo Hub th c th nghe c ton b cc thng tin lu chuyn trong mng ca mi my tnh khc m khng phi thc hin bt c th thut tn cng no. Kh nng bo mt ca Swich cao hn, do d liu ch di chuyn gia hai cng giao tip gn vo hai my tnh m thi. Trng hp k tn cng dng cc k thut nghe ln trn mng nh Manin-the-middle, th ngi qun tr hon ton c th pht hin cng nh khng ch c.

GI C C l y l l do duy nht m cc Hub cn tn ti trn th trng, khi m Switch mang mi c im hn hn Hub. Do cng ngh ch to n gin nn gi thnh cc loi Hub s r hn rt nhiu so vi Switch. Nh vy, nu khng b b buc qu v mt ti chnh, bn nn chn mua mt chic Switch thay cho Hub khi cn kt ni nhiu my tnh trong mng LAN li vi nhau. Vn k tip cn quan tm l nn xem xt cc thng s no c th chn mua mt chic Switch ph hp vi nhu cu s dng v chi ph u t. S LNG CNG Bn ang c bao nhiu my tnh trong mng? Bn d nh s gn thm bao nhiu my tnh na vo chic Switch sp mua? ng qun vic d phng mt vi cng khi chng b hng, v mt vi cng m rng vic kt ni Switch vi cc Switch khc c sn trong mng hay ni vi Router ADSL v im truy cp Wireless. Cc Switch thng c s lng cng l ly tha ca 2, nh 2, 4, 8, 16 cng. TC CNG KT NI Cng s dng cng ngh kt ni Ethernet, nhng mi dng Switch li h tr cc cng c tc kt ni khc nhau. Cng Ethernet thng thng s h tr tc 10Mbps, cc cng Fast Ethernet s h tr tc 100Mbps, cn cc cng GigaEthernet th t ngng 1000Mbps (hay 1Gbps). D nhin khi s dng cng 100Mbps. th bn s c th chia s cc tp tin, hnh nh hay video trong mng LAN nhanh hn hn khi dng cng tc 10Mbps. Nhng bn phi lu rng tc

ng truyn internet ADSL ch trong khong t 1Mbps 3Mbps, nn vic kt ni cng 10Mbps hay 100Mbps i ra internet s khng c g khc bit. Thm na, tc ca mt thit b c kh nng tng thch ngc vi cc tc thp hn. Nh cng 1Gbps c th hot ng cc tc 1000Mbps, 100Mbps, 10Mbps, card mng 100Mbps th hot ng c hai tc 100Mbps v 10Mbps. V th, t mt ngng tc no , th cc thit b phi ng b vi nhau, ngha l bn phi dng cc my tnh c card mng 1Gbps, ton b dy cp mng UTP CAT6 (category 6) ni vo cc cng 1Gbps ca Switch th mi c th lun chuyn tc 1Gbps gia cc my tnh vi nhau. Trng hp nu thiu s ng b, th kt qu t c l tc ti a nh nht m cc thit b trong h thng c th t c. V d nh card mng 10Mbps, dy cp UTP CAT5 100Mbps, cng Switch 1Gbps, th tc truyn d liu t my tnh n Switch cng ch l 10Mbps. CNG NGH C mt s cng ngh m bn cn quan tm xem thit b Switch mnh nh mua c c s dng trong qu trnh thit k hay khng. Mt Switch tt phi h tr cc cng truyn d liu theo dng song cng (full duplex), ngha l cng mt thi im th va c th gi, va c th nhn d liu. Nu ch c th hot ng trng thi n cng (half duplex), th ti mi thi im my tnh c th gi, hoc nhn d liu m thi. Ba cng ngh chuyn mch ca Switch cng cn c quan tm bao gm: Pass through (Switch va nhn c gi tin th chuyn i ngay, cch ny gip Switch hot ng nhanh nht, nhng d gy li), Fragment Free (ch c 64 byte d liu kim tra li, nu khng li th chuyn), v Store and Forward (c v lu ton b gi tin vo Switch, kim tra li ton b, nu khng pht hin li th chuyn i). Cng ngh Store and Forward hot ng chm nht, nhng n nh nht. N cng i hi Switch phi c b nh m ln lu v x l cng lc nhiu gi tin.

- -- -- Kh nng kim li (CRC Cyclic Redundancy Check) s gip Switch pht hin ra cc gi tin b li trong qu trnh chuyn nhn, v sa li n m khng cn phi yu cu sa li gi tin . Bng thng bn trong ca cc thit b Switch phi t mc cao, thng th phi trn 1Gbps. Cng ngh t ng nhn dng cp thng v cp cho MDI/MDI-X cn gip bn quan tm n cc chun bm cp khi kt ni nhiu thit b vi nhau. Cng ngh Ethernet xanh (Green Ethernet Technology), s t ng tt ngun trn cng khi khng c tn hiu kt ni v cung cp ngun ty theo chiu di ca cp, nhm tit kim in nng.

KIU DNG V CP NGUN Tuy ch l thit b mng, nhng chng thng c nm cc ni d thy tin cho vic kt ni v kim tra. V th, bn cng nn quan tm mt t n kiu dng v mu sc ca Switch m bn mun mua. H thng n LED cnh bo cng nn c y v r rng bn c th d dng quan st trng thi ca cc kt ni. Phn cp ngun cho thit b: Nu c th c, bn nn chn loi dng in trc tip qua ngun in xoay chiu dn dng, thay cho vic dng b nn in sang ngun in mt chiu. THNG HIU V CH BO HNH Mt thng hiu ni ting cng phn no gip m bo cht lng sn phm, tuy nhin bn ng qun tham kho ch bo hnh. c bit bn cn hi thm v ch cho mn thit b thay th trong thi gian bo hnh, v thit b Switch khi b hng s nh hng rt nhiu n ton b h thng mng ni b.