Cu 1 Lch s pht trin mng my tnh. nh ngha mng my tnh.

. Phn loi mng my tnh(theo khong cch a l; theo k thut chuyn mch). 1.1.Lch s pht trin mng my tnh Vo gia nhng nm 50 khi nhng th h my tnh u tin c a vo hot ng thc t vi nhng bng n in t th chng c kch thc rt cng knh v tn nhiu nng lng. Vo gia nhng nm 60 mt s nh ch to my tnh nghin cu thnh cng nhng thit b truy cp t xa ti my tnh ca h. Nhng dng u tin ca thit b u cui bao gm my c ba, my in, thit b x l tn hiu, cc thit b cm nhn. Vic lin kt t xa c th thc hin thng qua nhng vng khc nhau v l nhng dng u tin ca h thng mng.Trong lc a ra gii thiu nhng thit b u cui t xa, cc nh khoa hc trin khai mt lot nhng thit b iu khin, nhng thit b u cui c bit cho php ngi s dng nng cao c kh nng tng tc vi my tnh. Mt trong nhng sn phm quan trng l h thng thit b u cui 3270 ca IBM. H thng 3270 c gii thiu vo nm 1971 v c s dng dng m rng kh nng tnh ton ca trung tm my tnh ti cc vng xa. lm gim nhim v truyn thng ca my tnh trung tm v s lng cc lin kt gia my tnh trung tm vi cc thit b u cuiVo gia nhng nm 1970, cc thit b u cui s dng nhng phng php lin kt qua ng cp nm trong mt khu vc c ra i. Vi nhng u im t nng cao tc truyn d liu v qua kt hp c kh nng tnh ton ca cc my tnh li vi nhau. Vo nhng nm 1980 cc h thng ng truyn tc cao c thit lp Bc M v Chu u v t cng xut hin cc nh cung cp cc dnh v truyn thng vi nhng ng truyn c tc cao hn nhiu ln so vi ng dy in thoi. Ngy nay vi mt lng ln v thng tin, nhu cu x l thng tin ngy cng cao. Mng my tnh hin nay tr nn qu quen thuc i vi chng ta, trong mi lnh vc nh khoa hc, qun s, quc phng, thng mi, dch v, gio dc 1.2.nh ngha mng my tnhMng my tnh l mt tp hp cc my tnh c ni vi nhau bi ng truyn theo mt cu trc no v thng qua cc my tnh trao i thng tin qua li cho nhau. ng truyn l h thng cc thit b truyn dn c dy hay khng dy dng chuyn cc tn hiu in t t my tnh ny n my tnh khc. 1.3.Phn loi mng my tnh a.Theo khong cch a l Mng cc b - LAN local Area networks Mng th - MAN Metropolitan Area Networks Mng din rng WAN Wide Area Networks Mng ton cu GAN Global Area Networks b.Theo k thut chuyn mch Chuyn mch knh Circuit switched networks Chuyn mch thng bo Message switched networks Chuyn mch gi Package switched networks

Cu 2 ng truyn vt l, phn loi. Cc c trng c bn ca ng truyn vt l a. ng truyn vt l c dung chuyn cc tn hiu in t (cc gi tr d liu di dng cc xung nh phn) gia cc my tnh. Tt c tn hiu ny thuc mt dng song in t no , tri t tn s radio ti song cc ngn(viba) v tia hng ngoi. Ty theo tn s ca song in t c th dung cc ng truyn vt l khc nhau truyn cc tn hiu. Cc tn s radio c th truyn bng cp in hoc bng phng tin qung b. Sng cc ngn(viba) thng c dung truyn gia cc trm mt t v trm v tinh hoc truyn cc tn hiu qung b t mt trm pht ti nhiu trm thu Tia hng ngoi c th truyn gia hai im hoc qung b 1 im n nhiu my thu Tia hng ngoi v cc tn s cao hn ca nh sng c th c truyn qua cc loi si quang b. Cc c trng c bn ca ng truyn vt l - Gii thng (bandwidth) L o phm vi tn s m ng truyn c th p ng c - Thng lng (throughput) l tc truyn d liu trn ng truyn, thng c tnh bng s lng bit c truyn i trong 1s(bps) Thng lng cn c o bng 1 n v khc l baud biu th s lng thay i tn hiu trong 1s - suy hao l o s suy yu i ca tn hiu trn ng truyn c.Phn loi - ng truyn hu tuyn cable Cp ng trc (coaxial cable) Cp i xon (twisted-pi cable) : gm bc kim v khng bc kim (shielded) Cp si quang (fiber-optic cable) - ng truyn v tuyn (wireless) Radio, sng cc ngn, tia hng ngoi.

Cc mng c th s dng cc giao thc khc nhau ty s la chn ca ngi dng. Cu 4 Kin trc phn tng : nguyn tc, minh ha kin trc phn tng tng qut - Mc ch : gim phc tp ca vic thit k v ci t mng Mi h thng mng l 1 cu trrucs a tng, trong mi tng c xy dng trn tng trc . S lng tng, tn v chc nng ca mi tng ty thuc vo ngi thit k. Mi tng cung cp 1 s dch v nht nh cho tng cao hn. - Nguyn tc ca kin trc phn tng Cc h thng trong cng mng c cu trc tng nh nhau Hai h thng kt ni vi nhau. nh ngha mi quan h gia 2 tng k nhau, mi quan h gia 2 tng ng mc. Cch thc truyn v nhn d liu : d liu bn h thng gi t cc tng trn c chuyn xung tng di cng, qua ng truyn vt l truyn sang h thng nhn v c th Gia 2 h thng kt ni vi nhau ch c tng thp nht mi c lin kt vt l, cong tng cao hn ch l nhng lin kt logic u im : cho php xc nh c th quan h gia cc thnh phn, bo tr nng cp d dng. Nu khng phn tng khi c cng ngh mng mi phi vit li cc ng dng => tn thi gian v kinh t. - Minh ha kin trc phn tng M hnh OSI(open system interconnection) gm 7 tng : vt l, lin kt d liu, tng mng, giao vn, tng phin, trnh din,ng dng. M hnh TCP/IP gm 4 tng : Tng giao tip mng network interface physical, internet, transport, application Cu 5 M hnh OSI v tm tt cc chc nng cc tng M hnh OSI l mt c s dnh cho vic chun ho cc h thng truyn thng, n c nghin cu v xy dng bi ISO. Vic nghin cu v m hnh OSI c bt u ti ISO vo nm 1971 vi mc tiu nhm ti vic ni kt cc sn phm ca cc hng sn xut khc nhau v phi hp cc hot ng chun ho trong cc lnh vc vin thng v h thng thng tin. Theo m hnh OSI chng trnh truyn thng c chia ra thnh 7 tng vi nhng chc nng phn bit cho tng tng. Hai tng ng mc khi lin kt vi nhau phi s dng mt giao thc chung. Trong m hnh OSI c hai loi giao thc chnh c p dng: giao thc c lin kt (connection - oriented) v giao thc khng lin kt (connectionless) Giao thc c lin kt: trc khi truyn d liu hai tng ng mc cn thit lp mt lin kt logic v cc gi tin c trao i thng qua lin kt ny, vic c lin kt logic s nng cao an ton trong truyn d liu. Giao thc khng lin kt: trc khi truyn d liu khng thit lp lin kt logic v mi gi tin c truyn c lp vi cc gi tin trc hoc sau n. Nhim v ca cc tng trong m hnh OSI: Tng ng dng (Application layer): tng ng dng quy nh giao din gia ngi s dng v mi trng OSI, n cung cp cc phng tin cho ngi s dng truy cp v s dng cc dch v c m hnh OSI. Tng trnh by (Presentation layer): tng trnh by chuyn i cc thng tin t c php ngi s dng sang c php truyn d liu, ngoi ra n c th nn d liu truyn v m ha chng trc khi truyn bo mt. Tng giao dch (Session layer): tng giao dch quy nh mt giao din ng dng cho tng vn chuyn s dng. N xc lp nh xa gia cc tn t a ch, to ra cc tip xc ban u gia cc my tnh khc nhau trn c s cc giao dch truyn thng. N t tn nht qun cho mi thnh phn mun i thoi ring vi nhau. Tng vn chuyn (Transport layer): tng vn chuyn xc nh a ch trn mng, cch thc chuyn giao gi tin trn c s trc tip gia hai u mt (end-to-end). bo m c vic truyn n nh trn mng tng vn chuyn thng nh s cc gi tin v m bo chng chuyn theo th t. Tng mng (Network layer): tng mng c nhim v xc nh vic chuyn hng, vch ng cc gi tin trong mng, cc gi tin ny c th phi i qua nhiu chng trc khi n c ch cui cng. Tng lin kt d liu (Data link layer): tng lin kt d liu c nhim v xc nh c ch truy nhp thng tin trn mng, cc dng thc chung trong cc gi tin, ng cc gi tin... Tng vt l (Phisical layer): tng vt l cung cp phng thc truy cp vo ng truyn vt l truyn cc dng Bit khng cu trc, ngoi ra n cung cp cc chun v in, dy cp, u ni, k thut ni mch in, in p, tc cp truyn dn, giao din ni kt v cc mc ni kt Cu 6 Quan nim v tng theo cch tip cn ca m hnh OSI (khi nim thc th, im truy cp dch v , cc hm nguyn thy v s hot ng, quan h gia cc n v d liu cc tng k nhau) Trn quan im m hnh mng phn tng tng mi tng ch thc hin mt chc nng l nhn d liu t tng bn trn chuyn giao xung cho tng bn di v ngc li. Chc nng ny thc cht l gn thm v g b phn u (header) i vi cc gi tin trc khi chuyn n i. Ni cch khc, tng gi tin bao gm phn u (header) v phn d liu. Khi i n mt tng mi gi tin s c ng thm mt phn u khc v c xem nh l gi tin ca tng mi, cng vic trn tip din cho ti khi gi tin c truyn ln ng dy mng n bn nhn. Ti bn nhn cc gi tin c g b phn u trn tng tng tng ng v y cng l nguyn l ca bt c m hnh phn tng no. Thc th : thc th l 1 cu trc logic giao din vi 1 ng truyn vt l. Mi tng c 1 hoc nhiu thc th hot ng, mt n(entity) ci t cc chc nng tng n v giao thc truyn thng vi cc n trong cc h thng khc. Mi thc th truyn thng vi cc thc th tng trn v di n qua 1 giao din gm 1 hoc nhiu im truy cp dch v(SAP) Thc th tng n-1 cung cp thc th cho tng n thng qua vic gi cc hm nguyn thy, cc hm ny ch r chc nng cn thc hin v c dng truyn d liu thng tin iu khin. Cc hm nguyn thy : + Request yu cu: dung gi chc nng +Indication : (1) gi 1 chc nng. (2) ch bo 1 chc nng c gi 1 im truy cp dch v SAP + Respond : ngi dung dch v hon tt 1 chc nng c gi t (2) bi 1 hm Indication SAP . +Confirm: dung hon tt 1 chc nng c gi t trc bi hm request Tng n+1 ca A gi xung tng n di 1 hm request Tng m ca A to 1 n v d liu gi yu cu sang tng n ca B theo giao thc tng n xc nh. Nhn yu cu tng n ca B ch bo ln tng n+1 k n bng chnh hm indication Tng n+1 ca B tr li = hm respond gi xung tng n k di n Tng n ca B to 1 n v d liu tr li v tng n ca A theo giao thc tng n xc nh Nhn c tr li tng n ca A xc nhn vi SDU(service data unit), PDU(protocol data unit), PCI(protocol control information) Mt thc th tng n khng th truyn d liu trc tip ti 1 thc th tng n 1 h thng khc m phi chuyeent xung di chuyn qua tng thp nht. Khi xung n tng n-1 d liu c truyn t tng n xem nh 1 n v d liu cho dch v (SDU). Nu n-1 SDU qu di th n c ct nh thnh nhiu on n-1 PDU. Qu trnh tip din cho n tng vt l, sau d liu s c truyn qua tng vt l bn h thng nhn.

Cu 7 Cc phng thc hot ng trong m hnh OSI c lin kt v ko c lin kt. So snh cc phng thc ny. Gm c 2 phng thc hot ng chnh - Thit lp lin kt (logic) : hai thc th ng mc hai h thng s thng lng vi nhau v tp cc tham s s s dng trong giai on sau - Truyn d liu : d liu c truyn vi cc c ch kim sot v qun l km theo tng cng tin cy v hiu qu ca vic truyn d liu - Phng thc hot ng c lin kt : hy b lin kt(logic) gii phng cc ti nguyn h thng c cp pht cho lin kt dung cho cc lin kt khc. - Phng thc hot ng khng lin kt : ch c duy nht 1 giai on truyn d liu - So snh 2 phng thc hot ng : + c lin kt : cho php truyn d liu tin cy, do c kim sot v qun l cht ch theo tng lin kt logic. + Ko lin kt : cho php cc PDU c truyn i theo nhiu ng truyn khc nhau ti ch thch nghi s thay i ca mng. - Kh khn cho vic tp hp cc PDU chuyn n ngi dung vic la chn phng thc hot ng cho mi tng ph thuc vo yu cu tng hp v cht lng, hiu qu, tin cy ca vic truyn thng.

Cu 3 Kin trc mng my tnh : cc topology v giao thc mng Kin trc mng th hin cch ni cc my tnh vi nhau ra sao v tp hp cc quy tc, quy c m tt c cc thc th tham gia truyn thong trn mng phi tun theo m bo cho mng hot ng tt - Topology : l cch ni cc my tnh + im im : cc ng truyn c ni tng cp nt vi nhau. Mi nut c trch nhim lu tr tm thi, sau chuyn tip d liu i ti ch. Mng ny cn c gi l mng lu v chuyn tip(store and forward) + Qung b ( broadcast hay point tomulti point) tt c cc nut phn chia chung 1 ng truyn vt l. D liu c gi i 1 nt no s c th c tip nhn bi cc nt cn li. - Giao thc mng :l tp hp cc quy tc, quy c truyn thong Khi truyn tn hiu trn mng cn phi c cc quy tc, quy c v nhiu mt, t dng khun ca d liu n cc th tc gi nhn d liu kim sot hiu qu v cht lng truyn tin v x l cc li v s c.

Cu 8 Tng vt l : vai tr, chc nng, cc khi nim DTE, DCE -Vai tr v chc nng : Tng vt l cung cp cc phng tin in, c , chc nng, th tc kch hot, duy tr v hy b lin kt vt l gia cc h thng + Thuc tnh in : biu din cc bit v tc truyn bit + thuc tnh c : tnh cht vt l ca giao din vi 1 ng truyn + Thuc tnh chc nng : cc chc nng c thc hin bi cc phn t ca giao din vt l gia h thng v ng truyn + Thuc tnh th tc: lin quan n giao thc iu khin vic truyn cc xu bit qua ng truyn vt l - Khng c CDU cho tng vt l, khng c phn header cha thng tin iu khin(PCI) d liu c truyn i theo dng bit - Khi nim DTE v DCE : Thit b u cui d liu(DTE) ch cc my ca ngi dung cui(my tnh 1 trm cui). Tt c cc ng dng u nm DTE Mng my tnh kt ni cc DTE phn chia ti nguyn , trao i d liu v lu tr thng tin dung chung

- Thit b cui knh d liu (DCE) l cc thit b vi mng truyn thng VD: modem, transducer - Nhim v : chuyn i tn hiu ca ngi dng thnh dng tn hiu c chp nhn bi ng truyn v ngc li Cu 9 Tng lin k d liu, vai tr chc nng, cc giao thc(ng b, ko ng b ) ) giao thc HDLC, khun dng ca 1 Frame -Vai tr, chc nng : cung cp cc phng tin truyn thng tin qua lin kt vt l m bo tin cy thng qua cc c ch ng b ha, kim sot v kim sot lung d liu. - Cc giao thc (DLP) : Ko ng b (d b Asynchoronous) - ng b : hng k t v hng bit. - DLP d b : s dng phng thc truyn d b. Dng cc bit start v stop ng khung mi k t trong dng d liu cn truyn i. Ko cn c s ng b lin tc gia bn gi v bn nhn khng quan tm n cc tn hiu ng b. + u im : n gin + ng dng : cc my in bo hoc cc my trm cui tc thp - DLP ng b : chn cc k t c bit nh SYN, EOT hay 1 c gia d liu ca ngi dng bo kiu d liu ang n hoc n. H thng truyn thng yu cu 2 mc ng b ha + Mc vt l : ng b gia cc ng b ca bn gi v bn nhn + Mc lin kt d liu : phn bit d liu ca ngi dung vi cc c v cc vng thng tin iu khin - Giao thc hng k t : ng dng im im v a im - Cc phng thc truyn : 1 chiu(giao thc Kermit), 2 chiu lun phin(giao thc BSC), 2 chiu ng thi : t pht trin, giao thc gia cc nut mng chuyn mch IMP) - Giao thc hng bit :Giao thc HDLC : c pht trin bi ISO(3309 v 4335) + ng dng : im im v a im +Phng thc truyn : 2 chiu ng thi + Cc phng thc c xc nh t cc cu trc nh phn. Pha nhn d liu s c tip nhn ln lt tng bit mt +Khun dng tng qut ca 1 frame |Flay| Address| Control| Information|FCS|Flay| Flay : l vng m ng khung cho frame. M c chn l 01111110 Address : ghi a ch ca vng n frame Control : nh danh cho cc loi frame khc nh HDU Information : ghi thng tin cn truyn i FCS : ghi m kim sot li cho ni dung ca fame, s dng phng php CRC vi a thc sinh - HDLC s dng 3 loi frame chnh : loi U : frame iu khin thit lp lin kt d liu theo phng thc hot ng khc nhau v gii phng lin kt cn thit + Loi I cha thng tin truyn i ca ngi dung v c nh s th t kim sot + Loi S kim sot li v kim sot lung d liu trong qu trnh truyn tin loi frame iu khin

+ Giao thc lp 4 (Error Detection and Recovery Class Lp pht hin v phc hi li) l lp c hu ht cc chc nng ca cc lp trc v cn b sung thm mt s kh nng khc kim sot vic truyn d liu. Cu 10 Tng mng, vai tr, chc nng, cc k thut chn ng tp trung, phn tn; Cc k thut chn ng tnh, ng; Cc gii thut tm ng ti u; Giao thc X25PLP; Cc cng ngh chuyn mch nhanh : FrameRelay v ATM. Vai tr, chc nng : cung cp phng tin truyn n v d liu qua mng, thm ch qua mng ca cc mng cn phi p ng nhiu kiu mng v nhiu kiu dch v cung cp bi cc mng khc nhau. - Chc nng ch yu ca tng mng : chn ng v chuyn tip. Ngoi ra cn c chc nng khc nh thit lp, duy tr v gii phng lin kt logic, kim sot li, kim sot lung d liu, phn knh, dn knh, ct hoc hp d liu. - Cc k thut chn ng : + chn ng : chn ra ng truyn 1 n v d liu t trm ngun n trm ch, k thut ny phi thc hin 2 chc nng chnh + Quyt nh chn ng theo nhng tiu chun ti u no : tr trung bnh ca vic truyn gi tin. S lng nt trung gian gia ngun v ch ca gi. an ton ca vic truyn tin. Cp nht thng tin chn ng. + Phn loi k thut chn ng: . Da vo yu t phn tn cc chc nng chn ng trn cc nt mng c : k thut chn ng tp trung, phn tn. Da vo yu t thch nghi vi trng thi hin hnh ca mng c k thut chn ng tnh v thch nghi. . K thut chn ng tp trung (Disktra) : mt hoc 1 s trung tm a ch mng thc hin vic chn ng sau gi cc bng chn ng ti tt c cc nt theo ng chn . Thng tin chn ng ch c lu li trung tm iu kin mng, cc nt mng . K thut chn ng phn tn (Ford and fukeson) : Khng tn ti cc trung tm iu khin. Quyt nh chn ng c thc hin ti mi nt mng cn c s trao i thng tin gia cc nt mng, ty theo mc thch nghi ca gii thut c s dng. . K thut chn ng tnh : c th l tp trung hoc phn tn. Ko p ng vi bt k s thay i no trn mng ko c s trao i, ko o lng v ko cp nht thng tin tiu chun chn ng v chnh ng c chn 1 ln duy nht. Ko c s thay i gia chng. . u im : n gin . ng dng : s dng rng ri . K thut chn ng thch nghi : c kh nng p ng i vi cc trng thi khc nhau ca mng. Mc thch nghi : c trng bi s trao i thng tin chn ng trong mng. Mi nt hot ng 1 cch c lp vi thng tin ring thch nghi vi s thay i ca mng .Cc thng tin o lng c s dng cho vic chn ng : trng thi ca ng truyn, tr truyn dn, mc lu thng, cc ti nguyn sn sang trn mng Khi c bt k s thay i no trn mng do s c hoc khi them nt mi th cc trng thi u phi c cp nht. Cu 11 Tng giao vn : vai tr v chc nng; cc lp giao thc chun cho tng giao vn. Tng vn chuyn cung cp cc chc nng cn thit gia tng mng v cc tng trn. n l tng cao nht c lin quan n cc giao thc trao i d liu gia cc h thng m. N cng cc tng di cung cp cho ngi s dng cc phc v vn chuyn. Tng vn chuyn (transport layer) l tng c s m mt my tnh ca mng chia s thng tin vi mt my khc. Tng vn chuyn ng nht mi trm bng mt a ch duy nht v qun l s kt ni gia cc trm. Tng vn chuyn cng chia cc gi tin ln thnh cc gi tin nh hn trc khi gi i. Thng thng tng vn chuyn nh s cc gi tin v m bo chng chuyn theo ng th t. Tng vn chuyn l tng cui cng chu trch nhim v mc an ton trong truyn d liu nn giao thc tng vn chuyn ph thuc rt nhiu vo bn cht ca tng mng. Ngi ta chia giao thc tng mng thnh cc loi sau: - Mng loi A: C t sut li v s c c bo hiu chp nhn c (tc l cht lng chp nhn c). Cc gi tin c gi thit l khng b mt. Tng vn chuyn khng cn cung cp cc dch v phc hi hoc sp xp th t li. - Mng loi B: C t sut li chp nhn c nhng t sut s c c bo hiu li khng chp nhn c. Tng giao vn phi c kh nng phc hi li khi xy ra s c. - Mng loi C: C t sut li khng chp nhn c (khng tin cy) hay l giao thc khng lin kt. Tng giao vn phi c kh nng phc hi li khi xy ra li v sp xp li th t cc gi tin. Trn c s loi giao thc tng mng chng ta c 5 lp giao thc tng vn chuyn l: + Giao thc lp 0 (Simple Class - lp n gin): cung cp cc kh nng rt n gin thit lp lin kt, truyn d liu v hy b lin kt trn mng "c lin kt" loi A. N c kh nng pht hin v bo hiu cc li nhng khng c kh nng phc hi. + Giao thc lp 1 (Basic Error Recovery Class - Lp phc hi li c bn) dng vi cc loi mng B, y cc gi tin (TPDU) c nh s. Ngoi ra giao thc cn c kh nng bo nhn cho ni gi v truyn d liu khn. So vi giao thc lp 0 giao thc lp 1 c thm kh nng phc hi li. + Giao thc lp 2 (Multiplexing Class - lp dn knh) l mt ci tin ca lp 0 cho php dn mt s lin kt chuyn vn vo mt lin kt mng duy nht, ng thi c th kim sot lung d liu trnh tc nghn. Giao thc lp 2 khng c kh nng pht hin v phc hi li. Do vy n cn t trn mt tng mng loi A. + Giao thc lp 3 (Error Recovery and Multiplexing Class - lp phc hi li c bn v dn knh) l s m rng giao thc lp 2 vi kh nng pht hin v phc hi li, n cn t trn mt tng mng loi B. Cu 14- Tng ng dng : vao tr v chc anwng; kin trc truyn thng gia 2 tin trnh ng dng. Tng ng dng (Application layer) l tng cao nht ca m hnh OSI, n xc nh giao din gia ngi s dng v mi trng OSI v gii quyt cc k thut m cc chng trnh ng dng dng giao tip vi mng. cung cp phng tin truy nhp mi trng OSI cho cc tin trnh ng dng, Ngi ta thit lp cc thc th ng dng (AE), cc thc th ng dng s gi n cc phn t dch v ng dng (Application Service Element - vit tt l ASE) ca chng. Mi thc th ng dng c th gm mt hoc nhiu cc phn t dch v ng dng. Cc phn t dch v ng dng c phi hp trong mi trng ca thc th ng dng thng qua cc lin kt (association) gi l i tng lin kt n (Single Association Object - vit tt l SAO). SAO iu khin vic truyn thng trong sut vng i ca lin kt cho php tun t ha cc s kin n t cc ASE thnh t ca n.

Cu 13- Tng trnh din : vai tr v chc nng; ng cnh tng trnh din. Trong giao tip gia cc ng dng thng qua mng vi cng mt d liu c th c nhiu cch biu din khc nhau. Thng thng dng biu din dng bi ng dng ngun v dng biu din dng bi ng dng ch c th khc nhau do cc ng dng c chy trn cc h thng hon ton khc nhau (nh h my Intel v h my Motorola). Tng trnh by (Presentation layer) phi chu trch nhim chuyn i d liu gi i trn mng t mt loi biu din ny sang mt loi khc. t c iu n cung cp mt dng biu din chung dng truyn thng v cho php chuyn i t dng biu din cc b sang biu din chung v ngc li. Tng trnh by cng c th c dng k thut m ha xo trn cc d liu trc khi c truyn i v gii m u n bo mt. Ngoi ra tng biu din cng c th dng cc k thut nn sao cho ch cn mt t byte d liu th hin thng tin khi n c truyn trn mng, u nhn, tng trnh by bung tr li c d liu ban u.

Cu 12- Tng phin : vai tr v chc nng; khun dng tng qut c cc SPDU Tng giao dch (session layer) thit lp "cc giao dch" gia cc trm trn mng, n t tn nht qun cho mi thnh phn mun i thoi vi nhau v lp nh xa gia cc tn vi a ch ca chng. Mt giao dch phi c thit lp trc khi d liu c truyn trn mng, tng giao dch m bo cho cc giao dch c thit lp v duy tr theo ng qui nh. Tng giao dch cn cung cp cho ngi s dng cc chc nng cn thit qun tr cc giao dnh ng dng ca h, c th l: + iu phi vic trao i d liu gia cc ng dng bng cch thit lp v gii phng (mt cch lgic) cc phin (hay cn gi l cc hi thoi dialogues) + Cung cp cc im ng b kim sot vic trao i d liu. + p t cc qui tc cho cc tng tc gia cc ng dng ca ngi s dng. + Cung cp c ch "ly lt" (nm quyn) trong qu trnh trao i d liu. Trong trng hp mng l hai chiu lun phin th ny sinh vn : hai ngi s dng lun phin phi "ly lt" truyn d liu. Tng giao dch duy tr tng tc lun phin bng cch bo cho mi ngi s dng khi n lt h c truyn d liu. Vn ng b ha trong tng giao dch cng c thc hin nh c ch kim tra/phc hi, dch v ny cho php ngi s dng xc nh cc im ng b ha trong dng d liu ang chuyn vn v khi cn thit c th khi phc vic hi thoi bt u t mt trong cc im mt thi im ch c mt ngi s dng quyn c bit c gi cc dch v nht nh ca tng giao dch, vic phn b cc quyn ny thng qua trao i th bi (token). V d: Ai c c token s c quyn truyn d liu, v khi ngi gi token trao token cho ngi khc thi cng c ngha trao quyn truyn d liu cho ngi . Tng giao dch c cc hm c bn sau: + Give Token cho php ngi s dng chuyn mt token cho mt ngi s dng khc ca mt lin kt giao dch. + Please Token cho php mt ngi s dng cha c token c th yu cu token . + Give Control dng chuyn tt c cc token t mt ngi s dng sang mt ngi s dng khc.

Cu 15 M hnh TCP/IP v tm tt chc nng cc tng - M hnh TCP/IP + TCP/IP giao thc iu khin hoc giao thc lin mng l b giao thc cng lm vic vi nhau cung cp phng tin truyn lin mng + TCP/IP c pht trin vo thi k u ca internet vo nm 1974 +M hnh TCP/I c thit k da trn giao thc TCP/IP Gm 4 tng : ng dng, giao vn, mng v giao tip mng. - Mi tng s gii quyt 1 vn d liu lin quan n vic truyn d liu. Tng di cung cp cc dch v cho tng trn n. - m bo tng thch gia cc mng v s tin cy ca vic truyn thng tin trn mng th 1 b TCP/IP c chia thnh 2 phn ring bit: giao thc IP : lin kt mng. Giao thc TCP truyn d liu 1 cch tin cy. - Chc nng ca tng tng : + Giao tip mng : l tng thp nht ca TCP/IP c trch nhim nhn cc IP datagram v truyn i. Giao tip mng gm : >Vt l : lm vic vi cc thit b vt l truyn dng bt 0,1 t ni gi n nhn. >Lin kt d liu : d liu c t chc thnh khung d liu(frame). Phn u khung cha a ch v trng thi a ch. Phn cui dng pht hin li. - Tng mng : (tng internet) Dm nhim vic chn la ng i tt nht cho cc gi tin, giao thc c s dng chnh l giao thc IP. Nhn g/c gi gi d liu tng giao vn cng vi nh danh ca d liu m gi cn gi n. Thc hin cc ng truyn segment. Ti ni nhn s kim tra tnh hp l v s dng cc giao thc nh tuyn x l gi tin. Cui cng tng mng gi v nhn cc thng ip kim sot v sa li ICMP. - Tng giao vn : nhim v c bn l cung cp phng tin lin lc t chng trnh ng dng ny n ng dng khc (end to end). C th iu khin lung d liu. C th cung cp giao vn c tin cy m bo d liu n ni m khng c li v theo ng th t bng cch s dng giao thc TCP. Trong nhng mi trng truyn dn tt(cp quang) vic xy ra li l rt nh. S dng giao thc khc gi l UDP. - Tng ng dng l tng cao nht trong ng dung thc hin cc chng trnh ng dng ti cc dch v Internet. 1 ng dng tng tc vi 1 trong nhng giao thc tng ng dng nhn d liu. Qun l cc giao thc, h tr vic trnh by, m ha, qun l vic gi. H tr ng dng FTP(File Tranger Protocol)

Cu 16 So snh OSI vi TCP/IP - Ging nhau : u c phn dng chc nng. u c tng ng dng, mc d cc dch v mi tng l khc nhau. u c tng giao vn v tng mng. u s dng k thut chuyn mch gi. Mi quan h gia cc tng trn di v ng mc l ging nhau. - Khc nhau : TCP/IP n gin hn OSI. I khng c khi nim truyn thiu tin cy tng giao vn nh UDP ca TCP/IP. ng dng ca 2 m hnh l khc nhau. Internet c pht trin trn cc chun ca h TCP/IP, do vy TCP/IP c tin tng tn nhim trn cc chun ca n. TCP c chun ha v s dng trn th gii. M hnh OSI ko nh ra 1 giao thc c th no, ch ng vai tr nh 1 khung tham chiu hiu v to ra qu trnh truyn thng

Cu 18 Mng cc b(LAN) cc c trng phn bit mng LAN vi cc mng khc, cc topology dng trong mng LAN, cc phng thc truyn dn baseband v broadband. - c trng c bn ca mng 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). - Topology dung trong 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. - Cc phng thc truyn dn baseband v broadband : Cp ng trc s dng trong nhiu cc mng dng bus, hot ng theo 2 phng thc truyn dn : truyn dn theo di c s( ton b kh nng ca ng truyn dnh cho 1 knh duy nht) v truyn dn theo di rng. Phng thc truyn dn baseband: c hu ht cc mng cc b s dng. Tn hiu c th truyn di 2 dng tng t hoc s m ko cn iu ch. Hai loi cp thng s dng l: cp gy ng knh 0,25 inch vi di cp ti a gia 2 repeater l 200m v loi cp bo ng knh 0,5 inch vi di ti a l 500m. C 2 lm vic vi cng tc 100mb/s. Nhng, cp gy c suy hao tn hiu ln hn. Phng thc truyn dn broadband : chia di thng ca ng truyn thnh nhiu di tn con. Mi di tn con cung cp 1 knh truyn d liu tch bit s dng 1 cp modem c bit. y l k thut ghp knh theo tn s (FDM). Broadband l phng thc truyn dn 1 chiu cc tn hiu a vo ng truyn theo 1 hng.

Cu 19 Cc phng php truy nhp ng truyn vt l : CSMA/CD v phng php truy nhp c iu khin. - Phng php truy nhp ngu nhin CSMA/CD : Phng php a truy nhp s dng song mng c pht hin xung t c s dng h topo dng Bus. Tt c cc trm c ni trc tip vo bus. Mi trm u c th truy nhp 1 cch ngu nhin vo bus chung c th c xung t. + PP CSMA(nghe trc khi ni) : trc khi truyn d liu, trm cn phi nghe xem ng truyn ang bn hay ri. nu ri th truyn d liu i theo khun dng chun. nu ng truyn ang bn th phi thc hin 1 trong 3 gii thut kin nhn : trm tm rt lui ch i trong 1 khong thi gian ngu nhin no ri li bt u nghe ng truyn. Trm tip tc nghe n khi ng truyn ri th truyn d liu vi sc xut =1. Trm tip tc nghe n khi ng truyn ri th truyn d liu i vi sc xut p xc inh trc(0<p<1) + CSMA nghe trong khi ni : b xung them quy tc: khi 1 trm ang truyn, n vn tip tc nghe ng truyn. Nu pht hin thy xung t th n ngng ngay vic truyn nhng vn tip tc gi tn hiu song mang them thi gian na m bo tt c cc trm mng u c th nghe c s kin xung t. + Vi CSMA/CD : thi gian chim dng ng truyn c gim xung bng thi gian dung pht hin 1 xung t. - Phng php truy nhp c iu khin : Ch yu dng k thut chuyn th bi cp pht quyn truy nhp ng truyn. Th bi(token) l 1 n v d liu c bit, c kch thc v ni dung c quy nh ring cho mi phng php. - Phng php Token bus : + Nguyn l: cp pht quyn truy nhp ng truyn cho cc trm ang c nhu cu truyn d liu, 1 th bi c lu chuyn trn 1 vng logic c thit lp bi trm . Khi 1 trm nhn c th bi ht d liu hoc ht thi gian cho php. Trm phi chuyn th bi n trm tip theo trong vng logic. + Cc cng vic cn lm : thit lp vng logic(vng o) bao gm cc trm ang c nhu cu truyn d liu. V tr cc trm xc nh theo 1 chui th t, trong trm cui cng ca chui s lin tip sau b trm u tin. Mi trm bit a ch trm k nhau. Th t cc trm trn vng logic c th c lp vi th t vt l. Cc trm ko hoc cha c nhu cu truyn d liu th ko c a vo vng logic v chng ch c th tip nhn d liu. + Cc chc nng chnh cn thc hin duy tr vng logic : b sung cc trm vo vng logic. Loi b 1 trm khi vng logic. Qun l li trng a ch hoc t vng. Khi to vng logic. - Phng php token ring : + Nguyn l : dng th bi cp pht quyn truy nhp ng truyn. Th bi c lu chuyn theo vng vt l. Th bi l 1 n v d liu c bit, c 1 bit biu din trng thi s dng. Mt trm mun truyn d liu th phi i n khi nhn c th bi ri. Khi trm s

chuyn bit trng thi ca th bi bn v truyn d liu cng th bi theo chc nng ca vng. D liu n trm ch s c sao li, sau cng vi th bi i tip cho n khi quay li trm ngun. Trm ngun s xa b d liu, i bit trng thi ca th bi thnh ri v cho lu chuyn tip trn vng cc trm khc c th nhn c quyn truyn tip. S quay v li trm ngun ca d liu v th bi to ra 1 c ch bo nhn t nhin. Trm ch c th gi vo n v d liu cc thng tin v kt qu tip nhn d liu. Cc vn c th dn n ph v h thng : mt th bi trn vng ko cn th lu chuyn na hay mt th bi lu chuyn ko ngng. + Gii php : nu mt th bi quy nh trc 1 trm iu khin ch ng , trm ny s pht hin tnh trng mt th bi = c ch ngng thi gian. Khi thy mt th bi trm s phc hi bng cch pht i 1 th bi ri. Trm monitor s dng 1 bit trn th bi nh du khi gp 1 th bi bn i qua n. Nu n gp li th bi bn vi bit nh du khi gp 1 th bi bn i qua n. Nu n gp li th bi bn vi bit nh du th l trm ngun ko nhn li c n v d liu ca mnh v th bi bn c quay vng mi. Khi , trm monitor s i bit trng thi ca th bi thnh ri v chueyenr tueoes trn vng. Cc trm cn li trn vng c vai tr b ng theo di pht hin tnh trng s c ca trm monitor ch ng v thay th vai tr ca trm .

Cu 20- Ethernet v IEEE 802 *Ethernet l cng ngh ca mng LAN cho php truyn tn hiu vi tc 10Mbps n 10Gbps. Ethernet thng s dng cp xon i. Hin nay c khong 5% mng LAN s dng cng ngh Ethernet. Chun Ethernet u tin c a ra vo nm 1985 l IEEE 802.3. - Thit b u cui d liu (DTE) : my tnh c nhn, my ch - Thit b cui knh d liu(DCE) : b lp, b chuyn mch - Phng tin kt ni : cp xon i, cp ng, cp quang. - Nhng im c bn ca Ethernet : +Topo : bus, star +Phng thc truyn : base band +Phng php truy nhp L CSMA/CD. - Chun IEEE 802.3 : +Tc truyn 10 Mbps n 10Gbps +Loi cp : xon i, quang. *Vai tr v chc nng ca chun IEEE 802 : - Chun IEEE 802 gm chc nng vt l v lin kt d liu trong m hnh OSI - CHun IEEE chia tng lin kt d liu trong m hnh OSI thnh 2 tng con: tng iu khin truy nhp MAC v tng iu khin lin kt logic LLC. - Tt c cc mng LAN theo chun IEEE c cng tng LLC c nh ngha bi IEEE 802.2 - Giao din gia cc giao thc tng trn vi LLC thng qua cc im LSAP - LSAP l cc a ch lin kt logic, truy nhp dch v a ch Ethernet c nhiu a ch LSAP cho php lin kt gia cc thc th trn mng. - LSAP header |DSAP| SSAP|Cont| Data| DSAP : con tr t/bo cho NIC v ch b m lu tr thng tin nhn SSAP : v tr lu tr thng tin pht DSAP v SSAP cho php nhiu giao thc cng s dng chung NIC Cont kiu ca LLC Data : d liu t tng mng c chiu di ti a 1497 byte - Tng LLC cung cp dch v: +Loi 1 : dch v Datagram ko lin kt v ko c c ch bo nhn cung cp kt ni point to point, Mutipoint v broadcast +Loi 2 : dch v mch o, hng lin kt, cung cp cc dch v kim sot li v LSAP +Loi 3 : dch v datagram kiu khng lin kt v c c ch bo nhn. -Tng con MAC (Media Access Control hay Medium Access Control c ngha l "iu khin truy nhp mi trng") l tng con giao thc truyn d liu mt phn ca tng lin kt d liu trong m hnh 7 tng OSI. N cung cp cc c ch nh a ch v iu khin truy nhp knh (channel access), cc c ch ny cho php cc trm cui (terminal) hoc cc nt mng lin lc vi nhau trong mt mng, in hnh l mng LAN hoc MAN. Giao thc MAC khng cn thit trong lin lc im-ti-im song cng (full-duplex). Tng con MAC hot ng vi vai tr mt giao din gia tng con iu khin lin kt lgic LLC v tng vt l ca mng.

Tng MAC cung cp mt c ch nh a ch c gi l a ch vt l hoc a ch MAC. y l mt con s c cp mt cch phn bit cho tng bo mch mng, cho php chuyn giao cc gi d liu ti ch trong mt mng con, ngha l mt mng vt l khng c cc thit b nh tuyn, v d mt mng Ethernet. - Tng vt l (physical layer cn c th gi l tng thit b, hoc tng vt th) l tng th nht trong by tng m hnh OSI. Tng ny chu trch nhim ng i vi cc i hi v dch v t tng lin kt d liu. Tng ny m ch n phn cng (hardware) ca mng truyn thng, n h thng dy ni c th, hoc n s lin kt vin thng in t. Tng ny cn x l thit k in, khng ch xung t (collision control), v nhng chc nng h tng thp nht. Tng vt l l h tng c s ca mng truyn thng, cung cp phng tin truyn tn hiu th s dng bit. Hnh dng ca cc nt cm in (electrical connector), tn s pht sng l bao nhiu, v nhng ci thuc h tng tng t, c xc nh y. Mt v d tng t ca tng ny l v d v h tng ca mt mng li bu phm, bao gm vic xc nh nhng th nh giy th v mc chng hn. Chc nng v dch v chnh m tng vt l gii quyt l: +Thit lp v ngt mch mt lin kt vin thng trn mt phng tin truyn thng; +Tham gia vo mt tin trnh trong ti nguyn c nhiu ngi s dng cng mt lc, chng hn phn gii s tranh chp (contention) v khng ch lung (flow control); +Bin i th dng ca d liu s (digital data) trong thit b ca ngi dng ng b vi tn hiu c truyn qua ng truyn thng (Communication channel).

s c cp pht, phn DSP nh danh cho 1 a ch NASP trong min con tng ng.

cng gp phn nng cao tin cy.

Cu 21- Vn kim sot li : cc phng php kim sot li thng dng (phng php kim tra chn l, phng php kim tra vng CRC) -Phng php kim tra chn l : Phng php pht hin n gin nht l VRC. Theo ph ng php ny, mi xu bit biu dinkt truyn i c thm vo mt bit, gi l (parity bit) hay l bit chn l. Bit ny c gi tr(tu theo quy c) l 0 nu s l ng cc bit 1 trong xu l chn, 1 nu s cc bit 1 l l. Bn nhn s cn c vo pht hin li.Tuy nhin ph ng php ny khng nh v c bit li nn khng t sa c li m chyu cu pht li, mt khc n cng khng pht hin c li kp (tc l c 2n bit li). khc phc ngi ta dng thm ph ng php LRC. LRC kim tra bit chn l theo tng khi cc k t. Kt h p c hai ph ng php s cho php kim sot li theo c hai chiu, cho hiu qu cao h n so v i vic dng ring tng ph ng php. - Phng php kim tra vng CRC : T t ng ca phng php CRC: Chn tr c mt a thc (gi l a thc sinh) G(x) v i h s bc cao nht v thp nht u bng 1 Tm tp bit kim tra Checksum tho mn iu kin:a thc tng ng vi xu ghp(xu gc v checksum) phi chia ht (theo modulo 2) cho G(x).- Khi nhn tin, bn nhn kim tra li bng cch ly xau bit nhn c chia (modulo 2)cho G(x). Nu khng chia ht th c ngha l c li (ngc li t h c ng cha th khng nh l khng c li).Gi s G(x) c bc l r, xu bit gc tng ng v i da thc M(x) c bc m. Cc bc tnh checksum nh sau:(1)Thm r bit 0 vo cui xu bit cn truyn: xu ghp s gm c m+r bit tng ng vi a thc xr M(x). (2)Chia (modulo 2) xu bit tng ng cho xu bit tng ng vi G(x) (3)Ly xu bit b chia tr (modulo2) cho s d. Kt qu l xu bit c truyn i (xu gc+checksum). K hiu a thc tng ng v i n l T(x), r rng T(x) chia ht(modulo 2) cho G(x)

Cu 22 Vn kim sot lung d liu: phng php gii hn ti chung v phng php phn tn chc nng kim sot cho cc trm. *Phng php gii hn ti chung : Ti l s PDU c lu truyn trong mng n 1 im no . Mc tiu ca phng php l tm cch duy tr tng s PDU c lu chuyn trong mng lun < gii hn 1 gi tr no , gi tr ca mng c xc nh trc cn c vo ti nguyn ca n. thc hin c mc ch trn ngi ta cn to ra 1 N( giy thng hnh ca mng), mi PDU mun ha mng phi c giy thng hnh, khi ra khi mng phi tr giu thng hnh, khi khi to ngi qun tr cn c vo kh nng thc t ca cc trm phn chia cc giu thng hnh , mi mt trm ch c dng cc s giy thng hnh c cp. Tuy nhin, thch nghi vi s thay i ca mng th ngi ta cn kh nng cho php 1 trm ang c nhiu giy thng hnh s san bt cho cc trm thiu, lm c iu ny cn phi c giao thc iu khin gia cc trm. * Phng php phn tn chc nng kim sot Phng php ny khng yu cu duy tr gii hn ti chung ca mng m giao cho cc trm kim sot lung d liu i qua da trn ti nguyn cc b, ti nguyn chuyn PDU i trc, trnh s n tc ti ca cc trm, phng php ny tn km v phng tin ti nguyn v phi cp pht tri ln nng cao lu lng truyn thng.

Cu 23 Vn a ch ha : cc nguyn l, cu trc ca a ch. - c th trao i thng tin cc thc th truyn thng trong mng u phi c gn a ch theo mt h thng a ch ha thng nht m mi ng dng, mi ngi dng phi bit cc a ch ny thc hin qu trnh kt ni. - Trong m hnh OSI tng mng thc hin cc chc nng v a ch ca cc im truy cp mng c gi l calling np, xc nh cc thc th tham gia truyn thng v xc nh con ng ln gia cc thc th . Np c xem nh cc im c th a ch ha trong mt h thng v chng biu din cc im cui cng ca cc im lin kt trong tng mng. Khi nim v a ch mng con(sunnet) biu th cc thng tin cn thit nh danh 1 h thng cui hay ht cng kt ni(getway). - NASP phi m bo cc tnh cht: Khng nhp nhng an cho. p dng c cho tt c h thng. c lp vi vic chn ng. - Tp tt c cc a ch trong mi trng OSI c gi l a ch mng ton cc. Min ny c chia thnh nhiu mienf con(subdomain) theo phng thc phn cp, chun ISO 8348 nh ngha cc min con ca min a ch mng ton cc bao gm : + Mi nhm bao gm 4 min, mi min tng ng vi 1 kiu mng vin thng cng cng. + Mt min a l ISO dnh cho cc quc gia + Mt min cc t chc quc t c t ca ISO nh ngha c php tru tng v ng ngha ca cc a ch ng thi cng cho cc quy tc m ha a ch. - Cu trc ca a ch NASP: IDP bao gm 2 thnh phn v c coi l nh danh cho 1 min con ca a ch mng. AFI bao gm 2 ch s (00-99 c dng nh danh cho cc min con mc th 2 ng thi nh ngha khun dng ca IDI v nh ngha cu trc ca phn DFP tip sau IDI nh danh cho cc min con mc 3 trong cc gi tr ca DSP

Cu 24 Vn nh gi tin cy ca mng -Khi nim tin cy : tin cy ca mng l xc sut m mt mng hay 1 thnh phn ca n hot ng t yu cu trong mt khong thi gian cho trc v di nhng iu kin lm vic xc nh. + Xc sut l cng c ton hc o hiu sut hot ng. Khi mt s thit b ging nhau lm vic di nhng iu kin tng t nhau th chng li rt c th gp s c ti nhng thi im khc nhau. Bi vy, c th dng l thuyt xc sut m t s c . + Hot ng t yu cu( hiu sut) c th hin thng qua mt t hp cc yu stoos nh tnh v nh lng lin quan n cc chc nng m h thng phi m nhn. Thng l cc tnh nng k thut ca h thng nh t sut li, thng lng, tr + Thi gian + iu kin lm vic bao gm yu t v tr a l, thi tit, rung - nh gi tin cy thng qua kt ni. Mt cch n gin t tin cy cao l yu cu kt ni mng c d tha v ng truyn v thit b. Mt mng nh vy c th c s c mt s ng truyn hay nt mng m vn hot ng cho d mc hiu sut thp hn. phn tch mc d tha trong mt mng ta c th s dng cc tng ca l thuyt th - M hnh nh gi tin cy: - C 3 php o tin cy thng dng l : + Thi giant rung bnh gp s c + Thi giant rung bnh sa cha + Thi giant rung bnh gia cc s c. - Cc k thut nng cao tin cy : C th nng cao tin cy v sn sng ca mng bng cch gim s b chuyn tip(repeater) hoc cc b khuch i ng truyn(line amplifier) gia cc trm v phn tn cc thit b iu khin trn ton mng. To ra d tha v ng truyn v thit b nt

Cu 25 Vn an ton thng tin trn mng: Cc mc bo v an ton. - Cc mc bo v an ton mng : V khng th c mt gii php an ton tuyt i nn ngi ta thng phi s dng ng thi nhiu mc bo v khc nhau to thnahf nhiu lp ro cn i vi cc hot ng xm phm. Vic bo v thng tin trn mng ch yu l bo v thng tin ct gi trong cc my tnh, c bit l trong cc server mng. Bi th ngoi mt s bin pho nhm vo vic xy dng cc mc ro chn t ngoi vo trong cho cc h thng kt ni mng. + Lp bo v trong cng l Quyn truy nhp nhm kim sot cc ti nguyn ca mng v quyn hn trn ti nguyn . + Lp bo v tip theo l ng k tn/ mt khu : thc ra y cng l kim sot quyn truy nhp, nhng ko phi truy nhp mc thng tin m mc h thng. L phng php bo v ph bin nht v n n gin, t ph tn v cng rt hiu qu. + bo mt thng tin truyn qua mng, ngi ta s dng cc phng php m ha(encryption) d liu c bin i t dng nhn thc c thnh dng ko nhn thc c theo 1 thut ton no v s c bin i ngc li trm nhn. + Bo v vt l nhm ngn cn cc truy nhp vt l bt hp php vo h thng. Thng dng cc bin pho truyn thng nh ngn cm tuyt i ngi ko phn s vo phng t my mng, dng kha trn my tnh. + bo v t xa mt my tnh hoc cho c mt mng ni b, ngi ta thng dng cc h thng c bit l tng la(firewall). Chc nng ca cc tng la l ngn chn cc thm nhp tri php v thm tr c th lc b cc gi tin m ta ko mun gi i hoc nhn vo v nhng l do no .

Cu 26- Vn qun tr mng - H thng qun tr mng bao gm mt h qun tr, mt h b qun tr, mt c s d liu cha thng tin qun tr v giao thc qun tr mng. - H qun tr manager: cung cp giao din gia ngi qun tr mng v cc thit b c qun tr, ng thi thc hin cc nhim v nh l o lng lu thng trn mt on mng cc b xa, hoc ghi tc truyn v a ch vt l ca giao din LAN trn mt router. - H b qun tr Manager System bao gm tin trnh v cc i tng qun tr. + Tin trnh Agent thc hin cc thao tc qun tr mng nh t cc tham s cu hnh v cc thng k hot ng hin hnh cho 1 router trn 1 segment cho trc + Cc i tng qun tr Managed objects bao gm cc trm lm vic , cc my ch, hub, cc knh truyn gn vi cc i tng ny l thuc tnh(attributes) c th c xc nh tnh, ng hoc i hi o lng tip tc. - C s d liu cha thng tin qun tr mng c gi l c s thng tin qun tr c gn vi c hai bn. - Giao thc qun tr mng cung cp phng thc lin lc gia manager cc i tng b qun tr v cc agent. cu trc tin trnh truyn thng, giao thc phi xc nh cc n v d liu th hin cc thr tc ca n. - Kin trc qun tr ca ISO: + Qun tr s c +Qun tr k ton + Qun tr cu hnh + Qun tr hiu nng - Kin trc qun tr IEEE + LAN/MAN management Service + LAN/MAN management Protocol Entity + Convergence Protocol Entity

Cu 27 Giao thc IP. Giao thc TCP. Giao thc UDP * Giao thc IP Nhim v chnh ca giao thc IP l cung cp kh nng kt ni cc mng con thnh lin kt mng truyn d liu, vai tr ca IP l vai tr ca giao thc tng mng trong m hnh OSI. Giao thc IP l mt giao thc kiu khng lin kt (connectionlees) c ngha l khng cn c giai on thit lp lin kt trc khi truyn d liu. S a ch ha nh danh cc trm (host) trong lin mng c gi l a ch IP 32 bits (32 bit IP address). Mi giao din trong 1 my c h tr giao thc IP u phi c gn 1 a ch IP (mt my tnh c th gn vi nhiu mng do vy c th c nhiu a ch IP). a ch IP gm 2 phn: a ch mng (netid) v a ch my (hostid). Mi a ch IP c di 32 bits c tch thnh 4 vng (mi vng 1 byte), c th biu th di dng thp phn, bt phn, thp lc phn hay nh phn. Cch vit ph bin nht l dng k php thp phn c du chm (dotted decimal notation) tch cc vng. Mc ch ca a ch IP l nh danh duy nht cho mt my tnh bt k trn lin mng. Do t chc v ln ca cc mng con (subnet) ca lin mng c th khc nhau, ngi ta chia cc a ch IP thnh 5 lp, k hiu l A, B, C, D v E. Trong lp A, B, C cha a ch c th gn c. Lp D dnh ring cho lp k thut multicasting. Lp E c dnh nhng ng dng trong tng lai. Netid trong a ch mng dng nhn dng tng mng ring bit. Cc mng lin kt phi c a ch mng (netid) ring cho mi mng. y cc bit u tin ca byte u tin c dng nh danh lp a ch (0 - lp A, 10 - lp B, 110 - lp C, 1110 - lp D v 11110 - lp E). y ta xt cu trc ca cc lp a ch c th gn c l lp A, lp B, lp C * Giao thc TCP TCP l mt giao thc "c lin kt" (connection - oriented), ngha l cn phi thit lp lin kt gia hai thc th TCP trc khi chng trao i d liu vi nhau. Mt tin trnh ng dng trong mt my tnh truy nhp vo cc dch v ca giao thc TCP thng qua mt cng (port) ca TCP. S hiu cng TCP c th hin bi 2 bytes.

Mt cng TCP kt hp vi a ch IP to thnh mt u ni TCP/IP (socket) duy nht trong lin mng. Dch v TCP c cung cp nh mt lin kt logic gia mt cp u ni TCP/IP. Mt u ni TCP/IP c th tham gia nhiu lin kt vi cc u ni TCP/IP xa khc nhau. Trc khi truyn d liu gia 2 trm cn phi thit lp mt lin kt TCP gia chng v khi khng cn nhu cu truyn d liu th lin kt s c gii phng. Cc thc th ca tng trn s dng giao thc TCP thng qua cc hm gi (function calls) trong c cc hm yu cu yu cu, tr li. Trong mi hm cn c cc tham s dnh cho vic trao i d liu. * Giao thc UDP UDP (User Datagram Protocol) l giao thc theo phng thc khng lin kt c s dng thay th cho TCP trn IP theo yu cu ca tng ng dng. Khc vi TCP, UDP khng c cc chc nng thit lp v kt thc lin kt. Tng t nh IP, n cng khng cung cp c ch bo nhn (acknowledgment), khng sp xp tun t cc gi tin (datagram) n v c th dn n tnh trng mt hoc trng d liu m khng c c ch thng bo li cho ngi gi. Qua ta thy UDP cung cp cc dch v vn chuyn khng tin cy nh trong TCP. Khun dng UDP datagram c m t vi cc vng tham s n gin hn nhiu so vi TCP segment. UDP cng cung cp c ch gn v qun l cc s hiu cng (port number) nh danh duy nht cho cc ng dng chy trn mt trm ca mng. Do t chc nng phc tp nn UDP thng c xu th hot ng nhanh hn so vi TCP. N thng c dng cho cc ng khng i hi tin cy cao trong giao vn.

Cu 29 Cc dch v thng tin Internet : DNS, Telnet, ftp, www, th in t, DNS Domain Name System, l H thng tn min c pht minh vo nm 1984 cho Internet, ch mt h thng cho php thit lp tng ng gia a ch IP v tn min. H thng tn min (DNS) l mt h thng t tn theo th t cho my vi tnh, dch v, hoc bt k ngun lc tham gia vo Internet. N lin kt nhiu thng tin a dng vi tn min c gn cho nhng ngi tham gia. Quan trng nht l, n chuyn tn min c ngha cho con ngi vo s nh danh (nh phn), lin kt vi cc trang thit b mng cho cc mc ch nh v v a ch ha cc thit b khp th gii. TELNET TELecommunication NETwork cng c th l TErminal NETwork hay TELetype NETwork l mt giao thc mng (network protocol) c dng trn cc kt ni vi Internet hoc cc kt ni ti mng my tnh cc b LAN. Ti liu ca IETF, STD 8, (cn c gi lRFC 854 v RFC 855) c ni rng: Mc ch ca giao thc TELNET l cung cp mt phng tin truyn thng chung chung, c tnh lng truyn, dng rng 8 bit, nh hng byte. TELNET thng c dng cung cp nhng phin giao dch ng nhp, gia cc my trn mng Internet, dng dng lnh c tnh nh hng ngi dng. Tn ca n c ngun gc t hai ch ting Anh "telephone network" (mng in thoi), v chng trnh phn mm c thit k, to cm gic nh mt thit b cui c gn vo mt my tnh khc. FTP File Transfer Protocol, "Giao thc truyn tp tin" thng c dng trao i tp tin qua mng li truyn thng dng giao thc TCP/IP (chng hn nh Internet - mng ngoi b hoc intranet - mng ni b). Hot ng ca FTP cn c hai my tnh, mtmy ch v mt my khch). My ch FTP, dng chy phn mm cung cp dch v FTP, gi l trnh ch, lng nghe yu cu v dch v ca cc my tnh khc trn mng li. My khch chy phn mm FTP dnh cho ngi s dng dch v, gi l trnh khch, th khi u mt lin kt vi my ch. Mt khi hai my lin kt vi nhau, my khch c th x l mt s thao tc v tp tin, nh ti tp tin ln my ch, ti tp tin t my ch xung my ca mnh, i tn ca tp tin, hoc xa tp tin my ch v.v. V giao thc FTP l mt giao thc chun cng khai, cho nn bt c mt cng ty phn mm no, hay mt lp trnh vin no cng c th vit trnh ch FTP hoc trnh khch FTP. Hu nh bt c mt nn

tng h iu hnh my tnh no cng h tr giao thc FTP. iu ny cho php tt c cc my tnh kt ni vi mt mng li c nn TCP/IP, x l tp tin trn mt my tnh khc trn cng mt mng li vi mnh, bt k my tnh y dng h iu hnh no (nu cc my tnh y u cho php s truy cp ca cc my tnh khc, dng giao thc FTP). Hin nay trn th trng c rt nhiu cc trnh khch v trnh ch FTP, v phn ng cc trnh ng dng ny cho php ngi dng c ly t do, khng mt tin. World Wide Web, gi tt l Web hoc WWW, mng li ton cu l mt khng gian thng tin ton cu m mi ngi c th truy nhp (c v vit) qua cc my tnh ni vi mng Internet. Thut ng ny thng c hiu nhm l t ng ngha vi chnh thut ng Internet. Nhng Web thc ra ch l mt trong cc dch v chy trn Internet, chng hn nh dch v th in t. Web c pht minh v a vo s dng vo khong nm 1990, 1991 bi vin s Vin Hn lm Anh Tim BernersLee v Robert Cailliau (B) ti CERN, Geneva, Switzerland. Cc ti liu trn World Wide Web c lu tr trong mt h thng siu vn bn (hypertext), t ti cc my tnh trong mng Internet. Ngi dng phi s dng mt chng trnh c gi l trnh duyt web (web browser) xem siu vn bn. Chng trnh ny s nhn thng tin(documents) ti a ch (address) do ngi s dng yu cu (thng tin trong a ch c gi l tn min (domain name)), ri sau chng trnh s t ng gi thng tin n my ch (web server) v hin th trn mn hnh my tnh ca ngi xem. Ngi dng c th theo cc lin kt siu vn bn (hyperlink) trn mi trang web ni vi cc ti liu khc hoc gi thng tin phn hi theo my ch trong mt qu trnh tng tc. Hot ng truy tm theo cc siu lin kt thng c gi l duyt Web. Th in t, hay email (t ch electronic mail), i khi c dch khng chnh xc l in th, l mt h thng chuyn nhn th t qua cc mng my tnh. Email l mt phng tin thng tin rt nhanh. Mt mu thng tin (th t) c th c gi i dng m ho hay dng thng thng v c chuyn qua cc mng my tnh c bit l mng Internet. N c th chuyn mu thng tin t mt my ngun ti mt hay rt nhiu my nhn trong cng lc. Ngy nay, email chng nhng c th truyn gi c ch, n cn c th truyn c cc dng thng tin khc nh hnh nh, m thanh, phim, v c bit cc phn mm th in t kiu mi cn c th hin th cc email dng sng ng tng thch vi kiu tp HTML.

Cu 17- Qu trnh ng gi d liu TCP/IP

Data

Application : ng dng internet giao vn UDP data IP data Frame Data Link Frame header Internet Transport : giao vn giao tip mng

UDP header IP header Frame header

Cu 28 Cu trc cc lp a ch IP. Cho v d. Cu trc ca cc a ch IP nh sau: - Mng lp A: a ch mng (netid) l 1 Byte v a ch host (hostid) l 3 byte. - Mng lp B: a ch mng (netid) l 2 Byte v a ch host (hostid) l 2 byte. - Mng lp C: a ch mng (netid) l 3 Byte v a ch host (hostid) l 1 byte. Lp A cho php nh danh ti 126 mng, vi ti a 16 triu host trn mi mng. Lp ny c dng cho cc mng c s trm cc ln. Lp B cho php nh danh ti 16384 mng, vi ti a 65534 host trn mi mng. Lp C cho php nh danh ti 2 triu mng, vi ti a 254 host trn mi mng. Lp ny c dng cho cc mng c t trm.