giao thuc tcpip

8/2/2019 Giao Thuc Tcpip

1/122

n tt nghip Giao thc TCP/IP

V Khoa TTT4 K40 1

CHNG 1: GIITHIUV GIAO THC TCP/IP

1.1. Lch spht trin caTCP/IP v mng InternetMng Internet l mt mng my tnh ton cu, bao gm hng chc triu

ngi s dng, c hnh thnh t cui thp k 60 t mt th nghim ca B

quc phng M. Ti thi im ban u l mng ARPAnet ca Ban qun l

d n nghin cu Quc phng. ARPAnet l mt mng th nghim phc v cc

nghin cu quc phng, mt trong nhng mc ch ca n l xy dng mt

mng my tnh c kh nng chu ng cc s c (v d mt s nt mng b tn

cngv ph hu nhng mng vn tip tc hot ng). Mng cho php mt my

tnh bt k trn mng lin lc vi mi my tnh khc.

Kh nng kt ni cc h thng my tnh khc nhau hp dn mi ngi,

v li y cng l phng php thc t duy nht kt ni cc my tnh ca cc

hng khc nhau. Kt qu l cc nh pht trin phn mm M, Anh v Chu

u bt u pht trin cc phn mm trn b giao thc TCP/IP (giao thc c

s dng trong vic truyn thng trn Internet) cho tt c cc loi my. iu ny

cng hp dn cc trng i hc, cc trung tm nghin cu ln v cc cquan

chnh ph, nhng ni mong mun mua my tnh t cc nh sn xut, khng b

ph thuc vo mt hng cnh no.

Bn cnh cc h thng cc b LAN bt u pht trin cng vi s xuthin cc my bn (Desktop Workstations) vo nm 1983. Phn ln cc my

bn s dng Berkeley UNIX, phn mm cho kt ni TCP/IP c coi l

mt phn ca hiu hnh ny. Mt iu r rng l cc mng ny c th kt ni

vi nhau d dng.

Trong qu trnh hnh thnh mng Internet, NSFNET (c s ti trca

Hi khoa hc Quc gia M) ng mt vai tr tng i quan trng. Vo cui

nhng nm 80, NFS thit lp 5 trung tm siu my tnh. Trc , nhng my

tnh nhanh nht th gii c s dng cho cng vic pht trin v kh mi v

mt vi hng ln. Vi cc trung tm mi ny, NFS cho php mi ngi hotng trong lnh vc khoa hc c s dng. Ban u, NFS nh s dng

ARPAnet ni 5 trung tm my tnh ny, nhng ny b thi quan liu

v b my hnh chnh lm tht bi. V vy, NFS quyt nh xy dng mng

ring ca mnh, vn da trn th tc TCP/IP, ng truyn tc 56 Kbps. Cc


2/122


V Khoa TTT4 K40 2

trng i hc c ni thnh cc mng vng v cc mng vng c ni vi

cc trung tm siu my tnh.

Ngy nay mng Internet c pht trin nhanh chng trong gii khoa

hc v gio dc ca M, sau pht trin rng ton cu, phc v mt cch c

lc cho vic trao i thng tin trc ht trong cc lnh vc nghin cu, gio dcv gn y cho thng mi.

Internet s dng k thut chuyn mch gi v dng giao thc TCP/IP.

Ngy nay nhiu mng vi kin trc khc nhau c thni vo Internet nhcc

cu ni a giao thc.

1.2. Giao thc TCP/IP

Khi nim giao thc (Protocol) l mt khi nim cbn ca mng truyn

thng. C th hiu mt cch khi qut l tp hp tt c cc quy tc cn thit

(cc th tc, cc khun dng d liu, cc cch ph tr....) cho php cc giaothc trao i thng tin trn mng c thc hin mt cch chnh xc v an ton.

C rt nhiu h giao thc ang c s dng trn mng truyn thng hin nay

nh IEEE802.X dng trong mng cc b, CCITT (nay l ITU) dng cho lin

mng din rng v c bit l h giao thc chun ca ISO (t chc tiu chun

ho quc t ) da trn m hnh tham chiu by lp cho vic kt ni cc h

thng m. Trn Internet h giao thc c s dng l b giao thc TCP/IP .

Hai giao thc c dng ch yu y l TCP ( Transmision Control Protocol

) v IP (Internet Protocol ). TCP l mt giao thc kiu c kt ni (Connection-

Oriented), tc l cn phi c mt giai on thit lp lin kt gia mt cp thc

th TCP trc khi chng thc hin trao i d liu. Cn giao thc IP l mt

giao thc kiu khng kt ni (Connectionless), ngha l khng cn phi c giai

on thit lp lin kt gia mt cp thc th no trc khi trao i d liu .

Khi nim TCP/IP khng ch b gii hn hai giao thc ny. Thng th

TCP/IP c dng ch mt nhm cc giao thc c lin quan n TCP v IP

nh UDP (User Datagram Protocol), FTP (File Transfer Protocol), TELNET

(Terminal Emulation Protocol) v v.v...

gim phc tp ca vic thit k v ci t mng hu ht cc mngmy tnh hin c u c phn tch thit k theo quan im phn tng . Mi h

thng thnh phn ca mng c xem nh l mt cu trc a tng, trong

mi tng c xy dng trn cstng trc . S lng cc tng cng nh

tn v chc nng ca mi tng l tu thuc vo nh thit k. H giao thc ca

ISO (t chc tiu chun ho quc t) da trn m hnh tham chiu 7 lp cho


3/122


V Khoa TTT4 K40 3

vic kt ni cc h thng m l h giao thc c dng lm chun cc h

giao thc khc so snh vi n do vy trc khi i vo nghin cu giao thc

TCP/IP ta cn xem xt m hnh 7 lp OSI.

Trong m hnh OSI mc ch ca mi tng l cung cp cc dch v cho

tng cao hn tip theo, m t chi tit cch thc ci t cc dch v ny. Cc tngc tru tng ho theo cch l mi tng ch bit rng n lin lc vi tng

tng ng trn my khc. Trong thc t th mi tng ch lin lc vi cc tng k

trn v k di n trn mi h thng m thi.

Tr tng thp nht trong m hnh mng khng tng no c th chuyn

thng tin mt cch trc tip vi tng tng ng trong mng my tnh khc.

Thng tin trn my cn gi phi c chuyn i qua tt c cc tng thp hn.

Thng tin sau li c truyn qua Card mng ti my nhn v li c

truyn ln qua cc tng cho n khi n n tng gi thng tin i.

1.2.1. M hnh 7 lp OSI

M hnh ny bao gm 7 tng. Tn gi v chc nng cc tng c trnh by

trong hnh 1.1.

H thng mA H thng mB

7 APPLICATION NG DNG 7

6 PRESENTATION TRNH DIN 6

5 SESSION PHIN 5

4 TRANSPORT GIAO VN 4

3 NETWORK MNG 3

2 DATA LINK LIN KT DLIU 2

1 PHYSICAL VT L 1

Hnh 1.1: M hnh 7 lp OSI

Chc nng ca cc tng nhsau:1. Tng vt l (Physical): Lin quan n nhim v truyn dng bits khng

c cu trc qua ng truyn vt l, truy nhp ng truyn vt l nh

cc phng tin c, in, hm, vt l.

Giao thc tng 7

Giao thc tng 6

Giao thc tng 5

Giao thc tng4Giao thc tng 3

Giao thc tng 2

Giao thc tng1

ng truyn vt l


4/122


V Khoa TTT4 K40 4

2. Tng lin kt dliu (Data link): Cung cp phng tin truyn thng

tin qua lin kt vt l m bo tin cy, gi cc khi d liu vi cc c

chng b ho, kim sot li v kim sot lung d liu cn thit.

3. Tng mng (Network): Thc hin vic chn ng v chuyn tip thng

tin vi cng ngh chuyn mch thch hp, thc hin kim sot lung dliu v ct/ hp d liu nu cn.

4. Tng giao vn (Transport): Thc hin vic truyn d liu gia hai u

mt (end - to - end), thc hin c vic kim sot li v kim sot lung

d liu gia hai u mt. Cng c th thc hin vic ghp knh, ct / hp

d liu nu cn.

5. Tng phin (Session): Cung cp phng tin qun l truyn thng gia

cc ng dng, thit lp, duy tr, ng b ho v hu b cc phin truyn

thng gia cc ng dng.

6. Tng trnh din (Presentation): Chuyn i c php d liu p ngyu cu truyn d liu ca cc tng ng dng qua m hnh OSI.

7. Tng ng dng (Application): Cung cp cc phng tin ngi s

dng c th truy cp c vo mi trng OSI, ng thi cung cp cc

dch v thng tin phn tn.

1.2.2. Giao thc TCP/IP v m hnh 7 lp OSI

Mng Internet vi h giao thc TCP/IP c minh ho tng qut nh hnh

1.2 vi cc dch v m n cung cp v cc chun c s dng c so snh vi

kin trc h thng mOSI chng ta c mt cch nhn tng qut v h giaothc ny.

Hnh 1.2: Giao thc TCP/IP khi so snh vi m hnh OSI

OSI Model TCP/IP Architectual Model

Application

Presentation

Session

Transport

Network

Data link

Physical

Telnet FTP SMTP DNS SNMP

Transmision ControlProtocol (TCP)

UserDatagramProtocol (UDP)

RIP

ICMP

Internet Protocol (IP)ARP

Ethernet Tokenbus Token Ring FDDI

IEEE802.3 IEEE802.4 EEE802.5 ANSI X3 T95


5/122


V Khoa TTT4 K40 5

Trong :

TCP: (Transmistion Control Protocol)Th tc lin lc tng giao vn ca

TCP/IP. TCP c nhim vm bo lin lc thng sut v tnh ng n ca d

liu gia 2 u ca kt ni, da trn cc gi tin IP.

UDP: (User Datagram Protocol) Th tc lin kt tng giao vn ca

TCP/IP. Khc vi TCP, UDP khng m bo kh nng thng sut ca d liu,

cng khng c ch sa li. B li, UDP cho tc truyn d liu cao hnTCP.

IP: (Internet Protocol) L giao thc tng th 3 ca TCP/IP, n c trch

nhim vn chuyn cc Datagrams qua mng Internet.

ICMP: (Internet Control Message Protocol) Th tc truyn cc thng tin

iu khin trn mng TCP/IP. X l cc tin bo trng thi cho IP nh li v cc

thay i trong phn cng ca mng nh hng n s nh tuyn thng tin

truyn trong mng.

RIP: (Routing Information Protocol) Giao thc nh tuyn thng tin y

l mt trong nhng giao thc xc nh phng php nh tuyn tt nht chotruyn tin.

ARP: (Address Resolution Protocol) L giao thc tng lin kt d liu.

Chc nng ca n l tm a ch vt l ng vi mt a ch IP no . Mun vy

n thc hin Broadcasting trn mng, v my trm no c a ch IP trng vi

a ch IP ang c hi s tr li thng tin va ch vt l ca n.

DSN: (Domain name System) Xc nh cc a ch theo s t cc tn ca

my tnh kt ni trn mng.

FTP: (File Transfer Protocol) Giao thc truyn tp truyn tp t mtmy ny n mt my tnh khc. Dch v ny l mt trong nhng dch v c

bn ca Internet.

Telnet: (Terminal Emulation Protocol) ng k s dng my ch t xa

vi Telnet ngi s dng c th t mt my tnh ca mnh xa my ch, ng

k truy nhp vo my ch x dng cc ti nguyn ca my ch nh l mnh

ang ngi ti my ch.

FTP File Transfer ProtocolSMTP- Simple Mail Transfer ProtocolDNS Domain Name SystemSNMP Simple Network Manage Protocol

ICMP- Internet Control Message ProtocolARP - Address Resolution ProtocolFDDI - - Fiber Distributed Data InterfaceRPI - - Routing Information Protocol


6/122


V Khoa TTT4 K40 6

SMTP: (Simple Mail Transfer Protocol) Giao thc truyn thn gin: l

mt giao thc trc tip bo m truyn thin t gia cc my tnh trn mng

Internet.

SNMP: (Simple Network Management Protocol) Giao thc qun tr mng

n gin: l dch v qun tr mng gi cc thng bo trng thi v mng vcc thit b kt ni mng.

1.2.3. Giao thc lin mng IP

Mc ch chnh ca IP l cung cp kh nng kt ni cc mng con thnh

lin mng truyn d liu. Vai tr ca IP tng t vai tr ca giao thc tng

mng trong m hnh OSI. Mc d tInternet xut hin trong IP nhng giao

thc ny khng nht thit phi s dng trn Internet. Tt c cc my trm trn

Internet u hiu IP, nhng IP c th s dng trong cc mng m khng c s

lin h vi Internet.IP l giao thc kiu khng kt ni (Connectionless) tc l khng cn c

giai on thit lp lin kt trc khi truyn d liu. n v d liu dng trong

giao thc IP lIP Datagram hay gi tt l Datagram.

Mt Datagram c chia lm hai phn : Phn tiu (Header) v phn

cha dliu cn truyn (Data). Trong phn Header gm mt s trng cha

cc thng tin iu khin Datagram.

1.2.3.1.Cu trc ca IP Datagram

Cu trc tng qut ca mt IP Datagram nh sau:DATAGAM HEADER DATAGRAM DATA AREA

Cu trc chi tit ca mt IP Datagram Header c m t nh hnh 1.3.

Version IHL Type of

service

Total length

Identification Flags Fragment offset

Time to live Protocol Header checksum

Source IP addressDestination IP address

Options Padding

Datas

:

Hnh 1.3: Cu trc ca Datagram


7/122


V Khoa TTT4 K40 7

Trong :

Trng version (4 bits) cho bit phin bn ca IP ang c s dng,

hin nay l IPv4. Trong tng lai th a ch IPv6 sc s dng.

IHL (4 bits) Ch th di phn u (Internet Header Length) caDatagram tnh theo n v t ( 32 bits).

Type of service (8 bits), c t cc tham s v dch v. Khun dng ca

n c ch ra nh sau.

0 1 2 3 4 5 6 7

Precedence D T R Reserved

8 Bits ca trng Service c chia ra lm 5 phn c th nh sau :

Precedence (3 bits) ch th quyn u tin gi Datagram, cc mc u

tin t 0 (bnh thng) n mc cao nht l 7 (iu khin mng) chophp ngi s dng ch ra tm quan trng ca Datagram.

Ba bit D, T, R ni nn khiu truyn Datagram, c th nh sau:

Bit D (Delay)ch tr yu cu.

Bit T (Throughput) ch thng lng yu cu.

Bit R (Reliability) ch tin cy yu cu.

Reserved (2 bits) cha s dng.

Total Length (16 bits) : Ch di ton b Datagram k c phn Header.

n v tnh l Byte. Identification (16 bits) Trng ny c s dng gip cc Host ch

lp li mt gi b phn mnh, n cng cc trng khc nh Source

Address, Destination Address nh danh duy nht mt Datagram khi

n cn trn lin mng.

Flags( 3 bits) lin quan n s phn on cc Datagrams c th nh sau:

0 1 2

0 DF MF

Trong cc thnh phn:Bit 0 Cha s dng ly gi tr 0.

Bit 1 (DF) DF=0: Thc hin phn on.

DF=1: Khng thc hin phn on.

Bit 2 (MF) MF=0: Phn on ln cui.

MF=1: Phn on thm.


8/122


V Khoa TTT4 K40 8

Fragment offset (13 bits): Ch v tr ca on (Fragment) trong

Datagram. n v tnh l 64 bits (8 Bytes).

Time to live (8 bits): Cho bit thi gian tn ti ca Datagram trn lin

mng. trnh tnh trng mt Datagram b qun trn lin mng. Nu sau

mt khong thi gian bng thi gian sng m Datagram vn cha nch th n b hu.

Protocol (8 bits) Cho bit giao thc tng trn k tip s nhn vng d

liu trm ch. Giao thc tng trn ca IP thng l TCP hoc UDP.

Header Checksum (16 bits): y l m kim sot li 16 bits theo

phng php CRC cho vng Header nhm pht hin cc li ca

Datagram.

Source Address (32 bits) Cho bit a ch IP ca trm ngun.

Destination Address (32 bits) Cho bit a ch IP ca trm ch. Trong

mt lin mng a ch IP ca trm ngun v a ch IP ca trm ch lduy nht.

Options ( di thay i) Dng khai bo Options do ngi s dng

yu cu.

Padding ( di thay i) L mt vng m c dng m bo cho

phn Header lun kt thc mc 32 bits. Gi tr ca Padding gm ton

bit 0.

Data ( di thay i) Vng d liu c di l bi s ca 8 bits. Kch

thc ti a ca trng Data l 65535 Bytes.1.2.3.2.Qu trnh phn mnh cc gi dliu

Trong qu trnh truyn d liu, mt gi d liu (Datagram) c thc

truyn i qua nhiu mng khc nhau. Mt gi d liu nhn c t mt mng

no c th qu ln truyn i trong mt gi n ca mng khc, bi vy

mi loi cu trc mng cho php mt n v truyn cc iMTU (Maximum

Transmission Unit) khc nhau. y chnh l kch thc ln nht ca mt gi

m chng c th truyn c. Nu nh mt gi d liu nhn c t mt mng

no m kch thc ca n ln hn MTU ca mng khc th n cn cphn mnh ra thnh gi nh hn gi l Fragment truyn i, qu trnh ny

gi l qu trnh phn mnh. Dng ca mt Fragment cng ging nh dng ca

mt gi d liu thng thng. T th hai trong phn Header cha cc thng tin

xc nh mi Fragment v cung cp cc thng tin hp nht cc Fragments

ny li thnh cc gi nh ban u. Trng nh danh (Indentification)dng

xc nh Fragment ny thuc vo gi d liu no. Trng nh danh c mt gi


9/122


V Khoa TTT4 K40 9

tr duy nht cho mi gi d liu c vn chuyn. Mi thnh phn ca gi d

liu b phn mnh s c cng gi tr trng nh danh. iu cho php IP lp

rp li cc gi d liu b phn mnh mt cch ph hp.

Hu qu ca vic phn mnh d liu l cc gi b phn mnh sn ch

chm hn so vi mt gi khng b phn mnh. V vy phn ln cc ng dngu trnh khng s dng k thut ny nu c th. V s phn mnh to ra cc

gi d liu ph nn cn qu trnh s l ph lm gim tnh nng ca mng. Hn

na v IP l mt giao thc khng tin cy nn khi bt k mt gi d liu b phn

mnh no b mt th tt c cc mnh s phi truyn li. Chnh v l do ny nn

phi gi cc gi d liu ln nht m khng b phn mnh, gi tr ny l Path

MTU.

1.2.3.3. Phng php nh a chtrong TCP/IP

c th thc hin truyn tin gia cc my trn mng, mi my tnh trnmng TCP/IP cn phi c mta chxc nh gi l a chIP. Hin nay mi

a ch IP c to bi mt s 32 bits (IPv4)v c tch thnh 4 vng, mi

vng c mt Byte c th biu th di dng thp phn, nh phn, thp lc phn

hoc bt phn. Cch vit ph bin nht hay dng l cch vit dng k t thp

phn. Mt a ch IP khi sc biu din bi 4 s thp phn c gi tr t0

n 255 v c phn cch nhau bi du chm (.). Mi gi tr thp phn biu

din 8 bits trong a ch IP.Mc ch ca a chIP l nh danh duy nht

cho mt hosttrn mng .

IPv4 s dng 3 loi a ch trong trng ngun v ch l:1. Unicast: th hin mt a chn hng. a chn hng l a

ch dng nhn dng tng nt mt (im nt l tp cc thit b chuyn

mch nm trung tm nh Router chng hn ) c th l mt gi d liu

c gi ti mt a chn hng sc chuyn ti nt mang a ch

n hng .

2.Multicast: a cha hng. L a ch dng nhn dng mt tp hp

nt nhng khng phi l tt c. Tp hp nt bao gm nhiu nt khc

nhau hp thnh, gi d liu IP gi ti mt a ch Multicast sc giti tt c cc Host tham d trong nhm Multicast ny.

3.Broadcast: Th hin tt c cc trm trn mng. Thng thng iu

gii hn tt c cc Host trn mt mng con a phng.

Cc a ch IP c chia ra lm hai phn, mt phn xc nh mng (net

id) v mt phn xc nh host(host id). Cc lp mng xc nh s bits c

dnh cho mi phn mng v phn host. C nm lp mng l A, B, C, D, E,


10/122


V Khoa TTT4 K4010

trong ba lp u l c dng cho mc ch thng thng, cn hai lp D v

E c dnh cho nhng mc ch c bit v tng lai. Trong ba lp chnh

l A,B,C.

Hnh v sau cho thy cu trc ca mt a ch IP.

Mi lp a chc c trng bi mt s bits u tin ca Byte u tin

c cu trc chi tit nh hnh 1.4.

Hnh 1.4: Cu trc cc khun dng a ch

T cu trc phn lp a ch ta c th nhn thy:

Nh hn 128 l a ch lp A. Byte u tin xc nh a ch mng, ba

Bytes cn li xc nh a ch my trm.

T 128 n 191 l a ch lp B. Hai Bytes u xc nh a ch mng.

Hai Bytes tip theo xc nh a ch my trm.

class ID Nework ID Host ID

0 31

0 Network ID Host ID

3180 1 7

Khun dng a ch IP lp A

Khun dng a ch IP lp B

Khun dng a ch IP lp C

Khun dng a ch IP lp D

Khun dng a ch IP lp E

0


31161 2 15

1


31222 3 21

1

1

1

0

1 0 Multicast address

312 3 4

1

1

1

0

1 1 Reserved for future use

312 3 4

1

1

1

0

0


11/122


V Khoa TTT4 K4011

T 192 n 223 l a ch lp C. Ba Bytes u xc nh a ch mng.

Bytes cn li xc nh a ch my trm.

Ln hn 223 l cc a ch dng qung b hoc dng d tr cho cc

mc ch c bit v ta c th khng cn quan tm.

Nhn vo trn hnh ta c bng phn lp a ch IP nh bng 1.1.

Network class S mng S Hosts trong mng

A 126 16.777.214

B 16.382 65.534

C 2.097.150 254

Bng 1.1: Bng phn lp a ch

Tuy nhin khng phi tt c cc shiu mng (net id) u c th dng

c. Mt sa chc dnh cho nhng mc ch c bit.Lp A c s mng t nht, nhng mi mng li c nhiu hosts thch hp

vi cc t chc ln c nhiu my tnh.

Lp B c s mng v s hosts va phi.

Cn lp C c nhiu mng nhng mi mng ch c th c 254 hosts, thch

hp vi t chc c t my tnh.

tin cho vic qun tr cng nh thc hin cc phng php tm ng

trn mng. cc mng ln (lp A) hay mng va (lp B) ngi ta c th chia

chng thnh cc mng con (Subnets) . V d cho rng mt mng con c a ch

lp B l 191.12.0.50 khi coi 191.12.0.0 l a ch ton mng v lp a ch191.12.1. cho Subnet 1 v 191.12.2 cho Subnet 2.

C th dnh trn mt nhm 8 bits nh a ch Subnet v mt nhm

nh a ch cc my trong tng Subnet. Nh th tt nhin l s my trong mt

Subnet s t i tng t nh trong mng nh. S phn chia ny lm gim kch

thc ca bng nh tuyn trong Router/ Gateway, ngha l tit kim dung

lng nhv thi gian x l.

S phn chia mt mng thnh nhiu mng con pht sinh vn l s

lng bit dnh nh a ch mng con c th khc nhau v tu thuc vo nhqun tr mng. Do ngi ta a vo khi nim Subnet Mask. Subnet Mask

cng ging nha ch IP bao gm 32 bits. Mc ch ca i ch Subnet Mask

l chia nh mt a ch IP thnh cc mng nh hn v theo di vng no trn

a ch IP c dng lm a ch cho mng con (cn c gi l cc Subnet)

vng no dng lm a ch cho cc my trm.

Ni dung ca mt Subnet Mask c quy nh nh sau :


12/122


V Khoa TTT4 K4012

Cc bit 1 : dng chnh a ch mng trn a ch IP.

Cc bit 0 : dng chnh a ch my trm trn a ch IP.

V di vi mng A c a ch l 25.0.0.0, nu dnh 8 bits cho Subnet th

mt n c gi tr l 255.255.0.0 , nu dnh 16 bits cho Subnet th mt n c gi

tr l 255.255.255.0.Ta ch IP ta thc hin php ton logic AND vi a ch Subnet Mask kt

qu s to ra c a ch mng ni n. Kt qu ny c s dng tm bc

tip theo trong thut ton tm ng trn mng. Nu kt qu ny trng vi a

ch mng ti trm ang lm vic th s xt tip a ch my trm truyn i.

Theo cu trc ca Subnet Mask th ta thy tt c cc trm lm vic trong cng

mt mng con c cng gi tr Subnet Mask.

Vi phng php ny s bits dng nh a ch host c th nh hn 8

bits (i vi lp C) tc l mt a ch lp C c th phn nh hn na v khi

cc mng con ny thng c xc nh bi cc a ch c thm phn ch thchs bits dnh cho a ch mng, v d203.160.0.0/25 m t Subnet 203.160.0.0

(thuc lp C) nhng c 25 bits dng cho a ch mng v 7 bits dng cho a

ch Hosts tc l Subnet ny ch c ti a l 128 Hosts ch khng phi l 256

Hosts.

Trong tt c cc lp a ch mng cng nh cc Subnets, cc i chu

v cui ca mng c dng cho cc mc ch ring. Mt a ch IP cng vi

tt c cc bits a ch my trm c gi tr c l 0 (a chu mng) c dng

ch chnh mng (hay a ch xc nh mng). V da ch203.160.1.0c dng ch mng 203.160.1.0. Cn nu tt c cc bits a ch trong phn

a ch ca trm u c gi tr l 1 (a ch cui mng) th a ch ny c

dng lm a chqung b. V da ch qung b ca mng 203.160.1.0 l

203.160.1.255. Mt gi d liu gi n a ch ny sc truyn n tt c

cc my trm trn a ch ny.

Trn mng Internet, vic qun l v phn phi a ch IP l do NIC

(Network Information Center). Vi s bng n ca s my tnh kt ni vo

mng Internet, a ch IP trthnh mt ti nguyn cn kit, ngi ta phi

xy dng nhiu cng ngh khc phc tnh hnh ny. V d nh cng nghcp phta chIP ng nh BOOTP hay DHCP (Dynamic Host Configuration

Protocol). Khi s dng cng ngh ny th khng nht thit mi my trn mng

u phi c mt a ch IP nh trc m n sc Server cp cho mt a ch

IP khi thc hin kt ni. Tuy nhin gii php ny ch l tm thi trong tng lai

th a ch IPv6 sca vo s dng.


13/122


V Khoa TTT4 K4013

1.2.3.4.a ch IPv6

Cu trc Header ca gi IPv6 c trnh by trong hnh 1.5.

Version

Number

Priority Flow Lable

Pay load Length Next Header Hop limit

Source IP Address ( 128 Bits)

Destination IP Address (128 Bits)

Hnh 1.5: Cu trc Header gi IPv6

Cu trc ca gi IPv6 khng hon ton tng thch mt cch trc tip vi

cu trc ca gi IPv4, n c cu trc cho vic truyn dn cng nhanh cng

tt, v n vn cng hot ng vi IPv4.

IPv6 c mt sc im chnh sau y:

128 bits a ch thay cho 32 bits a ch. Thit lp v cu hnh n gin : IPv6 c th tng t cu hnh cc a

ch cc b.

nh dng Header n gin mt vi trng c bi hoc trthnh

khng bt buc. Snh dng Header mi ny ci thin tnh nng ca b

nh tuyn v d dng thm cc loi Header mi.

Ci tin s trgip i vi cc tu chn v cc mrng.

S trgip i vi vic xc nhn ng v s m ho d liu. S trgip

i vi vic xc nhn ng, tnh chn tht ca d liu, tnh b mt ca dliu l mt phn ca kin trc IPv6.

Khng ging nh IPv4 cc gi d liu trong IPv6 ni chung khng b

phn mnh. Nu s phn mnh c yu cu n sc thc hin khng

phi bng cc bnh tuyn m bng ngun ca cc gi d liu. i vi

mt gi d liu b phn mnh, Host ngun s sinh ra mt gi tr t nhn

din duy nht.

IPv6 c 128 bits a ch di hn bn ln so vi IPv4 nn kh nng theo l

thuyt c th cung cp mt khng gian a ch ln hn nhiu. y l khng

gian a ch cc ln vi mc ch khng ch cho Internet m cn cho tt c ccmng my tnh, cc h thng vin thng, h thng iu khin v thm ch cn

c cc vt dng trong gia nh. a ch IPv6 c phn ra l 3 loi chnh nh

sau :

1. Unicast Address: a chn hng l a ch dng nhn dng tng

nt mt (im nt l tp cc thit b chuyn mch nm trung tm nh


14/122


V Khoa TTT4 K4014

Router chng hn) c th l mt gi d liu c gi ti mt a chn

hng sc chuyn ti nt mang a chn hng .

2.Anycast Address: a ch bt k hng no. L a ch dng nhn

dng mt tp hp nt bao gm nhiu nt khc nhau hp thnh, c th l

mt gi s liu c gi ti mt a ch bt c hng no s cchuyn ti mt nt gn nht trong tp hp nt mng a ch Anycast .

3.Multicast Address : a cha hng. L a ch dng nhn dng mt

tp hp nt. Tp hp nt bao gm nhiu nt khc nhau hp thnh, c th

l mt gi s liu c gi ti mt a cha hng sc chuyn ti

tt c cc nt trong a ch Multicast .

1.2.3.5. Giao thc ARP

Khi hai my trn mng Internet mun kt ni vi nhau th chng phi

bit i ch ca nhau, a chc s dng l a ch Internet. Tuy nhin nuhai my cng trong mt mng vt l th chng khng th s dng a ch IP

lin lc vi nhau, chng ch c th kt ni vi nhau khi chng bit c a ch

vt l ca nhau. Vn t ra l lm sao mt trm hay mt Router c th nh

xa ch IP (32 bits hoc 128 bits ) sang a ch vt l (48 bits) khi chng cn

gi mt gi d liu qua mng vt l. Trc kia trong cc h thng s dng giao

thc TCP/IP th phi c mt bng ch ra s lin quan gia a ch IP v a ch

vt l (a ch MAC) tuy nhin ngy vn ny c gii quyt thng qua

giao thc xc nh a chARP (Address Resolution Protocol). Giao thc ARP

cho php mt trm c th bit c a ch vt l ca mt trm khc trn cngmt mng vt l khi n bit a ch IP ca trm kia.

Hnh 1.6 minh hoiu .

Hnh 1.6: Giao thc ARP

192.1.1.1 192.1.1.2

192.1.1.5 192.1.1.4

ARP requestARP response

ResponseNo response

No respons


15/122


V Khoa TTT4 K4015

Khi mt my trm c a ch129.1.1.1 mun bit a ch vt l ca my

trm c a ch129.1.1.4 th n gi i mt gi tin c bit c cha a ch IP

129.1.1.4n tt c cc trm khc (S dung ch Broadcast) yu cu tr

li cho bit a ch vt l ca my ny. Tt c cc trm trn mng u nhn

c thng bo ny nhng ch c trm c a ch IP l 129.1.1.4 nhn ra ach IP ca n nn n gi cho my 129.1.1.1 mt phc p tr li a ch vt l

ca n.

Tuy nhin nu bt c lc no mun kt ni, mi my trm u phi thc

hin qung b yu cu ARP nh vy s lm tng kh nng tc nghn trn mng

v tt c cc my trong mng u nhn c yu cu ny v phi x n.

trnh tnh trng ny trn mi my trm u c thit k mt vng nhgi lARP

table hocARP cache. Bng ny s lu gia ch IP tng ng vi a ch vt

l ca cc my trm gn nht m n nhn c v c cp nht tng khi

nhn c tr li ARP. Trc khi gi i mt yu cu ARP th mt my trm stm trong ARP table xem c a ch vt l no tng ng vi i ch IP m n

mun kt ni hay khng, nu c th n s gi d liu m khng phi pht yu

cu ARP. Bn cnh gim vic pht i cc yu cu ARP th khi mt my

trm no tr li mt yu cu ARP n s tng cp nht a ch IP v a ch

vt l ca ni yu cu vo ARP table. Cc ARP table ny tu theo cu trc khc

nhau m c phng php cp nht hoc loi ba ch khc nhau. Hnh 1.7 ch

ra cc thc hin mt yu cu ARP.

Hnh 1.7: Cc bc thc hin ARP

1. Trc khi thc hin kt ni th my trm phi bit a ch MAC tng

ng vi a ch IP.

2. N s tm trong ARP table xem c a ch no ph hp khng.

IP 1ARP request

ARP table(ARP cache)

Data link

2, 5

3

4


16/122


V Khoa TTT4 K4016

3. ARP table s tr li a ch MAC (nu c).

4. Nu a ch MAC khng c trong ARP table th my s pht ra yu

cu ARP ln trn mng, nu a ch MAC c trong ARP table th kt ni

c thc hin.

5. Cng vi vic nhn c tr li ARP th ARP table c cp nht.Khun dng ca mt gi tin ARP cng nh RARP dng cho mng Ethernet

c m t nh hnh 1.8.

Bit 0 Bit 16Type of Hardware(16bits)Type of Protocol(16bits)

Length of HardwareAddress

Length of ProtocolAddress

Operation(16bits)

Hardware address of the source stationIP address of the source station

Hardware address of the destination station

IP address of the destination station

Hnh 1.8: Khun dng gi tin ARP/RARP

ngha ca cc trng trong khun dng nh sau:

Type of Hardware (16bits): M t kiu giao din phn cng, thng c

dng ch cc mng LAN hot ng theo cc chun IEEE 802. Trng

ny mang gi tr 1 i vi cc mng Ethernet. Type of Protocol (16bits): M t kiu a ch giao thc cao cp (IP, IPX

Apple Talk), trng ny mang gi tr 0800 h 16 i vi a ch IP.

Length of Hardware Address: Ch th di a ch phn cng.

Length of Protocol Address: Ch th di a ch ca giao thc cao cp.

Operation (16bits): Cho bit gi tin ARP/RARP l gi mang thng tin hi

hay phc p:

Operation = 1: ARP Request.

= 2: ARP Response.

= 3: RARP Request.

= 4: RARP Response.

Hardware address of the source station: a ch vt l ca trm gi.

IP address of the source station: a ch IP ca ni gi.


17/122


V Khoa TTT4 K4017

Hardware address of the destination station: a ch vt l ca ch, trng

ny thng c thit lp l 0 trong cc ARP Reqest, v c in vo bng

cc th tc phc p ca trm ch.

IP address of the destination station: a ch IP ca nhn, n c thit lp

bi trm ngun.Khi cc gi tin ARP c truyn trn mng tu theo cu trc ca cc

mng khc nhau m c cc khung d liu gi i tng ng. Cc khung d liu

ny c phn bit vi cc khung tin loi khc bng mt trng kiu trong

phn tiu ca khung. Vi mng Ethernet, khung tin ARP c trng kiu

mang gi tr 0806 h 16.

1.2.3.6. Giao thc RARP(Reverse ARP)

Cc my tnh thng lu tra ch IP ca n trn b nhth cp, ni m

hiu hnh c th tm thy khi khi ng. Nhng vi nhng my tnh khngthng xuyn lm vic vi b nhth cp (chng hn chng lu gi tp tin trn

mt my Server xa) th chng khng bit a ch IP ca mnh. V vy mt

my tnh khng c a cng khi khi ng phi lin lc vi Server bit

c a ch IP ca n trc khi kt ni vo h thng s dng TCP/IP.

My tnh c th nhn bit c a ch vt l ca n t phn cng giao

tip mng c ci t trn n. Ta ch vt l ny, cc my tnh khng c b

nhth cp c th tm ra a ch IP ca n thng qua giao thc RARP.

Khun dng ca thng bo RARP v cbn ging khung dng ca thng

bo ARP, ch khc v cch thc khai bo mt s trng trong .

Cng nh thng bo ARP, mt thng bo RARP cng c ng trong

mt khung thng tin mng v c gi t my ny n my khc. Phn tiu

ca khung tin c cha mt trng kiu mang gi tr 8035 h 16 cho php

phn bit khung tin cha thng bo RARP vi cc khung tin dng khc. Hnh

1.9 minh ho cch thc m mt my s dng RARP xc nh a ch IP ca

n.

bit a ch IP ca mnh, u tin my A qung b mt yu cu RARP

n tt c cc my khc. A cung cp a ch vt l ca n trong gi tin RARP.Tt c cc my trn mng u nhn c yu cu ny nhng ch c my no

cung cp dch v RARP mi tin hnh x l v tr li yu cu ny. Nhng my

c gi l cc RARP Server. Trong mt mng con ni chung cn phi c

mt my tnh nh vy.


18/122


V Khoa TTT4 K4018

Hnh 1.9 Giao thc RARP

1.2.3.7. ARP u quyn

ARP u quyn l phng php m trong mt my thng l mt

Router tr li cc yu cu ARP cho cc my khc bng cch cung cp a ch

vt l ca chnh n. Bng cch to ra mt my khc, Router chp nhn trch

nhim chuyn cc gi. Mc ch ca ARP u quyn l cho php mt khu vc

s dng mt a ch mng vi nhiu a ch vt l.

Nh hnh 1.10 ARP u quyn cho php mt a ch mng c chia s

gia hai mng vt l. Router R tr li cho cc yu cu ARP mi mng cho cc

Hosts cc mng khc bng cch a ra a ch vt l ca n v sau n s

chuyn tip cc gi khi n nhn c. Router R bit my no nm mng vt

l no v dng ARP u quyn to ra o gic rng ch c mt mng tn ti. lm c vic R lu gi v tr ca cc Hosts v cho php tt c cc Hosts

trong mng lin lc vi nhau nh l kt ni trc tip.

Hnh 1.10: ARP u quyn ni hai mng vt l c cng a ch mng

Nh trong hnh, H1 mun gi mt gi n H4 n s dng yu cu ARP

hi a ch vt l ca H4. Do R c phn mm ARP u quyn n thu c yu

A 192.1.1.2

192.1.1.5 192.1.1.4RARP requestRARP response

Response

Main Network

Hidden Network

H1 H2

H3

Router

H4 H5


19/122


V Khoa TTT4 K4019

cu ARP v s quyt nh gi i tr li ARP bng a ch vt l ca n. H1 s

gi gi n R, khi R nhn c Datagram n s gi Datagram n H4.

1.2.3.8.nh tuyn cho IP Datagram

Vic nh tuyn cho IP Datagram trong lin mng rt phc tp. Thut ton

nh tuyn IP stnh ton v la chn ng i no thch hp nht gi mtDatagram qua cc mng vt l n trm ch l ni nhn Datagram. Cc phn

mm nh tuyn s tin hnh phn tch cc vn nh: xem xt kiu mng,

chiu di ca Datagram hay cc kiu dch v c m t trong Datagram

Header tm ng i tt nht.Trong vn nh tuyn ngi ta phn ra lm hai loi, l nh tuyn

trc tip v nh tuyn gin tip. Vic truyn tin gia hai my c gi l trctip nu hai my ny cng c ni vo mt mng vt l. Chuyn gin tip

c th

c hi

n khi khi hai my khng cng k

t n

i vo m

t m

ng v

t l. V v

y

vic truyn cc gi tin c thng qua cc Router. kim tra xem my gi v nhn Datagram c cng trong mt mng vt

l hay khng th bn gi tch ly phn a ch mng ca my ch trongDatagram. Vic xc nh a ch mng c thc hin n gin bng cch xemxt 4 bis u tin ca a ch IP v nh vy n s xc nh c bao nhiu bitsc dng nh a ch mng. a ch ny c dng so snh vi a chmng ca my gi nu bn nhn v bn gi cng kt ni vo mt mng vt lth qu trnh chuyn gi s l trc tip khng cn s dng Router. Khi mygi s tm a ch vt l ca my nhn bng cch tm trong ARP table hocdng ARP request. Nu hai my khng cng trong mt mng vt l th khi gi d liu sc chuyn n Router. S chuyn ny cng dng a ch vt l.Router ny s phn pht cc gi n ch cui cng hoc gi n n Router tiptheo. Tuy nhin cn ch rng a ch vt l ca Router khng phi l a chca ch cui cng do vic chuyn cc gi khng phi l trc tip.

Khi chuyn mt Datagram n ch cui cng c th s dng c haiphng php chn ng trc tip hoc gin tip. V d nh khi chuyn ccDatagram qua mng. Trm khi u s chuyn n n Router t chuynn ch cui cng. N l chn ng gin tip. Nhng khi cc gi ny nRouter cui cng th n phi chuyn trc tip n ch.

Nu mt Router nhn c mt Datagram m n cha phi l ch cuicng n s gim trng TTL i, nu TTL>0 n s gi Datagram i da vo ach IP ca ch cui cng v thng tin trong bng chn tuyn. Router phn phtcc gi theo nguyn l khng kt ni tc l khng mt Router no thit lpphin truyn vi mt Router khc trn mng.


20/122


V Khoa TTT4 K4020

Bng nh tuyn (Routing table)Bng nh tuyn l ni lu gi thng tin v cc ch c thn c v

cch thc n a ch. Khi phn mn IP Routing ti mt trm hay mtRouter nhn c yu cu truyn mt gi d liu th trc ht n phi tham

kho bng nh tuyn ca n quyt nh xem s phi gi Datagram n u.Tuy nhin khng phi bng thng tin chn ng ca mi trm (hay Router) lcha tt c cc thng tin v cc tuyn ng c thn c.

Trong mi bng thng tin chn ng bao gm cc cp (N,G) trong Nl a ch IP ca mng ch, cn G l a ch ca Router tip theo trn ngn mng N.

Nh vy, mi Router s khng bit c ng truyn y i nch. Trong bng nh tuyn cn c thng tin v cc cng c th vi n nhngkhng cng nm trn mt mng vt l, phn thng tin ny c che khut i v

c g

i lDefault Router. Khi khng tm th

y thng tin c

a

a ch

ch cn

n th cc gi d liu sc gi n cng truyn ngm nh.Vic thit lp bng nh tuyn s dng hai phng php l phng php

chn tuyn ng v phng php chn tuyn tnh. Phng php chn tuyntnh c cc ng truyn c tnh ton trc v c np vo mng khi mngkhi ng. Phng php ny khng quan tm n cc thng sng truyntc thi v cu hnh (Topology) ca mng nn cn c gi l thut ton chntuyn phi thch nghi. Phng php chn tuyn ng hay cn gi l phngphp chn tuyn thch nghi cho php thay i ng truyn gi da vo ccthay i ca thng s truyn ti v cu hnh ca mng. Phng php chn tuynng hay c s dng hn phng php chn tuyn tnh do c nhiu u imhn.

Qu trnh gi mt Datagram t trm ngun n trm ch gm cc bcsau: khi mt trm mun gi Datagram n mt trm khc trn lin mng, utin n sng gi Datagram v gi n mt Router gn nht. Datagram cngi c th s phi qua nhiu Routers trc khi n ch. Khi khung tin nRouter u tin, phn mm IP s ly Datagram c ng gi ra, la chonRouter tip theo cn phi qua. Sau Datagram li c t vo khung ric gi qua mng vt l n Router th hai. Qu trnh ny c th tip tc chon khi Datagram n c ch cui cng. Hnh 1.11 ch ra lc qu trnhchn tuyn cho Datagram:


21/122


V Khoa TTT4 K4021

Hnh 1.11 Lc IP routing

Header

v checksumhp l

Gim TTLTTL>0?

Tm a ch mngch trong bng

ch -ng

Router mcnh c sn

C a chvt l?

Gi i yu cu ARPv ch phc p

Gi gi n Routertip theo da vobng chn -ng

Hu gi

Gi thng boICMP n ni

gi gi

Nu tm thyRouter, tm a chtrong ARP table

Nhn -c phcp ARP, thmvo ARP table

Tm thyRouter ?

No

Yes

No

Yes

No

YesYes

No

No

Yes

Nhn -c gi


22/122


V Khoa TTT4 K4022

1.2.3.9.Qu trnh gi, nhn Datagrams

i vi IP trm ngun, khi nhn c mt Primitive Send (Hm dch v

nguyn thu yu cu gi d liu) ca tng trn, n s thc hin cc bc

sau:

To mt IP Datagram da trn cc tham s ca Primitive Send.

Tnh Checksum v ghp vo phn Header ca Datagram.

Ra quyt nh chn ng.

Chuyn Datagram xung tng di truyn qua mng.

Khi mt Gateway nhn c mt Datagram, n s thc hin cc bc sau:

Tnh Checksum, nu khng hp l th loi b Datagram.

Gim thi gian sng TTL (Time to Live) ca Datagram. Nu thi gian

sng ht th Datagram b loi b.

Ra quyt nh chn ng.

Nu thy cn thit th thc hin phn on cho Datagram.

Sa i li IP Header, bao gm Time to Live (TTL), Fragmentation v

Checksum.

Chuyn Datagram xung tng di truyn qua mng.

Khi nhn c Datagram, IP trm ch s thc hin cc bc sau:

Tnh Checksum, nu khng hp l th loi b Datagram .

Tp hp li cc on nu Datagram b phn mnh.

Chuyn d liu v cc tham s ln tng trn.

1.2.4. Giao thc TCP

TCP l mt giao thc kiu c lin kt (Connection Oriented), tc l phi

c giai on thit lp lin kt gia mt cp thc th TCP trc khi truyn d

liu.

Cng ging nh cc giao thc tng giao vn TCP nhn thng tin t cc

lp trn chia n thnh nhiu on nu cn thit. Mi gi d liu c chuyn

ti giao thc lp mng (thng l IP) truyn v nh tuyn. B x TCP can nhn thng bo nhn tng gi, nu n nhn thnh cng, cc gi d liu

khng c thng bo sc truyn li. TCP ca ni nhn lp rp li thng tin

v chuyn n ti tng cao hn khi n nhn c ton b.

Trc khi cc gi d liu c gi ti my ch ni gi v ni nhn phi

thng lng thit lp mt kt ni logic tm thi. Kt ni ny vc trng

strng thi mtrong sut phin truyn.


23/122


V Khoa TTT4 K4023

c im giao thc TCP

Trong b giao thc TCP/IP TCP l giao thc c pht trin nh l cch

kt ni cc mng my tnh khc nhau v cc phng php truyn dn v h

iu hnh. TCP thit lp kt ni hai ng gia hai h thng cn trao i thng

tin vi nhau thng tin trao i gia hai h thng c chia thnh cc gi. TCPc nhng c im sau:

1. Hai h thng cn kt ni vi nhau cn phi thc hin mt lot cc sbt

tay trao i nhng thng tin v vic chng mun kt ni. Qu trnh

bt tay m bo ngn trn s trn v mt mt d liu khi truyn.

2. Trong phin truyn thng tin, h thng nhn d liu cn phi gi ccxc

nhn cho h thng pht xc nhn rng n nhn c d liu.

3. Cc gi tin c thn ch khng theo th t sp xp ca dng d liu

lin tc bi cc gi tin i t cng mt ngun tin theo nhng ng dn

khc nhau i ti cng mt ch. V vy th tng ca cc gi tinphi c m bo sp xp li ti h thng nhn.

4. Khi pht hin gi tin b li th ni gi chpht li nhng gi tin b li

nhm trnh loi b ton b dng d liu.

Hnh 1.12 trnh by phng thc hot ng ca giao thc TCP.

Hnh 1.12: TCP cung cp kt ni tu cui n u cui

Application

TCP

Secssion

Presentation

IP

Dadalink

Physical

SendingApplication

TCP

Secssion

Presentation

IP

Dadalink

Physical

IP

Dadalink

Physical

IP

Dadalink

Physical

Receiving

Subnet Subnet

TCP End to End Commmunication

Router Router


24/122


V Khoa TTT4 K4024

n v d liu s dng trong giao thc TCP c gi l Segment. Khun

dng ca Segment c m t nh hnh 1.13.

Bit 0 15 16

31

Sourse Port Destination Port

Sequence Number

Acknowledgment Number

Data

Offset

(4 bits)

Reserved

(6 bits)

U

R

G

A

C

K

P

S

H

R

S

T

S

Y

N

F

I

N

Window (16 bits)

Checksum Urgent poier

Option Padding

TCPdata

Hnh 1.13: Khun dng TCP Segment

Cc tham s ca khun dng trn c ngha nh sau:

Source Port(16 bits): S hiu ca cng ngun.

Destination Port(16 bits): S hiu cng ca trm ch. S hiu ny l a

ch thm nhp dch v lp giao vn (CCISAP Addess) cho bit dch v

m TCP cung cp l dch v g. TCP c s lng cng trong khong

0216-1 tuy nhin cc cng nm trong khong t 01023 l c bit

nhiu nht v n c s dng cho vic truy cp cc dch v tiu chun,v d 23 l dch v Telnet, 25 l dch v mail . . . .

Sequence Number(32 bits): S hiu ca Byte u tin ca Segment tr

khi bit SYN c thit lp. Nu bit SYN c thit lp th Sequence

Number l s hiu tun t khi u (ISN) v Byte d liu u tin l

ISN+1. Tham s ny c vai tr nh tham s N(S) trong HDLC.

Acknowledgment Number (32 bits): S hiu ca Segment tip theo m

trm ngun dang ch nhn. Ngm bo nhn tt cc Segment m

trm trm ch gi cho trm ngun. Tham s ny c vai tr nh thams N(R) trong HDLC.

Data offset (4bits): S lng t 32 bit trong TCP header (Tham s ny

ch ra vng bt u ca vng d liu ).

Reserved(6 bits): Dnh dng trong tng lai.

Control bits: Cc bits iu khin

T tri sang phi:


25/122


V Khoa TTT4 K4025

URG : Vng con tr khn c hiu lc.

ACK : Vng bo nhn (ACK number) c hiu lc .

PSH: Chc nng PUSH.

RST: Khi ng li (reset) lin kt.

SYN : ng b cc s liu tun t (sequence number). FIN : Khng cn d liu t trm ngun .

Window (16bits): Cp pht credit kim sot lung d liu (cch ca

s). y chnh l s lng cc Byte d liu bt u t Byte c ch ra

trong vng ACK number, m trm ngun sn sng nhn.

Checksum (16bits): M kim sot li (theo phng php CRC) cho ton

b Segment.

Urgent Pointer(16 bits) : Con tr ny tr ti s liu tun t ca Byte i

theo sau d liu khn, cho php bn nhn bit c di ca d liu

khn. Vng ny ch c hiu lc khi bit URG c thit lp . Option ( di thay i): Khai bo cc option ca TCP, trong c

di ti a ca vng TCP data trong mt Segment .

Padding ( di thay i): Phn chn thm vo Header bo m phn

Header lun kt thc mt mc 32 bits. Phn thm ny gm ton s 0.

Vic kt hp a ch IP ca mt my trm v s cng c s dng to

thnh mt Socket. Cc my gi v nhn u c Socket ring. S Socket l duy

nht trn mng.

1.2.4.1.iu khin lung dliuTrong vic iu khin lung d liu phng php hay s dng l dng

phng php ca strt. Phng php ny gip cho vic nhn lung d liu

hiu qu hn.Phng php ca s trt cho php ni gi (Sender) c th gi i nhiu gi

tin ri sau mi i tn hiu bo nhn ACK (Acknowledgement) ca ninhn (Receiver).Vi phng php ca s trt khi cn truyn cc gi tin, giaothc st mt ca s c kch cnh ln cc gi tin. Nhng gi tin no nmtrong vng ca smt thi im nht nh sc truyn i. Hnh 1.14 minhho qu trnh ny. y kch thc ca s l 4. Tc l mi lc ca s ch gic 4 gi tin. u tin ca s gi s gi 4 gi tin t 1 n 4 v 4 gi tin ny sc gi cho bn nhn. Ca s tip tc trt gi tin th 5 c gi i ngaysau khi nhn c tn hiu ACK ca gi tin th nht t trm ch qua trnh nhvy c tip tc cho n khi gi tin cui cng c chuyn i.


26/122


V Khoa TTT4 K4026

Hnh 1.14: Hot ng ca ca s trt

Trong qua trnh gi v nhn d liu, c th c mt s gi tin mc d c gi i nhng khng c phc p (khng nhn c bo nhn) c ngha lbn nhn khng nhn c th nhng gi sc truyn li.

Ti bn nhn cng duy tr mt ca s trt tng t dng nhn v bonhn cc gi tin nhn c.

TCP cung cp mt kiu dch v gi l dch v chuyn lung ng tin cy.

TCP xem lung d liu nh l mt th t cc Bytes d liu c tch thnh ccSegments. Thng th mi Segment truyn trong lin mng sc lng vomt Datagram.

Vi k thut ca s trt, s gii quyt c hai vn quan trng ltruyn c hiu qu v iu khin lung dliu. TCP s dng k thut ca strt da trn k thut ca s trt trnh by trn. N cho php gi cnhiu Segment trc khi bo nhn n t ni nhn v do lm tng thnglng truyn trn mng. Bn cnh k thut ca s trt cn cho php bnnhn trnh c tnh trng d liu b mt bng cch lm gim lu lng d liu

gi n nu bm ca n khng cha thm nhiu d liu.K thut ca s trt ca TCP c tin hnh mc Byte ch khngphi mc Segment hay Packet nh trnh by trn. Cc Bytes ca lung dliu c nh s mt cch tun t v mt ca sc nh ngha bi ba contr nh hnh 1.15.

12 91011 8 567 4 123

Window

12 91011 8 567 4 123

12 91011 8 567 4 123

Window

Window

(a)

(b)

(c)

1

1 nhn -c ACK

2 Ch-a -c gi

H-ng tr-t

2


27/122


V Khoa TTT4 K4027

Hnh 1.15: Cu hnh ca s trt

Ti mi thi im, con tru tin tr vo mp bn tri ca s, con tr thhai tr vo mp bn phi ca s v con tr th ba xc nh v tr cc Bytes cgi i. Con tr bn phi v bn tri ca s xc nh kch thc ca ca s. Ccphn mm giao thc gi cc gi bn trong ca s khng c tr do danh giibn trong ca s lun lun di chuyn t bn phi qua bn tri.

Nh trong hnh 1.14 ch ra Byte th hai c gi v nhn c bonhn, Bytes th 3, 4 c gi nhng cha c bo nhn, Bytes th 5, 6 chac gi nhng sc gi m khng c tr. Cc Bytes ln hn 7 cha cgi cho n khi ca s di chuyn.

C mt s khc bit gia ca s trt TCP v ca s trt c trnh by trn l ca s trt TCP c th thay i kch thc theo thi gian. Trong mi bo nhn u c thng tin v trng thi bm ti bn nhn, cho bit bnnhn c th nhn thm c bao nhiu Bytes d liu na. Nu nhn c thngbo kch thc bm cn t th bn gi s gim kch cca ca s v n

khng gi s Bytes d liu qu kch thc ca bm. Cn nu thng bo rngkch thc ca bm tng th bn gi s tng tng ng kch thc ca cas.

V lin kt TCP l loi kin kt y , d liu c thc truyn theo chai hng, tc l ti mi thi im d liu c thc truyn t hai u cuica lin kt mt cch c lp vi nhau nn ti mi u ca lin kt s c thduy tr hai ca s mt gi d liu v mt nhn d liu.

1.2.4.1.Thit lp v hu b lin kt

Nh ta bit TCP l mt giao thc kiu c lin kt, tc l cn phi cgiai on thit lp mt lin kt gia mt cp thc TCP trc khi truyn d liuv hu b lin kt khi khng cn nhu cu trao i d liu na.Thit lp lin kt TCP

Mt lin kt c th c thit lp theo mt trong hai cch ch ng(active) v bng (passive). Nu lin kt c thit lp theo cch bng thu tin TCP ti trm mun thit lp lin kt s nghe v chyu cu lin kt t

12 91011 8 567 4 123

Window

1 2

3

3 Cc con tr

H-ng tr-t

2 1


28/122


V Khoa TTT4 K4028

mt trm khc. Tu trng hp ca li gi hm m ngi s dng phi ch racng yu cu kt ni hoc c th kt ni vi mt cng bt k.

Vi phng thc chng th ngi s dng yu cu TCP th thit lpmt lin kt vi mt Socket no vi mt mc u tin v an ton nht

nh. Nu trm xa kia p li bng mt hm Passive open tng hp hoc gi mt active open tng hp th lin kt sc thit lp. Nu lin kt cthit lp thnh cng th th hm Open success primitive c dng thng bocho ngi s dng bit (cng c s dng trong trng hp Passive Open)cn nu tht bi th hm Open failure primitive c dng thng bo.Hu b mt lin kt:

Khi khng cn nhu cu trao i d liu na th lin kt TCP c thchu b. Lin kt c thc hu b theo hai cch:

Hu b mt cch bt thng. Hu

b

m

t cch bnh th

ng.

Lin kt c hu b mt cch bnh thng khi ton b d liu ctruyn ht. Tc l hai bn khng cn nhu cu trao i d liu na.

Lin kt c th b hu b mt cch bt thng v mt l do no (dongi s dng hoc do TCP ng lin kt do khng th duy tr c lin kt).Ton b d liu ang truyn c th b mt.

1.2.4.3.Truyn v nhn dliu

Sau khi lin kt c thit lp gia mt cp thc th TCP th c th tinhnh vic truyn d liu. Vi lin kt TCP d liu c thc truyn theo c

hai hng.Khi nhn c mt khi d liu cn chuyn i t ngi s dng, TCP s

lu gi n ti bm gi. Nu cPUST c dng th ton b d liu trong bm sc gi i ht di dng cc TCP Sgment. Cn nu cPUST khngc dng th ton b d liu vn c lu gi trong bm chgi i khic chi thch hp.

Ti bn nhn, d liu gi n sc lu gi trong bm nhn. Nu dliu m c nh du bi cPUST th ton b d liu trong bm nhn sc gi ln cho ngi s dng. Cn nu d liu khng c nh du vi c

PUST th chng vn c lu trong bm. Nu d liu khn cn phi chuyngp th cURGENT c dng v nh du d liu bng bit URG bo rngd liu khn cn c chuyn gp.


29/122


V Khoa TTT4 K4029

1.2.5. Giao thc UDP

UDP (User Datagram Protocol) l mt giao thc kiu khng kt ni, c

s dng trong mt s yu cu ng dng thay th cho TCP. Tng t nh giao

thc IP, UDP khng thc hin cc giai on thit lp v hu b lin kt, khng

c cc cch bo nhn (Acknowledgement) nh trong TCP. UDP cung cp ccdch v giao vn khng ng tin cy. D liu c th b mt, b li hay b truyn

lun qun trn mng m khng h c thng bo li n ni gi hoc ni nhn.

Do thc hin t chc nng hn TCP nn UDP chy nhanh hn, n thng c

s dng trong cc dch v khng i hi tin vy cao. n v d liu dng

trong giao thc UDP l UDP Datagram. Khun dng ca mt UDP Datagrram

gm hai phn : Phn tiu (Header) cha cc thng tin iu khin v phn

Data cha dliu

Khun dng ca UDP Datagram c th nh hnh 1.16.UDP Source Port UDP Destination Port

UDP Message Length UDP Checksum

Data

... ...

Hnh 1.16: Khun dng UDP Datagram

Trong :

UDP Source Port(16 bits) : Cho bit a ch cng ca trm ngun. Nun khng c ch ra th trng ny c thit lp l 0.

UDP Destination Port(16 bits) : Cho bit a ch cng ca trm ch.

UDP Message Length (16 bits): Cho bit kch thc ca mt UDP

Datagram (k c phn Header). Kch thc ti thiu ca mt UDP

Datagram l 8 Bytes (ch c phn Header, khng c phn d liu).

UDP Checksum (16 bits): L m kim sot li theo phng php CRC .

Lp UDP c t trn lp IP, tc l UDP Datagram khi chuyn xung tng

di sc t vo IP Datagram truyn trn lin mng. IP Datagram ny

c ghp vo mt khung tin ri c gi ti lin mng n trm ch. Ti

trm ch cc PDU c gi t di ln trn, qua mi tng phn Header ca

PDU c g b v cui cng ch cn li phn d liu nh ban u c

chuyn cho ngi s dng.


30/122

n tt nghip Chng 3: Gii thiu chung vATM

V KhoaTTT4-K4038

CHNG 2: MNG INTERNET

2.1.T chc ca InternetInternet l mt lin mng, tc l mng ca cc mng con. Vy u tin l

vn kt ni hai mng con. kt ni hai mng con vi nhau, c hai vn

cn gii quyt V mt vt l, hai mng con ch c th kt ni vi nhau khi c

mt my tnh c th kt ni vi c hai mng ny. Vic kt ni n thun v vy

l cha th lm cho hai mng con c th trao i thng tin vi nhau. Vy vn

th hai l my kt ni c v mt vt l vi hai mng con phi hiu c

c hai giao thc truyn tin c s dng trn hai mng con ny v cc gi thng

tin ca hai mng con s c gi qua nhau thng qua . Cc Bridges,

Gateways hoc Routerc dng kt ni cc mng vi nhau

Bridge l mt thit b mng m c kh nng kt ni hai hoc nhiu mng

nhng cc mng ny phi dng chung giao thc chng thng c s

dng ni hai mng LAN cng loi vi nhau.

Router l mt nt mng trong c cha cc gii thut chn ng khi

nhn c mt Datagram th n s gi chuyn tip Datagram i n nt

mng tip theo tu vo a ch ca Datagram v gii thut chn ng.

Gateway l mt thit b thc hin chc nng dn ng. N thng l

mt thit bc lp m c th thc hin giao thc truyn t mng nysang mng khc.

Thng thng vic kt ni gia hai mng dng mt my tnh my tnh ny

c gi lInternet gateway hayRouter.

Hnh 1.17: Hai mng Net 1 v Net 2 kt ni thng qua Router.Khi kt ni trnn phc tp hn, cc Gateways cn phi bit v s

kin trc ca cc mng kt ni. V d trong hnh 1.18 cho thy nhiu mng

c kt ni bng Router.

Net 1 Net 2

Router Router


31/122


V KhoaTTT4-K4039

Hnh 1.18: Ba mng kt ni vi nhau thng qua cc Router

Nh hnh 1.18, Router R1 phi chuyn tt c cc gi thng tin n mt

my nm mng Net 2 hoc Net 3. Vi kch thc ln nh mng Internet, viccc Routers lm sao c th quyt nh v vic chuyn cc gi thng tin cho cc

my trong cc mng s trnn phc tp hn.

cc Routers c th thc hin c cng vic chuyn mt s ln cc gi

thng tin thuc cc mng khc nhau ngi ta ra quy tc l:

Cc Routers chuyn cc gi thng tin da trn a chmng ca ni n,

chkhng phi da trn a chca my my nhn.

Nh vy, da trn a ch mng nn tng s thng tin m Router phi lu

gi v s kin trc mng s tun theo s mng trn Internet ch khng phil s my trn Internet.

Trn Internet, tt c cc mng u c quyn bnh ng cho d chng c t

chc hay s lng my l rt chnh lch nhau. Giao thc TCP/IP ca Internet

hot ng tun theo quan im sau:

Tt cc cc mng con trong Internet nhl Ethernet, mt mng din rng

nhNSFNET back bone hay mt lin ktim-im gia hai my duy nhtu

c coi nhl mt mng.

iu ny xut pht t quan im u tin khi thit k giao thc TCP/IP l

c th lin kt gia cc mng c kin trc hon ton khc nhau, khi nim"mng" i vi TCP/IP bn i phn kin trc vt l ca mng. y chnh l

im gip cho TCP/IP t ra rt mnh.

Nh vy, ngi dng trong Internet hnh dung Internet lm mt mng

thng nht v bt k hai my no trn Internet u c ni vi nhau thng qua

Net 1

Net 2

Net 3

Router 1 Router 3

Router 2


32/122


V KhoaTTT4-K4040

mt mng duy nht. Hnh 1.19 m t kin trc tng th ca Internet di mt

ngi dng v kin trc tng qut ca Internet.

Hnh 1.19: (a) - Mng Internet di con mt ngi s dng. Cc myc ni vi nhau thng qua mt mng duy nht. (b) - Kin trc tng qut camng Internet. Cc Routers cung cp cc kt ni gia cc mng.

2.2.Mt s phng thc kt ni Internet ph bin :

Cc mng my tnh v my tnh to thnh Internet nm ri rc khp ni

trn th gii do o kt ni Internet l kt ni cc mng din rng (WAN). C rt

nhiu cng ngh kt ni mng din rng ang c s dng trn Internet nhng

c chia l hai loi chnh l loi dng dch vin thoi (Telephony) v loikhng dng dch vin thoi (Non- Telephony)

2.2.1. Cc h thng dng dch vin thoi

Cc h thng ny gm c:

2.2.1.1. Leased Line (ng dy thu bao)

Cch kt ni ny l cch kt ni ph bin nht hin nay gia hai im c

khong cch ln . Leased Line l cc mch s kt ni lin tc, c cc cng ty

vin thng cho thu. Chng c phn ra lm hai lp chnh l Tx ( theo chun

M , Canada ) v Ex (theo tiu chun ca Chu u, Nam M, Vit Nam..).T0/E0 tng ng vi mt knh thoi ring l chng to nn tng cho cc

dch v truyn s liu tc cao hn.

(a)

Internet

host

Router

Internet

Physicalnet

Host

(b)


33/122


V KhoaTTT4-K4041

2.2.1.2.Frame Relay v X25

X25 l giao thc truyn thng tin c th nh hng qua ng dy thu

bao X25 s dng a ch theo cch gn ging vi mng cc b. N cho php

truyn cc khung d liu s ho qua khong cch ln

Frame Relay l mt thay th cho X25 gip gim chi ph ca ngtruyn bng cch to mt mch truyn o cnh thay v truyn tng gi. Cng

ngh ny xo bc vic nh a ch v truyn thng tin sa li ca X25.

2.2.1.3. DSL (Digital Subscriber Line)

L mt bin th ca ng in thoi s chun, hot ng thng qua kt ni

ng in thoi thng thng. DSL c pht trin cung cp mt dch v

thay th cho truyn hnh nhng n ha hn lin kt tc cao v chi ph thp

2.2.1.3. ISDN ( Integrated Services Digital Network)

N l mt mch ni k thut s quay s (dial up digital circuit) khng ging

nh Leased-Line c kt ni cnh vo hai thit bu cui cnh. ISDN

cho php ngi dng to ra v hu b lin kt bt k gia hai ISDN adapter

no. Mt im khc na vi Leased-Line l ISDN c th dng cho kt ni tc

cao trong s dng Internet c nhn, gia nh mt cch d dnh v n hot

ng trn cng mt ng truyn vt l nhng dy in thoi. Do vy c

th d dng chuyn i tng truyn Telephone analog thnh ng truyn

ISDN bng cch i thit bu cui tng i trung tm. Tc cbn c

cung cp l 128 Kbps. Cc ng dy ISDN thng c dng ni t ngidng n cc nh cung cp dch v Internet. ng truyn ISDN c u im l

in thoi v my tnh c th dng chung mt ng truyn. Ngi dng c th

nhn in thoi gi ti, hoc gi in thoi i trong khi my tnh vn truy cp

Internet.

2.2.1.4. ATM (Asynchronous Transfer Mode)

L cng ngh mi trong ci t ng truyn trn ng in thoi chnh

ni gia cc thnh ph v cc cng ty . ATM cho php truyn cc dch v khc

nhau (tc khc nhau, yu cu thi gian tr khc nhau) trn cng mt ngtruyn vt l. ATM ha hn mt tc cao cho kt ni Internet. Vic s dng

ATM kt ni Internet sc trnh by trong phn cui ca n ny.

2.2.1.5.ng dy in thoi Analog

y l cch ph bin nht hin nay kt ni Internet bng cch dng mt

modem ni gia ng dy in thoi Analog v my tnh. Khi mun truy cp


34/122


V KhoaTTT4-K4042

Internet th ngi dng phi dng modem quay s n nh cung cp dch v

(ISP) m h kt ni . Modem s quay sn Modem ca nh cung cp dch v

v my tnh s s dng c Internet . Truy nhp kiu ny cho tc thp (Ti

a hin nay l 56 Kbps).

2.2.2 Cc h thng khng dng dch vin thoi

2.2.2.1.H thng cung cp cp quang lp cc b

C nhiu cng ty dch v t thit lp h thng cp quang . H thng ny

hon ton c to bi mt ng cp quang n thp ch ti tn im kt ni

pha ngi dng .Khi kt ni thng qua mt Router vo mng ,nhng mng

ny c th truyn d liu nhanh hn l tc tiu th d kiu pha ngi

dng

2.2.2.2.Modem cp

Modem cp l loi c bng truyn ln hot ng tc rt cao . Modem

cp hay c s dng kt ni vo mng truyn hnh cp . Nhng dch v ny

thng khng cn i ngha l n cung cp bng thng ti xung ln hn nhiu

so vi bng thng np ln. Modem cp c kt ni thng xuyn ch khng

ging nh modem in thoi thng thng.

2.2.2.3.Kt ni trc tip

LAN hoc cc my tnh ln chng hn nh minicomputer c th kt ni

trc tip vo Internet khi LAN kt ni vo Internet th tt c cc my trong

mng c th truy cp vo Internet

2.3.Cc dch v thng dng ca Internet

Internet cng ngy cng pht trin v cung cp cho con ngi nhiu loi

dch v di y trnh by mt s dch v thng dng ca Internet ngy nay :

2.3.1.Thin t

Thin t (Electronic Mail) cn c gi tt l E-mail. Mc ch ca n

l gi hoc nhn nhng thin t t ni ny qua ni khc mt cch nhanh

chng t vi giy cho ti vi pht hoc vi ting ng h.Ngy nay, nhs pht trin mnh m ca Internet ngi ta c th gi th

in t ti cc quc gia trn khp th gii. Vi s tin li nh vy cho nn E-

Mail hu nh trthnh mt nhu cu cn phi c ca mi ngi s dng my

tnh. Trn thc t, c rt nhiu h thng my tnh khc nhau v mi h thng li

c cu trc chuyn nhn thin t khc nhau. Vic ny c gii quyt bng


35/122


V KhoaTTT4-K4043

cch s dng mt giao thc chung cho thin t. Giao thc chung gi l

giao thc chuyn vn th t (Simple Mail Transfer Protocol vit tt l SMTP).

Nhvo SMTP ny m s chuyn vn thin t trn Internet trthnh d

dng nhanh chng cho tt c mi ngi.

2.3.2. Mng thng tin ton cu (World Wide Web- WWW)

y dch v mi v mnh nht trn Internet. WWW c xy dng da

trn mt k thut c tn gi l hypertext(siu vn bn). Hypertext l k thut

trnh by thng tin trn mt trang trong c mt s t c th "n" ra thnh

mt trang thng tin mi c ni dung y hn. Trn cng mt trang thng tin

c th c nhiu kiu d liu khc nhau nh Text, nh hay m thanh. xy

dng cc trang d liu vi cc kiu d liu khc nhau nh vy, WWW s dng

mt ngn ng c tn l HTML (HyperText Markup Language). HTML cho

php nh dng cc trang thng tin, cho php thng tin c kt ni vi nhau.Trn cc trang thng tin c mt s t c th "n" ra, mi t ny thc cht

u c mt lin kt vi cc thng tin khc. thc hin vic lin kt cc ti

nguyn ny, WWW s dng phng php c tn l URL (Universal Resource

Locator). Vi URL, WWW cng c th truy nhp ti cc ti nguyn thng tin

t cc dch v khc nhau nh FTP, Gopher, Wais... trn cc server khc nhau.

Vi s bng n dch v WWW, dch v ny cng ngy cng c m

rng v a thm nhiu k thut tin tin nhm tng kh nng biu t thng tin

cho ngi s dng. Mt s cng ngh mi c hnh thnh nh Active X, Java

cho php to cc trang Web ng thc s mra mt hng pht trin rt lncho dch v ny.

2.3.3. Dch v truyn tp - FTP

Mt trong nhng dch v ph bin nht c s dng trn mng Internet

l dch v truyn tp (file) qua cc my tnh. Dch v ny c dng chuyn

ti cc file gia cc my ch trn mng, gia my ch v my khch (client).

Cc file c thdng vn bn, nh tnh, nh video, cc th vin, c bit l cc

phn mm ng dng c cung cp min ph hoc th nghim.

Vic truyn file c thng qua mt giao thc ca Internet gi l giaothc FTP (File Transfer Protocol vit tt l FTP). Giao thc ny thc hin vic

truyn file gia cc my tnh khng ph thuc vo v tra l hay mi trng

hiu hnh. iu cn thit l 2 my u ni mng Internet v u c phn

mm c th hiu c giao thc FTP.


36/122


V KhoaTTT4-K4044

2.3.4. Dch v truy nhp txa -TELNET

Mt trong nhng cng c cbn ca Internet l Telnet. Telnet l mt giao

thc cho php ngi s dng c th truy nhp vo mt my tnh xa v khai

thc cc ti nguyn ca my hon ton ging nhang ngi trn my ca

mnh.iu kin cn bn s dng dch v Telnet l my tnh ca ngi s

dng phi c ni vo mng Internet. Ngoi ra ngi s dng phi c chng

trnh Telnet. Khi dng telnet vo mt my no n s hi tn truy nhp v

mt khu. Ging nh FTP, trn mng Internet c nhiu host cho php ngi s

dng truy nhp bng telnet nc danh, ch cn khai bo a ch E-Mail ca mnh.

2.3.5. Dch v tra cu theo chmc - Gopher

Gopher l mt dch v tra cu thng tin theo ch v s dng cc thc

n. Xut pht t nhu cu phn pht cc ti liu theo mt ch nht nh chongi s dng trn Internet, ngi ta thit lp cc my c lu tr ti liu.

Mun s dng nhng ti liu ny, ngi s dng cn c mt phn mm kt

ni vo my ch GOPHER, v my ny sa ra cc thc n cho ngi s

dng chn la. Ngoi ra trong mt s my cn lu tr cc ch dn kt ni hoc

a ch ca cc gopher khc. Thng qua cc client ca gopher, ngi s dng c

th nhn nhng file vn bn, hnh nh, ho, m thanh.

2.3.6. Dch v nhm tin - USENET

USENET l chc gi tt t ch usersNetwork v c coi l Mngnhm tin ln nht trn Internet. Mng nhm tin ny l do hng ngn my Phc

V Tin (News Host) c lin kt li vi nhau truyn t tin tc. Mc d

Mng li nhm tin dng Internet chuyn ti v phn phi mt phn ln tin

tc nhng tht ra n cch bit v khc vi Internet. Mng li nhm tin l do

hng ngn my phc v tin (News Host) kt ni li vi nhau trn ton cu. V

n k sinh trn Internet nn ngoi vic khai thc thng qua mng Internet n

cn c cch khai thc c lp khng qua mng Internet m ng k ring.

Mng nhm tin l mi trng tranh lun th gii. N cho php ngi s

dng c th trao i thng tin v mt ch m h cng quan tm. Th trnusernet c gi n v lu tr trn mt my ch cha tin. Ngi s dng c

tht cu hi, a ra kin tranh lun v mt ch no , gi thng bo

hoc cc ti liu vo usernet.


37/122


V KhoaTTT4-K4045

2.3.7. Dch v tm kim thng tin din rng WAIS (Wide Area InformationService).

WAIS l mt cng c tm kim thng tin trn mng Inetrnet thng qua

mt chui cc mc la chn, dch v WAIS cho php ngi dng tm kim

cc tp d liu c cha mt xu k t xc nh trc.Mng WAIS ton cu da trn cc th mc ca my ch (Directory of

server). y thc s l nhng kho tng d liu ngi dng tm kim.

Qu trnh thc hin cuc tm kim WAIS c th so snh vi vic tham

kho ti th vin. Bc u tin ca bn l chn nhng cun sch m bn mun

tm thng tin cho ch nh. Bn c th tp hp nhng cun sch ny trn

k sch cnh trc khi bn mmt ch. iu ny ging nh chn ch

t Directory of Server, sau bn bt u tm kim v tr lu tr thng tin i

vi nhng ch chn. ng thi WAIS cho php bn cp nht danh sch

nhng ti nguyn WAIS chun b cho bn tin hnh tm kim. WAIS server cn

thc hin m s ln xut hin ca t trong tp tnh im v gi v cho

client gip ngi s dng d dng la chn tp mnh cn.

2.3.8. Dch v hi thoi trn Internet - IRC

Internet Relay Chat (IRC - Ni chuyn qua Internet) l phng tin "thi gian

thc", ngha l nhng t bn g vo s xut hin gn nh tc thi trn mn hnh

ca ngi nhn v tr li ca h ca xut hin trn mn hnh ca bn nh vy.

Thay v phi chvi pht hay vi ngy i vi thng ip, bn c th trao i

tc thi vi tc g ch ca bn. IRC c th mang tnh c nhn nh e-mail,

ngi l khng khm ph c ni dung trao i ca bn, hoc bn c th to

"knh m" cho nhng ai bn mun cng tham gia. Ngoi vic trao i li,

ngi dng IRC cn c th gi file cho nhau nh hnh nh, chng trnh, ti

liu hay nhng th khc.


38/122


V KhoaTTT4-K4046

CHNG 3: GII THIU CHUNG V ATM

3.1.S ra i ca mng ATM

Trong nhng thp k gn y, cng ngh vin thng v cc nghnh cng ngh

ph tr pht trin ht sc nhanh chng. S pht trin to ra nhiu hthng vin thng vi cc tnh nng khc nhau. Tuy nhin mi h thng vin

thng thng ch c thit k phc v cho mt hoc mt s dch v nht

nh. Chng c thit k theo cc chun khc nhau, c c ch hot ng khc

nhau. iu ny dn n s a dng v phc tp trong h thng vin thng. Mt

khc do chng hot ng c lp vi nhau nn ti nguyn ca chng khng

c chia s cho nhau.

Mng t hp s a dch v ISDN ra i nhm mc ch xy dng mt h

thng vin thng c kh nng p ng c tt c cc loi dch v trong mt

mng duy nht. Mng t hp a dch v s bng rng (B-ISDN) l mng c khnng p ng cc yu cu .

Do yu cu p ng c a dch v trong c cc dch v bng rng

mng B-ISDN khng th s dung cc cng ngh chuyn mch knh v chuyn

mch gi thng thng. V vy kiu truyn khng ng b ATM (Asynchonous

Transfer Mode) c ITU-T khuyn ngh s dng trong mng B-ISDN, do

mng B-ISDN cn c th gi l mng ATM.

B-ISDN c kh nng phc v cho cc dch v chuyn mch knh v

chuyn mch gi theo hng a phng tin (Multimedia) hay n phng tin

(Monomedia), theo kiu hng lin kt (Connection- Oriented) hoc khng lin

kt (Connectionless). B-ISDN cung cp cc cuc ni thng qua cc chuyn

mch, cc cuc ni c nh hoc bn c nh, cc cuc ni t im n im

hoc t im n nhiu im v cung cp cc dch v theo yu cu.

3.2. Cc cim chnh ca ATM

Trong kiu truyn khng ng b, thut ng truyn bao gm c lnh vc

truyn dn v chuyn mch, do kiu truyn m ch c ch truyn dn v

chuyn mch thng tin trong mng. Thut ng khng ng b gii thch mtkiu truyn trong cc tin trong cng mt cuc ni c th lp li mt cch bt

thng nh lc chng c to ra theo yu cu c th m khng theo mt chu

k no. ATM c hai c im quan trng l :

D liu c truyn di dng cc t bo ATM (ATM cell) c kch thc

nh v c nh l 53 Bytes. Vic truyn tin vi tc cao cng cc t bo


39/122


V KhoaTTT4-K4047

nh lm gim tr truyn dn p ng cho cc dch v thi gian thc, ngoi

ra kch thc nh cn to iu kin cho vic hp knh tc cao c d

dng hn.

Kh nng nhm mt vi knh o (Virtual Channel) thnh mt ng o

(Virtual Path) nhm gip cho vic nh tuyn c d dng hn.Hnh 3.1 so snh s khc nhau gia kiu truyn ng b (STM) v kiu

truyn khngng b (ATM). Trong dng truyn ng b STM, cc phn t s

liu tng ng vi knh cho c nhn bit bi v tr ca n trong khung

truyn dn. Trong khi ATM cc gi thuc v mt cuc ni li tng ng vi

cc knh c th v n xut hin ti bt k v tr no.

Hnh 3.1: Nguyn l ATM v STM

Nh trn trnh by phn t d liu dng trong mng ATM l cc t

bo ATM c kch thc c nh l 53 Bytes. Phn tiu ca t bo (5 Bytes)

dng mang cc thng tin cn thit cho vic nhn dng cc tbo. Cch thc

truyn t bo ph thuc vo yu cu v tnh cht ca dch v v ti nguyn trn

mng.Tnh ton vn ca chui t bo c m bo khi truyn qua mng ATM.

Ni mt cch khc cc t bo thuc v cng mt knh o lun c truyn theo

mt th t nht nh.

ATM s dng k thut truyn theo kiu hng lin kt (Connection -

Oriented). Mt cuc ni lp ATM bao gm mt chng hay nhiu chng

T bo

Tiu t bo ATM

Thng tin t bo ATM

Knh khng s dngNguyn l ATM

Knh1 Knh 5 Knh 1 Knh 7 Knh 5 Knh 1

Khe thi gian

Khung thi gian s

Nguyn l STM

Knh

2

Knh

n

Knh

1

Knh

2

Knh

n

Knh

1


40/122


V KhoaTTT4-K4048

(Link), mi chng c gn mt s hiu nhn dng khng i trong sut cuc

ni. Cc s hiu nhn dng ny l cc knh o v ng o. Tuy vy ATM

cng cung cp mt s giao thc cho cc dch v truyn s liu khng lin kt

(Conectionless).

ATM cho php hot ng khng ng b gia pha pht v pha thu. Skhng ng b ny c th c x l d dng bng vic chn hay tch cc t

bo khng phn nhim (t bo rng) l cc gi khng mng thng tin. Mt

trong nhiu c tnh c bit ca ATM l n c kh nng m bo vn chuyn

tin cy bt c mt loi dch v no m khng cn quan tm n tc (tc

khng i hay tc thay i), yu cu cht lng hoc c tnh bng n t

nhin ca lu lng. ATM c th p dng cho mi mi trng mng. Ngoi ra

cc t bo ATM c di ng nht do vy vic nh tuyn, chn hay tch

ghp t bo c thc hin nhanh hn m khng cn qua tm n thng tin

c mang trong t bo ATM.

3.2.1.Cc u im ca ATM

Cng ngh ATM kt hp cc u im ca chuyn mch knh v

chuyn mch gi. Cng ngh ny loi b c nhng hn ch ca k thut

STM. Nhng u im chnh ca ATM l:

Kh nng truyn dn cc dch v vi cc tc khc nhau: cng ngh ATM

s dng cc t bo kch thc nh, c nh v kh nng phn b di thng

linh hot nn trong mng ATM tc truyn ca cc knh khng b hn ch

vo cc tc chun nh trong STM. Tc cc dch v trong mng ATMc th thay i rt ln (t nh nh truyn s liu n ln nh HDTV). Thm

vo tc dch v cho php thay i rt nhanh, mang tnh t bin.

Kh nng truyn dn cc dch v vi tc cao. Trong mng ATM vic x

l chuyn mch thc hin hon ton bng thit b phn cng v trong cc

nt chuyn mch khng c yu cu iu khin lung, iu khin li nh

trong mng STM nn gim ti thiu thi gian x l nt chuyn mch.

iu ny cho php tc x l nhanh do tc mmg ATM l rt ln.

Kh nng ghp/ phn knh d dng: vic ghp/ phn knh trong mng ATMch da trn cc ch s nhn dng knh nn cc knh vi tc truyn khc

nhau hon ton c th c ghp/ phn d dng.

Vic qun l, iu hnh mng d dng: vic thit lp hay hu b cc cuc

ni da vo cc nhm knh o, ng o nn d dng thit lp hay hu b

cc cuc ni.


41/122


V KhoaTTT4-K4049

Kh nng s dng hiu sut ng truyn, cc t bo ATM c th c gn

cho cc knh mt cch linh ng, khi ng truyn ri s c truyn i

nh tng hiu sut ng truyn.

Tr nh: vic s dng cc t bo c kch thc nh, s dng ng truyn

tc cao cho php t c tr nh.3.2.2.Cc dch v m ATM cung cp

1. Dch v CBR (Constant Bit Rate) trong dch v ny, tc truyn ca cc t

bo l khng thay i nh dch v thoi, video: thng dch v ny yu cu

t l mt t bo thp, tr nh.

2. Dch v VBR (Variable Bit Rate) trong dch v ny tc truyn t bo

thay i, cc dch v VBR c chia lm hai loi : VBR yu cu thi gian

thc v VBR khng yu cu thi gian thc.

3. Dch v ABR (Available Bit Rate) dch v bit c sn: dch v ny ch ctrong mng ATM. T l mt t bo v s thay i tr truyn khng c

chun ho. Cn c vo cc trng thi lu lng mng ATM s cho php

ngi s dng truyn vi tc khng thp hn tc ti thiu ng k

vi mng.

4. Dch v UBR (Unspecifed Bit Rate) dch v ny c a ra nhm khai

thc ti a kh nng ca mng ATM. Dch v ny vo trong mng khng

ph thuc vo trng thi ca mng do dch v ny khng quan tn n mt

t bo hay cc thng s QoS khc.

3.3. Cu trc phn lp ca mng ATM

Nh trong chng 1 cp n m hnh tham chiu cc h thng m

ca OSI. Mi h thng m u bao gm tp hp cc h thng con sp xp theo

th t t trn xung di. Mt h thng con mc N bao gm mt hoc vi thc

th. S trao i tin gia hai thc th cng lp ca hai h thng khc nhau c

thc hin qua giao thc ng cp (quan h ngang cp). Cc n v s liu trao

i gia hai thc th cng cp c gi l n v s liu giao thc PUD

(Protocol Data Unit). im m ti cc thc th ca lp N+1 truy nhp vo

dch v ca lp N c gi l im truy nhp dch v lp N (SAP-Service

Access Point). Hnh 3.2 ch ra mi quan h gia nhng thc th thng qua cc

giao thc.


42/122


V KhoaTTT4-K4050

Hnh 3.2: Mi quan h gia cc thc th trong m hnh OSI

Cc n v s liu dch v lp N (N-SDU: N-Service Data Unit) c

trao i gia lp N v lp N+1 thng qua giao din lp N . Mt PDU lp N bao

gm thng tin iu khin giao thc PCI (Protocol Control Infomation) lp N v

s liu t lp N+1. Hnh 3.3 ch ra cc kiu n v s liu khc nhau v mi

quan h gia chng.

Hnh 3.3 : Kiu n v s liu v mi quan h gia chng

PDU lp N+1

SDU lp N

PDU lp N

Lp N+1

PCI lp N

Lp N

Thc th lp N+1 Thc th lp N+1

Thc th lp N Thc th lp N

Giao thc ng cp lp N+1

Giao thc ng cp lp N

N-SDU

N-PDU

N-SAP

Lp cung cpdch v

Lp s dngdch v

Giao din lp N


43/122


V KhoaTTT4-K4051

3.3.1 M hnh tham chiu giao thc ca B-ISDN (B-ISDN Protocol

Reference Model)

Cu trc mng B-ISDN v mt logic bao gm bn lp c lp vi nhau.

Bn lp ny c lin kt vi nhau thng qua ba mt phng: mt phng ngi

s dng(User Plane), mt phng iu khin (Control Plane) v mt phng qunl(Management Plane). Cu trc ca m hnh tham chiu c trnh by trong

hnh 3.4.

Hnh 3.4: M hnh tham chiu giao thc B-ISDN

Trong :

CLNS : S liu khng lin kt.

CONTS : S hiu hng lin kt.

SAR: Lp con thit lp v tho t bo (Segmentation And Reassembly).

CS : Lp con hi t (Convergence Sublayer).

TC : Lp con hi t truyn dn (Transmission Convergence).

PM: Lp con ng truyn vt l (Physical Medium).

So snh m hnh tham chiu giao thc B-ISDN vi m hnh OSI

M hnh tham chiu ca ATM khng tng thch hon ton vi m hnh

OSI. Tu theo tng trng hp c th m ta xem xt m hnh tham chiu ca

ATM tng ng vi cc lp khc nhau ca m hnh OSI. Khi xt vi cc

Mt phng qun l

iu khinMt phng

Qunllp

Mt ph ng cangi s dng Q

u

nlmthng

iukhin

vbohiu

SliuCLN

S

SliuCON

S

Video

Thoi

Lp con hi t(CS)------- Lp tng thch ATM(ALL)--L con to v tho t bo SAR

L ATM

Lp con hi t truyn dn(TC)---------------------Lp vt l-----------

Lp con ng truyn vt l(PM)


44/122


V KhoaTTT4-K4052

chc nng bn trn khng thuc ATM (IP, IPX.. ..) th lp vt l ca ATM

tng ng vi lp 1 trong m hnh OSI, lp ATM v AAL tng ng vi lp 2

ca m hnh OSI, nhng trng a ch trong phn tiu ca t bo ATM li

c ngha nh lp th 3 ca m hnh OSI. Hnh 3.5 ch ra mi quan h gia m

hnh tham chiu ca B-ISDN v m hnh 7 lp OSI.

Hnh 3.5: Mi quan h gia m hnh ca B-ISDN v m hnh 7 lp OSI

Mt phng ngi s dng (User Plane)Dng thng tin ti cc lp trong m hnh c iu khin trong User

Plane, mt phng ny cn c cc chc nng nh sa li truyn dn, iu khin

tc nghn, gim st dng d liu.Mt phng iu khin (Control Plane)Chu trch nhim thit lp, gii phng v gim st cc kt ni. ATM l

c ch truyn nh hng (Connection- Oriented). iu ny c ngha l mi ktni trong lp ATM trc tin phi c gn mt b nhn dng s duy nhtthng qua cc th tc bo hiu ca mt phng iu khin. S ny c th l bnhn dng ng o (VPI) hoc b nhn dng knh o (VCI).Mt phng qun l (Management Plane).Mt phng ny c hai chc nng l qun l mt phng v qun l lp.

Qun l mt phng phi hp cc chc nng v th tc ca cc mtphng qun l. Qun l mt phng chu trch nhim v cc chc nng nh bohiu trao i v dng thng tin OAM iu khin cc th tc bo hiu (nghal bo hiu cho bo hiu). Chng ta cn knh ny v bo hiu trong cc mngbng rng phc tp v rng hn bo hiu knh D trong N-ISDN.

Lp AAL

Lp ATM

Lp Datalink

Lp vt l

Chuynmch

Dnknh

nhtuyn

Qun ltc nghn

AAL 1 AAL 2AAL3/4

AAL 5

Lp con hit truyn

Lp con hit truyn

Lp con ph

thuc mitr-ng vt l

Lp con ph thuc mi tr-ng vt l

Cc giao dinSDH Sonet

Cp quang100Mbps

Lp cao hn


45/122


V KhoaTTT4-K4053

Thng tin v OAM c dng gim st cht lng mng v qun l lutr ti lp ATM.

Cc lp trong m hnh gm c :

Lp vt l. Lp ATM. Lp tng thch ATM (AAL). Cc lp bc cao.

Chc nng ca cc lp ny c ch ra trong bng 3.1.

Q

U

n

l

l

p

Cc lp cao hn

A

L

L

CS

Nhn/gi cc PDU t/n cc lp cao hn v to dng CS-

PDU.

Kim tra s khi phc chnh xc cc CS-PDUs.

Pht hin s mt cc t bo ca CS-PDU.

Cung cp mt vi chc nng ALL trong phn tiu CS-PDU.

Chn cc t bo b xung vo CS-PDUs.

iu khin lung, gi cc thng ip tr li hoc yu cu truyn

li cc t bo li.

SAR

To cc t bo t CS-PDU, khi phc cc CS-PDUs t t bo .

To ra trng kiu on nh BOM, COM, EOM, SSM.

Kim tra m d vng CRC ca trng d liu ca t bo.

To ra hai Bytes tiu v hai Bytes cui cng ca SAP-PDU.

ATM

iu khin lung chnh.

To ra hoc tch phn tiu ca t bo.

c v thay i phn tiu ca t bo.

Thc hin phn knh/ ghp knh cc t bo.

L

P

v

T

Lp con

hi t

truyn (TC)

Thm vo hoc ly ra cc t bo trng (kh ghp gia tc t

bo v tc truyn dn).

To v kim tra m HEC.

Nhn bit gii hn ca t bo .

Bin i dng t bo thnh cc khung ph hp vi h thng

truyn dn .

Pht / khi phc cc khung truyn dn.


46/122


V KhoaTTT4-K4054

L

Lp con

ng

truyn

vt l(PM)

ng b bit.

Thu, pht s liu.

Bng 3.1: Chc nng ca cc lp trong B-ISDN

3.3.2.Lp vt l

S khc nhau ca lp vt l ATM vi lp vt l trong m hnh OSI ltrong m hnh OSI ti lp ny cng vic ca n lin quan n vic truyn ticc phn t b nht l cc bits t im ny n im khc. Cn trong ATMphn t b nht li l cc t bo. V vy chc nng chnh ca lp vt l trongATM l ti cc t bo v chc nng ny c thc hin bi lp con hi ttruyn dn. Lp con ny ng trn lp con ng truyn vt l. Do vy trong

ATM lp vt l c chia thnh hai lp con l: Lp ng truyn vt l (PM) lin quan n cc chc nng thng thng

ca lp vt l nh kh nng truyn dn cc bits, m ho, gii m, bin iquang in.....

Lp con hi t truyn (TC) thc hin cc chc nng nh chn hoc tch cct bo trng, to v x l m iu khin li tiu , nhn bit gii hn tbo, khun dng t bo, phi hp tc ti trng ca cc khun dng vnchuyn khc nhau c s dng ti lp vt l.

Theo hng t lp vt l ti lp ATM, lung s liu chuyn ti qua danh

gii gia hai lp l lung cc t bo hp l. T bo hp l l t bo m mo ut bo khng c li. Vic kim tra li mo u t bo c thc hin lp conTC. Theo hng ngc li, t lp ATM ti lp vt l, lung t bo ATM cghp thm thng tin phn tch t bo v thng tin v khai thc v bo dng(OAM) lin quan n lung t bo ny.

3.3.2.1.Lp con ng truyn vt l PM (Physical Medium).

Lp ny l lp thp nht trong m hnh, cc chc nng ca n hon ton

ph thuc v mi trng truyn dn vt l c th. Lp ny cung cp cc kh nng

truyn dn bits, n cng lm nhim v m ho dng bits theo m ng truyn vnu cn thit thc hin bin i quang in. Lp PM cn c nhim v ng b bit.

Tu loi giao din l in hay quang m ngi ta s dun g cc loi m ng

truyn khc nhau.

Cc t bo ATM c truyn i theo nguyn tc sau: cc Bytes trong t

bo c gi i theo th t t 153, ngha l trng tiu c gi trc, cc


47/122


V KhoaTTT4-K4055

bits trong Byte c gi i theo th t t bit th 8 n bit th 1. Cc t boc truyn l mt chui lin tc. m bo phn Payload c phn bit viphn Header, Payload c pht i di dng i tn. Tu theo phngphp pht t bo vo trong ng truyn vt l m c cc thut m ha, gii m

khc nhau. Ch pht t bo trc tip ln lp vt l dng phng php DSS(Distributed Sample Scrambing) v a thc sinh l x31+x28+1, phng php sp

xp t bo vo cc khung truyn dn ang tn ti dng thut ton SSS(Synchronous Sample Scrambing) vi a thc sinh l x43+1.

Khong cch cc i gia cc t bo k tip nhau ca lp vt l l 26 tbo lp ATM: Ngha l sau 26 t bo lp ATM cc t bo vt l c chn vo to ra dung lng thch hp vi tc ca giao din. T bo vt l cngc chn khi khng c t bo ATM c truyn i. Cc t bo lp vt l cchn thm c th l t bo rng hoc l cc t bo lp vt l theo yu cu v

OAM. Cc t bo OAM lp vt l c dng truyn ti cc thng tin OAMca lp vt l. S lng t bo OAM c chn ph thuc v cc yu cu vOAM. Tuy nhin trong mt chng truyn dn nhiu nht l sau 26 v t nht lsau 512 t bo, phi c mt t bo OAM.

3.3.2.2.Lp con hi t truyn

Lp con hi t truyn c cc chc nng sau : Thm v v ly ra cc t bo rng. Khi ti mc vt l khng c cc t bo

cha thng tin hu ch, t bo khng xc nh hoc t bo OAM th cc t

bo rng s c chn vo cho tc dng cc t bo ph hp vi tc truyn dn cho trc ca ng truyn. To v kim tra m HEC. Gi tr ca m HEC c tnh thng qua 4 Bytes

u trong phn Header ca t bo ATM v s dng a thc sinh x8+x2+x+1.Gi tr ca HEC chnh l phn d ca php chia Modul 2 ca tch 4 Bytesu vi x8cho a thc sinh x8+x2+x+1. Qu trnh pht hin v sa li cm t trong hnh 3.6.

Ch sa sai

Ch pht hin

li

Khng pht hin thy li

Khng c li

Pht hin ra li nhm

(gi li b hu)

Pht hin ra li n(sa sai)

Pht hin ra li(gi li b hu)


48/122


V KhoaTTT4-K4056

Hnh 3.6: C ch pht hin v sa li HEC

Phn thu hot ng theo hai phng thc. Phng thc ngm nh dng

sa cc li n. Mo u t bo c kim tra v khi pht hin thy li n

th li ny s c sa. Nu pht hin thy li nhm th t bo s b hu.

Sau khi pht hin ra li (n hay nhm) th h thng t ng chuyn sangch pht hin li.

Nu h thng tip tc pht hin ra li th t bo vn b hy d li l li

n hay li nhm. H thng duy tr ch pht hin li cho ti khi khng

tip tc pht hin ra t bo li na, lc ny h thng s t ng quay v ch

sa sai.

Nhn bit gii hn t bo

Chc nng ny cho php u thu nhn bit c gii hn t bo. Vic nhn

bit da vo s tng quan gia cc bits trong phn tiu v m HEC

tng ng. Qu trnh ny c trnh by trong hnh 3.7.

Hnh 3.7: S nhn bit gii hn t bo

u tin u thu c t trng thi tm ng b (HUNT). trng thi

ny h thng s thc hin kim tra tng bit mt trong phn Header ca t

bo. Nu khng pht hin ra li th h thng s t ng chuyn sang trng

thi tin ng b PreSYN. trng thi PreSYN, h thng tip tc thc hinkim tra cho t bo tip theo. Nu sau ln khng pht hin li th h

thng chuyn sang trng thi ng b SYN, cn nu c li th li tr v

trng thi tm ng b HUNT. trng thi ng b, h thng li tip tc

kim tra cho t bo tip theo. Nu pht hin ra li th t ng chuyn v

trng thi tm ng b HUNT. Cc tham s v c chn phi tho mn

Trng thitm ng b

(HUNT)

Trng thitin ng b(PreSYN)HEC sai

HEC ng

Trng thi

ng b(SYN)

Kim tra tng t bo

Kim tra tng t b

Kim tra tng bit

HEC sailin tipln

HEC ng

lin tipln


49/122


V KhoaTTT4-K4057

c cc yu cu v an ton v tnh hot ng ca qu trnh phn tch t

bo. Cc tham s ny c a ra trong khuyn ngh I.432 nh bng sau.

Lp vt l trn c s SDH 7 6

Lp vt l trn c s t bo 7 9

Bin i dng t bo thnh cc khung truyn dn. y l chc nng chuyn

i cc t bo thnh khung truyn dn ti trm pht v khi phc li cc t

bo t khung ti trm thu. Cc h thng thng c dng l h thng phn

cp s ng b SDH (Synchronous Digital Hierarchy) v h thng truyn

dn da trn c s t bo (Cell-base Interface).

Pht v khi phc cc khung truyn dn.

y l chc nng di cng trong lp con TC, n c chc nng to ra cc

khung truyn dn v ghp cc t bo ATM vo khung ri gi i. Ti trmthu thc hin vic khi phc t bo. Cu trc ca khung ph thuc vo h

thng truyn dn c s dng. Kch thc ca khung ph thuc vo tc

ng truyn.

3.3.3.Lp ATM

Lp ATM l thnh phn ch yu ca mng ATM, n nm trn lp vt l,

cc dch v chnh ca mng u c th tm thy lp ny. Cc chc nng ca

lp ATM hon ton c lp vi cc chc nng ca lp vt l di n . Lp

ATM c cc chc nng chuyn cc t bo t lp tng thch ATM (AAL) nlp vt l truyn i v ngc li t lp vt l n cc lp AAL s dng

ti h thng mi. Cc n v thng tin trong lp ATM l cc t bo. Mi t bo

c mt b nhn dng s cha trong Header gn n ti kt ni xc nh.

ATM s dng cc u ni o vn chuyn thng tin v c chia lm

hai mc: mc ng o v mc knh o.

Knh o VC(Virtual Channel) l knh thng tin cung cp kh nng truyn

n hng cc t bo ATM .

ng o VP(Virtual Path) l s kt hp c tnh cht logic hoc ca mt

nhm cc knh o thnh mt b m n c cng mt c tnh lu lng v

c truyn i cng mt ng trong mng. Mt ng truyn vt l (nh

cp quang chng hn) c th cha nhiu ng kt ni o. Hnh 3.8 m t

qu trnh kt hp cc VCs, VPs v ng truyn.

VC

VPVC

VPVC

VP

VCVP

VCVP

VC

-ng truyn dn

VP


50/122


V KhoaTTT4-K4058

Hnh 3.8: S kt hp cc knh o, ng o

3.3.3.1.Mt s khi nim lin quan n knh o v ng o

Cc khi nim ny gm c lin kt ng o, lin kt knh o, cuc ni

knh o, cuc ni ng o.

Cuc ni knh o VCC l tp hp ca mt s lin kt. Theo nh nghaca ITU-T: VCC l s mc ni ca cc lin kt knh o gia hai im truy nhp

vo lp tng thch ATM. Thc cht VCC l mt ng ni logic gia hai

im dng truyn cc t bo ATM. Thng qua VCC th t truyn cc t bo

ATM s c bo ton. C 4 phng php c dng thit lp mt cuc ni

knh o ti giao din UNI.

Cc VCCs c nh (Permanent) hoc bn c nh (Semi-Parmanent) c

thit lp ti thi im nh trc m khng cn bo hiu.

Mt VCC c thit lp/gii phng bng cch s dng mt th tc bo hiutrao i.

Thit lp/gii phng mt VCC u cui c thc hin bng mt th tc

bo hiu t ngi s dng n mng.

Nu mt PVC ang tn ti gia hai UNI, th mt VCC trong VPC ny c

th c thit lp/ gii phng bng vic s dng mt giao thc bo hiu t

ngi s dng ti ngi s dng.

Cuc ni ng o VPC (Virtual Path Connection) l s mc ni ca mt

s lin kt ng o. VPC l s kt hp logic ca cc VCCs (Virtual Channel

Connection). Trong mt VPC mi lin kt knh o u c mt s nhn dngVCI (Virtual Channel Indentifier) ring. Tuy vy nhng VCs thuc v cc VP

khc nhau c th c cng s VCI. Mi VC c nhn dng duy nht thng qua

t hp hai gi tr VPI v VCI. C 3 phng php sau c s dng thit lp/

gii phng mt VPC gia cc im cui VPC:

Mt VPC c thit lp/gii phng da trn mt knh nh trc v do

khng cn th tc bo hiu.

Vic thit lp/gii phng VPC c th c iu khin bi khch hng. Cc

th tc qun l mng dng cho mc ch ny. Mt VPC cng c th c thit lp/gii phng bi mng s dng cc th

tc qun l mng.

Nhim v trung tm ca lp ATM l bin i a ch mng cc lp caothnh cc gi tr VPI v VCI tng ng. Cc gi tr VPI v VCI c to ra

da trn s hiu nhn dng ca im truy nhp dch v SAP. Ti u thu,


51/122


V KhoaTTT4-K4059

trng tiu c tch ra khi t bo ATM. Ti y gi tr VPI v VCI c

dng nhn dng im truy nhp dch v.

Phn knh v hp knh cc t bo: Ti u pht cc t bo thuc v cc

knh o v ng o khc nhau c hp thnh mt dng t bo duy nht. Ti

u thu dng t bo ATM c phn thnh cc ng o v knh o c lp i ti cc thit b.

Bin i VPI/VCI Nu cc t bo c nh tuyn thng qua cc chuyn

mch ATM hoc cc nt ni xuyn th cc gi tr VPI/VCI a ti cc thit b

ny cn phi c bin i thnh cc gi tr VPI/VCI mi xc nh ch mi

ca t bo.

3.3.3.2.Nguyn l chuyn mch ATM

Vic chuyn mch cc t bo ATM c thc hin trn c s cc gi tr

VCI, VPI. Nh trnh by trn VCI, VPI ch c gi tr trn mt chng ktni c th. Khi t bo n nt chuyn mch, gi tr ca VPI hoc c gi tr VPI,

VCI u c thay i cho ph hp vi chng tip theo. Thit b chuyn mch

ch da trn gi tr VPI c gi l chuyn mch VP (VP Switch), nt ni

xuyn (ATM Cross- Connect) hoc b tp trung (Concentrator). Nu thit b

chuyn mch thay i c hai gi tr VPI,VCI th n c gi l chuyn mch

VChoc chuyn mch ATM.

Hnh 3.9 m t mt cuc ni VCC thng thng, T l nt chuyn mch

ni m VCI, VPI u b thay i, A, B l cc thit b u cui, D1, D2 l cc b

ni xuyn, ni ch thay i gi tr VPI, ai, xi, yi l cc gi tr VCI, VPI tngng.

D1 D2

B

T

A

D1,D2 : B ni xuynT: chuyn mch ATMA,B : Thit b u cui

a1.x1VPI=x1

VCI=a1VPI=x2

VPI=y1

a1.x2a2.y1

a2.y2VPI=y2

Cuc ni knh o VCC

VCI=a2


52/122


V KhoaTTT4-K4060

Hnh 3.9: Cuc ni knh o thng qua cc nt chuyn mch v b ni xuyn

Hnh 3.10 l s nguyn l chuyn mch VP. Chuyn mch VP l ni

bt u v kt thc ca cc lin kt ng o, do vy n phi chuyn cc gi tr

VPI u vo thnh cc gi tr VPI tng ng u ra sao cho cc lin kt

ny thuc v cng mt cuc ni ng o cho trc. Lc ny gi tr VCI cgi khng i.

Hnh 3.10 Nguyn tc chuyn mch VP

VCI1

VCI2

VCI3

VCI4

VCI5

VCI6

VPI1

VPI2

VPI3

VPI4

VPI6

VPI5

VCI3

VCI4

VCI1

VCI2

VCI5VCI6

Chuyn mch VP


53/122

n tt nghip Chng 3: Gii thi

giao thuc tcpip

Documents