Tài Liệu Mạng Máy Tính Tiếng Việt

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.
com
Mc lc
Trao i d liu & Mng my tnh ......................................................................................... 7
i vi c gi ...................................................................................................................... 7
iu kin tin ................................................................................................................... 7
Tng quan v Trao i d liu v Mng my tnh ................................................................. 7
Phn loi mng my tnh .................................................................................................. 8
Lin kt theo khong khng gian ...................................................................................... 8
Lin kt ni b................................................................................................................... 8
Qun l ............................................................................................................................. 9
Cu trc mng .................................................................................................................. 9
Cc ng dng mng......................................................................................................... 9
Cc loi mng my tnh trong DCN ...................................................................................... 9
Mng khu vc c nhn (PAN) trong DCN....................................................................... 10
Mng khu vc ni b (LAN) trong DCN .......................................................................... 10
Mng khu vc trung tm (MAN) trong DCN.................................................................... 11
Mng khu vc rng (WAN) trong DCN ........................................................................... 12
Mng internet trong DCN ................................................................................................ 13
Cc cng ngh mng LAN trong DCN................................................................................ 14
Cng ngh Ethernet trong DCN...................................................................................... 14
Cng ngh Fast-Ethernet trong DCN.............................................................................. 15
Cng ngh Giga-Ethernet trong DCN ............................................................................. 15
Cng ngh Mng LAN o trong DCN ............................................................................. 15
Khng gian mng trong DCN.............................................................................................. 16
Cu trc khng gian Point-to-Point trong DCN ................................................................ 17
Cu trc khng gian bus (Bus Topology) trong DCN....................................................... 17
Cu trc ngi sao (Star Topology) trong DCN ................................................................. 18
Cu trc vng trn (Ring Topology) trong DCN............................................................... 19
Cu trc hn n (Mesh Topology) trong DCN ............................................................... 19
http://vietjack.com/ Trang chia s cc bi hc online min ph
Trang 1
http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Cu trc cy (Tree Topology) trong DCN ........................................................................ 20
Daisy Chain trong DCN .................................................................................................. 21
Cu trc lai (Hybrid Topology) trong DCN ....................................................................... 21
M hnh mng my tnh trong DCN .................................................................................... 22
Cc tc v c phn tng trong DCN........................................................................... 22
M hnh OSI trong DCN.................................................................................................. 23
M hnh Internet trong DCN ............................................................................................ 25
Bo mt mng my tnh trong DCN.................................................................................... 25
Mt m ha kha Private trong DCN .............................................................................. 27
Mt m ha kha Public trong DCN................................................................................ 27
Tiu ha tin (Message Digest) trong DCN....................................................................... 28
Gii thiu Tng vt l trong DCN......................................................................................... 28
Cc tn hiu..................................................................................................................... 28
Suy truyn (transmission impairment) ............................................................................. 29
Phng tin truyn ti .................................................................................................... 30
Dung lng knh............................................................................................................ 30
K thut dn/ghp (multiplexing) ..................................................................................... 31
S chuyn mch ............................................................................................................ 31
Truyn ti k
thut s (digital) trong DCN ................................................................................................. 31
Bin i s ti s (digital-to-digital) trong DCN................................................................. 31
M ha dng d liu trong DCN ..................................................................................... 32
M ha n cc uni-polar trong DCN ................................................................. 32
M ha c cc trong DCN ..................................................................................... 33
Trang 2

Return to Zero (RZ) ........................................................................................... 34
Manchester ......................................................................................................... 35
Manchester vi sai (differential) ........................................................................ 35
M ha song cc (bipolar encoding) trong DCN ............................................... 35
M ha khi trong DCN .................................................................................................. 36
S bin i t d liu tng t sang K thut s trong DCN.......................................... 36
Ly mu .................................................................................................................... 37
Lng t ha trong DCN ...................................................................................... 37
M ha ...................................................................................................................... 38
Cc ch truyn ti ...................................................................................................... 38
Truyn ti song song .............................................................................................. 38
Truyn ti theo dy (chui).................................................................................... 39
Truyn ti theo chui khng ng b .................................................................. 39
Truyn ti theo chui ng b .............................................................................. 39
Truyn ti tng t (analog) trong DCN ............................................................................. 39
S chuyn i t k thut s thnh tng t trong DCN ................................................ 40
S chuyn i t tng t sang tng t trong DCN .................................................... 42
Phng tin truyn ti trong DCN....................................................................................... 45
Phng tin t tnh......................................................................................................... 46
Cp xon i (twisted pair cable)..................................................................................... 46
Cp ng trc ................................................................................................................. 47
Cc dy dn in (Power Lines) ..................................................................................... 48
Cp quang...................................................................................................................... 49
Truyn ti khng dy trong DCN......................................................................................... 50
Truyn ti v tuyn.......................................................................................................... 51
Truyn ti sng cc ngn ............................................................................................... 52
Truyn ti ca tia hng ngoi .......................................................................................... 53
S truyn nh sng ........................................................................................................ 53
K thut ghp knh trong DCN ........................................................................................... 54
Trang 3

K thut ghp knh bng chia tn s (FDM) trong DCN ................................................. 54
K thut ghp knh phn chia theo thi gian (TDM) trong DCN...................................... 55
Ghp knh phn chia theo bin sng trong DCN ....................................................... 56
Ghp knh phn chia m ha (CDM) trong DCN ........................................................... 56
S chuyn mng trong DCN .............................................................................................. 56
Chuyn mch (Circuit Switching) .................................................................................... 57
Chuyn mng tin bo...................................................................................................... 58
Chuyn mch gi d liu ................................................................................................ 59
DCN - Gii thiu v Tng data-link...................................................................................... 59
Chc nng ca tng data-link ......................................................................................... 60
Pht hin v chnh sa li trong DCN ................................................................................. 61
Cc kiu li ..................................................................................................................... 61
Pht hin li .................................................................................................................... 62
Kim tra chn l (Prity Check) .............................................................................. 62
Cyclic Redundancy Check (CRC) ........................................................................ 63
Chnh sa li................................................................................................................... 64
DCN - Giao thc v kim sot data-link .............................................................................. 64
Kim sot lung trong tng data-link ............................................................................... 64
Kim sot li trong tng data-link..................................................................................... 65
Stop and Wait ARQ ........................................................................................... 66
Go-Back-N ARQ ................................................................................................ 67
Selective Repeat ARQ (lp c la chn) ...................................................... 69
Gii thiu Tng mng trong DCN ....................................................................................... 70
Cc chc nng Tng-3................................................................................................... 70
Cc c im ca Tng mng........................................................................................ 70
nh v mng trong DCN ..................................................................................................... 71
nh tuyn Tng mng trong DCN...................................................................................... 73
nh tuyn Unicast.......................................................................................................... 74
nh tuyn Broadcast...................................................................................................... 74
Trang 4

nh tuyn Multicast........................................................................................................ 75
nh tuyn Anycast ......................................................................................................... 76
Cc giao thc nh tuyn Unicast.................................................................................... 77
Giao thc nh tuyn vecto khong cch (Distance Vector Routing
Protocol) ................................................................................................................... 77
Giao thc nh tuyn trng thi kt ni (Link State) .................................... 77
Cc giao thc nh tuyn Multicast.................................................................................. 78
Cc thut ton nh tuyn ............................................................................................... 78
Flooding .................................................................................................................... 78
ng truyn ngn nht ....................................................................................... 79
Lin mng trong DCN......................................................................................................... 79
K thut Tunneling trong DCN ........................................................................................ 80
S phn mnh gi d liu trong DCN............................................................................. 81
Cc giao thc Tng mng trong DCN ................................................................................ 82
Giao thc phn gii a ch (ARP) ................................................................................... 82
Giao thc thng bo iu khin internet (ICMP).............................................................. 84
IP phin bn 4 (IPv4) ...................................................................................................... 84
IP phin bn 6 (IPv6) ...................................................................................................... 85
Gii thiu Tng truyn ti trong DCN .................................................................................. 85
Cc tnh nng ................................................................................................................. 86
Giao tip end-to-end ....................................................................................................... 86
Giao thc TCP trong DCN.................................................................................................. 87
Cc c im.................................................................................................................. 87
Header............................................................................................................................ 87
Ghi a ch....................................................................................................................... 89
Qun l kt ni ................................................................................................................ 90
S thnh lp ............................................................................................................ 90
S tho b ............................................................................................................... 91
Qun l bng thng ........................................................................................................ 91
Trang 5

Kim sot lung v Kim sot li .................................................................................... 91
S ghp knh................................................................................................................. 91
Kim sot tc nghn ....................................................................................................... 92
Qun l ng h bm gi ............................................................................................... 92
ng h bm gi thi gian sng (Keep-alive timer ()....................................... 92
ng h bm gi truyn ti li (retransmission timer) ...................................... 92
ng h bm gi tip tc (persist timer) ............................................................. 92
Thi gian i (timed-wait) ..................................................................................... 93
Phc hi li s tm dng ................................................................................................ 93
Giao thc UDP trong DCN ................................................................................................. 93
Yu cu ca UDP ........................................................................................................... 94
Cc c im.................................................................................................................. 94
UDP Header................................................................................................................... 94
ng dng UDP............................................................................................................... 95
Gii thiu Tng ng dng trong DCN ................................................................................. 95
M hnh Client-Server trong DCN ....................................................................................... 96
Giao tip trong DCN........................................................................................................ 98
Th tc gi hm t xa trong DCN ........................................................................ 98
Giao thc Tng ng dng trong DCN................................................................................. 99
H thng tn min (Domain Name System) trong DCN.................................................. 99
Giao thc truyn ti mail n gin (Simple Mail Transfer Protocol) trong DCN................ 99
Giao thc truyn ti file (File Transfer Protocol) trong DCN ........................................... 100
Giao thc POP (Post Office Protocol) trong DCN ......................................................... 100
Giao thc truyn ti siu vn bn (HTTP) trong DCN ................................................... 100
Dch v mng trong DCN.................................................................................................. 101
Cc dch v th mc ..................................................................................................... 101
Cc dch v file.............................................................................................................. 102
Cc dch v trao i thng tin ........................................................................................ 102
Cc dch v ng dng................................................................................................... 103
Trang 6

Ti liu tham kho v DCN ............................................................................................... 104
Cc ng link hu ch v DCN................................................................................... 104
Trao i d liu & Mng my tnh

Trao i d liu lin quan ti s truyn ca cc d liu dng s gia hai hoc nhiu my tnh v
mt mng my tnh hoc mt mng d liu l mt mng truyn thng m cho php cc my tnh
trao i d liu vi nhau. S kt ni vt l gia cc thit b my tnh c kt ni mng c thit
lp s dng phng tin cp hoc phng tin khng dy. Mng my tnh c bit n nhiu
nht l mng internet.
Phn hng dn ny s cung cp cho bn cc c s ca s trao i d liu v mng my tnh
DCN v cng s a bn qua cc khi nim a dng lin quan ti DCN (Data Communication and
Computer Network).
Lot bi hng dn ca chng ti da trn ngun ti liu ca: Tutorialspoint
i vi c gi
Phn hng dn ny c chun b cho nhng ngi am m v khoa hc my tnh gip h
hiu cc khi nim c bn lin quan ti DCN. Sau khi hon thnh phn hng dn ny, bn s
thy chnh mnh mt mc trung bnh trong s hiu bit v DCN v t bn c th nng cao
trnh ca mnh ln.
iu kin tin
Trc khi bt u tin hnh phn hng dn ny, chng ti gi s rng bn c nhng s hiu
bit c bn v cc khi nim my tnh nh bn phm, chut,, mn hnh, u vo, b nh s cp, v
b nh th cp l g.
Tng quan v Trao i d liu v Mng

my tnh
Mt h thng cc my tnh c lin kt vi nhau v cc thit b ngoi vi c in ton ha nh
cc my in c gi l mng my tnh. S lin kt ny bn trong cc my tnh lm cho thng tin
Trang 7

chia s trong chng c d dng. Cc my tnh c th kt ni vi mi my khc bi phng tin
kt ni dy dn hoc khng dy.
Phn loi mng my tnh

Mng my tnh c phn loi trn c s cc yu t a dng. Chng bao gm:
Lin kt theo khong khng gian (geographical span)
Lin kt ni b (inter-connectivity)
Qun l
Cu trc
Lin kt theo khong khng gian

Mt mng lin kt theo khong khng gian c th l mt trong cc loi sau:
N c th c kt ni qua bn ca bn, bn trong cc thit b Bluetooth. Xp dy khng di

hn vi mt.
N c th c kt ni qua mt ta nh, bao gm cc thit b trung gian kt ni tt c cc

tng.
N c th c kt ni qua mt thnh ph.
N c th c kt ni qua nhiu thnh ph hoc nhiu tnh.
N c th c kt ni qua ton th gii.
Lin kt ni b
Cc thnh phn ca mt mng c th c kt ni vi nhau theo cch khc nhau trong mt s
kiu. Bi mi lin h, chng ta c th chia thnh: theo cch logic, theo cch vt l hoc theo c hai
cch.
Mi thit b n c th c kt ni vi mi thit b khc trn mng, lm cho mng khp

nhau.
Tt c cc thit b c th c kt ni ti mt trung gian n nhng khong khng gian l

khng kt ni, to cu trc bus.
Mi thit b c kt ni ch ti cc thit b ngang hng bn phi v tri, to cu trc tuyn.
Tt c thit b c kt ni vi nhau vi mt thit b n, to cu trc hnh sao.
Trang 8
Tt c cc thit b c kt ni mt cch ty s dng tt c cc cch trn kt ni mi

thit b vi nhau, kt qu l to ra mt cu trc lai (hn hp).
Qun l
T quan im qun l, mt mng c th l mng t nhn m s hu bi mt h thng t qun l
n v khng th c truy cp t bn ngoi min logic v vt l ca n. Mt mng c th l mng
cng cng khi n c truy cp bi tt c.
Cu trc mng
Cc mng my tnh c th c phn bit vo trong cc kiu khc nhau nh Client-Server,

ngang bng hoc lai (hn hp), ph thuc vo cu trc ca n.
C th c mt hoc nhiu h thng ng vai tr nh server. Cc h thng khc l client, a

cc yu cu ti server phc v cc ngh. Server nhn v x l cc yu cu ca client.
Hai h thng c th c kt ni ngang bng theo kiu Point-to-Point hoc back-to-back.

Chng cng mt mc v c gi l ngang bng.
C th c mt mng hn hp m bao gm c hai kiu cu trc trn.
Cc ng dng mng
Cc h thng my tnh v cc thit b ngoi vi c kt ni t chc thnh mt mng. Chng
cung cp cc li th sau:
Chia s ngun ti nguyn nh my in v cc thit b lu gi.
Trao i thng tin (email, FTP).
Chia s thng tin bng vic s dng web hoc internet.
Tng tc vi ngi s dng khc s dng cc trang web ng.
in thoi IP
Video cuc hp
in ton song song
Th tn ngay lp tc (instant messaging)
Cc loi mng my tnh trong DCN

Trang 9

Hiu theo ngha chung, cc mng c phn bit da trn kt ni theo khong khng gian ca
chng. Mt mng c th c khong cch nh bng vi in thoi ca bn v Bluetooth tai nghe
ca n v ln nh mng internet, tri rng ton th gii.
Mng khu vc c nhn (PAN) trong DCN

Mt mng khu vc c nhn (PAN) l mt mng nh nht ca c nhn ngi s dng. N c th
bao gm Bluetooth. PAN c dy kt ni di ti 10 mt. PAN c th bao gm bn phm v chut
my tnh khng dy, cc Bluetooth, my in khng dy v cc iu khin t xa.
V d, Piconet l mt mng khu vc c nhn Bluetooth m c th cha ti 8 thit b c kt ni

vi nhau theo loi chnh-ph.
Mng khu vc ni b (LAN) trong DCN

Mt mng my tnh kt ni bn trong mt ta nh v qun l di h thng qun tr n c gi
chung nh l mt mng khu vc ni b (LAN). Thng thng th LAN tri rng cc vn phng ca
t chc, cc trng hc. S lng cc h thng c kt ni trong LAN c th a dng t t nht 2
cho ti nhiu nht l 16 triu.
LAN cung cp mt cch hu ch vic chia s ngun ti nguyn gia nhng ngi s dng. Cc
ngun ti nguyn nh cc my in, cc file trn server, v internet l d dng c th chia s trong
cc my tnh.
Trang 10
LAN c to thnh t cc thit b mng v thit b tuyn c gi tr r. N c th bao gm cc

server ni b phc v lu gi cc file v cc ng dng c chia s ni b khc. N hu nh iu
hnh trn cc a ch IP t nhn v khng bao gm thit b tuyn nng. LAN lm vic di min ni
b v c kim sot bi trung tm gia.
LAN s dng hoc cng ngh Ethernet hoc cng ngh Token-ring. Ethernet c s dng rng
ri trong cng ngh LAN v s dng cu trc ngi sao, trong khi Token-ring th him khi c nhn
thy.
LAN c th c kt ni bng dy, khng dy, hoc c hai.
Mng khu vc trung tm (MAN) trong DCN

MAN ni chung m rng tri qua mt thnh ph nh mng cp TV. N c th trong loi Ethernet,
Token-ring hoc giao din d liu c phn phi bi si quang (cp quang) FDDI.
Metro Ethernet l mt dch v m c cung cp bi ISPs. Dch v ny cho nhng ngi s dng
ca n kh nng m rng mng khu vc ni b. V d, MAN c th gip mt t chc kt ni
tt c cc vn phng ca n trong mt thnh ph.
Trang 11
Xng sng ca MAN l cc cp quang cng sut v tc cao. MAN lm vic gia mng khu
vc ni b LAN v mng khu vc rng WAN. MAN cung cp ng link cho cc mng LAN ti cc
mng WAN hoc internet.
Mng khu vc rng (WAN) trong DCN

Nh tn gi cp, WAN bao ph mt khu vc rng m c th kt ni qua cc tnh v ngay c
mt quc gia. Ni chung, cc mng vin thng l WAN. Nhng mng ny cung cp s kt ni ti
cc mng MAN v LAN. T khi chng c trang b vi ng trc tc cao, cc mng WAN s
dng cc thit b mng rt t .
Trang 12
WAN c th s dng cc cng ngh tin tin nh Asynchronous Transfer Mode (ATM), Frame
Relay, v mng quang hc ng b (SONET). WAN c th c qun l bi nhiu chnh quyn
khc nhau.
Mng internet trong DCN

Mt mng ca cc mng c gi l internet. N l mng ln nht tn ti trn hnh tinh ca chng
ta. Mng internet ny kt ni rng ri tt c cc mng WAN v n c th c s kt ni ti cc mng
LAN v mng Home. Internet s dng b giao thc TCP/IP v s dng IP nh giao thc a ch
ca n. Ngy nay, internet c thc hin rng ri s dng IPv4. Bi v s thiu cc khong
khng gian a ch, n dn dn chuyn t IPv4 sang IPv6.
Internet cho nhng ngi s dng kh nng chia s v truy cp ti lng thng tin khng l trn
ton th gii. N s dng WWW, FTP, cc dch v th in t, audio v video. Ti mc ln,
internet lm vic trn loi mu client-server.
Internet s dng ng trc tc cao ca cc si cp quang. kt ni cc chu lc khc nhau,
cc si c t di bin m c bit nh cp thng tin ngm.
Internet c trin khai rng ri trn mng ton cu WWW s dng cc trang c kt ni HTML
v c th truy cp bi phn mm khch c bit nh cc trnh duyt web. Khi mt ngi s dng
yu cu mt trang s dng mt vi trnh duyt t trn web server bt c u trn th gii, web
Trang 13

server phn hi cc trang HTML chnh xc theo yu cu. Vic tr hon trao i thng tin ny xy ra
mc rt thp.
Internet phc v nhiu yu cu m lin quan ti cc kha cnh ca i sng. Mt trong s chng l:
Cc website
E-mail
Tin nhn
Blog
a phng tin x hi
Marketing
Lin kt mng
Chia s ngun ti nguyn
Audio and Video
Cc cng ngh mng LAN trong DCN

Di y chng ti a ra cc miu t ngn gn v cc cng ngh mng LAN:
Cng ngh Ethernet trong DCN

Ethernet l cng ngh LAN c trin khai rng ri. Cng ngh ny c pht minh bi Bob
Metcalfe v D.R.Boggs vo nm 1970. N c tiu chun ha trong IEEE 802.3 nm 1980.
Ethernet chia s phng tin. Mng m s dng phng tin c chia s c xc sut cao s va
chm d liu. Ethernet s dng cng ngh CSMA/CD (Carrier Sense Multi Access/Collision
Detection) pht hin cc s va chm. Khi xy ra s va chm trong Ethernet, tt c cc host ca
n quay tr li, ch i trong mt khong thi gian ngu nhin, v sau truyn ti li d liu.
B lin kt Ethernet l th giao din mng c trang b vi a ch 48 bit MAC. iu ny gip cho
cc thit b Ethernet khc nhn din v giao tip mi cc thit b iu khin t xa trong Ethernet.
Ethernet truyn thng s dng cc chi tit k thut 10BASE-T. S 10 y l ch tc 10MBPS,
BASE i din cho di gc, v T i din cho Thick Ethernet. 10BASE-T Ethernet cung cp tc
truyn ti ln ti 10MBPS v s dng cp ng trc hoc cp cp xon Cat-5 vi b lin kt RJ-5.
Ethernet theo kiu cu trc ngi sao vi di di ln ti 100 mt. Tt c cc thit b c kt ni
ti mt trc/nt chuyn i trong mt kiu ngi sao.
Trang 14
Cng ngh Fast-Ethernet trong DCN

phc v cc nhu cu ang ni ln nhanh chng v cc cng ngh phn mm v phn cng,
Ethernet m rng chnh n thnh Fast-Ethernet. N c th chy trn UTP, cp quang, v khng
dy. N c th cung cp tc ln ti 100MBPS. Tiu chun ny c t tn l 100BASE-T
trong IEEE 803.2 s dng cp xon i Cat-5. N s dng k thut CSMA/CD cho phng tin
c lin kt bng dy chia s trong cc host v cng ngh CSMA/CA (CA l vit tt ca
Collision Avoidance-trnh s va chm) cho mng LAN khng dy.
Fast Ethernet trn cp c nh r di tiu chun 100BASE0FX m cung cp tc ln ti 100
MBPS trn cp. Ethernet thng qua cp c th c m rng ti 100 mt trong ch ghp i
mt na (half-duplex) v c th t chiu di ln nht ln ti 2000 mt trong ch full-duplex
thng qua cc si ch .
Cng ngh Giga-Ethernet trong DCN

Sau khi c gii thiu vo nm 1995, Fast-Ethernet ch tn ti trng thi tc cao ca n ch
trong 3 nm ti khi Giga-Ethernet c gii thiu. Giga-Ethernet cung cp tc ln ti 1000 mbit
mi giy. IEEE 802.3ab tiu chun ha Giga-Ethernet kt ni qua UTP s dng cc cp Cat-5, Cat5e v Cat-6. IEEE 802.3ah nh ngha Giga-Ethernet kt ni qua si.
Cng ngh Mng LAN o trong DCN

LAN s dng Ethernet m lm vic trn phng tin c chia s. Phng tin c chia s
trong Ethernet to mt min Broadcast (pht thanh)n v mt min Collision (va chm) n. S
gii thiu ca cc thit b chuyn mch ti Ethernet c g b vn min va chm n v
mi thit b kt ni chuyn i cc cng vic trong phm vi min va chm n ring bit ca n.
Nhng ngay c khi cc thit b chuyn mch cng th phn chia mt mng thnh cc min
Broadcast ring bit.
Mng LAN o l mt gii php phn chia mt min Broadcast n thnh nhiu min Broadcast.
Host trong mt VLAN khng th giao tip ti mt host khc. Theo mc nh, tt c cc host c
t trong cng mt VLAN.
Trang 15
Trong s trn, cc VLAN khc nhau c phn bit trong cc mu khc nhau. Cc host trong
mt VLAN, ngay c khi c kt ni trn cng mt Switch cng khng th tm thy hoc giao tip
vi host khc trong VLAN khc. VLAN l cng ngh tng-2 (Layer-2) m lm vic gn gi trn
Ethernet. gi cc gi thng tin gia hai VLAN khc nhau, mt thit b Layer-3 nh Router c
yu cu.
Khng gian mng trong DCN

Mt Khng gian mng (Network Topology) l s sp xp m vi n cc h thng my tnh v cc
thit b mng c kt ni vi nhau. Khng gian c th nh r c hai kha cnh vt l v logic ca
mng. C khng gian vt l v logic c th l cng hoc khc nhau trong cng mt mng.
Trang 16
Cu trc khng gian Point-to-Point trong DCN

Cc mng ngang hng Point-to-Point cha hai host nh my tnh, b chuyn mch hoc cc cu
dn, cc server c kt ni back-to-back s dng mt phn n ca cp. Thng th, vic tip
nhn kt thc ca mt host c kt ni gi s kt thc khc v ngc tr li.
Nu cc host c kt ni mt cch logic theo kiu ngang hng point-to-point, th khi c th c

nhiu thit b trung gian. Nhng cc host cui khng nhn bit c cc mng nm di v nhn
thy nhau khi chng c kt ni mt cch trc tip.
Cu trc khng gian bus (Bus Topology) trong DCN

Trong cu trc ny, tt c cc thit b chia s cc ng kt ni hoc cp n. Cu trc khng gian
bus c vn trong khi nhiu host gi d liu ti cng mt thi im. V th, cu trc khng gian
bus hoc s dng cng ngh CSMA/CD hoc nhn ra mt host nh Bus Master gii quyt vn
ny. N l mt mu n ca mng ni m mt s hng hc ca mt thit b khng nh hng
ti cc thit b khc. Nhng s hng hc ca ng dy thng tin c chia s c th lm cc
thit b khc dng hot ng cc chc nng ca n.
Trang 17

C cc u cui ca bng tn c chia s c cc thit b terminator u dy cui. D liu c
gi ch theo mt hng v ngay sau khi n tin ti cui, terminator g b d liu khi ng dy
dn.
Cu trc ngi sao (Star Topology) trong DCN

Tt c cc host trong cu trc ngi sao c kt ni ti mt thit b trung tm, c bit nh l
hub, s dng mt s kt ni point-to-point. C s tn ti mt s kt ni point-to-point gia cc host
v hub. Thit b hub c th l bt k thit b no sau y:
Thit b Tng-1 nh hub hoc b lp
Thit b Tng-2 nh cng chuyn mch hoc cu ni
Thit b Tng-3 nh cc ng dn (router) hoc cng.
Nh trong mt cu trc Bus Topology, hub hot ng nh l mt im n ca s hng hc. Nu

hub li, s lin kt ca tt c cc host ti cc host khc s gp trc trc. Mi s trao i thng tin
gia cc host, ch din ra thng qua hub. Cu trc ngi sao khng t khi lin kt thm mt
host, ch mt cp c yu cu v vic nh hnh l n gin.
Trang 18
Cu trc vng trn (Ring Topology) trong DCN

Trong cu trc vng trn, mi thit b host kt ni chnh xc vi hai thit b khc, to mt cu trc
hnh trn. Khi mt host c gng giao tip hoc gi thng tin n mt host m khng lin k vi
n, d liu i qua tt c cc host trung gian. kt ni thm mt host trong cu trc tn ti,
ngi qun l c th ch cn thm mt cp.
Vic hng hc ca bt k host no s gy ra vic ton cu trc gp s c. V th, mi kt ni trong

vng l mt im li. C nhiu phng thc m dng cc vng d phng.
Cu trc hn n (Mesh Topology) trong DCN

Trong kiu cu trc ny, mt host c kt ni ti mt hoc nhiu host. Kiu cu trc ny c cc
host lin kt point-to-point vi mi host khc hoc c th cng c cc host m ch kt ni vi mt
vi host theo kiu point-to-point.
Trang 19
Cc host trong cu trc Mesh cng lm vic nh l rle cho cc host khc m khng c cc kt ni
trc tip point-to-point. Cu trc Mesh c hai kiu sau:
Hn n ton phn (full mesh): Tt c cc host c kt ni point-to-point ti mi host khc

trong mng. V th cho mi host mi, n(n-1)/2 kt ni c yu cu. N cung cp cu trc
mng thch hp nht trong tt c cc cu trc mng.
Hn n cc b (partially mesh): Khng phi tt c cc host c kt ni point-to-point ti

mi host khc. Cc host kt ni vi nhau trong mt vi kiu ty . Cu trc ny tn ti ni
m chng ta cn cung cp s tin cy ti mt vi host ngoi cu trc.
Cu trc cy (Tree Topology) trong DCN

Cng c bit nh l cu trc phn th bc, y l mu ph bin nht ca cu trc mng c
s dng hin ti. Cu trc ny m phng cu trc ngi sao v k tha cc c tnh ca cu trc
bus.
Cu trc ny phn chia mng thnh nhiu mc/tng ca mng. Phn ln trong cc mng LAN, mt
mng c chia thnh ba kiu thit b mng. Mc thp nht l tng truy cp (access-layer) m my
tnh c th nh km. Mc trung c bit nh l mc phn phi, m lm vic nh l b iu chnh
mediator gia mc cao hn v mc thp hn. Mc cao nht c bit nh l tng li, v l im
trung tm ca mng, v d: gc ca cy m t cc nhnh r ra.
Trang 20
Tt c cc host lng ging c kt ni point-to-point gia chng. Tng t nh cu trc bus, nu

mt gc b trc trc th ton b mng cng s b li. Mc d n khng l im li n. Mi kt ni
phc v nh l mt im li, vic thiu st m phn mng h thng thnh on n v (on khng
th chia ra c).
Daisy Chain trong DCN

Cu trc ny kt ni tt c cc host trong mt kiu tuyn. Tng t vi cu trc Vng trng, tt c
cc host c kt ni vi ch hai host, tr host kt thc. Ngha l, nu host kt thc trong chui
Daisy c kt ni th khi n tr thnh cu trc Vng trn.
Mi kt ni trong cu trc chui Daisy i din cho mt im li n. Mi lin kt li chia mng

thnh hai on. Mi host trung gian lm vic nh l rle cho cc host trung gian ca n.
Cu trc lai (Hybrid Topology) trong DCN

Mt cu trc lai l mt cu trc m thit k ca n cha nhiu hn mt cu trc. Cu trc lai k
tha cc u v nhc im ca tt c cc cu trc trn.
Trang 21
Hnh nh trn i din cho mt cu trc lai ty . Cc cu trc kt ni c th cha cc thuc tnh
ca cc cu trc ngi sao, vng trn, bus, v chui Daisy. Hu ht cc mng WAN c kt ni vi
ngha ca cu trc vng trn kp (dual-ring) v cc mng c kt ni ti chng l hu ht cc cu
trc ngi sao. Internet l v d in hnh nht ca cu trc lai.
M hnh mng my tnh trong DCN

Ngnh k thut xy dng mng l mt nhim v phc tp, m lin quan n phn mm, xy dng
chip, phn cng, mch in t. d dng hn cho vic xy dng mng, khi nim mng c
phn chia thnh nhiu tng. Mi tng tham gia vo mt nhim v c th v c lp vi cc tng
khc. Nhng ni chung, hu ht tt c cc nhim v xy dng Subnet (Mng ph) thuc vo tt c
cc tng. Cc tng chia s d liu gia chng v chng ch ph thuc vo ln nhau nhn u
vo v gi u ra.
Cc tc v c phn tng trong DCN

Trong cu trc tng ca m hnh mng, mt tin trnh mng tng th c phn chia thnh cc
nhim v nh. Mi nhim v nh sau c ch nh ti mt tng c th m lm vic theo chuyn
mn ti mt tin trnh vi ch mt nhim v. Mi tng ch thc hin mt cng vic c th.
Trang 22

Trong h thng trao i thng tin c phn tng, mt tng ca mt host gii quyt mt nhim v
c thc hin bi hoc c thc hin bi tng ngang hng ca n trn host iu khin t xa.
Nhin v c bt u c th bi tng thp nht hoc bi tng cao nht. Nu nhim v c bt
u bi tng cao nht, n c thng qua cc tng di thc hin vic x l tin trnh xa hn
na. Tng thp nht thc hin iu tng t, n x l nhim v v thng qua cc tng thp hn.
Nu nhim v c bt u bi hu ht cc tng, th khi path o ngc c to ra.
Mi tng chung vi nhau tt c cc phng tin thc hin, cc giao thc, v cc phng thc m
n yu cu chy cc phn ca nhim v. Tt c cc tng xc nh i tc bi phn u v phn
cui kt ni.
M hnh OSI trong DCN

Mt mng lin kt h thng m l mt tiu chun m cho tt c cc h thng giao tip. M hnh
OSI c xy dng bi T chc tiu chun quc t (ISO). M hnh ny c 7 tng sau:
Trang 23
Tng ng dng (Application Layer): Tng ny c trch nhim cung cp giao din ti ng
dng ngi dng. Tng ny bao quanh cc giao thc m tng tc mt cch trc tip vi
ngi s dng.
Tng trnh by (Presentation Layer): Tng ny xc nh cch d liu trong nh dng t

nhin ca host iu khin t xa nn c trnh by trong nh dng t nhin ca host.
Tng phin (Session Layer): Tng ny duy tr cc phin gia cc host t xa. V d, sau khi
vic xc thc ngi dng/mt khu c thc hin, host t xa duy tr cc phin ny trong
chc lt v khng yu cu li vic xc thc trong khng thi gian kt ni.
Tng vn chuyn (Transport Layer): Tng ny chu trch nhim cho s phn phi end-toend gia cc host.
Tng mng (Network Layer): Tng ny chu trch nhim v ch nh a ch v a ch duy

nht cc host trong mt mng.
Tng lin kt d liu (Data Link Layer): Tng ny chu trch nhim c v vit d liu t
v trn cc ng dn. Cc li kt ni c pht hin ti tng ny.
Tng vt l (Physical Layer): Tng ny nh ngha phn cng, dy cp, u ra,.
Trang 24
M hnh Internet trong DCN

Internet s dng dy giao thc TCP/IP, m c bit nh l dy internet. Dy ny nh ngha kiu
M hnh Internet m cha cu trc c 4 tng. M hnh OSI l m hnh giao tip chung nh M hnh
Internet l nhng g m internet s dng cho tt c giao tip ca n. Internet l c lp trong cu
trc mng phn tng ca n v th l M hnh ca n. M hnh ny c cc tng sau:
Tng ng dng (Application Layer): Tng ny xc nh giao thc m cho ngi s dng
kh nng tng tc vi mng. V d: FTP, HTTP.
Tng vn chuyn (Transport Layer): Tng ny nh ngha cch d liu nn c trao i

gia cc host. Giao thc chnh ti tng ny l Giao thc iu khin truyn ti (TCP). Tng
ny m bo d liu phn phi gia cc host theo th t v chu trch nhim cho s phn
phi end-to-end.
Tng Internet: Giao thc internet (IP) lm vic trn tng ny. Tng ny l phng tin cho
vic to a ch v nhn ra host. Tng ny nh ngha tuyn (routing).
Tng lin kt (Link Layer): Tng ny cung cp k thut ca gi v nhn d liu thc s.
Khng ging i tc M hnh OSI ca n, tng ny l c lp vi cu trc mng v phn
cng nm di.
Bo mt mng my tnh trong DCN

Trong nhng ngy u tin ca internet, s s dng ca n c gii hn trong cc trng i
hc v lnh vc qun s cho mc ch nghin cu v pht trin. Sau , khi tt c cc mng c
sp nhp vi nhau v cu thnh internet, d liu s dng trao i thng qua mng trao i cng
cng. Con ngi thng c th gi d liu v c th l nhy cao nh cc giy y nhim ngn
Trang 25

hng, tn ti khon s dng, mt khu, ti liu c nhn, cc chi tit mua hng trn mng hoc cc
ti liu th tn tm s.
Tt c cc mi e da ti s bo mt l c ch tm, v d: chng ch xy ra nu c tnh kch hot.
Cc mi e da ti s bo an c th c phn chia thnh cc loi sau:
S gin on
S gin on l mt mi e da ti s bo an m trong tnh kh dng ca cc ngun ti
nguyn b nh km. V d: mt ngi s dng khng th truy cp vo server m b chn.
Vi phm quyn ring t (privacy breach)

Trong mi e da ny, quyn ring t ca mt ngi s dng b dung ha (b can thip).
Mt ai , ngi m khng c cp quyn ang truy cp vo d liu gi hoc nhn bi
mt ngi s dng c xc nhn.
Tnh nguyn vn
Kiu e da ny bao gm bt c s sa i hoc chnh sa no trong ni dung ban u
ca thng tin. Tp nh km chn v nhn d liu c gi bi ngi gi v sau tp
nh km hoc chnh sa hoc to ta d liu li v gi ti ngi nhn. Ngi nhn nhn
d liu m inh ninh rng n c gi bi ngi gi ban u.
Tnh xc thc
Mi e da ny xut hin khi mt nh km hoc mt ngi e da ti s bo an, gi danh
mt ngi chn tht v truy cp vo cc ngun ti nguyn hoc giao tip vi nhng ngi
s dng chn tht khc.
Khng cng ngh no trong th gii ngy nay c th cung cp tnh an ton l 100%. Nhng nhng
bc c th c xy dng bo v d liu trong khi n di chuyn trong mt mng khng an
ton hoc internet. Cng ngh c s dng ph bin nht hin nay l Cryptography-mt m hc.
Trang 26
Mt m l mt cng ngh mt m ha d liu thun vn bn m lm cho n kh hiu v bin

dch. C mt s thut ton mt m ha c sn ngy nay nh sau:
Kha mt (secret key)
Kha cng cng (public key)
Tiu ha tin (message digest)
Mt m ha kha Private trong DCN

C ngi gi v ngi nhn c mt kha mt. Kha ny c s dng mt m ha d liu ti
im cui ca ngi gi. Sau khi d liu c mt m ha, n c gi trn min cng cng ti
ngi nhn. Bi v ngi nhn bit v c kha mt ny, cc gi d liu c mt m ha c th
d dng c gii m.
V d ca Mt m ha kha mt l Tiu chun m ha d liu (DES). Trong mt m ha kha mt,
n c yu cu c mt kha ring cho mi host trn mng, iu ny lm cho n kh qun
l.
Mt m ha kha Public trong DCN

Trong h thng mt m ha ny, mi ngi s dng c kha mt ring v n khng c trn min
chia s. Kha mt ny khng bao gi c tit l trn min cng cng. Song song vi kha mt,
mi ngi s dng c kha cng cng ring. Kha cng cng lun lun c to vi mc ch
chung v c s dng bi ngi gi mt m ha d liu. Khi ngi dng nhn d liu c
mt m ha, anh ta c th d dng gii m n bi vic s dng kha mt ring ca mnh.
V d ca Mt m ha kha cng cng l Rivest-Shamir-Adleman (RSA).
Trang 27
Tiu ha tin (Message Digest) trong DCN

Trong phng thc ny, d liu thc khng c gi, thay cho , mt gi tr bm (hash) c
tnh ton v c gi. im cui ngi s dng khc, tnh ton gi tr bm ring ca n v so
snh vi gi tr va nhn. Nu c hai gi tr bm c kt ni, th khi n chp nhn, nu khng
th n s loi b.
V d ca Tiu ha tin (Message Digest) l MD5 hashing. N c s dng rng ri trong vic xc
nhn, ti ni ny mt khu ngi s dng c kim tra vi mt khu lu trn server.
Gii thiu Tng vt l trong DCN

Tng vt l trong m hnh OSI ng vai trong tng tc vi phn cng thc v ra tn hiu lnh k
thut. Tng vt l ch l tng ca m hnh OSI m gii quyt s kt ni vt l ca hai trm khc
nhau. Tng ny nh ngha thit b phn cng, cp, dy c s dng din t cc tn hiu nh
phn.
Tng vt l cung cp dch v ca n cho tng d liu-kt ni. Tng d liu-kt ni tham gia vo cc
khung trong tng vt l. Tng vt l bin i chng sang cc xung in t, m biu din d liu nh
phn. D liu nh phn sau c gi qua cc phng tin c dy hoc khng dy.
Cc tn hiu
Khi d liu c gi qua trung gian tng vt l, u tin n cn bin i thnh cc tn hiu in t.
D liu chnh n c th l analog (tng t) nh ging ni con ngi, hoc s nh file trn a. C
d liu analog v d liu s c th c biu din trong cc tn hiu s hoc tng t.
Tn hiu s
Tn hiu s l ri rc v biu din dy ca cc mch in p. Cc tn hiu s c s dng
trong h thng mch in ca h thng my tnh.
Tn hiu tng t
Tn hiu tng t l trong kiu sng lin tc v c biu din bi cc sng in t lin
tc.
Trang 28
Suy truyn (transmission impairment)

Khi tn hiu di chuyn qua cc thit b trung gian, chng c khuynh hng yu i. iu ny l do
nhiu l do sau:
S suy yu
ngi nhn bin dch d liu mt cch chnh xc, tn hiu phi khe. Khi tn hiu di
chuyn qua cc thit b trung gian, n c khuynh hng yu i. Khi n ph qua mt khong
cch no , n khng cn mnh na.
S phn tn
Khi tn hiu di chuyn qua cc thit b trung gian, n c khuynh hng tri rng v ln
nhau. phn tn ph thuc vo vic tn sut c s dng.
S bin dng chm

Cc tn hiu c gi qua trung gian vi tc v tn s c xc nh trc. Nu tc
v tn sut tn hiu khng kt ni, c cc kh nng l tn hiu n ch vi kiu ty . Trong
k thut s, iu ny rt quan trng khi m mt s bit n ch nhanh hn so vi nhng bit
c gi trc .
Noise
S xo trn ngu nhin hoc s bin ng trong tn hiu tng t hoc s c gi l
Noise trong tn hiu, m c th lm sai lch cc thng tin thc t c mang. Noise c th
c c trng trong mt trong cc hng sau:
o Noise nhit
Nhit rung trong cc dy dn in t trung gian c th gy Noise trong phng tin.

n mt mc nht nh, Noise nhit l khng th trnh khi.
o S iu bin tng h
Khi nhiu tn s chia s mt phng tin, s giao thoa ca chng c th gy Noise

trong thit b trung gian. Noise iu bin tng h xut hin nu hai tn s ang
chia s mt thit b trung gian v mt trong s chng c di qu mc hoc thnh
Trang 29

phn ca chnh n khng thc hin chc nng chnh xc, th khi tn sut tng
hp c th khng c phn pht nh mong i.
o Xuyn m
Loi Noise ny xy ra khi mt tn hiu ngoi lai xm nhp vo phng tin. iu

ny l bi v tn hiu trong mt thit b trung gian b nh hng bi tn hiu trong
thit b trung gian th hai.
o Xung lng xung
Noise ny c gii thiu bi v nhng nhiu khng thng xuyn nh in hc,

mch ngn, hoc cc thnh phn li. D liu s hu nh b nh hng bi loi
Noise ny.
Phng tin truyn ti

Phng tin m qua thng tin gia hai h thng my tnh c gi, gi l phng tin truyn
ti. Phng tin truyn ti c hai dng:
Phng tin c ch ng
Tt c cc dy dn/cp trao i thng tin l phng tin c ch ng, nh UTP, cp
ng trc v si quang. Trong phng tin ny, ngi gi v ngi nhn c kt ni mt
cch trc tip v thng tin c gi thng qua chng.
Phng tin khng c ch ng

Khng dy hoc khng gian m c coi l phng tin khng c ch ng, bi v
khng c s kt ni no gia ngi gi v ngi nhn. Thng tin tri rng trong khng kh
v mt ai bao gm ngi nhn thc s c th thu thp c thng tin.
Dung lng knh

Tc truyn ti ca thng tin c gi l dung lng bng tn. Chng ta tnh ton n nh l t l
d liu trong th gii k thut s. N ph thuc vo nhng yu t sau:
B rng bng thng: Gii hn k thut ca phng tin c s.
T l li: S nhn thng tin khng chnh xc do Noise.
Trang 30
M ha: S mc c s dng cho tn hiu.
K thut dn/ghp (multiplexing)

L mt k thut trn v gi nhiu lung d liu qua mt thit b trung gian n. K thut ny yu
cu phn cng h thng, m gi l b ghp knh (MUX), dn cc lung v gi chng trn mt
thit b trung gian, b gii knh (DMUX) nhn thng tin t thit b trung gian v phn pht cho
cc ch n khc nhau.
S chuyn mch
Chuyn mch l mt k thut m bi n d liu/thng tin c gi t ngun ti ch m khng
c kt ni trc tip. Cc mng c cc thit b lin kt vi nhau, m nhn d liu t cc ngun
c kt ni trc tip, lu gi d liu, phn tch n v sau chuyn n ti thit b lin kt k tip
gn nht vi ch n.
Chuyn mch c th c phn loi nh sau:
Truyn ti k thut s (digital) trong DCN

D liu hoc thng tin c th c lu trong hai cch, tng t hoc k thut s. mt my tnh
s dng d liu, th d liu phi dng k thut s ri rc. Tng t nh d liu, cc tn hiu c
th trong dng tng t hoc k thut s. truyn ti d liu theo k thut s, u tin n cn
bin i ti dng s.
Bin i s ti s (digital-to-digital) trong DCN

Phn ny gii thch cch bin i d liu s sang tn hiu s. N c th c thc hin theo hai
cch, m ha dng v m ha khi. Cho tt c cc giao tip, m ha dng l cn thit trong khi
m ha khi th khng bt buc.
Trang 31
M ha dng d liu trong DCN

Tin trnh bin i d liu s thnh cc tn hiu s c gi l m ha dng d liu. D liu s
c tm thy trong nh dng nh phn. N c biu din (lu gi) bn trong bi dy cc s 1 v
0.
Tn hiu s c biu din bi tn hiu ri rc m miu t cho d liu s. C 3 kiu gin m ha

dng c sn nh hnh di y:
M ha n cc uni-polar trong DCN

Cc gin m ha n cc s dng mc in p n biu din d liu. Trong trng hp
ny, biu din m nh phn 1, in p cao c truyn ti v biu din 0, khng c in p
c truyn ti. N cng c gi l Unipolar-Non-return-to-zero, bi v khng c iu kin khc,
n ch biu din hoc 1 hoc 0.
Trang 32
M ha c cc trong DCN
Gin m ha c cc s dng nhiu mc in p biu din cc gi tr nh phn. m ha ny
c 4 kiu sau:
Polar Non-Return to Zero (Polar NRZ)

N s dng hai mc in p khc nhau biu din cc gi tr nh phn. Ni chung,
in p khng nh biu din 1 v in p ph nh biu din 0. N cng l NRZ bi v
khng c iu kin khc.
Gin NRZ c hai bin th: NRZ-L v NRZ-l.
Trang 33
NRZ-L thay i mc in p khi mt bit khc c bt gp, trong khi NRZ-l thay i
mc in p khi 1 c bt gp.
Return to Zero (RZ)

Vn vi NRZ l ngi nhn khng th gii quyt khi mt bit kt thc v khi bit k tip
c bt u, trong khi ng h xung ngi gi v ngi nhn khng c ng b.
Trang 34
RZ s dng 3 mc in p, in p khng nh biu din 1, in p ph nh biu

din 0 v in p 0 khng biu din g. Cc tn hiu thay i trong cc bit ch khng phi
gia cc bit.
Manchester
Gin m ha ny l mt s kt hp ca RZ v NRZ-L. Thi gian bit c phn chia
thnh hai na. N truyn qua phn gia ca bit v thay i pha khi mt bit khc c
nhp.
Manchester vi sai (differential)

Gin m ha ny l s kt hp ca RZ v NRZ-l. N cng qua phn gia ca bit nhng
thay i pha ch khi 1 c nhp.
M ha song cc (bipolar encoding) trong DCN

M ha song cc s dng ba mc in p: khng nh, ph nh v khng. in p 0 i din cho
bit nh phn 0, bit nh phn 1 c biu din bi s thay i ca in p khng nh v ph nh.
Trang 35
M ha khi trong DCN

m bo s chnh xc ca khung d liu c nhn, cc bit cn d tha c s dng. V d,
trong s ngang hng, mt bit tng ng c thm to php tnh thm 1 giy trong khung
ngang hng. Theo cch ny, s lng bit u tin c tng ln. N c gi l m ha khi.
M ha khi c biu din bi k hiu gch cho, mB/nB. N c ngha l, khi m bit c thay
th bng khi n bit vi n>m. m ha khi c thit lp theo 3 bc:
Phn tch;
Thay th;
Kt ni.
Sau khi m ha khi c thc hin, n l dng c m ha cho vic truyn ti.
S bin i t d liu tng t sang K thut s trong

DCN
Microphones to m thanh tng t v camera to cc video tng t, m c xem nh l cc
d liu tng t. bin i d liu tng t ny qua cc tn hiu k thut s, chng ta cn
chuyn i tng t thnh k thut s.
D liu analog l mt lung d liu lin tc trong dng sng, trong khi d liu k thut s l ri
rc. chuyn i sng tng t thnh d liu k thut s, chng ta s dng B bin iu m
xung PCM (Pulse Code Modulation).
Trang 36

PCM l mt trong nhng phng thc c s dng ph bin nht chuyn i d liu tng t
thnh d liu k thut s. N bao gm ba bc:
Ly mu (Spamling)
Lng t ha (Quantization)
M ha (Encoding)
Ly mu
Tn hiu tng t c ly mu mi khong T. Hu ht cc nhn t quan trng trong mu l t l

m ti tn hiu tng t c ly mu. Theo thuyt Nyquist, t l mu phi l t nht 2 ln trong
tn s ca tn hiu.
Lng t ha trong DCN
Vic ly mu em li cc trng ri rc t tn hiu tng t lin tc. Mi mu ri rc ch bin

ca tn hiu tng t ti mt thi im. Lng t ha c thc hin gia gi tr ln nht v gi tr
nh nht ca bin . Lng t ha l gi tr gn ng ca gi tr tng t tc thi.
Trang 37
M ha
Trong vic m ha, mi gi tr gn ng sau c bin i thnh dng nh phn.
Cc ch truyn ti
Ch truyn ti quyt nh cch d liu c truyn ti gia 2 my tnh.D liu nh phn trong
mu 1s v 0s c th c gi bi mt trong hai cch khc nhau: Song song (Parallel) v Chui
(Serial).
Truyn ti song song
Cc bit nh phn c t chc vo trong cc nhm vi di c c nh trc. C ngi gi v

ngi nhn c kt ni song song vi s dng d liu cn bng. Cc my tnh phn bit gia th
t cao thp ca cc dng d liu. Ngi gi gi tt c cc bit cng mt lc trn tt c cc dng.
Bi v cc dng d liu l cn bng vi s bit trong mt nhm hay l khung d liu, mt nhm y
cc bit (khung d liu) c gi theo cch tng t. Li th ca truyn ti song song l tc
Trang 38

cao, cn vn ca n l chi ph v s dng cc dy dn, khi n l cn bng vi s bit c gi
theo cch song song.
Truyn ti theo dy (chui)

Trong truyn ti ny, cc bit c gi ln lt tng chui mt theo mt hng c thao tc sp
xp trc. Truyn ti theo chui ch yu cu mt knh giao tip.
Truyn ti theo chui c th l ng b hoc khng ng b.
Truyn ti theo chui khng ng b

N c t tn nh vy l bi v n khng quan trng v vn tnh ton thi gian (s phi hp
v thi gian). Cc bit d liu l cc mu ring v chng gip ngi nhn nhn ra c cc bit u
v cui. V d, mt bit 0 c t lm tin t trn mi byte d liu v mt hoc nhiu hn bit 1
c thm vo sau cui.
Hai khung d liu (cc byte) lin tc c th c mt khong cch gia chng.
Truyn ti theo chui ng b

Vn tnh ton thi gian trong truyn ti ng b l quan trng khi khng c phng tin no
theo sau nhn ra c cc bit d liu u v cui. Khng c phng thc mu hoc tin t/hu
t no. Cc bit d liu c gi trong ch tng lot m khng duy tr khong cch gia cc
byte. Lot n ca cc bit d liu c th cha mt s cc byte. V th, s tnh ton thi gian tr ln
rt quan trng.
N gip cho ngi nhn nhn ra c v phn bit cc bit vo trong cc byte. Li th ca truyn
ti ny l tc cao, v n khng c nhng tp ph nhn ra cc bit u v cui nh trong truyn
ti khng ng b.
Truyn ti tng t (analog) trong DCN

Trang 39

gi mt d liu k thut s qua mt phng tin tng t, n cn c chuyn i thnh tn
hiu tng t. C hai trng hp v nh dng d liu:
Bandpass:Cc b lc c s dng lc v truyn cc tn s. Mt bandpass l mt di tn s
m c th truyn qua b lc.
Low-pass: L mt b lc m truyn cc tn hiu tn s thp.
Khi d liu k thut s c bin i sang tn hiu tng t bandpass, n c gi l s chuyn
i t k thut s sang tng t. Khi tn hiu tng t low-pass c bin i thnh tn hiu tng
t bandpass, n c gi l s chuyn i t tng t thnh tng t.
S chuyn i t k thut s thnh tng t trong

DCN
Khi d liu t mt my tnh c gi ti mt my khc thng qua b phn truyn tng t, u
tin n c bin i thnh cc tn hiu tng t. Cc tn hiu tng t ny c chnh sa
phn nh d liu k thut s.
Mt tn hiu tng t c c trng bi bin , tn s v pha. C 3 kiu bin i t k thut s
thnh tng t:
iu ch s theo bin tn hiu (ASK)

Trong k thut chuyn i ny, bin ca tn hiu tng t c chnh sa phn nh
d liu nh phn.
Trang 40
Khi d liu nh phn biu din k s 1, bin c gi; nu khng th n c thit lp l

0. C tn s v pha gi nguyn nh trong tn hiu ban u c mang.
iu ch s theo tn s tn hiu (FSK)

Trong k thut ny, tn s ca tn hiu tng t c chnh sa phn nh d liu nh
phn.
Trang 41

K thut ny s dng 2 tn s, f1 v f2. Mt trong s chng, v d f1, c chn biu
din k s nh phn 1 v ci khi c s dng biu din k s 0. C bin v pha
ca sng mang c gi khng thay i.
iu ch s theo pha tn hiu (PSK)

Trong k thut ny, pha ca tn hiu ban u c chnh sa phn nh d liu nh
phn.
Khi mt k hiu nh phn mi c nhp vo, pha ca tn hiu c thay i. Bin v

tn s ca tn hiu ban u c gi nguyn.
iu ch pha cu phng (QPSK)

QPSK lc pha phn nh hai k s nh phn ti mt thi im. iu ny c thc hin
trong hai pha khc nhau. Lung d liu nh phn chnh c phn chia cn bng thnh hai
lung ph. D liu chui c chuyn i song song trong c hai lung d liu ph v sau
mi lung c chuyn i thnh tn hiu k thut s bng vic s dng k thut NRZ.
Sau , c hai tn hiu k thut s c hp nht li vi nhau.
S chuyn i t tng t sang tng t trong DCN

Cc tn hiu tng t c chnh sa biu din d liu tng t. S chuyn i ny c bit
n vi tn gi S bin iu tng t (Analog Modulation). S bin iu tng t c yu cu
khi bandpass c s dng. S bin i ny c th c thc hin theo 3 cch:
Trang 42
S bin iu bin
Trong s bin iu ny, bin ca tn hiu mang c chnh sa phn nh d liu
tng t.
Trang 43

S bin iu bin c thc hin bi mt in k nhn (multiplier). Bin ca tn hiu
bin iu (d liu tng t) c nhn bi bin ca tn s mang, m sau phn nh
d liu tng t.
Tn s v pha ca tn hiu mang c gi khng thay i.
S bin iu tn s
Trong k thut bin iu ny, tn s ca tn hiu mang c chnh sa phn nh s
thay i ca cc mc in p ca tn hiu bin iu (d liu tng t).
Bin v pha ca tn hiu mang c gi nguyn.
Trang 44
S bin iu pha
Trong k thut bin iu ny, pha ca tn hiu mang c bin iu phn nh s thay
i trong in p ca tn hiu d liu tng t.
S bin iu pha l tng t nh s bin iu tn s, nhng trong s bin iu pha, tn

s ca tn hiu mang khng c tng. Tn s ca tn hiu mang l tn hiu c thay i
phn nh s thay i trong bin ca tn hiu bin iu.
Phng tin truyn ti trong DCN

Trang 45

Phuong tin truyn ti chnh l phng tin vt l m qua trao i thng tin c din ra trong
mng my tnh.
Phng tin t tnh

Mt trong nhng cch tin li nht truyn ti d liu t mt my tnh ti my khc, c t trc
khi s ra i ca mng, l lu n trn mt vi phng tin lu gi v truyn vt l t mt trm
ny n trm khc. Mc d n l cch c trong th gii internet tc cao ngy nay, nhng khi
kch c ca d liu l ln, phng tin t tnh vn c s dng.
V d, mt ngn hng phi kim sot v truyn ti lng d liu ln v khch hng ca n, m lu
mt bn sao d phng ca n ti mt a im xa v a l cho mt s l do an ton v gi an
ton cho n trnh khi nhng tai ng khng bo trc. Nu ngn hng cn gi mt bn sao d
liu d phng ln, th khi vic truyn ti qua internet l khng to c s tin c. Cc kt ni
WAN c th khng h tr tc cao nh th. Ngay c khi chng h tr, th chi ph l qu cao v
khng thch hp.
Trong nhng trng hp nh vy, bn sao lu d liu d phng c lu trong cc bng t hoc
a t, v sau c gi ti nhng a im xa.
Cp xon i (twisted pair cable)

Cp xon i c to bi hai dy ng bc nha cch in xon li vi nhau to thnh mt
phng tin truyn thng duy nht. Trogn s hai dy ny, ch c mt dy mang tn hiu thc s v
dy cn li c s dng tip t. Cc xon gia cc dy l hu ch trong vic gim Noise
(nhiu in t) v nhiu xuyn m.
Trang 46
C hai kiu cp xon i:
Cp xon i c bo v (Shielded Twisted Pair - STP)
Cp xon i khng c bo v (Unshielded Twisted Pair - UTP)
Cc cp STP gm cp dy cp c bo v trong dy kim loi. iu ny lm cho n kh nng cao

hn chng li nhiu in t v nhiu xuyn m.
UTP c 7 loi, mt kiu ph hp vi tng cch s dng ring. Trong cc mng my tnh, Cat-5,
Cat-5e, v Cat-6 c s dng ph bin. Cc cp UTP c kt ni bi cc b kt ni RJ45.
Cp ng trc
Cp ng trc c hai dy ng . Dy li nm trong trung tm v n c lm bng dy dn c.
Li c bao trong v. Dy th hai c qun quanh trn v v c bao bc bng v cch in.
Tt c c bao bc bi v nha.
Trang 47
Bi v cu trc ca n, cp ng trc c kh nng truyn c cc tn hiu tn s cao hn cp

xon i. Cu trc c bc xung quanh cung cp cho n tnh khng cao vi nhiu in t v
nhiu xuyn m. Cc cp ng trc cung cp t l bng thng cao ti 450 mbps.
C 3 kiu cp ng trc, RG-59 (cp TV), RG-58 (Ethernet mng), v RG-11 (Ethernet dy). y
RG l vit tt ca Radio Government.
Cc cp c kt ni vi nhau bng cc b kt ni BNC v BNC-T. u kt ni BNC c s
dng kt thc dy ti cc im cui.
Cc dy dn in (Power Lines)
Power Line Communication (PLC) l cng ngh Layer-1 (Tng vt l) m s dng cc cp in
truyn ti cc tn hiu d liu. Trong PLC, d liu c bin iu c gi thng qua cc cp.
Ngi nhn trn b gii bin iu im cui v bin dch d liu.
Bi v cc dy dn in c trin khai rng ri, PLC c th lm cho tt c cc thit b in c
kim sot v gim st. PLC lm vic trong ch half-duplex (cho php tn hiu c truyn theo
c hai hng nhng khng cng mt lc).
Trang 48

C 2 kiu PLC:
PLC bng thng rng
PLC bng thng hp
PLC bng thng hp cung cp t l truyn ti d liu tn s thp ln ti 100 kbps, khi chng lm
vic ti mc tn s thp (3-5000 kHz). Chng c th tri rng vi kilomet.
PLC bng thng rng cung cp t l truyn ti d liu tn s cao ln ti 100 Mbps v lm vic ti
cc mc tn s cao (1.8-250 MHz). Chng khng th tri rng nh PLC hp.
Cp quang
Cp quang lm vic da trn cc c tnh ca nh sng. Khi nh sng chiu tia nng vo gc ti
hn, n c xu hng khc x gc 90 . c tnh ny c s dng trong cp quang. Li ca
si cp quang hc c lm t thy tinh hoc nha cht lng cao. T mt u ca n, nh sng
c pht ra, n i qua si v ti u khc cc my d nh sng d lung nh sng v chuyn i
chng thnh d liu in t.
Cp quang cung cp tc cao nht. N gm hai ch , mt l si ch n v hai l si a
ch . Si n ch c th mang mt tia nh sng n sc trong khi si a ch c kh
nng mang cc tia sng khc nhau ca nh sng.
Trang 49
Cp quang cng bao gm si n hng v song hng. kt ni v truy cp cc cp quang ,

cc b kt ni c s dng. N c th l Subscriber Channel (SC), Straight Tip (ST), hoc MTRJ.
Truyn ti khng dy trong DCN

Truyn ti khng dy l mt kiu ca phng tin khng iu khin. Giao tip khng dy khng
bao gm lin kt vt l c thit lp gia hai hoc nhiu thit b, giao tip theo phng thc
khng cn dy dn. Cc tn hiu khng dy c tri rng trong khng kh v c nhn v c
bin dch bi cc ngten thch hp.
Khi mt angten c nh km ti mch in t ca my tnh hoc thit b khng dy, n chuyn
i d liu tn hiu s thnh cc tn hiu khng dy v tri rng ra cc dy tn s ca n. B nhn
tn hiu trn u khc nhn nhng tn hiu ny v chuyn i chugns tr thnh tn hiu k thut s.
Mt phn nh ca quang ph in t c th c s dng cho truyn ti khng dy.
Trang 50
Truyn ti v tuyn
Tn s v tuyn l d dng hn to ra bi v bin sng rng ca n, n c th xuyn qua cc
bc tng v cc cu trc tng t. Cc sng v tuyn c th c bin sng t 1mm n
100,000 km v c tn s t 3 Hz (tn s thp) n 300 GHz (tn s cao). Cc tn s v tuyn c
th chia nh thnh 6 di.
Cc sng v tuyn tn s thp c th truyn qua cc bc tng trong khi cc tn s v tuyn
cao hn c th truyn theo ng thng. Nng lng ca cc sng tn s thp gim mnh khi
chng bao ph khong cch di. Sng tn s cao c nhiu nng lng hn.
Cc di tn s thp hn nh VLF, LF, MF c th truyn ti khong cch 1000 Km, qua b mt tri
t.
Cc sng v tuyn tn s cao l d b hp th bi ma v nhng vt cn khc. H s dng tng

in ly ca kh quyn. Cc sng v tuyn tn s cao nh di HF v VHF l tri rng ln trn. Khi
chng gp tng kh quyn, chng b khc x tr li mt t.
Trang 51
Truyn ti sng cc ngn

Cc sng in t trn 100 MHz truyn theo ng thng v cc tn hiu qua chng c th c
gi bi chm tia sng n mt trm c th. Bi v cc sng cc ngn truyn theo ng thng,
c trm gi v trm nhn phi c cn chnh trn mt ng thng.
Cc sng cc ngn c bin t 1mm n 1 mt v tn s t 300 MHz n 300 GHz.
Cc angten sng cc ngn tp trung cc sng to mt chm sng. Nh trn hnh, nhiu angten
c th c cn chnh t c khong cch xa hn. Cc sng cc ngn c cc tn s cao
hn v khng m xuyn qua nhng vt cn.
S truyn sng cc ngn ph thuc phn ln vo cc iu kin thi tit v tn s n ang s
dng.
Trang 52
Truyn ti ca tia hng ngoi

Tia hng ngoi nm gia di nh sng nhn thy v cc sng cc ngn. N c bin sng t 700
nm n 1mm v tn s t 300 GHz n 430 THz.
Tia hng ngoi c s dng cho cc mc ch truyn ti thng tin rt ngn nh truyn hnh v
iu khin t xa ca n. Do s truyn tia hng ngoi theo mt ng thng c nh hng
bi mi trng t nhin. Bi v di tn s cao, tia hng ngoi khng xuyn qua cc vt cn c.
S truyn nh sng
Cc di quang ph in t m c s dng truyn ti d liu l nh sng hoc tn hiu quang
hc. N cn c bit n vi ngha l LASER.
Bi v tn s ca nh sng, n c khuynh hng truyn theo ng thng. Do , trm gi v trm
nhn phi nm trn ng thng. Bi v s truyn laser l khng nh hng, ti c hai u truyn
ti, b pht laser v b d sng (photo-detector) cn c ci t. Ni chung dng laser c
rng l 1 mm, v th vic cn chnh hai b th cm xa nhau l mt cng vic cn s chnh xc
cao.
B pht laser lm vic nh my pht Tx v photo-detector lm vic nh my nhn Rx.
Trang 53

Cc b pht laser khng xuyn qua c cc vt cn nh tng, ma v xng m dy. Thm
vo , lung laser b bp mo bi gi, nhit khng kh hoc cc s thay i nhit trn
ng truyn.
Laser l an ton cho vic truyn ti d liu, tuy nhin n l kh r chm tia laser c rng 1
mm m khng gin on s truyn thng tin.
K thut ghp knh trong DCN

Dn knh (Multiplexing) l mt k thut m theo cc lung d liu k thut s v d liu tng
t khc nhau ca d tryn ti c th c x l ng thi qua mt ng link c chia s. K
thut dn phn chia thit b trung gian cng sut cao thnh trung gian cng sut thp theo lgic m
sau c chia s bi cc lung d liu khc nhau.
S truyn ti thng tin c th qua khng kh (tn s v tuyn), s dng mt phng tin vt l
(cp), v nh sng (si quang). Tt c cc phng tin trung gian c kh nng thc hin k thut
dn.
Khi nhiu trm gi c gng gi d liu thng qua mt thit b trung gian n, mt thit b c
gi l b dn phn chia cc knh (di) vt l v cp pht knh chng ti chng. Trn mt u ca
s truyn ti, mt thit b gii dn nhn d liu t mt thit b trung gian n, xc nh mi di, v
gi ti cc trm nhn khc nhau.
K thut ghp knh bng chia tn s (FDM) trong DCN

Khi vt mang l tn s, FDM c s dng. FDM l mt k thut tng t. FDM phn chia di
bng thng sng mang hoc quang ph vo cc knh hp l v cp pht mt ngi s dng ti
mi knh. Mi ngi s dng c th s dng tn s knh mt cch c lp v s truy cp ring ti
n. Tt c cc knh c phn chia theo cch chng khng ln nhau. Cc knh c ring
r bi cc di bo v. Di bo v l mt tn s m khng c s dng bi bt k knh no.
Trang 54
K thut ghp knh phn chia theo thi gian (TDM)

trong DCN
TDM c ng dng ln u tin trn cc tn hiu k thut s nhng n cng c th c p dng
trn cc tn hiu tng t. Trong TDM, knh c chia s c phn chia gia ngi dng ca n
bng phng thc khe thi gian. Mi ngi dng c th truyn ti d liu ch trong khe thi gian
c cung cp. Cac d liu k thut s c phn chia thnh cc khung, mi khung c chia
thnh cc khe thi gian, v d: khung ca mt kch thc ti u c th c truyn i trong khe
thi gian cho.
TDM lm vic trong ch c ng b. C cc u trm, v d nh b ghp knh v b gii
knh phi c ng b theo thi gian vic chuyn i knh c xy ra mt cch ng thi.
Khi knh A truyn ti khung ca n ti mt u, b gii knh cung cp phng tin ti knh A trn
u kia. Ngay sau khi khe thi gian ca knh A l ht, n chuyn ti knh B. Trn u khc, b gii
knh lm vic theo phng thc ng b v cung cp phng tin ti knh B. Cc tn hiu t cc
knh khc nhau truyn qua ng truyn theo phng thc chen vo.
Trang 55
Ghp knh phn chia theo bin sng trong DCN

nh sng c bin sng khc nhau (cc mu khc nhau). Trong phng thc si quang hc,
nhiu tn hiu mang c ghp vo trong mt si quang hc bng vic s dng cc bin sng
khc nhau. y l mt k thut ghp k tng t v c thc hin theo nguyn l ging nh
FDM nhng y s dng nh sng nh l cc tn hiu.
Ngoi ra, trn mi bin sng, vic ghp knh phn chia thi gian c th khng kt hp cht ch
thu nhn c nhiu tn hiu hn.
Ghp knh phn chia m ha (CDM) trong DCN

Nhiu tn hiu d liu c th c truyn ti qua mt tn s n bng vic s dng k thut ghp
knh phn chia m ha. FDM phn chia tn s vo cc knh nh hn nhng CDM cho php
nhng ngi s dng n c mt bng thng y v truyn ti cc tn hiu mi lc khi s dng
mt m ha duy nht. CDM s dng cc m ha trc giao tri rng cc tn hiu.
Mi trm c ch nh vi mt m ha duy nht, gi l chip. Cc tn hiu truyn i mt cch c
lp vi nhng m ny, bn trong ton b bng thng. Trm nhn bit trc m chip ca tn hiu
m n phi nhn.
S chuyn mng trong DCN

S chuyn mng l tin trnh gi cc gi d liu t mt port ti mt port khc hng ti im
ch n. Khi d liu n mt port, n c gi l s thm nhp, v khi d liu ri mt port, n
c gi l s i ra. Mt h thng thng tin c th bao gm mt s cc thit b chuyn mng v
cc nut. Ti mc rng, chuyn mng c th c phn chia thnh hai loi chnh:
Trang 56
Khng kt ni: D liu c truyn i qua s lm vic ca cc bng chuyn tip. Khng
cn phi thit lp trc mi giao tip.
Kt ni c iu hng: Trc khi chuyn mng d liu hng ti ch n, cn

thit lp trc mch song song vi ng truyn gia cc u kt ni. D liu sau
c hng trn cc mch . Sau khi vic truyn ti kt thc, cc mch c th c gi
tip tc cho s dng sau ny hoc c th c g b ngay lp tc.
Chuyn mch (Circuit Switching)

Khi hai nt giao tip vi nhau thng qua mt ng truyn ph hp, n c gi l s chuyn
mch. Cn mt tuyn ng c nh trc m t d liu s truyn qua v cc d liu
khc khng c chp nhn. Trong s chuyn mng, truyn d liu, mch phi c thit lp
sao cho s truyn ti d liu c th din ra.
Cc mch c th l lu di hoc mang tnh tm thi. Cc ng dng m s dng chuyn mng c
th c phn chia thnh 3 giai on sau:
Xy dng mt mch
Truyn ti d liu
Ngt kt ni mch
Trang 57

Chuyn mch c thit k cho cc ng dng m thanh. in thoi l v d ph hp nht ca s
chuyn mch. Trc khi mt ngi s dng to cuc gi, mt ng truyn o gia ngi gi v
ngi nhn c thit lp qua mng.
Chuyn mng tin bo

K thut ny nm trong khong gia ca s chuyn mch v s chuyn gi d liu. Trong chuyn
mng tin bo, ton b tin bo c xem nh l mt n v d liu v c chuyn/truyn i trong
trng thi nguyn vn ca tin bo.
Mt ci chuyn mng lm vic trong s chuyn mng tin bo, u tin n nhn ton b tin bo v
m n ti khi c cc ngun ti nguyn c sn truyn ti trm tip theo. Nu trm tip khng c
ngun ti nguyn cung cp cho tin bo c kch c ln, th tin bo c gi v trong trng
thi i.
K thut ny c cho l thay th cho chuyn mch. Khi trong k thut chuyn mng, ton b
ng truyn c ng khi ch cho hai thc th. K thut chuyn mng tin bo c thay i
bng k thut chuyn mng gi. Chuyn mng tin bo c 3 nhc im sau:
Mi ci chuyn mng trong ng truyn cn kho lu ln cung cp ch cho ton b

tin bo.
Bi v k thut gi-v-truyn ti v i ti khi cc ngun ti nguyn l sn sng, chuyn

mng tin bo l kh chm.
Trang 58
K thut chuyn mng tin bo khng phi l mt gii php cho phng tin d liu lung v
cc ng dng thi gian thc.
Chuyn mch gi d liu

Nhng nhc im ca s chuyn mng tin bo lm ny sinh tng v s chuyn mch gi d
liu. Ton b tin bo c phn chia thnh mnh nh hn c gi l cc gi d liu. Thng tin
chuyn mng c thm vo phn u ca mi gi v c truyn i mt cch c lp.
N d dng hn cho cc thit b trung gian lu gi mt gi d liu c kch c nh hn v chng
khng tn qua nhiu ngun ti nguyn c trn ng truyn hoc trn b nh ni vi ca cc ci
chuyn mng.
Chuyn mch gi d liu ci thin hiu sut dy dn khi cc gi d liu t nhiu ng dng c th
c ghp thng qua vt mang. Internet s dng k thut chuyn gi d liu. S chuyn gi d
liu cho ngi s dng kh nng phn bit cc lung d liu da trn c s cc quyn u tin.
Cc gi d liu c gi v truyn ti ch theo quyn u tin ca chng lm tng cht lng
dch v.
DCN - Gii thiu v Tng data-link

Tng data-link (D liu-Lin kt) l tng th hai trong M hnh tng OSI. Tng ny l mt trong
nhng tng phc tp nht v c cc chc nng v nhim v phc tp. Tng data-link n cc chi
Trang 59

tit ca phn cng nm di v biu din chnh n ti tng trn, nh l mt tng trung gian
giao tip.
Tng data-link lm vic gia hai host m c kt ni trc tip vi nhau. S kt ni trc tip ny
c th l ngang hng point-to-point hoc l pht thanh truyn hnh. Cc h thng trn mng pht
thanh truyn hnh c xem nh l trn cng mt lin kt. S lm vic ca Tng data-link c
khuynh hng phc tp hn khi n lm vic vi nhiu host trn mt min va chm n.
Tng data-link chu trch nhim bin i lung d liu ti cc tn hiu theo tng bit mt v
gi lung d liu qua phn cng nm di. Ti im nhn d liu, tng d liu nht d liu t
phn cng kiu cc tn hiu in t, tp hp chng trong mt nh dng khung c th nhn ra
c v gi ti tng trn.
Tng d liu c hai tng ph:
iu khin lin kt logic: N lm vic vi cc giao thc, iu khin lung v iu khin li.
iu khin truy cp phng tin: N lm vic vi s iu khin thc t ca phng tin.
Chc nng ca tng data-link

Tng lin kt thc hin nhiu nhim v thay mt cho tng trn. l:
Dng khung
Tng data-link mang cc gi d liu t Tng mng v gi chng vo cc Khung. Sau ,
n gi mi khung theo phng thc tng bit mt trn phn cng. Ti u nhn, Tng datalink nht cc tn hiu t phn cng v tp hp chng vo trong cc khung.
Ghi a ch
Tng data-link cung cp k thut ghi a ch phn cng tng-2. a ch phn cng c gi
s l duy nht trn ng lin kt. N c m ha vo phn cng ti thi im to.
ng b
Khi cc khung d liu c gi trn ng lin kt, cc thit b phi c ng b theo
trnh t cho vic truyn ti din ra.
Kim sot li
Trang 60

i khi cc tn hiu gp phi vn khi truyn ti v cc bit b li. Nhng li ny c pht
hin v c c gng phc hi li cc bit thc s. N cng cung cp k thut bo co
li ti ngi gi.
Kim sot lung

Cc trm trn cng mt ng kt ni c th c tc hoc cng sut khc nhau. Tng d
liu m bo kim sot d liu cho cc thit b kh nng chuyn i d liu trn cng
mt tc .
a truy cp
Khi host trn ng lin kt c chia s c gng truyn ti d liu, s va chm c th
xy ra vi mt xc sut cao. Tng d liu cung cp k thut nh CSMA/CD trang b kh
nng truy cp mt phng tin c chia s trong nhiu h thng.
Pht hin v chnh sa li trong DCN

C rt nhiu l do nh nhiu in t, nhiu xuyn m m c th lm cho d liu b li trong qu
trnh truyn ti. Cc tng trn lm vic trn mt s quan im rng ri v cu trc mng v khng
nhn thc c tin trnh d liu phn cng thc s. Hu ht cc ng dng khng c tnh nng
m d kin c trong trng hp chng nhn d liu li. Cc ng dng nh m thanh v video
c th khng b nh hng vi mt s li v chng vn hot ng tt.
Tng lin kt-d liu s dng mt s k thut kim sot li m khung d liu (lung bit d liu)
c truyn vi mc chnh xc nht nh. Nhng hiu phng thc m cc li c kim
sot, n l quan trng bit v cc kiu li c th xy ra.
Cc kiu li
C 3 kiu li:
Li bit n
Trong mt khung d liu, ch c mt bit b li, cc bit cn li khng b li.
Trang 61
Li nhiu bit
Khung d liu c nhn c nhiu hn mt bit b li.
Li tng lot
Khung d liu nhn c nhiu hn mt bit lin tip b li.

K thut kim sot li c th bao gm hai cch sau:
Pht hin li
Chnh sa li
Pht hin li
Cc li trong cc khung d liu c nhn c pht hin bng k thut Parity Check and Cyclic
Redendancy Check. Trong c hai trng hp, mt vi bit thm c gi song song vi d liu
thc xc nhn rng cc bit nhn ti u trm khc l ging vi khi chng c gi. Nu kim
tra b m ti trm nhn li, cc bit c xem nh l b li.
Kim tra chn l (Prity Check)

Mt bit thm c gi song song vi cc bit u bo hiu s lng bit c gi tr bng 1s (to 1
s hc) trong mt nhm bit cho trc l mt s chn hay s l.
Ngi gi trong khi to mt khung d liu tnh s 1 trong . V d, nu ngang bc chn c s
dng v 1s l chn th khi mt bit vi gi tr 0 c thm vo. Theo cch ny th 1s vn l chn.
Nu 1s l l, lm cho mt bit chn, gi tr 1 c thm vo.
Trang 62

Trm nhn n gin ch cn tnh s 1s trong khung d liu. Nu s 1s l chn th ngang bc chn
c s dng, khung c cho l khng b li v c chp nhn. Nu tnh s 1s l l th ngang
bc l c s dng, khung vn khng b li.
Nu mt bit n b li khi truyn ti, trm nhn c th pht hin n bng cch tnh s 1s. nhng khi
nhiu hn mt bit b li, th n rt kh trm nhn c th pht hin ra li.
Cyclic Redundancy Check (CRC)

CRC l mt hng tip cn khc pht hin li nu khung d liu c nhn cha d liu c
hiu lc. K thut ny bao gm s phn chia nh phaann ca cc bit d liu c gi . S chia
c to ra bng cch s dng a thc. Trm gi thc hin hot ng chia trn cc bit c gi
v tnh ton s d. Trc khi gi cc bit thc s, ngi gi thm phn d vo cui cc bit d liu
thc. Cc bit d liu thc cng vi phn d ca n c gi l mt codeword. Ngi gi truyn ti
cc bit d liu nh l cc codeword.
Ti u nhn khc, ngi nhn thc hin hot ng chia trn cc codeword s dng cng mt s
chia CRC. Nu ngi nhn nhn c kt qu cha tt c l s 0, cc bit d liu c chp nhn,
nu khng th, cc d liu c cho l b li.
Trang 63
Chnh sa li
Trong th gii k thut s, chnh sa li c th c thc hin theo hai cch:
Chnh sa li ngc v pha trc (BEC) Khi ngi nhn pht hin mt li trong d liu
nhn c, n gi yu cu tr li cho ngi gi truyn ti li n v d liu.
Chnh sa li thun chiu v pha sau (FEC) Khi ngi nhn pht hin mt vi li trong
d liu nhn c, n chy m chnh li, m gip n t ng phc hi v chnh sa mt
vi loi li.
Trong cch u tin, BEC, l n gin v ch c th c s dng mt cc hiu qu khi vic truyn
ti li l khng tn km. V d, cc si quang hc. Nhng trong trng hp truyn ti khng dy,
vic truyn ti li c th qu tn km. Trong trng hp ny, FEC c s dng.
chnh sa li trong khung d liu, ngi nhn phi bit chnh xc bit no trong khung b li.
xc nh v tr bit trong li, cc bit cn li c s dng, ng vai tr nh l cc bit ngang hng
(chn l) pht hin li. V d, chng ta s dng cc t ASII (d liu 7 bit), sau c 8 loi thng
tin chng ta cn: 7 bit u tin ni cho chng ta bit bit no l li v bit cn li ni rng n
khng b li.
Vi m bit d liu, r bit tha c s dng. r bit c th cung cp 2r kt ni ca thng tin. Trong m+r
codeword, s khng kh nng xy ra m r bit chnh n b li. V th s lng r bit c s dng
phi thng bo v m+r v tr cng vi thng tin khng li, v d nh m+r+1.
DCN - Giao thc v kim sot data-link

Tng data-link chu trch nhim cho vic thc hin k thut kim sot lung point-to-point v li.
Kim sot lung trong tng data-link

Khi mt khung d liu (d liu Tng-2) c gi t mt host ti mt host khc thng qua mt thit
b trung gian, n c yu cu rng trm gi v trm nhn phi cng lm vic cng mt tc .
l, trm gi gi ti mt tc ti trm nhn c th x l v truy cp d liu. iu g xy ra
khi tc (phn cng/phn mm) ca trm gi v nhn khc nhau? Nu trm gi ang gi vi tc
qu nhanh, th trm nhn c th qu ti, v d liu c th b tht lc.
Hai kiu k thut c th c trin khai kim sot lung l:
Trang 64
Dng v i
K thut kim sot lung ny lm trm gi dng li sau khi gi mt khung d liu v i
ti khi bit c khung d liu gi c nhn.
Ca s trt
Trong k thut kim sot lung d liu ny, c trm gi v trm nhn c u ng v
s lng khung m sau lng khung c tha nhn ny c gi. Nh chng ta
hc, k thut kim sot dng v i lng ph ti nguyn, giao thc ny c gng s dng
cc ngun ti nguyn bn di cng nhiu cng tt.
Kim sot li trong tng data-link

Khi khung d liu c truyn ti, c mt kh nng m khung d liu c th b tht lc trong qu
trnh gi hoc n b li khi nhn c. Trong c hai trng hp, trm nhn khng nhn c
khung d liu chnh xc v trm gi khng bit g v bt c s tht thot no. Trong nhng trng
hp nh vy, c trm nhn v trm gi c trang b mt s giao thc m gip n pht hin cc
li truyn ti nh tht lc khung d liu. V th, hoc ngi gi truyn ti li khung d liu hoc
ngi nhn yu cu ngi gi truyn ti li khung d liu trc .
Cc yu cu i vi k thut kim sot li:
Trang 65
Pht hin li - Trm gi v trm nhn, hoc c hai hoc khng, phi chc chn rng c
mt s li trong s truyn.
ACK khng nh - Khi trm nhn nhn mt khung d liu chnh xc, n nn tha nhn
khung d liu .
ACK ph nh - Khi trm nhn nhn mt khung li hoc mt khung bn sao, n gi mt

NACK tr li cho trm gi v trm gi phi truyn ti li khung d liu chnh xc.
S truyn ti li: Trm gi duy tr mt ng h v thit lp mt khong thi gian tr. Nu

tn hiu tha nhn v khung d liu c truyn trc khng n trc khong thi
gian tr, trm gi truyn ti li khung, v n ngh rng khung d liu b tht lc khi truyn ti.
C 3 kiu k thut c sn m Tng data-link c th trin khai kim sot li bng Cc yu cu lp

li t ng Automatic Repeat Requests (ARQ):
Stop and Wait ARQ
Trang 66
Trnh truyn ti sau c th xy ra trong ARQ dng-v-i:

o
Trm gi duy tr mt b m thi gian tr.
Khi mt khung c gi, trm gi bt u tnh thi gian tr.
Nu tn hiu tha nhn khung n ng gi, trm gi truyn ti khung k tip trong
hng.
Nu tn hiu tha nhn khung khng n ng gi, trm gi cho rng hoc khung
hoc tn hiu tha nhn b tht lc trong qu trnh truyn. Trm gi truyn ti li
khung v bt u tnh thi gian tr.
Nu tn hiu tha nhn ph nh c nhn, trm gi truyn ti li khung .
Go-Back-N ARQ
Trang 67

K thut ARQ dng v i khng ti a ha s dng ngun ti nguyn. Khi tn hiu tha
nhn c nhn, trm gi rnh ri v khng thc hin cng vic g. Trong k thut GoBack-N ARQ, c trm gi v trm nhn duy tr mt ca s.
Kch c ca s gi cho trm gi kh nng gi nhiu khung d liu m khng cn nhn

tn hiu tha nhn trc mi khung. Ca s nhn cho trm nhn kh nng nhn nhiu
khung d liu v pht tn hiu tha nhn chng. Trm nhn theo di s th t dy ca
khung d liu n.
Khi trm gi gi tt c cc khung d liu trong ca s, n kim tra s th t dy no n
nhn tn hiu tha nhn khng nh. Nu tt c cc khung u l tn hiu khng nh, trm
gi gi b thit lp cc khung k tip. Nu trm gi thy rng n nhn NACK hoc
Trang 68

khng nhn bt c ACK no cho mt khung c th, n truyn ti li tt c cc khung d
liu sau khi m n khng nhn bt c mt ACK khng nh no.
Selective Repeat ARQ (lp c la chn)

Trong Go-Back-N ARQ, n gi s rng trm nhn khng c bt c khong khng gian m
no cho kch c ca s ca n, v phi x l mi khung khi n n. iu ny bt buc trm
gi phi truyn ti li tt c cc khung d liu m khng c tha nhn.
Trong ARQ lp li c la chn, trm nhn trong khi theo di s th t cc dy, m cc

khung trong b nh v gi NACK ch vi khung m b li.
Trm gi trong trng hp ny, ch gi gi d liu m NACK c nhn.
Trang 69
Gii thiu Tng mng trong DCN

Tng-3 trong M hnh OSI c gi l tng mng. Tng mng qun l cc chc nng gn lin vi
host v ghi a ch mng, qun l cc Subnet (Mng ph) v hot ng internet.
Tng mng c trch nhim v nh tuyn truyn cc gi d liu t ngun ti ch n trong hoc
ngoi mt Subnet. Hai Subnet khc nhau c th c gin ghi a ch khc nhau hoc cc kiu ghi
a ch khng tng thch. Ging vi cc giao thc, hai Subnet c th iu hnh trn cc giao thc
khc nhau m khng tng thch vi nhau. Tng mng c trch nhim nh tuyn cho cc gi d
liu t ngun ti ch n, thit k gin ghi a ch v cc giao thc khc nhau.
Cc chc nng Tng-3

Cc thit b m lm vic trn Tng mng ch yu da trn vic nh tuyn. nh tuyn c th bao
gm nhiu nhim v m t c mt mc ch n. iu ny c th l:
Ghi a ch cc thit b v cc mng.
a n bng nh tuyn hoc cc tuyn tnh.
Sp hng cc d liu vo v ra, v sau chuyn tip chng theo cc rng buc ca cht
lng cc dch v thit lp cho nhng gi d liu .
Kt ni internet gia hai Subnet.
Truyn cc gi d liu ti ch vi c gng ti a.
Cung cp c ch iu hng kt ni v c ch t kt ni.
Cc c im ca Tng mng
Vi nhng tnh nng tiu chun ca n, Tng 3 c th c nhiu c im sau:
Cht lng ca s qun l dch v
Cn bng ti v qun l lin kt
S bo mt
Quan h qua li ca cc giao thc khc nhau v cc Subnet vi gin khc nhau.
Trang 70
Mng logic khc nhau thit k qua thit k mng vt l.
L3 VPN v cc ng c th c s dng cung cp s kt ni thch hp end-to-end.
Giao thc internet c mong i v trin khai rng ri Tng mng gip giao tip cc thit b endto-end thng qua internet. N c hai phin bn. IPv4 cai tr th gii hng thp k nay nhng by
gi ang dn b loi khi khng gian a ch. IPv6 c to ra thay th cho IPv4 v hy vng
gim thiu c nhng hn ch ca IPv4.
nh v mng trong DCN

Ghi a ch Tng 3 l mt trong nhng nhim v chnh ca Tng mng. Cc a ch mng thng
dng logic, v d: y l nhng a ch trn c s phn mm m c th c thay i bi cc cu
hnh thch hp.
Mt a ch mng thng tr ti host/nt/ server hoc n c th biu din y mt mng. a ch
mng thng c nh hnh trn th giao din mng v ni chung c thit k bi h thng vi
a ch MAC (a ch phn cng hoc a ch Tng 2) ca thit b cho giao tip Tng 2.
Tn ti 3 loi a ch mng khc nhau:
IP
IPX
AppleTalk
y chng ta ang bn lun v IP khi chng ta ch s dng loi a ch ny trong thc hnh.
Trang 71
Ghi a ch IP cung cp k thut phn bit gia cc host v mng. Bi v cc a ch IP c

gn theo th t c th bc, mt host lun lun di mt mng c th. Host m cn giao tip
bn ngoi Subnet ca n, cn bit a ch mng ch n, ni m cc gi d liu c gi n.
Cc host trong Subnet khc cn mt k thut xc nh v tr mi host. Nhim v ny c th c
thc hin bi DNS. DNS l mt server m cung cp a ch Tng 3 ca host iu khin t xa c
thit k gin vi tn min ca n hoc FQDN. Khi mt host c c a ch Tng 3 (a ch IP)
ca host iu khin t xa, n chuyn tt c cc gi d liu ca n ti cng (gateway) ca n. Mt
cng l mt cu dn (router) c trang b vi tt c thng tin m ch huy tuyn ng cc gi d
liu ti host ch.
Cc router gip cc bng nh tuyn, m c thng tin sau:
Phng thc tip cn mng
Cc router khi nhn mt yu cu chuyn tip, chuyn tip gi d liu ti router gn k hng ti
ch n.
Router k tip trn ng truyn lm vic theo phng thc tng t v cui cng gi d liu n
ch.
Trang 72

a ch mng c th l mt trong nhng th sau:
Unicast (c nh trc ti mt host)
Multicast (c nh trc ti mt nhm)
Broadcast (c nh trc ti tt c)
Anycast (c nh trc ti host gn nht)
Mt router khng bao gi chuyn hng truyn ti Broadcast, theo mc nh. S truyn Multicast
s dng s x l c bit khi n phn ln l mt lung video hoc audio vi quyn u tin cao
nht. Anycast th tng t nh Unicast, ngoi tr cc gi c chuyn ti ch gn nht trong khi
nhiu ch l c sn.
nh tuyn Tng mng trong DCN

Khi mt thit b c nhiu ng truyn tip cn ch n, n thng chn mt ng truyn m
c a thch hn cc ng truyn cn li. Tin trnh la chn ny c coi nh l nh tuyn.
nh tuyn c thc hin bi cc thit b mng c bit c gi l cc router hoc n c th
c thc hin bi cc tin trnh phn mm. Phn mm trn c s cc router gii hn chc
nng v phm vi.
Mt router lun lun c nh hnh vi mt s tuyn mc nh. Mt tuyn mc nh ni cho router
bit ni chuyn n mt gi d liu nu khng c tuyn no c tm thy cho mt ch n c
th. Trong trng hp c nhiu ng truyn cng tn ti tip cn cng mt ch n, router c
th iu khin lung da trn cc thng tin sau:
Tnh s router (hop)
B rng thng
Metric
Prefix-length
Thi gian tr hon
Cc tuyn c th c nh hnh tnh hoc nh hnh ng. Mt tuyn c th c nh hnh

c a thch hn cc tuyn cn li.
Trang 73
nh tuyn Unicast
Hu ht s truyn ti trn internet v intranet c bit n nh l d liu Unicast hoc s truyn
ti Unicast c gi vi ch n c xc nh. nh tuyn d liu Unicast qua internet c
gi l nh tuyn Unicast. N l mu n gin nht ca nh tuyn bi v ch n c bit. V
th, router phi quan st vo bng nh tuyn v chuyn tip gi d liu ti router tip theo.
nh tuyn Broadcast
Theo mc nh, cc gi Broadcast khng c nh tuyn v chuyn tip bi cc router trn bt k
mng no. Router to cc min Broadcast. Nhng n c th nh hnh chuyn tip cc
Broadcast trong mt vi trng hp c bit. Mt thng bo Broadcast c nh trc ti tt c
cc thit b mng.
nh tuyn Broadcast c th c thc hin theo 2 cch (thut ton):
Mt router to mt gi d liu v sau gi n ti tng host. Trong trng hp ny, router

to nhiu bn sao ca gi d liu n vi cc a ch ch n khc nhau. Tt c cc gi
c gi nh l Unicast nhng bi v chng c gi ti tt c, n m phng nh khi
router ang pht sng.
Phng thc ny dng nhiu di bng thng v router phi c a ch ch n ca mi
nt.
Trang 74
Cch th 2, khi mt router nhn mt gi d liu m c pht sng, n gin n tri tt c

nhng gi ny ra ton b giao din. Tt c cc router c nh hnh theo cng mt cch.
Phng thc ny l d i vi CPU nhng c th gy ra vn v cc bn sao gi d liu

c nhn t cc router cng bc.
o ngc ng truyn chuyn ti (reverse path forwarding) l mt k thut, trong
router bit trc v ngun m t n nhn Broadcast. K thut ny c s dng
pht hin v loi b cc bn sao.
nh tuyn Multicast
nh tuyn Multicast l mt trng hp c bit ca nh tuyn Broadcast. Trong nh tuyn
Broadcast, cc gi c gi ti tt c cc nt ngay c khi chng khng mun n. Nhng trong
nh tuyn Multicast, d liu ch c gi ti cc nt m mun nhn gi d liu .
Trang 75
Router phi bit rng c cc nt, m mun nhn cc gi Multicast (lung d liu), ri sau ch c
cc nt c chuyn ti. nh tuyn Multicast lm vic bng qua giao thc cy trnh hin
tng lp.
nh tuyn Multicast cng s dng k thut o ngc ng truyn chuyn ti, pht hin v
loi b cc bn sao v vng lp.
nh tuyn Anycast
nh tuyn Anycast l mt k thut m nhiu host c th c cng mt a ch logic. Khi mt gi
c nh tuyn trc ti a ch logic ny c nhn, n c gi ti host m gn nht trong
tuyn.
Trang 76
nh tuyn Anycast c thc hin vi s gip ca DNS server. Bt c khi no mt gi anycast

c nhn, n c yu cu hi vi DNS ti ni gi n. DNS cung cp a ch IP m l IP gn
nht c nh hnh trn n.
Cc giao thc nh tuyn Unicast

C hai loi giao thc nh tuyn Unicast c sn l:
Giao thc nh tuyn vecto khong cch (Distance Vector Routing

Protocol)
Vecto khong cch l giao thc nh tuyn n gin m a ra quyt nh nh tuyn trn
s cc router gia ngun v ch n. Mt tuyn vi s router t hn c xem nh l
tuyn tt nht. Mi router biu th tuyn tt nht thng qua so snh vi cc router khc. Sau
cng, tt c cc router xy dng a hnh mng da trn c s cc router ngang bc vi
n.
V d: Giao thc thng tin nh tuyn (RIP).
Giao thc nh tuyn trng thi kt ni (Link State)

Giao thc trng thi kt ni l mt giao thc phc tp hn Vecto khong cch. N a vo
ti khon trng thi ca cc lin kt ca tt c cc router trong mt mng. K thut ny gip
tuyn xy dng mt th chung ca ton b mng. Tt c cc router sau tnh ton
Trang 77

ng truyn tt nht cho mc ch nh tuyn. V d, M ng truyn ngn nht u tin
(OSPF) v H thng trung gian ti h thng trung gian (ISIS).
Cc giao thc nh tuyn Multicast

Cc giao thc nh tuyn Unicast s dng cc th trong khi cc giao thc nh tuyn Multicast
s dng cc cy, v d: cy bng qua trnh cc hin tng lp. Cy tt nht ny c gi l
cy bng qua ng truyn ngn nht.
DVMRP - Giao thc nh tuyn Multicast vecto khong cch (Distance Vector Multicast
Routing Protocol)
MOSPF - M ng truyn ngn nht u tin (Multicast Open Shortest Path First)
CBT - Core Based Tree
PIM - Giao thc Multicast c lp (Protocol independent Multicast)
Ngy nay, Giao thc Multicast c lp c s dng ph bin. N c hai phin bn:
Ch PIM c (PIM Dense Mode)

Ch ny s dng cc cy trn c s ngun. N c s dng trong mi trng c
nh LAN.
Ch PIM tha (PIM Sparse Mode)

Ch ny s dng cc cy c chia s. N c s dng trong mi trng tha nh l
WAN.
Cc thut ton nh tuyn

Cc thut ton nh tuyn nh sau:
Flooding
Flooding l phng thc n gin nht chuyn tip gi d liu. Khi mt gi c nhn, router gi
n ti tt c cc giao din ngoi tr giao din m t n c nhn. iu ny to ra qu nhiu
trng ti trn mng v rt nhiu gi d liu lang thang trong mng.
Time to Live (thi gian sng) c th c s dng trnh vic lp v hn cc gi. Tn ti mt
cch tip cn khc vi flooding, m c gi l Flooding c la chn gim chi ph trn mng.
Trang 78

Trong phng thc ny, router khng trn ngp trn tt c cc giao din, m ch cc giao din
c chn.
ng truyn ngn nht

Quyt nh nh tuyn trong cc mng, phn ln c a ra trn c s chi ph gia ngun v
ch n. Vic tnh ton router ng vai tr rt quan trng y. ng truyn ngn nht l mt k
thut m s dng cc thut ton a dng quyt nh chn mt ng truyn vi s router nh
nht.
Cc thut ton ng truyn ngn nht ph bin l:
Thut ton Dijkstra
Thut ton Bellman Ford
Thut ton Floyd Warshall
Lin mng trong DCN

Trong th gii ngy nay, cc mng di cng mt chnh quyn qun l chung thng c phn
tn v mt a l. C th tn ti yu cu ca vic kt ni hai mng khc nhau ca cng mt loi
cng nh khc loi. nh tuyn gia hai mng c gi l lin mng.
Cc mng c xem nh l khc nhau trn c s cc tham s a dng nh giao thc, a hnh
hc, gin ghi a ch v Tng mng.
Trong lin mng, cc router bit v a ch ca nhau v cc a ch trn chng. Chng c th c
nh hnh tnh trn mng khc nhau hoc chng c th c bit bi s dng giao thc nh tuyn
lin mng.
Trang 79
Cc giao thc nh tuyn m c s dng trong mt t chc hoc mt chnh quyn qun l c
gi l cc Giao thc cng (kt ni d mng) ni b (IGP). RIP, OSPF l cc v d ca IGP. nh
tuyn gia cc t chc hoc chnh quyn khc nhau c th c Giao thc cng i ngoi (EGP), v
ch c mt EGP nh Giao thc kt ni d mng khung (BGP).
K thut Tunneling trong DCN

Nu chng l hai mng ring bit t xa nhau v a l, m mun giao tip vi nhau, chng c th
trin khai mt ng dn ph hp hoc chng phi truyn d liu qua cc mng trung gian.
Tunneling l mt k thut m t hai hoc nhiu mng ging nhau giao tip vi nhau, bi truyn
qua cc mng trung gian phc tp. Tunneling c nh hnh ti c hai u.
Trang 80
Khi mt d liu nhp t mt u ng, n c nh ghi. D liu c nh ghi ny sau c

truyn bn trong mng trung gian tin ti u ng khc. Khi d liu tn ti trong ng, th ghi
ca n c g b v c phn pht ti phn khc ca mng.
C hai u c v nh c kt ni trc tip vi nhau v vic nh th ghi lm d liu truyn ti
qua mng trung gian m khng cn s chnh sa no.
S phn mnh gi d liu trong DCN

Hu ht cc on Ethernet c n v truyn ti ti a (MTU) ca n c c nh ti 1500 byte.
Mt gi d liu c th c di gi di hn hoc ngn hn ph thuc vo ng dng. Cc thit b
trong ng truyn cng c cng sut phn cng v phn mm m cho bit lng d liu m thit
b c th kim sot v kch c gi d liu n c th x l.
Nu kch c gi d liu nh hn hoc bng ti kch c gii hn m ng truyn c th kim sot,
n c x l bnh thng. Nu n l ln hn, n c phn thnh cc phn nh hn v sau
chuyn tip. iu ny c gi l s phn mnh gi d liu. Mi mnh cha cng mt a ch ch
n v ngun v c truyn qua ng truyn mt cch d dng. Ti u nhn, n c kt hp
li.
Nu mt gi d liu vi thit lp bit DF (khng phn mnh) ti 1 n mt router m khng th kim
sot gi v di ca n, gi ny s b b ri.
Trang 81

Khi mt gi c nhn bi mt router c thit lp bit MF (nhiu mnh) n 1, router sau bit
rng n l mt gi c phn mnh v cc phn ca gi ban u ang trn ng chuyn n.
Nu mt gi c phn mnh qu nh, chi ph s tng ln. Nu mt gi c phn mnh qu to,
router trung gian c th khng th x l n v n c th b b ri.
Cc giao thc Tng mng trong DCN

Mi my tnh trong mt mng c mt a ch IP m t n c th c xc nh duy nht. Mt a
ch IP l a ch logic Tng mng (Tng 3). a ch ny c th thay i bt c lc no khi my tnh
khi ng li. Mt my tnh c th c mt IP ti mt thi im ny v IP khc ti thi im khc.
Giao thc phn gii a ch (ARP)

Trong khi giao tip, mt host cn a ch Tng-2 (MAC) ca thit b ch n m s hu cng min
Broadcast hoc mng. Mt a ch MAC c gn vo trong Th giao din mng (NIC) ca mt
thit b v khng bao gi thay i.
Theo cch hiu khc, a ch IP trn min cng cng him khi b thay i. Nu NIC b thay i trong
trng hp li, a ch MAC cng thay i theo. Theo cch ny, giao tip Tng-2 din ra, mt thit
k bn gia hai chng n c yu cu.
Trang 82
bit a ch MAC ca host t xa trn mt min Broadcast, mt my tnh c nhu cu khi ng

vic giao tip gi mt thng bo truyn thng ARP hi: a ch IP ny l ai?. Bi v n l mt
Broadcast, tt c cc host trn on mng (min Broadcast) nhn gi d liu ny v x l n. Gi
d liu ARP cha a ch IP ca host ch, host gi i mong i c giao tip vi n. Khi mt
host nhn mt gi ARP chuyn n cho n, n tr li li vi tn hiu a ch MAC ring ca n.
Mt khi mt host nhn a ch MAC ch n, n c th giao tip vi host t xa bi s dng giao
thc lin kt Tng-2. MAC ny ti thit k bn IP c lu gi trong b nh n ARP ca c
host gi v host nhn. Tip , nu chng yu cu giao tip, chng c th trc tip lin h vi
ARP tng ng.
o ngc ARP l mt k thut m host bit a ch MAC ca host t xa nhng yu cu bit a
ch IP tin hnh giao tip.
Trang 83
Giao thc thng bo iu khin internet (ICMP)

ICMP l mt giao thc chn on v bo co li mng. ICMP s hu giao thc IP ph hp v s
dng IP nh l giao thc mang. Sau khi xy dng gi ICMP, n c ng gi trong gi IP. Bi v
IP chnh n l mt Giao thc n lc ti a khng ng tin cy (best-effort non-reliable), v th n l
ICMP.
Bt k s phn hi no v mng c gi tr li host ban u. Nu mt s li trong mng xy ra,
n c bo co bi s hot ng ca ICMP. ICMP cha hng t cc thng bo pht hin v bo
co li.
ICMP-echo v ICMP-echo-reply l cc thng bo ICMP c s dng ph bin nht kim tra
kh nng tip cn ca host dng end-to-end. Nu c bt k vn trong mng truyn ti, ICMP s
bo co vn .
IP phin bn 4 (IPv4)
IPv4 l gin ghi a ch 32 bit c s dng nh l k thut ghi a ch host TCP/IP. Ghi a ch
IP cho mi host trn mng TCP/IP kh nng c xc nh l duy nht.
IPv4 cung cp gin ghi a ch c th bc m cho n kh nng phn chia mng thnh cc
Subnet, tng ng vi mi s r rng ca cc host. Cc a ch IP c phn chia thnh cc loi
sau:
Hng A - N s dng b tm u tin cho cc a ch mng v ba b tm cn li cho a

ch host.
Hng B - N s dng hai b tm u tin cho cc a ch mng v hai b tm cn li cho

a ch host.
Hng C - N s dng ba b tm u tin cho cc a ch mng v b tm cui cng cho a

ch host.
Hng D - N cung cp gin ghi a ch IP phng ngc li vi cu trc th bc ca 3

hng trn.
Hng E - N c s dng nh l th nghim.
Trang 84

IPv4 c khng gian a ch r rng c s dng nh l cc a ch c nhn (khng th nh
tuyn trn internet), v cc a ch cng cng (c cung cp bi ISPs v c th nh tuyn trn
internet).
Mc d IP l khng ng tin cy; n cung cp k thut Phn phi vi n lc tt nht - Best-EffortDelivery.
IP phin bn 6 (IPv6)
Vic dng cn kit cc a ch IPv4 (cc a ch IPv4 khng p ng c nhu cu ngy cng ln)
ny sinh s sng to tip theo v IPv6. IPv6 ghi a ch cc nt ca n vi min a ch 128 bit
rng ri cung cp nhiu khong khng gian a ch cho tng lai s dng trn hnh tinh.
IPv6 gii thiu k thut ghi a ch Anycast nhng g b khi nim Broadcast. IPv6 cho cc
thit b kh nng t kim c mt a ch IPv6 v giao tip trong Subnet . S nh hnh t ng
ny xa b s ph thuc vo cc server Giao thc nh hnh host ng (DHCP). Theo cch ny,
ngay c khi DHCP server trn Subnet b ngng hot ng, cc host vn c th giao tip vi
nhau.
IPv6 cung cp c im mi l tnh lu ng IPv6. IPv6 lu ng trang b cc thit b c th di
ng vng quanh m khng cn thay i cc a ch IP ca chng.
IPv6 vn ang trong s chuyn tip (qu trnh qu ) v c chp nhn thay th hon ton
cho IPv4 trong mt vi nm ti. Hin ti, c mt vi mng ang chy trn IPv6. C mt vi k
thut chuyn tip c sn cho IPv6 cho cc mng kh nng giao tip v di ng vng quanh mt
cch d dng trn Ipv4 l:
Dual stack implementation
Tunneling
NAT-PT
Gii thiu Tng truyn ti trong DCN

Mt Tng tip theo trong M hnh OSI c cng nhn l Tng truyn ti (Tng-4). Tt c cc
modun v phng thc lin quan ti s truyn ti ca d liu hoc lung d liu c phn loi
trong tng ny. Nh tt c cc tng khc, tng ny giao tip vi tng truyn tri ngang hng vi n
trong host t xa.
Trang 85

Tng truyn ti ngh 2 kiu kt ni l peer-to-peer v end-to-end gia hai tin trnh trn cc host
t xa. Tng truyn ti nhn d liu t tng trn (tng ng dng) v sau phn mnh n thnh
cc phn c kch c nh hn, v gi chng xung tng di (Tng mng) cho vic phn phi.
Cc tnh nng
Tng ny l tng u tin m phn mnh d liu thng tin, c cung cp bi tng ng
dng, thnh nhng n v nh hn gi l on. N nh s mi byte trong on v tip tc
duy tr s tnh ton.
Tng ny bo m rng d liu phi c nhn theo cng mt hng m theo n c

gi.
Tng ny cung cp s phn phi end-to-end ca d liu gia cc host m c th hoc c

th khng s hu cng mt Subnet.
Tt c cc tin trnh mng chnh d nh giao tip thng qua mng c trang b vi im
truy cp dch v truyn ti (TSPs) m cng c bit n nh l s hiu cng.
Giao tip end-to-end

Mt tin trnh trn mt host xc nh host ngang bc ca n trn mng t xa bi s lm vic ca
TSPs, m cng c bit nh l s hiu cng. TSPs c xc nh r rng v mt tin trnh m c
gng giao tip vi tin trnh ngang bc ca n bit v iu ny trc.
V d, khi mt DHCP client mun giao tip vi DHCP server t xa, n lun lun yu cu trn port
s 67. Khi mt DNS client mun giao tip vi DNS server t xa, n lun lun yu cu trn port s
53 (UDP).
Trang 86

C hai giao thc Tng truyn ti chnh l:
Giao thc iu khin truyn ti (Transmission Control Protocol - TCP)

N cung cp s giao tip ng tin cy gia hai host.
Giao thc d liu ngn ngi s dng (User Datagram Protocol - UDP)
N cung cp s giao tip khng ng tin cy gia hai host.
Giao thc TCP trong DCN

Giao thc iu khin truyn ti (TCP) l mt trong nhng b giao thc quan trng nht ca giao
thc internet. N l giao thc c s dng rng ri truyn ti d liu trong mng giao tip nh
internet.
Cc c im
TCP l giao thc ng tin cy. l, ngi nhn lun lun gi tn hiu hoc khng nh
hoc ph nh v gi d liu ti ngi gi, m ngi gi lun lun bit c liu gi d
liu mnh gi c c tip cn n ch hay l n cn gi li n.
TCP bo m rng d liu tin ti ch n trong mt th t ging vi khi n c gi.
TCP l mt kt ni iu hng. TCP yu cu rng kt ni gia hai im t xa phi c

thit lp trc khi gi d liu thc s.
TCP cung cp k thut pht hin v phc hi li.
TCP cung cp s giao tip end-to-end.
TCP cung cp iu khin lung v cht lng dch v.
TCP iu hnh ch point-to-point trong client/server.
TCP cung cp server kp y , v d: N c th thc hin cc chc nng ca n trn c

hai trm nhn v trm gi.
Header
di ca Header l di ti thiu 20 byte v ti a l 60 byte.
Trang 87
Port ngun (16 bit) - N xc nh cng ngun ca tin trnh ng dng trn thit b gi.
Port ch n (16 bit) - N xc nh cng ch n ca tin trnh ng dng trn thit b

nhn.
S dy (32 bit) - S th t dy ca cc byte d liu ca mt on trong mt phin.
S tn hiu tha nhn (32 bit) - Khi mt c hiu ACK c thit lp, s ny cha s th
t dy k tip ca byte d liu v lm vic nh l tn hiu tha nhn ca d liu c nhn
trc .
Offset d liu (4 bit) - Trng ny bao hm c hai: kch c ca header v offset ca d

liu trong gi hin ti trong ton b on TCP.
D tr (3 bit) - D tr cho tng lai s dng v theo mc nh tt c c thit lp l 0.
Cc c du hiu (mi c mt bit):

o NS - Nonce Sum bit c s dng bi tin trnh tn hiu Thng bo nghn hin hin
(Explicit Congestion Notification).

o CWR - Khi mt host nhn gi d liu vi thit lp ECE, n thit lp Gim ca s tc
nghn bit rng ECE nhn.

o ECE - C hai ngha:
Nu bit SYN l xa v 0, th sau ECE ngha l gi IP c thit lp bit Tri

qua nghn (congestion experience-CE).
Nu bit SYN c thit lp ti 1, ECE ngha l thit b l ECE c nng lc.
Trang 88

o URG - N ch dn rng trng im tr khn cp (urgent pointer) c d liu quan
trng v nn c x l.
o ACK - N ch dn rng trng Tn hiu tha nhn l c ngha. Nu ACK l xa v
0, n ch rng gi d liu khng cha bt k tn hiu tha nhn no.

o PSH - Khi thit lp, n l mt yu cu ti trm nhn ti d liu PUSH (ngay sau khi
n n) ti ng dng nhn m khng m n.

o RST - t li c hiu c cc c im sau:
N c s dng t chi mt kt ni ang nhp vo.
N c s dng loi b mt on.
N c s dng khi ng li mt kt ni.
o SYN - C hiu ny c s dng thit lp mt kt ni gia cc host.

o FIN - C hiu ny c s dng tho mt kt ni ra v khng c d liu no
thm c trao i sau . Bi v cc gi vi c hiu SYN v FIN c cc s th t

dy, chng c x l theo th t chnh xc.
C ca s - Trng ny c s dng iu khin lung gia hai trm v ch dn s

lng byte m ngi nhn c cp pht cho mt on, v d: bao nhiu d liu l
trm nhn mong i.
Tng kim tra - Trng ny cha s tng kim tra v Header, d liu v cc Header gi.
im tr khn cp - N tr ti byte d liu khn cp nu c hiu URG c thit lp ti 1.
Cc tnh nng - N cung cp chc nng thm vo m khng c ph bi header chnh

quy. Trng tnh nng l lun lun c miu t trong 32 bit. Nu trng ny cha d liu
t hn 32 bit, vt m c s dng ph cc bit cn li tip cn gii hn 32 bit.
Ghi a ch
Giao tip TCP gia hai host c thc hin theo ngha ca s hiu cng (TSAPs). Cc s hiu
cng c th l dy t 0 n 65535 m c phn chia nh sau:
Cc cng h thng (0-1023)
Trang 89
Cc cng ngi dng (1024-49151)
Cc cng c nhn/ng (49152-65535)
Qun l kt ni
Giao tip TCP lm vic trong M hnh server/client. Client khi to kt ni v server chp nhn v
t chi n. 3 cch c s dng cho qun l kt ni l:
S thnh lp
Client khi to kt ni v gi on d liu vi mt s th t dy. My server gi tn hiu tha nhn
quay tr li vi s th t dy v ACK ca on client m l mt s nhiu hn s th t dy ca
client. Client sau khi nhn ACK ca on ca n s gi mt tn hiu tha nhn ca s phn hi
ca server.
Trang 90
S tho b
Hoc server hoc client c th gi phn on TCP vi c hiu FIN thit lp ti 1. Khi u nhn
phn hi tr li bi tn hiu tha nhn, s iu hng ca giao tip TCP c ng v kt ni
c tho b.
Qun l bng thng

TCP s dng khi nim c ca s cung cp s cn thit ca qun l bng thng. C ca s ni
co trm gi ti u t xa, s lng phn on byte d liu m trm nhn ti u ny c th nhn.
TCP s dng pha khi to chm bi s dng c ca s 1 v tng c ca s theo hm m sau mi
giao tip thnh cng.
V d, client s dng c ca s l 2 v gi 2 byte d liu. Khi tn hiu tha nhn ca on ny
c nhn, c ca s c gp i ln thnh 4 v on c gi k tip s c di l 4 byte.
Khi tn hiu tha nhn ca on 4 byte d liu c nhn, client thit lp c ca s ln 8, v c
tip tc nh th.
Nu mt tn hiu tha nhn b l, v d: d liu tht lc trong mng truyn ti hoc n nhn NACK,
th khi c ca s b gim xung mt na v pha khi to chm bt u li.
Kim sot lung v Kim sot li

TCP s dng s hiu cng (port) bit rng tin trnh ng dng no n cn phi bn giao on
d liu. Song song vi , n s dng cc s th t dy ng b chnh n vi host t xa. Tt
c cc on d liu c gi v c nhn vi cc s th t dy. Trm gi bit on d liu cui
nhn bi trm nhn khi n nhn ACK. Trm nhn bit v on d liu cui gi bi Trm gi bi
lin h s th t dy ca gi d liu nhn gn y.
Nu s th t dy ca on nhn gn y khng kt ni vi s th t dy trm nhn mong i, th
khi n b loi b v NACK c gi tr li. Nu hai on d liu n cng vi mt s th t
dy, gi tr hng thi gian TCP c so snh a ra mt quyt nh.
S ghp knh
K thut kt ni hai hoc nhiu lung d liu trong mt phin truyn ti (session) c gi l
ghp knh. Khi mt TCP client khi to mt kt ni vi server, n lun lun lin h ti mt port r
rng m ch dn tin trnh ng dng. Client chnh n s dng s hiu cng c to ngu nhin t
pool s hiu cng t nhn.
Trang 91

S dng k thut ghp knh TCP, mt client c th giao tip vi mt s tin trnh ng dng khc
nhau trong mt phin n. V d, mt client yu cu mt trang web m cha cc kiu d liu khc
nhau (HTTP, SMTP, FTP), thi gian tr phin TCP c tng v phin c gi m trong thi
gian di hn m 3 kiu chi ph c th c trnh.
iu ny cho h thng client kh nng nhn nhiu kt ni thng qua mt kt ni o n. Cc
kt ni o ny khng tt cho cc server nu thi gian tr l qu di.
Kim sot tc nghn

Khi mt lng ln d liu c gi ti h thng m vt kh nng kim sot, tc nghn xy ra.
TCP kim sot tc nghn bi k thut ca s. TCP thit lp mt c ca s ni cho u khc bit
bao nhiu on d liu gi. TCP c th s dng 3 thut ton cho kim sot li:
S tng ln tnh cng, s gim i tnh nhn (AI, MD)
Khi to chm
Phn ng li thi gian tr
Qun l ng h bm gi
TCP s dng cc kiu ng h bm gi iu khin v qun l cc nhim v a dng:
ng h bm gi thi gian sng (Keep-alive timer ()
ng h bm gi ny c s dng kim tra tnh nguyn vn v tnh hiu lc ca mt

kt ni.
Khi thi gian sng ht hn, host gi mt cc d (probe) kim tra nu kt ni vn tn ti.
ng h bm gi truyn ti li (retransmission timer)
ng h bm gi ny duy tr phin trng thi ca d liu c gi.
Nu tn hiu tha nhn ca d liu c gi khng nhn trong thi gian truyn ti li, on
d liu c gi li.
ng h bm gi tip tc (persist timer)
Phin TCP c th c dng bi host khi gi c ca s 0.
khi phc li phin, mt host cn gi c ca s vi gi tr ln hn.
Trang 92
Nu on ny khng bao gi tip cn c ti u kt ni khc, c hai u c th i trong

thi gian v hn.
Khi thi gian tip tc ht hn, host gi li c ca s ca n cho u kt ni khc bit.
ng h bm gi tip tc gip trnh cc b tc trong giao tip.
Thi gian i (timed-wait)
Sau khi loi b mt kt ni, host i trong thi gian i kt thc kt ni mt cch hon
ton.
y l m bo rng u kt ni khc nhn c tn hiu tha nhn ca yu cu kt

thc kt ni ca n.
Thi gian i c th ti a l 240 giy.
Phc hi li s tm dng
TCP l mt giao thc ng tin cy. N cung cp s th t dy ti mi byte c gi trong on.
N cung cp k thut phn hi, v d: khi mt host nhn mt gi d liu, n i ti ACK m gi c s
th t hng k tip c mong i (nu n khng phi l on cui cng).
Khi mt TCP server dng s giao tip gia ng v bt u li tin trnh ca n, n gi TPDU
Broadcast ti tt c cc host ca n. Cc host sau c th gi on d liu cui cng m cha
bao gi nhn v mang ti pha trc.
Giao thc UDP trong DCN

Giao thc User Data Protocol l giao thc giao tip Tng truyn ti n gin nht c sn trong b
giao thc TCP/IP. N bao gm s lng ti thiu cc k thut giao tip. UDP c coi nh l giao
thc truyn ti khng ng tin cy nhng n d dng cc dch v IP m cung cp k thut phn
phi vi n lc ti a.
Trong UDP, trm nhn khng to mt tn hiu tha nhn ca gi d liu nhn c v trm gi
khng i cho tn hiu tha nhn ca gi d liu gi. Vic thu gn ny lm cho giao thc ny
khng ng tin cy cng nh d hn x l.
Trang 93
Yu cu ca UDP
Mt cu hi c th ny sinh, ti sao chng ta cn mt giao thc khng ng tin cy truyn ti d
liu? Chng ta trin khai UDP ni m cc gi tha nhn chia s lng quan trng ca bng thng
song song vi d liu thc s. V d, trong trng hp lung video, hng nghn gi d liu c
chuyn tip ti nhng ngi s dng ca n. Vic tha nhn tt c cc gi ny l rc ri v c th
cha mt lng hao ph bng thng ln. K thut phn phi tt nht ca giao thc IP nm di
bo m n lc ti a phn phi cc gi d liu ca n, nhng ngay c khi mt vi gi d liu
trong lung video b tht lc, th n cng khng gy tai hi nghim trng v c th c b qua mt
cch d dng. Vic tht lc mt s gi d liu trong truyn ti lung video v m thanh i khi
khng ai .
Cc c im
UDP c s dng khi tn hiu tha nhn ca d liu khng gi bt c ngha quan trng
no.
UDP l mt giao thc tt vi d liu chy trong mt hng.
UDP l n gin v ph hp vi cc giao tip trn c s truy vn.
UDP l kt ni khng iu hng.
UDP khng cung cp k thut kim sot tc nghn.
UDP khng bo m phn phi d liu theo th t.
UDP l stateless (ngha l khng lu d liu ca client trn server).
UDP l giao thc ph hp cho truyn d liu cc ng dng nh VoIP, lung a phng
tin.
UDP Header
UDP Header l n gin nh tnh nng ca n.
Trang 94

UDP header cha 4 tham s quan trng:
Cng ngun (source port) - Thng tin 16 bit c s dng xc nh cng ngun ca mt
gi d liu.
Cng ch n (destination port) - Thng tin 16 bit c s dng xc nh ng dng
trn thit b ch n.
di - Trng di xc nh di ton b ca gi UDP (bao gm header). N l trng
16 bit v gi tr ti thiu l 8 byte, v d: kch c ca chnh UDP header.
Tng kim tra (checksum) - Trng ny lu gi gi tr tng kim tra c to bi trm gi
trc khi gi. IPv4 c trng ny nhng ty khi trng tng kim tra khng cha bt c
gi tr no, n c to l 0 v tt c cc bit ca n c thit lp v 0.
ng dng UDP
Di y l mt s ng dng m UDP c s dng truyn ti d liu:
Cc dch v tn min (DNS)
Giao thc qun l mng n (Simple Network Management protocol)
Giao thc truyn ti file thng (Trival File Transfer Protocol)
Giao thc thng tin nh tuyn (Routing Information Protocol)
Kerberos (l mt giao thc mt m)
Gii thiu Tng ng dng trong DCN

Tng ng dng l tng trn cng trong M hnh OSi v M hnh tng TCP/IP. Tng ny tn ti
trong c hai M hnh bi v tm quan trng ca n, ca vic tng tc vi ngi s dng v cc
ng dng ngi s dng. Tng ny dng cho cc ng dng m c bao gm trong h thng trao
i thng tin.
Mt ngi s dng c th hoc khng th tng tc trc tip vi cc ng dng. Tng ng dng l
ni cc giao tip thc s c khi to v phn nh. Bi v tng ny l tng trn cng ca cc
tng, n khng phc v bt k tng no khc. Tng ng dng nhn s gip ca tng truyn ti
v tt c cc tng bn di n giao tip hoc truyn ti d liu ca n ti host t xa.
Trang 95

Khi mt giao thc tng ng dng mun giao tip vi giao thc tng ng dng ngang bc vi n
trn host t xa, n truyn d liu hoc thng tin ti tng truyn ti. Tng truyn ti thc hin phn
vic cn li vi s gip ca tt c tng di n.
C mt s m h v vic tm hiu tng ng dng v giao thc ca n. Khng phi mi ng dng

ngi s dng u c th t trong tng ng dng, ngoi tr cc ng dng m tng tc vi h
thng giao tip. V d, thit k phn mm hoc b son vn bn khng c xem nh l cc
chng trnh tng ng dng.
Hiu theo ngha khc, khi chng ta s dng mt trnh duyt, m thc s ang s dng HTTP
tng tc vi mng. HTTP l giao thc Tng ng dng.
V d khc l giao thc Truyn ti file, m gip mt ngi s dng truyn cc file vn bn hoc nh
phn qua mng. Mt ngi s dng c th s dng giao thc ny trong phn mm GUI hoc
CuteFTP v mt ngi s dng khc c th s dng FTP trong ch dng lnh (command line).
V th, bt chp phn mm no bn s dng, n l giao thc m c cho l tng ng dng s
dng bi phn mm . DNS l mt giao thc m gip cc giao thc ng dng ngi dng nh
HTTP thc hin cng vic ca n.
M hnh Client-Server trong DCN

Hai tin trnh ng dng t xa c th giao tip ch yu theo hai kiu khc nhau:
Trang 96
Peer-to-peer: C hai tin trnh c chy ti cng mt mc v chng chuyn i d liu

s dng mt vi ngun c chia s.
Client-Server: Mt tin trnh t xa hot ng nh l mt Client v yu cu mt vi ngun t

tin trnh ng dng khc hot ng nh l Server.
Trong M hnh client-server, bt c tin trnh no c th hot ng nh l client hoc server. N

khng yu cu kiu, c ca thit b, hoc sc mnh tnh ton ca n m lm cho n thnh server.
N l kh nng phc v yu cu m lm mt thit b l Server.
Mt h thng c th hot ng nh Server v Client mt cch k tip nhau. l, mt tin trnh

ang thc hin nh l Server v tin trnh khc ang hot ng nh l mt Client. iu ny c th
cng xy ra khi c hai tin trnh client v server u trn cng mt thit b.
Trang 97
Giao tip trong DCN

Hai tin trnh trong M hnh client-server c th tng tc theo nhiu cch:
Trong mu ny, tin trnh hot ng nh l Server m mt socket s dng mt cng bit v i
ti khi mt vi yu cu ca client ti. Tin trnh th hai hot ng nh l mt client cng m mt
socket nhng thay v i cho mt yu cu n, cc tin trnh client yu cu u tin.
Khi yu cu c ti server, n c lu gi. N c th hoc l mt thng tin chia s hoc l mt

yu cu ngun.
Th tc gi hm t xa trong DCN
y l mt k thut m mt tin trnh tng tc vi tin trnh khc theo phng thc gi hm. Mt
tin trnh (client) gi th tc nm trn host t xa. Tin trnh trn host t xa c xem nh l Server.
C hai tin trnh c cp pht cc stub. S giao tip ny xy ra theo cch sau:
Tin trnh client gi client stub. N truyn tt c cc tham s gn vi ti chng trnh a

phng ti n.
Trang 98

Tt c cc tham s sau c mang v mt tn hiu gi h thng c to ra gi chng
ti bn khc ca mng.
Kernel gi d liu qua mng v u kt ni khc nhn n.
Host t xa truyn d liu ti server stub ti ni m n c mang.
Cc tham s c truyn ti hm v hm sau c chy.
Kt qu c gi tr li ti client theo cch tng t.
Giao thc Tng ng dng trong DCN

C mt vi giao thc m lm vic cho nhng ngi s dng trong tng ng dng. Cc giao thc
tng ng dng c th c phn chia i khi thnh 2 loi:
Giao thc m c s dng bi ngi s dng. V d: email
Giao thc m gip v h tr cc giao thc c s dng bi ngi s dng. V d: DNS.
Mt s giao thc tng ng dng c miu t bn di y:
H thng tn min (Domain Name System) trong DCN

H thng tn min (DNS) lm vic trn M hnh client-server. N s dng giao thc UDP cho giao
tip tng truyn ti. DNS s dng min c th bc trn c s gin tn. DNS server c nh
hnh vi a ch tn min y (FQDN) v cc a ch email c nh x vi cc a ch Giao
thc internet tng ng ca n.
Mt DNS server c yu cu vi FQDN v n phn hi tr li vi a ch IP c nh x vi n.
DNS s dng UDP cng 53.
Giao thc truyn ti mail n gin (Simple Mail

Transfer Protocol) trong DCN
SMTP c s dng truyn ti mail in t t mt ngi s dng ti ngi s dng khc.
Nhim v ny c thc hin bi phn mm email client (user agents) m ngi s dng ang
dng. User Agents gip ngi s dng phn loi v nh dng email v lu gi n ti khi internet
c sn. Khi mt email c trnh gi, tin trnh gi c kim sot bi Dch v th in t
(MTA) m thng i km trong phn mm email client.
Trang 99

Message Transfer Agent (MTA) s dng SMTP chuyn tip email ti MTA khc (bn server).
Trong khi SMTP c s dng bi ngi s dng ch gi email, Server thng s dng SMTP
gi cng nh nhn email. SMTP s dng TCP cng s 25 v 587.
Phn mm client s dng Giao thc truy cp thng bo internet (Internet Message Access Protocol
- IMAP) hoc cc giao thc POP nhn cc email.
Giao thc truyn ti file (File Transfer Protocol) trong

DCN
Giao thc truyn ti file (FTP) l giao thc c s dng rng ri nht cho truyn ti file qua mng.
FTP s dng TCP/IP cho giao tip v n lm vic trn cng TCP 21. FTP lm vic trn M hnh
client/server m mt client yu cu file t server v server gi ngun ti nguyn c yu cu tr
li client.
FTP s dng kim sot out-of-band, v d: FTP s dng cng TCP 20 cho trao i thng tin kim
sot v d liu thc s c gi qua cng TCP 21.
Client yu cu server mt file. Khi server nhn mt yu cu cho mt file , n m mt kt ni TCP
cho client v truyn ti file . Sau khi qu trnh truyn ti kt thc, server ng kt ni. Vi mt file
th hai, client yu cu li v server m li mt kt ni TCP mi.
Giao thc POP (Post Office Protocol) trong DCN

Giao thc POP phin bn 3 l mt giao thc thu hi mail n gin c s dng bi User Agents
thu hi cc mail t server.
Khi mt client cn thu hi mail t server, n m mt kt ni vi server trn cng TCP 110. Ngi
s dng sau c th truy cp mail ca anh ta v ti chng xung ti my a phng. POP 3 lm
vic theo 2 ch . Ch ph bin nht l ch xa, l xa email t server t xa sau khi
chng c ti xung ti cc thit b a phng. Ch th hai, l ch gi, khng xa
email t server v cung cp cho ngi s dng mt tnh nng truy cp vo mail sau trn
server.
Giao thc truyn ti siu vn bn (HTTP) trong DCN

HTTP l nn tng ca World Wide Web. Siu d liu l h thng ti liu c t chc cht ch m
s dng cc siu lin kt lin kt cc trang trong cc ti liu vn bn. HTTP lm vic trn M
hnh client server. Khi mt ngi s dng mun truy cp vo bt k trang HTTP no trn internet,
Trang 100

thit b client ti u kt ni ngi dng khi to mt kt ni TCP ti server trn cng 80. Khi
server chp nhn cc yu cu ca client, client c quyn truy cp vo cc trang web.
truy cp vo cc trang web, mt client thng s dng cc trnh duyt web, c chc nng cho
khi to, duy tr, v ng cc kt ni TCP. HTTP l mt giao thc stateless, m ngha l server duy
tr khng thng tin no v cc yu cu sm hn bi cc client.
Cc phin bn HTTP
HTTP 1.0 s dng HTTP khng c. Mt i tng c th c gi qua mt kt ni TCP

n.
HTTP 1.1 s dng HTTP c. Trong phin bn ny, nhiu i tng c th c gi qua
mt kt ni TCP n.
Dch v mng trong DCN

Cc h thng my tnh v cc h thng in ton ha gip con ngi ngy nay lm vic mt cch
hiu qu v to ra nhng iu khng tng. Khi nhng thit b ny c kt ni li vi nhau to
thnh mt mng, kh nng ca n c nng ln nhiu ln. Mt s mng my tnh c th cung cp
cc dch v c bn:
Cc dch v th mc
Nhng dch v ny c nh x gia tn v gi tr ca n, m c th l gi tr bin hoc c nh.
H thng phn mm ny gip lu gi thng tin, t chc n, v cung cp cc phng thc a
dng truy cp n.
Accounting
Trong mt t chc, s cc ngi s dng c tn v mt khu ca chng nh x ti chng.
Cc dch v th mc cung cp cc phng thc lu gi thng tin ny trong mu b mt v
lm cho chng c sn s dng khi c yu cu.
S xc nhn v s cho php

Cc s y nhim ngi dng c kim tra xc nhn mt ngi s dng ti thi gian
ng nhp v hoc theo nh k. Cc ti khon ngi s dng c th c thit lp trong
Trang 101

cu trc c th bc v s truy cp ca n ti cc ti nguyn c th c kim sot bi s
dng cc gin y quyn.
Cc dch v tn min (DNS)

DNS c s dng rng ri v l mt trong nhng dch v ct yu m trn internet lm
vic. H thng ny nh x cc a ch IP ti cc tn min, m l d dng hn nh v
gi li hn cc a ch IP. Bi v mng iu hnh vi s gip ca cc a ch IP v con
ngi c khuynh hng nh tn cc web, DNS cung cp a ch IP ca web m c nh
x ti tn ca n t back-end trn cc yu cu ca mt tn web t ngi s dng.
Cc dch v file
Cc dch v file bao gm chia s v truyn ti cc file qua mng.
Chia s file
Mt trong nhng l do khin cho s ra i ca mng l chia s file. Chia s file cho nhng
ngi s dng ca n kh nng chia s d liu cu h vi ngi s dng khc. Ngi
s dng c th ti mt file ln ti mt server c th, m c truy cp bi tt c nhng
ngi s dng c nh.
Truyn ti file
y l mt hot ng sao chp hoc di chuyn file t mt my tnh ti my tnh khc
hoc ti nhiu my tnh, vi s gip ca tng mng nm di. Mng cho nhng ngi
s dng ca n kh nng xc nh v tr ca ngi s dng khc trong mng v truyn
ti nhng file.
Cc dch v trao i thng tin
Email
Th in t l mt phng thc giao tip v l mt ci g m mt ngi s dng my
tnh khng th lm vic m khng c n. y l c s ca cc c im ca internet hin
nay. H thng email c mt hoc nhiu server th in t. Tt c ngi s dng ca n
c cung cp mt ID duy nht. Khi mt ngi s dng gi email ti ngi s dng khc,
n c truyn ti thc s gia nhng ngi s dng vi s gip ca server th in
t.
Trang 102
Mng x hi
Cc cng ngh gn y cho ra nhiu cng ngh x hi ha. My tnh hiu con ngi, c
th tm thy ngi c bit hoc bn b khc, c th kt ni vi h, v c th chia s
ngh, hnh nh v video.
Internet Chat
Internet chat cung cp cc dch v truyn ti vn bn ngay lp tc gia cc host. Hai hoc
nhiu ngi c th giao tip vi nhau s dng cc dch v Internet Relay Chat. Ngy nay,
voice chat v video chat cng rt ph bin.
Din n tho lun

Din n tho lun cung cp mt k thut kt ni nhiu ngi vi cng mt mng
internet. N cho nhng ngi s dng kh nng t cc cht vn, cc cu hi, cc li
ngh, m c th c gi bi tt c ngi s dng. Mt s ngi s dng khc cng
c th phn hi li.
Truy cp t xa
Dch v ny cho ngi s dng kh nng truy cp vo d liu trn my tnh t xa.
c im ny c bit n nh l Mn hnh t xa. iu ny c th c thc hin thng
qua mt s thit b iu khin, v d: in thoi di ng hoc my tnh ti nh.
Cc dch v ng dng
Chng khng l ci g nhng cung cp cc dch v c s mng ti nhng ngi s dng nh cc
dch v web, qun l d liu, v chia s ngun ti nguyn.
Chia s ngun ti nguyn

s dng cc ngun ti nguyn mt cch hiu qu v kinh t nht, mng cung cp mt
phng thc chia s chng. iu ny c th bao gm cc server, cc my in, v cc
phng tin lu gi.
C s d liu
Trang 103

Dch v ng dng ny l mt trong nhng dch v quan trng nht. N lu d liu v thng
tin, x l n, v cho ngi s dng kh nng khi phc n mt cch kinh t. C s d
liu gip cc t chc to cc quyt nh trn c s cc s liu thng k.
Cc dch v web
World Wide Web tr thnh t ng ngha vi internet. N c s dng kt ni vi
internet v truy cp cc file v cc dch v thng tin c cung cp bi cc server.
Ti liu tham kho v DCN

Cc ti liu di y cha cc thng tin thm v Giao tip d liu v Mng my tnh (Data
Communication & Computer Networks). Bn nn s dng chng nng cao kin thc ca mnh
cng nh gip bn hiu hn nhng ch trong lot bi hng dn ny.
Cc ng link hu ch v DCN
Tutorialspoint Lot bi hng dn ca chng ti xy dng da trn ngun ny.
Computer Networks on Wikipedia - Vit v Mng my tnh trn Wikipedia.
Trang 104

Tài Liệu Mạng Máy Tính Tiếng Việt

Uploaded by

Document Information

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Tài Liệu Mạng Máy Tính Tiếng Việt

Uploaded by

Copyright:

Available Formats

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Trao i d liu & Mng my tnh

Tng quan v Trao i d liu v Mng

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Phn loi mng my tnh

Lin kt theo khong khng gian (geographical span)

Lin kt theo khong khng gian

N c th c kt ni qua bn ca bn, bn trong cc thit b Bluetooth. Xp dy khng di

N c th c kt ni qua mt ta nh, bao gm cc thit b trung gian kt ni tt c cc

N c th c kt ni qua mt thnh ph.

N c th c kt ni qua nhiu thnh ph hoc nhiu tnh.

N c th c kt ni qua ton th gii.

Mi thit b n c th c kt ni vi mi thit b khc trn mng, lm cho mng khp

Tt c cc thit b c th c kt ni ti mt trung gian n nhng khong khng gian l

Mi thit b c kt ni ch ti cc thit b ngang hng bn phi v tri, to cu trc tuyn.

Tt c thit b c kt ni vi nhau vi mt thit b n, to cu trc hnh sao.

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Tt c cc thit b c kt ni mt cch ty s dng tt c cc cch trn kt ni mi

Cc mng my tnh c th c phn bit vo trong cc kiu khc nhau nh Client-Server,

C th c mt hoc nhiu h thng ng vai tr nh server. Cc h thng khc l client, a

Hai h thng c th c kt ni ngang bng theo kiu Point-to-Point hoc back-to-back.

C th c mt mng hn hp m bao gm c hai kiu cu trc trn.

Chia s ngun ti nguyn nh my in v cc thit b lu gi.

Trao i thng tin (email, FTP).

Chia s thng tin bng vic s dng web hoc internet.

Tng tc vi ngi s dng khc s dng cc trang web ng.

in ton song song

Th tn ngay lp tc (instant messaging)

Cc loi mng my tnh trong DCN

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Mng khu vc c nhn (PAN) trong DCN

V d, Piconet l mt mng khu vc c nhn Bluetooth m c th cha ti 8 thit b c kt ni

Mng khu vc ni b (LAN) trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

LAN c to thnh t cc thit b mng v thit b tuyn c gi tr r. N c th bao gm cc

Mng khu vc trung tm (MAN) trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Mng khu vc rng (WAN) trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Mng internet trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Chia s ngun ti nguyn

Audio and Video

Cc cng ngh mng LAN trong DCN

Cng ngh Ethernet trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com

Cng ngh Fast-Ethernet trong DCN

Cng ngh Giga-Ethernet trong DCN

Cng ngh Mng LAN o trong DCN

http://vietjack.com/ Trang chia s cc bi hc online min ph

http://vietjack.com/data_communication_computer_network/index.jsp Copyright vietjack.com