73570955 dk thiet bi qua mang internet

8/2/2019 73570955 DK Thiet Bi Qua Mang Internet

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MC LC LUN VN TT NGHIP


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CHNG 1. GII THIU

1.1. Gii thiu

iu khin t xa v ang l mt xu hng pht trin mang tnh quy lut. S

pht trin nhanh chng ca khoa hc k thut ni chung v ngnh in t-vin thng

ni ring l nn tng cho xu hng ny. V s tin li ca n, iu khin t xa c th

c s dng bt k ni no. Ngi s dng c th bt k u trn th gii cng c

th iu khin c nhng b phn ngoi vi nh, cng s hay mt ni no c

nh sn.Lc ny khng cn gii hn v khong cch na.

Trong k thut iu khin t xa, mi trng truyn dn c th l dy dn in

hay khng kh vi tn hiu truyn c th l tn hiu in hng ngoi hay sng v

tuyn....c bit, k thut hng ngoi hay v tuyn c khai thc trit trong vic

ch to cc thit b u xa. Tuy nhin k thut iu khin dng tia hng ngoi v v

tuyn b hn ch v khong cch v bng thng. khc phc nhc im trn c th

s dng phng php khc l iu khin t xa qua mng ethernet, Internet hoc LAN. tng ca n l s dng mng c sn truyn tn hiu iu khin, nh m vn

khong cch c khc phc.

Nh ta bit, ngy nay mng li Internet-Ethernet pht trin v ph bin

khp ni trn th gii. C th xem s bng n ca Internet ngy nay cng ging nh

s bng n ca tivi vo nhng nm 40-50 ca th k trc. Chnh iu ny cng lm

cho Internet ng tr trong mi ngc ngch ca cuc sng, v do vic iu khin t

xa qua mng tr nn d dng, thun tin hn v l mt nhu cu tt yu ca cuc sng

hin i ngy nay.

iu khin t xa qua mng c 2 u im ni bc:

Th nht chng ta c th s dng mng Internet c sn.


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Th hai c th s dng nhiu ni v c nhiu ng dng m con ngi

khng th tip cn mt cch trc tip c.

Cc thit b iu khin t xa qua mng ang tng bc xm nhp vo trong cc

sinh hot gia nh do tnh n gin tin dng, tin cy tng i n nh. B iu

khin c th lm mt s cng vic trong gia nh khi ta ang xa nh nh: m my

bm nc, tt bp in, tt m bng n...

1.2. Phng n thc hin

Thit k ca ti nhm xy dng h thng iu khin t xa thng qua mng

internet. M hnh ca h thng c m t nh hnh sau.

Internet

SwitchIP

tnh

Device1

Device 2

IPtnh

.

.

.

remote

client

Device N

IPtn

h


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Thit k gm 2 phn chnh:

Phn th nht: l phn giao tip ngi dng ti my u xa iu

khin thit b. Trong ti, phn ny c thit k l mt software

s c ci t trn my tnh u xa (remote host) to giao din

cho ngi dng, truyn cc lnh iu khin qua mng ti thit b v

nhn cc khung d liu bo trng thi t thit b n ngi dng.

Phn mm ny c vit bng ngn ng Visual Basic trn mi

trng h iu hnh Window, h tr lp trnh mng v giao din

p. Phn thit k software s c ni k cc chng sau. Phn th hai: l Thit b giao tip mng v iu khin. giao tip

c mng Ethernet. Thit b c thit k gm 1 chip Ethernet

controller dng to khung Ethernet, truy xut mng, iu khin

thit b giao tip vi chip vt l giao tip mng ( y ta s dng IC

ENC28J60 ca Microchip h tr chun IEEE 802.3).


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CHNG 2. L THUYT MNG ETHERNET

2.1. Tng quan v Ethernet

Ngun gc ca Ethernet c pht trin t nhng th nghim i vi cp ng

trc c thc hin tc 3 Mbps v s dng nghi thc CSMA/CD (carrier sense

multiple access collision detect) cho mng LAN vo nm 1970 bi tp on Xerox. S

thnh cng ca n ny sm gy s ch v dn n s pht trin ca Ethernet

10 Mps bi ba tp on: Digital Equipment, Intel, Xerox.

Thnh ng Ethernet c ngun gc vi mng LAN ( Local-Area Network) v vic

s dng chun IEEE 802.3. Chun ny c bit vi nghi thc CSMA/CD. C ba tc

c c dng cho mng Ethernet vi ng truyn l cp ng trc, cp i hay

si quang.

10Mbps10 base-T Ethernet.

100Mbps Ethernet tc cao (Fast Ethernet).

1000MbpsGigabit Ethernet.

Ethernet 10-Gigabit pht trin v c a ra cng chun IEEE 802.3ae cui

2001 v u 2002. N cng tng thch vi chun IEEE 802.3.

Ethernet c to ra phn ln t k thut mng LAN (hin ti ang c s dng

cho gn 85% cho mng LAN ni PC v cc my trm-workstations). Bi v ghi

thc ca n c mt s c im sau:

D dng s dng, thc hin, qun l v bo tr.

Cho php thc hin mng tc thp.

Cung cp rt a dng m hnh mng (topology).

Bo mt thnh cng vic kt ni chung.


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2.2. M hnh tham chiu OSI

Mt hnh OSI (Open Systems Interconnection) l mt m hnh cho php hai h

thng khc nhau bt k thng tin vi nhau bt chp cu trc bn di. Mc ch ca

m hnh OSI l m rng thng tin gia hai h thng khc nhau m khng cn thay i

logic phn cng v phn mn bn di ca mi h thng. M hnh OSI khng phi l

mt nghi thc, n ch l mt m hnh hiu v thit k kin trc mng cho linh ng,

vng chc v lin thng.

M hnh OSI l cu trc phn lp thit k cc h thng mng cho php thng

tin qua tt c cc loi h thng my tnh. N bao gm 7 lp ring bit nhng c milin quan vi nhau, mi lp nh ngha mt phn on x l khi chuyn dch thng tin

qua mng. Hnh sau m t m hnh 7 lp ca OSI.

Hnh 2-1 m hnh OSI 7 lp

Qu trnh x l ti lp 7, k tip chuyn t lp ny sang lp khc theo th t. Ti

mi lp (ngoi tr lp 7 v lp 1), header ca lp tng ng s c cng vo n v

d liu trc khi chuyn xung cho lp di k tip. Khi n v d liu c nh

dng i qua lp vt l, n i thnh tn hiu in t v vn chuyn dc theo lin kt

vt l.

Khi t n ch, tn hiu i vo lp 1 v c i ngc thnh bit. Cc n v

d liu k tip c chuyn ln qua cc lp OSI. Khi mi khi d liu ti lp k cao


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hn, cc u v ui c gn lc trc s c loi b ti cc lp tng ng. Khi n

n lp 7 th thng ip tr thnh dng thch hp cho ng dng.

2.2.1. Lp vt l (Physical Layer)

Chc nng lp vt l l truyn mt dng bit trn mt mi trng vt l. N lin

quan n cc qui nh v in v c ca giao tip v mi trng truyn. N cng nh

ngha cc th tc v cc chc nng m cc thit b vt l v cc giaor tip phi thc

thi.

2.2.2. Lp lin kt d liu (Data Link Layer)Lp ny c nhim v chia nh d liu a xung t lp mng thnh cc frame

d liu (mt frame thng di t vi trm byte n hng ngn byte) truyn i v t

chc nhn sao cho ng th t cc frame. Lp ny cng cung cp kh nng truyn

khng li trn ng truyn vt l cho cc lp cao hn. Vn t ra y l phi

xc nh c ch xc nhn 1 frame c truyn thnh cng hay khng ? (Acknowledge

frame) v x l nhiu (truyn li).

Lp lin kt d liu lin quan n s truyn, kim tra li v iu khin lung d

liu. Chc nng chnh ca lp lin kt d liu hat ng nh mt li chn bo v cho

cc lp cao hn, iu khin qu trnh truyn v nhn. Kim tra li v iu khin lp

vt l nh l chc nng chnh m bo cc lp trn nhn d liu t lp mng khng

c li. Chun IEEE 802 chia lp lien kt d liu thnh hai lp con l: Logical Link

Control (LLC) v Media Access Control (MAC).

Lp con Logical Link Control (LLC) c nhim v bo v lp trn t bt c

phng php truy cp c th no hoc truy cp ng truyn c th no. Cc lp trn

khng lo lng v cch kt ni ca chng ti mng Ethernet bi v LLC iu khin giao

din ny.

Lp con Media Acess Control (MAC) c nhim v cho mt vi hat ng. Trn

ng truyn lp con MAC c trch nhim trong vic nhn d liu t lp lp con

Logical Link Control v ng cc gi sn sng cho vic truyn. Lp MAC xc nh


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cc knh ng truyn rnh. Nu ng truyn rnh MAC s truyn d liu trn cp

v lun gim st trng thi ca lp vt l cho vic bo hiu c xung t. Nu c xung

t, MAC cng iu khin qu trnh thu hi d liu v truyn li. MAC gii quyttranh chp cho mi trng dung chung. N bao gm cc quy nh ng b, c v kim

sot li cn thit truyn thng tin t v tr ny n v tr khc, cng nh cc a ch

vt l ca trm nhn. Cc nghi thc MAC c dung c th vi tng LAN (Ethernet,

Token ring, Token bus).

2.2.3. Lp mng (Network Layer)

iu khin hot ng ca cc subnet, tc l tm ng cho mt packet i t

ngun n ch (truyn d liu gia 2 my bt k trong mng).

Vn ln nht ca lp ny l tm ng (Routing), gii quyt xung t

(Collsision Detect), gii quyt vn a ch (Addressing), vn tnh chi ph

(Accounting).

Lp mng m nhn d liu t lp giao vn v thm cc thng tin ph hp cho

gi v cung cp ng truyn ph hp cng nh nhng mc kim tra li. D liu

c nh dng cho ph hp vi ng truyn.

2.2.4. Lp giao vn (Transport Layer)

Chc nng c bn ca lp ny l chia nh gi d liu c a t lp bn trn

xung thnh nhng n v nh hn truyn qua mng vi s m bo l d liu s

ti ni mt cch chnh xc (kim tra s sepuence, error detection pht hin li, flow

control iu khin lung). Lp ny cung cp cho cc lp bn trn phng tin truyn

cc message c lp vi cc lp bn di (end to end hai h thng thc s kt ni

vi nhau).

Lp giao vn m bo s ti u cho vic truyn d liu t ngun n ch bng

cch iu khin lung d liu ca mng v thc hin s yu cu m bo dch v cho

lp phin. Lp giao vn xc nh kch c ca gi da trn s lng d liu c gi

v kch tht gi ln nht cho php truyn trn ng truyn. Nu d liu gi ln hn


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gi c kch tht ti a, n s thc hin chia d liu thnh cc thch tht ph hp mt

cch tun t. N ng thi thm cc thng tin nh iu khin li ph hp vi t l

d liu ca mt gi.

Khi nhn d liu t lp mng, lp giao vn s m bo rng d liu nhn c

ng th t v kim tra lp v mt khung.

2.2.5. Lp phin (Session Layer)

Cung cp nhng phng tin cho php 2 thc th ca lp ng dng c th t

chc v ng b cuc i thoi v qun l s trao i thing tin gia chng (cc dch

v cc qu trnh c th trao i vi nhau, to v kt thc kt ni gia cc qu trnh

trn cc my khc nhau). Lp phin lin quan n s giao tip gia hai thit b vin

thng. Lp ny to ra nhng qui lut cho vic khi ng v kt thc giao tip gia hai

thit b, cng nh s phc hi li. Nu c li v s giao tip li c pht hin, lp

phin s truyn li d liu hon thnh qu trnh giao tip. Lp phin yu cu mt s

phc v tt t lp giao vn khng yu cu truyn li, hoc truyn hai hng, yu

cu nhiu s gim st (monitoring) v hi tip (feedback).

2.2.6. Lp trnh by (Presentation Layer)

Lp ny biu din nhng thng tin c truyn (c hiu l c php v ng

ngha). N ng nht cc thng tin gia cc h thng vi nhau. Lp trnh by gii

quyt cc vn lin quan n thng dch d liu v thay i m gia cc thit b, m

chng nh dng d liu khc nhau. Ngoi ra, lp ny cng iu khin s thng dch

s khc nhau gia cc thit b v cc tp tin nh dng (file formats), cng nh cung

cp dch v thao tc trn d liu nh nn v m ha (compression & cryptography).

2.2.7. Lp ng dng (Application Layer)

a cc ng dng thit thc cho ngi s dng, ng vi mi ng dng c mt

nghi thc khc nhau. Lp ng dng l lp giao tip gia ngi dng v mng. Lp ny

nh hng trc tip n nhng chng trnh ng dng dnh cho ngi s dng (user

application programs) cung cp cch thc truy cp mng. Lp ng dng thng lin


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quan vi cc ng dng nh: FTP (truyn nhn file), Telnet (gii quyt s khc nhau

phn cng cng nh phn li gia cc terminal), e-mail (truyn nhn mail), file

sharing

2.3. S lc v chun IEEE 802.3

Chun IEEE 802.3 l mt phn ca h chun cho mng cc b v metropolitan.

Mi quan h gia cc thnh vin ca chun c trnh by bn di.

Hnh 2-2 H chun ca mng cc b.

Cc chun ny lin quan n lp vt l v lp data link c nh ngha bi

International Organization Standardization (ISO).

2.4. Cu trc khung Ethernet IEEE 802.3

Chun IEEE 802.3 nh ngha mt khung nh dng d liu c bn cho tt c

cng vic m MAC thc hin. Thm vo , mt vi chc nng la chn c thm

vo cho khung d liu. Mt khung d liu gm c 7 trng nh hnh v.


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Hnh 2-3 Cu trc Frame Ethernet

Phn u khung Preamble

Preamble ch ra s bt u ca mt khung truyn. N gm mt dy cc gi tr bit

0 v 1 xen k nhau bo hiu cho trm nhn (receiving stations) rng c khung ang

ti. V n cng cung cp mt phng tin ng b ha nhng phn khung nhn ca

lp vt l nhn vi mt lung bits vo.

Preamble bao gm 7 bytes nh sau:

10101010 - 10101010 - 10101010 - 10101010 - 10101010 - 10101010 - 10101010

Start Frame Delimiter (SFD)

SFD l mt chui 8 bit (1 byte) 10101011. N theo sau Preamble v ch ra s bt

u ca chui thng tin vi hai bit cui l 11. Sau byte ny chnh l a ch.

Destination Address (DA) a ch ch

a ch ch bao gm 6 bytes xc nhn trm s nhn khung. N cha a ch

vt l (physical address) ca ch sp n ca gi. a ch vt l ca h thng l mt

mu bit c m ha trn NIC (Network Interface Card). Nu gi phi i qua mng

LAN ny n mng LAN khc n ch ca n, trng DA cha a ch vt l ca

router ni mng LAN hin hnh v mng LAN k. Khi gi t n mng ch, trng

DA cha i ch vt l ca thit b ch.


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Trong chui bits ny, bit pha bn tri ca trng DA ch ra a ch n

(individual address) nu l bit 0 hoc a ch nhm (group address) nu l bit 1. Bit th

hai bn tri ch ra DA c qun l cc b hay qun l ton cc. Nhng bit cn lic gn xc nhn mt trm n, nhm trm hoc tt c trm trn mng (network).

Source Address (SA) a ch ngun

a ch ngun bao gm 6 bytes cha a ch vt l ca thit b cui cng chuyn

tip gi. Thit b c th l trm ang gi hoc router mi xy ra nht nhn v

chuyn tip gi. a ch ngun th lun lun l a ch n v bit pha tri th lun l

bit 0.

Length/type of PDU field

Lengh/type field gm 2 bytes. Ch ra s byte trong PDU (Protocol Data Unit)

ang n. Nu chiu di ca PDU l c nh, trng ny c dung ch ra loi hoc

nn ca cc giao thc khc. V d, Novel v Internet dng n lm r nghi thc

mng ang dung PDU.

Data field Trng d liu (802.2 frame)

Trng d liu gm tun t n bytes. Chiu di ti thiu v ln nht ca d liu l

t 46 bytes n 1500 bytes. D liu c gi qua lp mng vi mt vi thng tin iu

khin. Nu d liu c chiu di t hn 46 byte trong mt gi, mt c ch t bit s

m ti thiu 46 bytes. PDU c to ra bi lp ph trn (LLC) ri lien kt

n khung 802.3.

Frame Check Sequence (CRC)

Frame Check Sequence bao gm 4 bytes. Mt vng cha 32 bits m kim tra li

v pht hin sai theo m CRC-32 v tnh trn tt c cc trng (fields) ngoi tr

Preamble, SFD, FCS.


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2.5. Lp con MAC v phng thc truy cp CSMA/CD

2.5.1. Media Access Control (MAC)Lp con MAC nm lp 2 trong m hnh OSI. C chc nng l gii quyt tranh

chp cho mi trng dng chung. N bao gm cc quy nh ng b, kim sot li cn

thit chuyn thng tin t v tr ny n v tr khc, cng nh cc a ch vt l ca

trm m bo khung d liu c truyn nhn ng trm.

Hnh 2-4 V tr lp con MAC trong m hnh OSI

MAC Control l 1 lp con (sublayer) ty chn nm trong lp Data link (trong m

hnh 7 lp ca OSI). N c s dng chung vi lp con CSMA/CD MAC. MAC

Control cung cp kh nng iu khin thi gian thc v thao tc hot ng ca lp con

MAC. Lp con MAC Control s dng cc dch v khng kt ni (connectionless) ca

lp con MAC pha di truyn khung iu khin v khung d liu. MAC Control

khng cung cp bt k c ch no m bo khung truyn khng b mt mt. Cc c

ch m bo truyn khung khng b mt mt, nh truyn li cc khung b li, b hy

b, s c MAC Control Client (Logic link control) h tr. V hot ng ca

MAC Control l ty chn, nn MAC Control Client khng th nhn bit c s tn

ti ca thc th MAC Control trong mt trm.

Hot ng ca lp con MAC control trong sut i vi CSMA/CD MAC.

mng Ethernet lp con MAC s dng phng thc truy cp CSMA/CD (Carrier Sense


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multiple access with collision detect) truy cp knh truyn vi 2 ch truyn l:

song cng (full duplex) v bn song cng (half duplex).

2.5.2. Phng thc truy cp CSMA/CD

Khi c nhiu ngi s dng cng truy cp 1 knh truyn dng chung m khng

c quy lut th s dn n xung t. iu ny s dn n d liu s b sai v tr thnh

nhiu. Do mt mng LAN cn c mt c ch qun l lu lng, ti thiu ha

cc xung t v cc i ha cc khung c phn phi thnh cng. C ch truy cp

c dng trong mng Ethernet theo chun IEEE-802.3 l Carrier Sense Multiple

Access with Collision Detect (CSMD/CD), tm dch l a truy cp cm nhn sng

mang c pht hin xung t.

Thit k ban u l phng thc a truy cp (Multiple Access - MA) trong

mi trm truy cp n mt lin kt l ngang bng nhau v bnh quyn. Vi MA th

khng c qun l lu lng, bt c trm no mun truyn th s truyn v da vo xc

nhn kim tra khung truyn l thnh cng hay khng.

Trong mt h thng CSMA, bt c trm no mun truyn trc tin phi lng

nghe sng mang bng cch kim tra in p. Nu khng c in p trn ng truyn

th ng truyn xem nh l rnh v n c th bt u truyn. CSMA c th gim

thiu s xung t nhng tt nhin khng th loi b chng mt cch hon ton. Xung

t vn xy ra nu mt trm cha cm nhn c tn hiu sng mang t mt trm khc

no trn ng truyn do hin tng tr ca truyn sng.

khc phc tnh trng nh trn cn phi c b pht hin xung t CollisionDetect CD. Trong CSMA/CD mt trm mun pht th phi chc chn l ng

truyn rnh, ri mi truyn d liu. Trong lc truyn d liu, trm lun kim tra xem

c in p cao vt tri hay khng, nu c tc l c xung t xy ra. Nu pht hin c

xung t, trm s ngng truyn v i mt lng thi gian ngu nhin nu ng

truyn rnh n s thc hin truyn li.


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2.5.3. Ch bn song cng (Half Duplex Ethernet)

Half Duplex Ethernet l m hnh truyn thng ca Ethernet s dng giao thc

CSMA/CD (Carrier Sense Multiple Access/Collision Detect). Vi CSMA/CD hay

nhiu hn cc trm chia s mt ng truyn chung. truyn mt frame, mt trm

phi ch cho mt khong thi gian rnh trn ng truyn khi khng c mt trm

khc ang truyn. Sau n truyn frame bng cch thng bo (broadcast) n trn

ng truyn m n nghe tt c cc trm trn mng. Nu mt trm khc c gng

truyn truyn d liu ti cng mt thi im, mt ng xut hin. Trm truyn

sau c truyn mt Jam bo m tt c cc trm c thng bo frame truyn bli v mt ng . Trm sau gi cho mt khong thi gian ngu nhin trc khi n

lc truyn li. Tin trnh c lp li cho n khi frame truyn thnh cng.

Cc nguyn tc c bn cho vic truyn mt frame:

Mng c quan st bi mt carrier, hoc s hin din ca mt trm truyn.

Tin trnh ny th c bit nh carrier sense.

Nu mt carrier tch cc c pht hin, sau ng truyn c tr hon.Trm tip tc quan st mng cho n khi carrier ngng.

Nu mt carrier khng c pht hin, v khong khng c carrier th bng

hoc ln hn khang thi gian chung gia hai khung d liu (interframe gap),

sau trm lp tc bt u truyn li frame.

Trong khi trm ang truyn frame, n quan st ng truyn c ng hay

khng.

Nu mt ng c pht hin, trm truyn ngng gi khung d liu (frame

data) v gi mt chui jame 32 bits. Nu ng c pht hin rt sm

trong lc truyn frame, th trm truyn s hon thnh vic truyn preamble

ca frame trc khi bt u truyn chui jame. Chui jame c pht i

m bo chiu di ca ng thng bo ti cc trm khc.

Sau khi gi chui jame, trm truyn ch mt khong thi gian ngu nhin

c chn t b pht random number trc khi bt u tin trnh truyn li.


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Tin trnh ny gi l backoff. C th mt ng c lp li b gim i do

trm ang ng ch mt khong thi gian ngu nhin trc khi truyn li.

Nu ng xut hin li, th vic truyn c lp li, nhng thi gian tr

hon ngu nhin c tng vi mi n lc truyn li. iu ny lm gim kh

nng ng ca trm khc.

Tin trnh ny lp li n khi mt trm truyn mt frame khng c ng .

Ngay khi mt trm thnh cng truyn mt frame, n s reset li collision

counter n s dng tng thi gian backoff sau mi ln ng lp li.

Slot Time

Slot time l mt thng s cho mng hot ng half duplex Ethernet. N c

xc nh l 512 bits time cho mng Ethernet hot ng ti 10 v 100 Mb/s, v 4096 bit

time cho Gigabit Ethernet. m cho mi ni truyn tin cy trong vic pht hin ng

, thi gian truyn nh nht cho mt frame phi t nht l mt slot time, v thi gian

yu cu cho ng truyn n tt c cc trm trn mng phi nh hn mt slot

time. V th, mt trm khng th hon thnh truyn frame trc khi pht hin rng mt

ng xut hin.

Cc tn hiu truyn bi cc khong tr hon ng cc trm Ethernet khi

chng truyn sut trn mng. Cc khong truyn bao gm thi gian yu cu cho tn

hiu truyn qua cc phn cp, v thi gian tr hon ng logic khi cc tn hiu

chuyn qua cc thnh phn in trong Network Interface Cards (NICs) v cc hub. i

vi cc phn cp di hn v nhiu hub trn trm, n cho tn hiu truyn t mt mng

cui n mng khc. Thi gian mt tn hiu truyn gia hai trm c khong cch xa

nht trong mng c bit nh l propagation delay ln nht ca mng.

Mt trm pht hin rng frame m n ang truyn bt gp mt ng , cc

tn hiu ca n phi truyn qua mng n trm khc pht hin cc ng . Trm ny

phi truyn mt chui jame ch mt ng c pht hin. Chui jame ny

phi truyn qua li mng trc khi c pht hin bi trm ang truyn. Tng mt


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vng truyn ti a (round trip propagation delay) v thi gian yu cu truyn mt

chui jame l cc thnh phn xc nh chiu di ca Ethernet slot time.

Slot time l mt thng s quan trng v:

512 bits slot time thit lp kch c nh nht ca mt Ethernet frame l

64 bytes. (4096 bits slot time cho Gigabit Ethernet yu cu mt vng

m rng c thm vo frame kch c truyn nh nht l 512

bytes). Bt k frame c chiu di t hn 64 bytes th c xem nh l

mt collision fragment hay runt frame, v t ng c b ra bi

trm nhn. Slot time thit lp mt gii hn kch c ca mt mng trong gii hn

phn chiu di cp ti a v s ln lp li c th trn ng dn. Nu

kch c ca mng qu ln, mt hin tng c bit nh late

collisions c th xut hin. ng tr c xem nh mt li trong

mng bi v ng n qu tr trong vic truyn frame t ng i

x bi chc nng iu khin truy cp ng truyn Ethernet. Frame

ang c truyn s b b, yu cu mt phn mm ng dng pht hin

mt v bt u truyn li.

Slot time m bo nu c mt ng sp xut hin, n s c pht

hin trong 512 bits u tin (4096 cho Gigabit Ethernet) ca frame

truyn. Mt phn cng Ethernet n gin gi frame truyn li sau mt

ng .

i vi Gigabit Ethernet, slot time phi c tng t 512 n 4096 bits time. V

Gigabit Ethernet c tc data cao hn, tn hiu truyn ch cho mt khong cch rt

nh trong phm vi 512 bits time. Ti tc mt slot time 512 bits s c h tr mt

mng kch c ti a khong 20 mt. Mt mng nh l khng thc t, v th chp nhn

ca vic m rng mt sng mang c gii thiu tng slot time n 4096 bits. Vic

tng kch c ca slot time v vic gii hn s ln lp li trong mt mng, kch c mt

mng 200 mt c th c h tr bi Gigabit Ethernet.


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Backoff

Backoff l qu trnh x l mt trm ang truyn tnh ton ch bao lu sau mt

ng trc khi n lc truyn li frame. Nu tt c cc trm ch cng khong

thi gian trc khi truyn li, sau ng khc s chc chn xut hin. iu ny

c trnh bng cch mi trm pht mt s ngu nhin tn khong thi gian n phi

ch trc khi kim tra sng mang. Khong thi gian ny c bit nh l backoff

delay ca trm.

Thut backoff thc hin trong Ethernet l truncated binary exponential

backoff. Sau mt ng , mi trm pht mt s ngu nhin nm trong tm ch r cagi tr. Sau n ch s slot time trc khi n lc truyn li. Tm gi tr tng theo s

m sau mi ln truyn li b hng. N lc ln u c tm l 0 n 1, ln th hai l 0

n 3, ln ba l 0 n 7 v c th tip tc. Nu ng lp li, th tm tip tc m

rng n 10 n lc khi n i t 0 n 1023. Sau tm ca gi tr nm gia t 0 n

1023. Nu mt trm khng thnh cng trong vic truyn sau 16 ln n lc, th MAC

thng bo excessive collision error. Frame c truyn li sau b b i, ta cn

phn mm ng dng pht hin mt frame v bt u mt s truyn li.

Cc kt qu binary exponential backoff trong khong tr hon nh nht trc khi

truyn li khi lu lng trn LAN l thp. Khi lu lng cao, ng lp li l

nguyn nhn lm tm tng ln, v th lm gim c hi ng sau . Trong mt

mng, ni m lu lng c mc cao, ng lp li s bt u gy ra li qu ng

(excessive collision error) c pht i. Li qu ng ch ra rng lu lng

ti tng n im m n khng th c kh nng c gi trn mt mng Ethernetn l.

Capture Effect

Khi mng ang hot ng di mt ti ln, thut ton binary exponential backoff

c th trnh by mt s khng cng bng c bit nh capture effect. Vn ny

sinh t vic nm gi ca collision counter. Mi trm s cp nht b m ng mt

cch c lp ca n v ch sau mt n lc truyn li. Ch c thnh cng b m ng


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tr v zero sau khi pht mt gi thnh cng. iu ny cho thun li mt trm n

bt cho php n capture mng c mt khong thi gian m rng.

Mt v d ca hiu ng bt gm hai trm c nhiu data gi v c th gi data

nhanh nh c cho php. C hai ng vi n lc truyn li u tin v chn

backoff l 0 hoc 1. Trm A chn 0, v trm B chn 1. Trm A truyn li trong lc

trm B ch mt slot time. Sau khi trm A hon thnh vic truyn ca n v ht khong

interframe gap, c hai trm sn sng truyn li v ng xut hin. y l ng

u tin ca trm A i vi frame ny, v th n chn mt backoff l 0 hoc 1. Tuy

nhin, y l ng ln th hai ca trm B cho frame ny, v th n chn mtbackoff gia 0 v 3. V vy trm A c kh nng truyn cao hn trong lc trm B ch

li. Nu iu ny xy ra th ly s ging nh vy v li ng , cho nn ly cc s l

cho trm B (ly s chn th xu hn).

Mt kch bn ging nh vy c th lp i lp li ch c th kt thc khi hng ca

trm A l n lc cui cng hoc khi trm cui cng trm B tin ti n lc th 16. Sau

16 ln n lc trm B s reset li b m ng ca n cho php n tr li cnh tranh

nhiu hn. Nhng n cng b ra frame n n lc truyn li, yu cu n xp hng

frame cho vic truyn li bng phn mm.

Vo nm 1994 mt thut ton backoff mi c gi l binary logarithm

arbitration method (BLAM) c a ra lm gim vn hiu ng bt. Mt nhm

lm vic IEEE 802.3w c to ra thm BLAM nh mt c im khng bt buc

cho chun Ethernet. Mc d kt qu m phng chng minh rng BLAM a ra mt ci

tin xc nh trn thut ton binary exponential backoff, cng vic kt hp n votrong chun Ethernet khng bao gi c hon thnh v mt thay i (dch) trong r

nt full duplex Ethernet v thiu s ch cp nht phn cng half duplex.

2.5.4. Ch song cng Ethernet (Full Duplex)

Tiu chun IEEE 802.3x xc nh mt mode th hai ca hot ng Ethernet,

c gi l full duplex, b qua nghi thc CSMA/CD. Nghi thc CSMA/CD l

half duplex. iu ny ch r rng mt trm c th truyn data hay nhn data,


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nhng khng cng mt lc. Mode full duplex cho php hai trm ng thi chuyn

data trn mt lin kt im im cung cp ng truyn v nhn c lp. T mi

trm c th truyn v nhn data cng mt lc, thng lng ca lin kt c gp iln. Mt trm 10 Mb/s hot ng mode full duplex cung cp bng thng ti a 20

Mb/s. Mt trm 100 Mb/s cung cp bng thng 200 Mb/s.

Hot ng full duplex b gii hn n chun sau:

ng truyn vt l phi l cp h tr truyn v nhn ng thi m

khng nhiu. Cc phng tin truyn ch r gp yu cu ny l: 10-

Base-T, 10Base-FL, 100Base-TX, 100Base-FX, 100Base-T2,1000Base-CX, 1000Base-SX, 1000Base-LS, v 1000Base-T.

Phng tin truyn khng th h tr full duplex: 10Base5,

10Base2, 10Base-FP, 10Base-FB v 100Base-T4.

Hot ng full duplex b gii hn lin kt im--im ni chnh

xc hai trm. T khng c s cnh trnh cho vic chia s ng

truyn, ng khng c th xut hin v nghi thc CSMA/CD l

khng cn thit. Frame c th c truyn, gii hn ch bi yu cu

khong cch gia nh nht gia cc frame lin tip.

C hai trm trn ln kt phi c kh nng v cu hnh cho hot ng

full duplex.

Hot ng full duplex c mt vi thun li:

Thng lng l gp i cho php truyn v nhn ng thi. Hiu sut ca lin kt tng bi s loi b kh nng ng .

Cc phn on chiu di th khng gii hn hn bi s yu cu half

duplex Ethernet m bo ng c truyn n tt c cc trm

trong khong yu cu 512 bits time. V d, 100Base-FX c gii

hn phn chiu di 412 mt trong mode half duplex, nhng c th

h tr phn chiu di 2km trong mode full duplex.


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mode full duplex , chun Ethernet thm vo hot ng iu khin lung

(flow control) l PAUSE frame. PAUSE frame cho php mt trm cui tm thi

ngng lu thng t ni khc n trm.

2.6. Giao thc TCP/IP

2.6.1. Gii thiu tng quan

M hnh TCP/IP ch c 4 lp. M hnh tham chiu ca TCP/IP khng trc tip

ging m hnh ca OSI. Mc d mi m hnh mng u c chung mt mc ch l

truyn thng d dng gia cc mng, gia cc loi my tnh chy trn nn h iuhnh khc nhau. Nhng mi m hnh mng u c c im ring v cch thc thi

cng cht t khc nhau. M hnh OSI do ISO to ra trong mt thi gian di, n c

dng lm m hnh chun cho cc m hnh khc. Cn TCP/IP ra i do yu cu cp

thit ca chnh ph M trc tnh hnh lc by gi, do s pht trin ca TCP/IP

khng b nng bi nhng yu cu cht ch nh OSI.

Do c tnh ca OSI l mt m hnh tham kho nn vic p dng OSI vo thc t

l kh c th thc hin (hiu sut km v d liu khi truyn trong mng phi qua tt c

cc lp ca m hnh OSI). Do , OSI ch l mt tiu chun cc nh nghin cu

da vo pht trin cc m hnh khc ti u hn. C rt nhiu m hnh khc nhau

c pht minh, tuy nhin hin nay trn th gii cng vi s pht trin nh v bo

ca Internet th m hnh TCP/IP l c s dng ph bin nht.

B giao thc TCP/IP l rt quan trng trong vic la chn cch thc truyn thng

nhm hn ch li v tng hiu qu. TCP/IP c cc c im ni bc sau:

c lp vi cu hnh mng: TCP/IP c th dung cho mng bus, start, ring,

cho mng cc b, mng din rng hay cc lin mng.

c lp vi phn cng vt l ca mng: TCP/IP c th dung cho Ethernet,

token-ring hay bt c loi phn cng no.


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L mt chun giao thc m: TCP/IP c th thc hin trn nhiu h iu

hnh (Operating System OS) khc nhau, nn n thch hp dung cho cc

mng hn tp cc loi phn cng v phn mm nh Internet.

nh a ch mt cch tng qut: mi trm trn mng TCP/IP c mt a

ch IP duy nht c dng lin lc vi bt k trm no khc trn mng.

H tr c lc mng theo m hnh Client Server.

Cc protocol chun lp ng dng: TCP/IP khng nhng cung cp cho lp

trnh vin phng php truyn d liu gia cc ng dng m cn cung

cp c s ca nhiu giao thc lp ng dng.

2.6.2. Kin trc ca TCP/IP

Pht trin t m hnh tham chiu OSI, TCP/IP c phn lm 4 lp:

Lp truy xut mng (Network Access layer).

Lp lin mng (Internet Layer).

Lp giao vn (Transport layer).

Lp ng dng (Application layer).

Vic phn lp ny m bo mt s nguyn tc sau:

Mt lp c to ra khi cn n mc tru tng ha tng ng.

Mi lp cn thc hin cc chc nng c nh ngha r rng.

Vic chn chc nng cho mi lp cn ch ti vic nh ngha cc

quy tc chun ha quc t.

Ranh gii cc mc cn chn sao cho thng tin i qua l t nht ( tham

s cho chng trnh con l t).

S mc phi ln cc chc nng tch bit khng nm trong cng

mt lp v nh m hnh khng qu phc tp.

Mt mc c th c phn thnh cc lp nh cn thit.


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Cc mc con c th li b loi b.

Hai h thng khc nhau c th truyn thng vi nhau nu chng bo

m nhng nguyn tc chung (ci t cng mt giao thc truyn

thng).

Cc chc nng c t chc thnh mt tp cc lp ng mc cung cp

chc nng nh nhau. Cc lp ng mc phi s dng giao thc chung.

Mt lp khng nh ngha mt giao thc n, n nh ngha mt chc nng

truyn thng c th thi hnh bi mt s giao thc. Do vy, mi lp c th cha nhiu

giao thc, mi giao thc cung cp mt dch v ph hp cho chc nng ca lp. Mi

lp phi c chun ha giao tip vi lp tng ng vi n. Trn l thuyt, giao

thc ch lin quan ti lp ca n m khng quan tm ti lp trn hoc di ca n.

Tuy nhin phi c s ng lm sao chuyn d liu gia cc lp trn mt my

tnh, bi mi lp li lin quan ti vic gi d liu t ng dng ny ti mt ng dng

tng ng trn mt my khc. Lp cao hn da vo lp thp hn chuyn d liu

qua mng pha di. D liu chuyn xung ngn xp t lp ny xung lp thp hn

cho ti khi c truyn qua mng nh giao thc ca lp vt l. Ti ni nhn, d liu

i ln ngn xp ti ng dng nhn. Nhng lp ring l khng cn bit cc lp trn v

di n x l ra sao, n ch cn bit cch chuyn thng tin ti lp m thi. S c

lp cc hm truyn thng trn cc lp khc nhau gim thiu s tch hp cng ngh ca

u vo mi b giao thc. Cc ng dng mi c th thm vo m khng cn thay i

lp vt l ca mng, phn cng c th c b sung m khng cn vit li cc phn

mn ng dng.

Cc lp kin trc m hnh TCP/IP v cc nghi thc tng ng nh sau:

OSI TCP/IP TCP/IP Protocol Stack

Applicationlayer Process/Application

layerFTP, SMTP, TELNET,

SNMPPresentation

layer


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Session layer

Transport layer Transport layer TCP or UDP

Network layer Internet layer IP, ARP, RARP, ICMP

DataLink layer Network Accesslayer

Network interface cardTransmission mediaPhysical layer

Tng quan hai m hnh OSI model v TCP/IP model

TCP (Transmission Control Protocol): mt nghi thc c cu ni (connection-

oriented) cung cp kh nng truyn dng d liu khng li, hai chiu song cng (full

duplex) cho cc qu trnh ca ngi s dng.

UDP (User Datagram Protocol): mt khi thc khng thit lp cu ni

(connectionless) cho cc qu trnh ca user. Do , n khng dm bo d liu khi

truyn c n ni chnh xc hay khng.

ICMP (Internet Control Message Protocol): nghi thc s l li v iu khin

thng tin gia cc gateway v cc host.

IP (Internet Protocol): y l protocol cung cp dch v phn phi cc packet cho

TCP, UDP v ICMP.

ARP (Adress Resolution Protocol): protocol nh x mt a ch Internet vo

trong mt a ch phn cng.

RARP (Reverse Address Resolution Protocol): nh x mt a ch phn cng

thnh mt a ch Internet.

2.6.3. Lp truy xut mng (Network Access Layer)

TCP/IP khng nh ngha lp ny m dung chung vi cc chun khc tn ti

nh IEEE, X25(RS232, Ethernet, X21/X21 bis, X35). Bn cht ca lp ny l

vic qui nh cc i lng tn hiu, cc phng cch giao tip truyn cc dng bit

trn knh truyn.


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Khng ging nhng giao thc ca lp cao hn l s dng dch v ca lp di

n v cung cp dch v cho lp trn, giao thc ca tng mng cn phi bit chi tit ca

mng vt l pha di (cu trc ca gi, a ch...) nh dng ng thng tin s ctruyn tun theo nhng rng buc ca mng. Lp mng ca TCP/IP cha chc nng

ca tt c 2 lp thp nht ca m hnh tham chiu OSI (lp lin kt d liu v lp vt

l). Lp mng thng khng c ngi dng ti v thit k ca TCP/IP che du

nhng chc nng ca lp thp nht ny v nhng iu cn bit cho ngi s dng

cng nh ngi lp trnh ch l nhng giao thc ca cc lp cao hn (IP, TCP,

UDP...). Mi khi c cng ngh phn cng mi xut hin, nhng giao thc ca lp

mng phi c pht trin TCP/IP c th s dng phn cng mi (thng thng

chnh l cc trnh iu khin ca chnh nh cung cp phn cng ). Cc chc nng

trnh din trong lp ny bao gm ng gi gi thng tin IP thnh cc Frame c

truyn dn trn mng v chuyn a ch IP thnh a ch vt l s dng bi mng my

tnh. Mt s cc im mnh ca TCP/IP l a ch ca n c phi hp sao cho trn

mng Internet khng c mt thit b mng no cng a ch. a ch ny phi c

chuyn i thch hp vi a ch mng vt l ni m d liu c truyn i.Hai v d RFCs m t giao thc s dng cho lp mng l:

RFC 826, giao thc chuyn i a ch chuyn i a ch IP thnh a ch

Ethernet.

RFC 894, mt chun cho vic truyn gi tin IP qua mng Ethernet m t

cch thc ng gi chuyn thng tin qua mng Ethernet.

Khi ci t trong UNIX, giao thc ca lp ny c xem nh s phi hp ca

chng trnh iu khin thit b v cc chng trnh lin quan. Nhng n v tng

ng vi nhng thit b mng lm nhim v ng gi d liu v chuyn giao cho mng.

2.6.4. Lp lin mng (Internet Layer)

Lp ny nh ngha n v d liu truyn v nh tuyn cho cc n v d liu

. IP l mt protocol quan trng nht ca b TCP/IP v tt c cc protocol trong b

TCP/IP u phi dng n n v tt c d liu phi lu chuyn qua n.


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2.6.4.1. Gi tin IP (Internet Protocol)

IP l mt nghi thc khng kt ni (connectionless protocol), tc l khng thit

lp mt giao tip trc tip (end-to-end) trc khi truyn d liu. IP khng m bo

phn pht chnh xc d liu n ch, cc gi d liu c th n ch khng ng th

t, c th b sao chp hay tht lc (do IP phi kt hp vi TCP). n v d liu ca

IP l datagram c cha a ch IP ca ngun v ch. IP c nhim v tm ng cho

datagram nn c th phn mnh hay hp nht cc datagram thch hp vi kch

thc packet ln nht cho php trn ng truyn.

nh dng IP datagram header (32 bits header):

Version Header length Type of service Total length of datagramIdentification Flags Fragment

offsetTime to live Protocol Header checksum

Source addressDestination address

Option:

Strick source routeLoose source routeRecord routeTime stamp

SecurityData (max 65535 bytes)

IP datagram header

Destination Address

4 bytes

Source Address

4 bytes

Type Field

2 byte

IP data

46 1500 bytes

CRC

4 bytesHnh 2-5 M t ng gi IP ln khung Ethernet

Verision (VER) 4bits: nh s phin bn ca IP, phin bn hin hnh l 4 (IPv4)

vi gi tr nh phn l 0100.

Header length (HLEN) 4bits: nh ngha chiu di ca IP header ch ra bi s

ca 4 bytes. Dung 4bits tc gi tr ti a l 15 tng ng 60bytes.


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Service type (1 bytes): nh ngha cch m datagram c qun l. N bao gm

cc bits nh ngha th t u tin ca datagram. N cng cha cc bit lm r loi dch

v pha gi mong mun tin cy, tr

Total length (2 bytes): nh ngha chiu di tng th ca mt datagram. Ti a l

65535 bytes.

Identification: c dung vi cc phn on. Mt datagram khi i qua cc

mng khc nhau c th c chia thnh cc on ph hp vi kch thc khung ca

mng. khi xy ra hin tng ny th mi on c nh danh vi mt s th t trong

trng ny.

Flags: cc bits trong c c quan h vi phn on. V d datagram c th hoc

khng c phn on, c th on u, on gia hoc on cui

Fragmentation offset: y l mt con tr ch ra lch ca d liu trong

datagram gc (nu c phn on).

Time to live: nh ngha s bc nhy ti a mt datagram c th i qua trc

khi b drop (loi b). My ch ngun khi to ra datagram s khi ng gi tr trongtrng ny. K tip khi datagram qua Internet, mi router m datagram i qua s gim

gi tr i 1. nu gi tr ny bng 0 trc khi n ch cui cng th datagram s b drop.

Protocol: nh ngha loi d liu nghi thc no ca lp trn ng gi trong

datagram (TCP, UDP, ICMP).

Header checksum (16 bits): dung kim tra header ch khng kim tra phn cn

li ca gi.

Source address (4 bytes): a ch IP ngun ca datagram.

Destination address (4 bytes): a ch IP ca ch cn gi datagram n.

Options: trng chn la cho nhiu chc nng i vi IP datagram. N c th

mang cc thng tin v kim sot nh tuyn nh: timing, qun l v cn bng.

IP li cha 4 nghi thc gip l: ARP, RARP, ICMP v IGMP.


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ARP (Adrees Resolution Protocol) c dng qung b tm a ch vt l t

c ch IP. Protocol ny c dng trong mng ni b v nh dng a ch vt l ca

mng phh thuc vo phn cng mng.

RARP (Reverse Address Resolution Protocol) tm a ch IP khi bit a

ch vt l.

ICMP (Internet Control Message Protocol) l c ch c dung bi my ch v

router. ICMP cho php IP thng bo pha gi nu datagram khng c pht ng.

c trng nht ca ICMP l tin ch ping thng c cc lp trnh vin dng kim tra

cc node c cn hot ng hay khng.

IGMP (Internet Group Message Protocol): nghi thc IP lin quan n 2 thng tin

l unicasting v multicasting. Unicasting l thng tin gia mt ngi gi v mt ngi

nhn. n l thng tin mt mt. Tuy nhin, mt s qu trnh thnh thong cn gi mt

thng ip n nhiu ngi nhn ng thi. Trng hp ny l multicasting, tc l

thng tin mt nhiu. multicasting c rt nhiu ng dng.

2.6.4.2. a ch IP

a ch IP gm 32 bits, thng c m t dng thp phn v mi byte cch

nhau bi du . l danh hiu duy nht trn mng. a ch ny c 2 phn: phn c ch

mng v a ch ni b. C 3 lp a ch A, B, C dnh cho 3 loi mng ln, va v

nh; 1 lp a ch multicasting (lp D) v mt lp d tr (E).

Trong c mt lp a ch c bit dng kim tra thit b mng l:

127.x.x.x (loopback)

Bit trngs

Lp(Class)

Phm vi a ch Kch thckhng gian a ch

0xxx A 0.0.0.0 127.255.255.255 224 = 16777216


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10xx B 128.0.0.0 191.255.255.255 216 = 65536110x C 192.0.0.0 223.255.255.255 28 = 2561110 D 224.0.0.0 239.255.255.2551111 E 240.0.0.0 255.255.255.255

Khng gian a ch IP

Khi mt mng phc tp c a ch thuc lp A, B hoc C c mt vi subnet tham

d to cu trc mng th local s c chia lm 2 phn: subnet address v host

address. Kch thc v vic gn trng s ca subnet part c qun l bi t chc ni

b.

phn bit cc subnet cho cc host v router th cn dng mt subnetsmask.

l b 32 bits, bit 1 ph phn network v subnet, bit 0 dng mask out s host trong

a ch IP.

Class A 0 Net ID Host ID

Class B 1 0 Net ID Host IDClass C 1 1 0 Net ID Host IDClass D 1 1 1 0 Multicast address

Class E 1 1 1 1 Reserved for future use

Khun dng a ch lin mng Subnet address

Cc a ch c bit:

Nhn dng mng: a ch IP tham kho ti mt mng co phn local part l

zero. Tng t i vi mt subnet. Cc a ch ny khng c gn cho

host v router.

Qung b trn mng: a ch 255.255.255.255 c mt mc ch c bit,

l dung gi mt message ti mi host trn mng ni b. broadcasts

thng dng khi mt host cn nh v ti mt server. Cng c th gi mt

massega ti mi host trn mng xa bng cch t local part a ch ln

1.

Qung b trn subnet: Mt broadcasts c th nh hng ti mt subnet

c bit. Khi host address trong a ch IP c c ln 1; cn nu


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mun pht rn ton nt mng (node) th c subnet address v host address

c c ln 1.

a ch t kha (loopback address): i nghch vi a ch qung b l

cc message khng c ri khi local host. Khi thng dung mt

loopback address, c ngha l node dng kim tra phn mm mng.

l a ch bt u bng 127.xxx.xxx.xxx.

This host on network: a ch 0.0.0.0 c ngha l bn thn host l phn t

ca mng. vi cc host trn cng mt mng cc b ch c phn host

address l mang s ca host trn mng n, cn cc phn khc l zero.

H thng tn vng: c th tra tm tn a ch ca mt host no ,

ngi ta dung h thng tn vng gi mt server gi l nameserver.

2.6.4.3. Gi tin ARP (Adrees Resolution Protocol)

Mt c ch s dng chuyn a ch IP thnh a ch vt l l ARP (Address

Resolution Protocol). Khi hai my tnh cng ni vo mt mng vt l, chng bit c

a ch IP ca nhau nhng truyn thng gia hai my, chng phi bit c a ch

vt l ca nhau. ARP gii quyt vn chuyn t a ch IP 32 bits sang a ch

Ethernet 48 bits. Ngi ta s dng hai c ch l: ARP request v ARP reply.


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Host A Host DHost CHost B

ARP Request

Host A Host DHost CHost B

ARP Reply

Hnh 2-6 M t hat ng ca khung ARP

Chuyn giao trc tip: a ch vt l l mt hm ca a ch IP v d s dng trn

mng token ring proNET-10 l mng cho php t a ch IP v a ch vt l thai

mi. Ngi ta c th t a ch IP l 192.5.48.3 v a ch vt l l 3, khi ta c Pa=f(Ia).

Chuyn giao a ch ng c thc hin bng cch my tnh mun gi thng tin

gi mt thng bo ti tan b cc my tnh trn mng, trong thng bo c cha a

ch IP ca my tnh n cn lin lc, mi my s nhn c thng bo v my no thy

a ch IP ca mnh th tr li mt thng bo cha a ch vt l. Khi hai my tnh

c th ni chuyn vi nhau.

Ngoi ra, ngi ta cn s dng bng ch ng lu tr tm thi cc a ch s

dng mi nht ( Address Reslution Cache) tng tc ca vic chuyn giao a ch.

Mt gi thng tin ARP l mt Ethernet Frame c truyn trc tip t my ny

ti my khc. V khng phi s dng IP, gi tin ny khng c a ch IP cng nh

khng cn c dn ng, n phi c gi broadcast ti tt c cc my trn mng

Ethernet (vi a ch FFFF_FFFF_FFFF).

Gi thng tin ARP c m t nh sau:


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Hardware Type Protocol Type

Sender MAC address (bytes 0-3)

Hareware len ARP operationProtocol len

Sender MAC address (bytes 4-5) Sender IP address (bytes 0-1)

Dest MAC address (bytes 0-1)Sender IP address (bytes 2_3)

Dest MAC address (bytes 2-5)

Dest IP address ( bytes 0-3)

0 7 8 15 16 31

Hnh 2-7 Gi tin ca ARP

Protocol type: 0x0800 cho IP (0000.1000.0000.0000).

Hardware len = 6 bytes cho ethernet.

Protocol len = 4 bytes cho IP.

ARP operation:

o 1= yu cu

o 2 = p li

o 3/4 = RARP yu cu/p li

Destination Address6 bytes

Source Address6 bytes

Frame type2 bytes

(ARP) Data28 bytes

CRC4 bytes

Hnh 2-8 Trng ca khung ARP

a ch ch (ethernet destination address):

FF:FF:FF:FF:FF:FF l a ch broadcast cho ARP request.

a ch ngun (ethernet source address) l a ch ca ARP yu cu.

Frame type:


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o ARP yu cu hoc p li (ARP request/rely) : 0x0806

o RARP yu cu hoc p li (RARP request/rely): 0x08035

o IP: 0x0800

2.6.5. Lp giao vn (Transport Layer)

Lp vn chuyn c 2 nhim v nh sau:

Cung cp dch v cho lp qu trnh bn trn n v cc ng dng cng vi

giao din thch hp cho mng.

Phn pht message ca cc lp trn gia cc host.

Lp giao thc ngay trn lp Internet l Host to Host Transport Layer hay thng

gi l Transport Layer. Hai giao thc quan trng ny l Transmission Control Protocol

(TCP) v User Datagram Protocol (UDP). TCP cung cp dch v chuyn giao thng

tin kt ni (connection oriented), n bao gm c kim tra v sa li. UDP cung cp

dch v km tin cy hn (unreliable) v khng th thit lp lin kt trc

(connectionless). C hai giao thc u chuyn giao thng tin gia lp ng dng v lpInternet. Chng trnh ng dng c th la chn dch v no thch hp vi ng dng

ca n.

IP phn pht mt datagram t mt my ch ngun n my ch ch, to thnh

mt nghi thc my ch-my ch. Cc h u hnh ngy nay tr gip mi trng x l

nhiu ngi s dng. Mt chng trnh thc thi gi l process. Mt my ch ang

nhn mt datagram cng c th chy nhiu process ng thi.

Cc nghi thc giao vn ca b nghi thc TCP/IP nh ngha mt tp kt ni khi

nim cho cc process ring c gi l cc ports nghi thc, hay n gin hn l ports.

Mt ports nghi thc l m im n (thng l mt b m) cha d liu dng cho

mt process c th. Giao tip gia cc processes v cc ports tng ng c cung cp

bi h iu hnh ca my ch.

IP l mt nghi thc my ch - my ch, c ngha l n c th nhn pht gi t

mt thit b vt l n thit b vt l khc. Cc nghi thc mc giao vn ca TCP/IP l


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cc nghi thc port to port lm vic pha trn ca cc nghi thc IP phn pht gi t

port gc n port ch ti cui truyn.

Mi port c nh ngha bng mt s nguyn dng c mang trong header

ca gi lp giao vn. Mt khung ti lp giao vn dng a ch port 16 bits, dng

cho cc ports t 0 n 65535.

2.6.5.1. Giao thc UDP (User Datagram Protocol)

UDP (User Datagram Protocol) l mt nghi thc khng tin cy, ch c gng ht

mnh phn pht d liu. UDP ch cung cp c bn cn thit cho phn pht end-to-

end. N khng cung cp bt c chc nng nh s th t no v do khng th lm

r gi no b hng khi bo co v li. UDP c th khm ph ra mt li xut hin tc

l ICMP c th thng bo pha gi l mt user datagram hng v b loi. Tuy nhin

n khng c kh nng bit l gi no b mt. UDP cho php truyn d liu trn mng

vi chi ph thp do s phn pht d liu khng tin cy. Cc dch v dng UDP l

TFTP, DSN, SNMP

Gi thng tin UDP:

Mi gi thng tin UDP gi l mt Datagram c phn lm 2 phn header v

data trong header cha thng tin v a ch cng ngun, a ch cng ch, di

ca gi v checksum.

Chech sum: 16 bits l s b 1 ca tng b 1ca cc 2 bytes trong phn header, d

liu v phn header gi (pseudo header) . Nu phn header v text cha mt s l bytes

th byte cui cng c mvo bn phi vi 0 16 bit cho mc ch Checksum.

Phn m th khng c truyn nh mt phn ca header.


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Source port Destinationport

Message length Checksum

Data

Data

Data

Destination

Address

Source

Address

Type

field

IP

header

UDPdata CRC

Hnh 2-9 ng gi UDP vo khung Ethernet

Phn knh, hp knh v Ports.

Phn knh, hp knh chnh l vic la chn nhng tin trnh ng dng trong mt

s ln cc tin trnh s dng giao thc UDP, ngi ta chn ra nhng ng dng tng

ng vi gi thng tin chuyn n.

Port 1 Port 2 Port 3

UDP: Demultiplexing

Based on Port

IP Layer

UDP Datagramarrives

Hnh 2-10 S phn knh v hp knh ca ARP

Vic ny gii quyt bng c ch cng Port mechanism c ch ny gn mi ng

dng vi mt con s gi l port number v mi gi thng tin m n gi i u mang

mt trng SOURCE PORT.

Ti ni nhn, da vo thng tin trng DESTINATION PORT m gi thng tin

c truyn n cng tng ng vi ng dng. V d mi bng TCP/IP u c dch


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v FTP (File Transfer Protocol) gn vi cng 21 v TFTP (Trivial File Transfer

Protocol) gn vi cng 69 ca UDP.

Vic s dng cc port number cng c nhiu cch.

o Dng nhng cng dnh ring cho tng ng dng c ng k

trc (Well-known port assignment).

o Mt port number s c sinh ra khi c mt ng dng i hi

(Dynamic binding).

Cch tip cn kt hp cc kiu trn (Hybrid) trong ngi ta va s dng Well-

known port assignment cho mt s port number va c th nh ngha cc port number

khc khi cn thit. Mt khung ti lp giao vn dng a ch port 16 bits, dng cho

cc ports t 0 n 65535.

V sao ngi lp trnh ng dng la chn UDP nh mt dch v giao vn? C

mt s l do:

Mt s lng ln cc gi thng tin nh c truyn, thng tin cho vic kt ni v sa

li c th ln hn nhiu so vi thng cn truyn. Trong trng hp ny, UDP l gii

php hiu qu nht.

Nhng ng dng kiu Query-Respon cng rt ph hp vi UDP, cu tr li c

th dng lm s xc nhn ca mt cu hi. Nu khng nhn c s tr li sau mt

thi gian no , ng dng ch cn gi i mt cu hi khc.

Mt s ng dng t n cung cp cng ngh ring chuyn giao thng tin

cy, v khng i hi dch v ny ca transport layer.

y l giao thc n gin v truyn nhanh, nn n thng c s dng trong

cc ng dng iu khin thi gian thc. Do trong Lun Vn ny chn giao thc

UDP lm giao thc truyn khung iu khin ca lp trn.


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2.6.5.2. Giao thc TCP (Transmission Control Protocol)

TCP (Transmission Control Protocol) l mt nghi thc tin cy. TCP l mt nghi

thc port-to-port tin cy v nh hng kt ni. TCP to ra mt mch o gia pha gi

v nhn trong sut qu trnh truyn.TCP bt u truyn bng cch thng bo cho pha

nhn bit (thit lp kt ni) v khi kt thc truyn th gi mt kt thc kt ni. N c

gng phn pht d liu n ch, kim tra li, truyn li nu cn, thng bo li cho lp

trn nu truyn khng thnh cng. Do , vic s dng TCP cng lm tng chi ph.

TCP cung cp y cc dch v lp giao vn i vi p dng. TCP l mt nghi

thc port to port tin cy v nh hng kt ni. TCP to ra mt mch o gia pha giv nhn trong sut qu trnh truyn. TCP bt u truyn bng cch thng bo cho pha

nhn bit (thit lp kt ni) v khi kt thc truyn th gi kt thc kt ni.

S tin cy ca TCP m bo bng vic pht hin li v truyn li cc khung b

hng: tt c cc an phi c nhn v xc nhn trc khi xem nh cuc truyn l

han thnh v mch o c lai b.

Ti u gi, TCP chia cuc truyn thnh cc n v d liu nh hn v ng githnh cc khung gi l an. Mi an bao gm vic nh s nhm sp li theo th t

khi nhn. Cc an c ti qua mng bn trong cc IP datagram. Ti u nhn, TCP

gom mi datagram khi chng n v xp li theo th t da vo cc s c nh.

TCP gi trn internet cc datagram. Header ca Internet Protocol mang nhng

trng thng tin bao gm a ch ngun v ch ca my ch. TCP header theo sau

header ca internet v cung cp thng tin c th ti nghi thc TCP.


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Source port Destination port

Sequence Number

Acknowledgment Number

Checksum Urgent pointer

Option Padding

Data

Data offset reserved URG

ACK

PSH

RST

SYN

FIN

Window

Hnh 2-11 nh dng Gi TCP

Source port: 16 bits a ch ngun.

Destination: 16 bits a ch ch.

Sequence Number: 32 bits mt dng d liu t chng trnh p dng c th

c chia thnh hai hay hoc nhiu an TCP. S th t ch ra v tr ca d

liu trong dng d liu gc.

Acknowledgment Number: 32 bits dng xc nhn c nhn d liu t

thit b khc. S ny ch xc nhn khi bit ACK trong trng iu khin c

t. Trong trng hp ny, s th t ch ra mong i k tip.

Data offset: 4 bits ch ra ni d liu bt u.

Reserved: 6 bits dnh cho tng lai.

Control bits: 6 bits (t tri sang phi).

URG: khi c t ch ra tnh hp l ca trng urgent pointer. C biturgent v con tr ch ra rng d liu trong an l khn cp.

ACK: khi c t ch ra tnh hp l ca trng Acknowledgment number.

C hai u c dng vi nhau v c chc nng khc nhau ty vo lai

an.

PSH: c dng thng bo pha gi l cn mt tc trung bnh cao hn.

RST: dng xa kt ni khi c nhm ln s th t.


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SYN: dng ng b vic nh s cho ba lai an: yu cu kt ni, khng

nh kt ni(vi bit ACK), v xc nhn khng nh (vi bit ACK c t).

FIN: c dng cho kt thc ni cho ba an v xc nhn ca khng nh

kt thc.

Window: 16 bits s d liu c ch ra trong trng acknowledgment m

pha gi ang m nhn.

Chech sum: 16 bits l s b 1 ca tng s b 1 ca 16 bytes trong phn

header v text. Nu phn header v text cha mt s l bytes header v text

c kim tra, th byte cui cng c m vo bn phi vi 0 16

bytes cho mc ch Checksum. Phn m th khng c truyn nh mt

phn ca header. Trong khi tnh checksum, t bn thn ca trng checksum

c thay th vi 0 (c ngha l chechsum s thay th nhng bit 0 ny).

Chechsum cng bao gm 96 bit header gi (Pseudo header) c thm vo u

header ca TCP. Header gi ny cha a ch ngun ,a ch ch, nghi thc, chiu di

TCP. Phn ny c a ra bo v TCP trong vic truyn lc khung. Nhng thngtin ny c mang bi Internet Protocol v c truyn qua TCP/Network interface

trong arguments hoc kt qu ca vic gi bi TCP trn IP.

s s

Source address

Zero PTCL TCPLength

Destination address

Hnh 2-12 Khung TCP

TCP length l chiu di byte ca header v chiu di d liu nhng n

khng bao gm 12 bytes header gi .

Urgent pointer (16 bits): Trng ny giao tip vi gii tr hin hnh ca

Urgent pointer nh l mt mc offset t s tun t trong khung. Urgent


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CHNG 3. ENC28J60 MICROCHIP STAND-ALONEETHERNET CONTROLLER WITH SPI INTERFACE

3.1. M t tng quan

ENC28J60 l IC giao tip mng Ethernet lp vt l tng ng trong m

hnh OSI. N h tr tuyn song cng trn knh truyn c bng thng t 10-

20Mbps. ng thi nhm trnh xung t trn knh truyn, ENC28J60 lm vic

trn protocol CSMA/CD pht hin v ti thiu ha xung t. ENC28J60 c

giao tip vi cc thit b khc theo chun SPI.

The ENC28J60 is a stand-alone Ethernet controller with an industry

standard Serial Peripheral Interface (SPI). It is designed to serve as an Ethernet

network interface for any controller equipped with SPI. The ENC28J60 meets all

of the IEEE 802.3 specifications. It incorporates a number of packet filtering

schemes to limit incoming packets. It also provides an internal DMA module for

fast data throughput and hardware assisted checksum calculation, which is used in

various network protocols. Communication with the host controller is

implemented via an interrupt pin and the SPI, with clock rates of up to 20 MHz.

Two dedicated pins are used for LED link and network activity indication.

ENC28J60 c cc thng s sau:

IEEE 802.3 compatible Ethernet controller Integrated MAC and 10BASE-T PHY Supports one 10BASE-T port with automaticpolarity detection and correction Supports Full and Half-Duplex modes Programmable automatic retransmit on collision Programmable padding and CRC generation Programmable automatic rejection of erroneous

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3.3. S khi



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Chip ENC28J60 c by khi chc nng chnh:

1. An SPI interface that serves as a communication channel between the host

controller and the ENC28J60.

2. Control Registers which are used to control and monitor the ENC28J60.

3. A dual port RAM buffer for received and transmitted data packets.

4. An arbiter to control the access to the RAM buffer when requests are made

from DMA, transmit and receive blocks.

5. The bus interface that interprets data and commands received via the SPI

interface.

6. The MAC (Medium Access Control) module that implements IEEE 802.3

compliant MAC logic.



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7. The PHY (Physical Layer) module that encodes and decodes the analog

data that is present on the twisted pair interface.

3.1.1. Nhm thanh ghi iu khin



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3.3.1.1. Chc nng ca thanh ghi



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3.4. Giao tip vi VK

3.1.1. Truyn gi

3.4.1.1. Thit lp vic truyn

3.4.1.2. Tin trnh gi

3.4.1.3. Trng thi truyn

3.1.1. Nhn gi

M hnh bus trong mng CSMA/CD cho php mi nt nhn mi gi cgi ln mng. B lc nhn s xc nh gi no c php lu vo b m nhn.

Khng phi mi gi u c quan tm, ch c nhng gi c a ch ch tha b

lc nhn mi c chuyn vo b nh. NIC a ra mt s la chn cho b lc

nhn v cch qun l mt gi hon chnh cho vic lu tr gi ang n.

3.4.1.4. Tin trnh nhn

3.4.1.5. B m thu



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1.2. Chun SPI

The ENC28J60 is designed to interface directly with the Serial Peripheral

Interface (SPI) port available on many microcontrollers. The implementation

used on this device supports SPI mode 0,0 only. In addition, the SPI port

requires that SCK be at Idle in a low state; selectable clock polarity is not

supported. Commands and data are sent to the device via the SI pin, with

data being clocked in on the rising edge of SCK. Data is driven out by the

ENC28J60 on the SO line, on the falling edge of SCK. The CS pin must be

held low while any operation is performed and returned high when finished.



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