ATM Chinh Sua

7/31/2019 ATM Chinh Sua

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ATM

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Li m u

Do cc nhc im ca mng vin thng ngy nay, i hi cn c mt mnglin kt cc dch v cho nn mng N.ISDN ra i v cc nhu cu dch v bang rngang tang ln. T t ra vn phi c mt mng t hp duy nht (B-ISDN),chnh trn c sny ATM hnh thnh v pht trin. s pht trin ca k thut ATMl kt qu trc tip ca cc tng mi v khi nim h thng c h trbi ccthnh tu to ln trong cng ngh bn dn v cng nghquang in t. ATM c khnng p ng c mt lot cc dch vbng rng khc nhau, k ctrong lnh vcgia nh cng nh trong thng mi. m u im ca n c cp v kin

trc mng ATM s xt phn sau.Ni dung ti gm 3 chng:

Chng 1: Gii thiu chung v ATM

Chng 2: Cc c im k thut ATM

Chng 3: Mng ATM


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Mc lcLi m u .................................................................................................................. 1Mc lc........................................................................................................................ 2Danh mc hnh nh ..................................................................................................... 5Danh mc bng biu .................................................................................................... 7chng 1: Gii thiu chung v ATM .......................................................................... 9

1.1.S ra i ca mng ATM .................................................................................. 91.2. Cc c im chnh ca ATM ........................................................................ 10

1.2.1.Cc u im ca ATM .............................................................................. 111.2.2.Cc dch v m ATM cung cp ................................................................. 12

1.3. Cu trc phn lp ca mng ATM ................................................................. 131.3.1 M hnh tham chiu giao thc ca B-ISDN (B-ISDN Protocol ReferenceModel) ................................................................................................................ 141.3.2.Lp vt l .................................................................................................. 18

1.3.2.1.Lp con ng truyn vt l PM (Physical Medium). ....................... 191.3.2.2.Lp con hi t truyn .......................................................................... 20

1.3.3.Lp ATM................................................................................................... 233.3.3.1.Mt s khi nim lin quan n knh o v ng o ....................... 243.3.3.2.Nguyn l chuyn mch ATM ............................................................ 25

1.4. T bo ATM.................................................................................................... 271.4.1.Phn loi t bo ATM ............................................................................... 271.4.2. Cu trc t bo ATM ................................................................................ 28

1.4.2.1.S hiu nhn dng knh oVCI (Virtual Channel Identifier) ............. 301.4.2.2.S hiu nhn dng ng o VPI (Virtual Path Indentifier) .............. 301.4.2.3.Kiu t bo PT(Payload Type)............................................................ 311.4.2.4.CLP(Cell Loss Priority) ...................................................................... 321.4.2.5.HEC(Header Error Control) ................................................................ 321.4.2.6.GFC(Generic Flow Control) ............................................................... 32

Chng 2: Cc c im k thut ATM .................................................................. 342.1.Lp tng thch ATM (AAL).......................................................................... 34


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2.1.1. Tng quan ................................................................................................. 342.1.2.AAL1 ......................................................................................................... 38

2.1.2.1.Lp con SAR...................................................................................... 382.2.1.2.Lp con CS ......................................................................................... 39

2.1.3.AAL2 ......................................................................................................... 402.1.4.AAL 3/4 ..................................................................................................... 40

2.1.4.1.Lp con SAR ....................................................................................... 412.1.5.AAL5 ......................................................................................................... 44

2.1.5.1.Lp con SAR. ..................................................................................... 454.1.5.2.Lp con CS ......................................................................................... 45

2.2. Chuyn mch ATM ........................................................................................ 462.2.1.Tng quan .................................................................................................. 462.2.2.Chc nng ca nt chuyn mch ATM ..................................................... 462.2.3. Cu to chung ca cc phn t chuyn mch........................................... 492.2.4.Phn t chuyn mch phn chia khng gian(hay phn t chuyn mchtheo kiu ma trn) ............................................................................................... 49

2.2.4.1.B m u vo .................................................................................. 502.2.4.2.B m ti u ra ................................................................................ 512.2.4.3.B m ti giao im ca ma trn chuyn mch ................................ 52

2.2.5.Phn t chuyn mch phn chia thi gian ................................................. 532.2.5.1.Phn t chuyn mch dng kiu BUS(Bus-Type Switching Element)......................................................................................................................... 532.2.5.2.Phn t chuyn mch kiu vng ......................................................... 532.2.5.3.Phn t chuyn mch s dng b nh trung tm ................................ 54

2.2.6.So snh cc cu trc chuyn mch ............................................................ 552.2.7.Cuc ni o c nh PVC (Permanent Virtual Connection) ..................... 562.2.8.Cuc ni o tm thi SVC (Switched Virtual Channel) ........................... 572.2.9.X l phn tiu ca t bo trong h thng chuyn mch ..................... 58

2.2.9.1.Phng php chuyn mch tnh ng (Self- Routing SwitchingElement) .......................................................................................................... 58


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2.2.9.2.Phn t chuyn mch dng bng iu khin (Table-ControlledSwitching Element) ......................................................................................... 59

2.3 Cc mng chuyn mch: .................................................................................. 602.3.1 Phn loi .................................................................................................... 602.3.2 Mng chuyn mch n tng: ................................................................... 61

2.3.2.1 Ma trn chuyn mch m rng: .......................................................... 612.3.2.2 Mng chuyn mch hnh phu: ........................................................... 622.3.2.3 Mng chuyn mch trn: .................................................................... 62

2.3.3 Mng chuyn mch a tng:...................................................................... 632.3.3.1 Mng mt ng:................................................................................ 632.3.3.2 Mng a ng: .................................................................................. 64

Chng 3: Mng ATM ............................................................................................. 673.1 Cu trc mng vin thng ATM ...................................................................... 673.2 Qun l mng ATM: ........................................................................................ 69

3.2.1 iu hnh cu trc v tn: ......................................................................... 703.2.2 Qun l cc c tnh khai thc ca mng: ................................................. 71


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Danh mc hnh nhhnh 1.1 Nguyn l ATM v STM ............................................................................ 10Hnh 1.2 Mi quan h gia cc thc th trong m hnh OSI ................................... 13Hnh 1.3 Kiu n v s liu v mi quan h gia chng ......................................... 14Hnh 1.4 M hnh tham chiu giao thc B-ISDN .................................................... 15Hnh 1.5 Mi quan h gia m hnh ca B-ISDN v m hnh 7 lp OSI ............... 16Hnh 1.6 C ch pht hin v sa li HEC ............................................................... 21Hnh 1.7 S nhn bit gii hn t bo ................................................................. 22Hnh 1.8 S kt hp cc knh o, ng o ............................................................ 23Hnh 1.9 Cuc ni knh o thng qua cc nt chuyn mch v b ni xuyn ......... 26Hnh 1.10 Nguyn tc chuyn mch VP ................................................................... 26Hnh 1.11 Nguyn l chuyn mch VC .................................................................... 27Hnh 1.12 Phn loi t bo ........................................................................................ 28Hnh 1.13a Khun dng t bo ATM ti giao din NNI ........................................... 29

Hnh 1.13b Khung dng t bo ATM ti giao din UNI ........................................ 30Hnh 1.14 Khun dng trng PT trong t bo mng thng tin .............................. 31Hnh 2.1 Qu trnh hnh thnh t bo ....................................................................... 39Hnh 2.2 Cu trc AAL1 ........................................................................................... 41Hnh 2.3 cu trc ca AAL3/4 .................................................................................. 43Hnh 2.4 Cu trc SAR-PDU ca AAL3/4 ............................................................... 44

hnh 2.5 Cu trc CPCS-PDU ca AAL3/4 .............................................................. 45Hnh 2.6 Cu trc CPCS-PDU ca AAL5 ............................................................... 46Hnh 2.7 Hot ng ca AAL5 ................................................................................. 47Hnh 2.8 Nguyn l chuyn mch ATM .................................................................. 49Hnh 2.9 Phn t chuyn mch kiu ma trn ........................................................... 52Hnh 2.10 Phn t chuyn mch kiu ma trn c bm u vo .......................... 53Hnh 2.11 Cu trc phn t chuyn mch ma trn vi bm u vo .................. 54Hnh 2.12 Cu trc phn t chuyn mch kiu ma trn c bm ti giao im .... 54Hnh 2.13 Phn t chuyn mch kiu BUS ............................................................. 55Hnh 2.14 Cu trc phn t chuyn mch kiu vng ................................................ 56


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Hnh 2.15 Cu trc phn t chuyn mch s dng b nhtrung tm ..................... 56Hnh 2.16 Thit lp SVCs thng qua bo hiu ........................................................ 59Hnh 2.17 C ch xl u khung trong h thng chuyn mch tnh ng .... 61

Hnh 2.18 C ch xl tiu ca phn t chuyn mch dng bng iu khin . 62Hnh 2.19 Phn loi cc mng chuyn mch ........................................................... 62Hnh 2.20 Ma trn chuyn mch mrng ................................................................ 63Hnh 2.21 Mng chuyn mch hnh phu ................................................................ 64Hnh 2.22 Mng chuyn mch trn .......................................................................... 65Hnh 2.23 Mng chuyn mch gp vng ba tng ..................................................... 66

Hnh 2.24 kthp gia mng phn phi v mng Banyan ....................................... 67Hnh 2.25 mng sp xp mng gi t bo v mng Banyan ..................................... 67Hnh 3.1 Cu trc mng vin thng ......................................................................... 70


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Danh mc bng biu

Bng 1.1 Chc nng ca cc lp trong B-ISDN ...................................................... 18

Hnh 1.2 Cu trc trng PT vi t bo OAM ......................................................... 31Hnh 2.1 Phn loi cc nhm AAL .......................................................................... 38


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chng 1: Gii thiu chung v ATM

1.1.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 h thng

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 vphc 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 kh nng 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 githng thng. V vy kiu truyn khng ng b ATM (Asynchonous Transfer

Mode) c ITU-T (ITU l T chc vin thng quc t thuc Lin hip quc, InternationalTelecommunication Union - Telecommunication Standardization Sector ) khuyn ngh s dng

trong mng B-ISDN, do mng B-ISDN (Broadband Integrated

Services Digital Network, Th h tip theo ca ISDN da trn k thut ATM) 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 cccuc 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.


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1.2. Cc c im 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 mt kiu

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 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 1.1 so snh s khc nhau gia kiu truyn ng b (STM) v kiutruyn khng ng b (ATM). Trong dng truyn ng b STM, cc phn t s liu

tngng 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 1.1: Nguyn l ATM v STM

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


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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 t bo. Cch thc truyn t

bo ph thuc vo yu cu v tnh cht ca dchv 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 (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. S

khng 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 btc 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.

1.2.1.Cc u im ca ATMCng 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


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trong STM. Tc cc dch v trong mng ATM c 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 nngghp/ phn knh d dng: vic ghp/ phn knh trong

mng ATM ch 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 ddng: 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.

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.

1.2.2.Cc dch v m ATM cung cp1. 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.


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3. Dch v ABR(Available Bit Rate) dch v bit c sn: dch v ny

ch c trong 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.

1.3. 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 theoth 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

thcng 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 vlp N (SAP-Service Access Point). Hnh 3.2 ch ra mi quan

h gia nhng thc th thng qua cc giao thc.


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Hnh 1.2: 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) lpN v s liu

t lp N+1. Hnh 1.3 ch ra cc kiu n v s liu khc nhau v mi quan h gia

chng.

Hnh 1.3 : Kiu n v s liu v mi quan h gia chng

1.3.1 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 qun l

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

PDU lp N+1

SDU lp N

PDU lp N

Lp N+1

PCI lp N

Lp N


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(Management Plane). Cu trc ca m hnh tham chiu c trnh by trong hnh

1.4.

Hnh 1.4: 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 OSIM hnh tham chiu ca ATM khng tng thch hon ton vi m hnh

OSI. Tu theotng 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 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

M t hn un l

iu khinM t hn

Qunl

Mt phng caQunlmt

iu

khin

Sliu

Sliu

Video

Thoi

Lp con hi t(CS)

L ATMLp con hi t truyn dn(TC)


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3 ca m hnh OSI. Hnh 1.5 ch ra mi quan h gia m hnh tham chiu ca B-

ISDN v m hnh 7 lp OSI.

Hnh 1.5: 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 kt ni

trong lp ATM trc tin phi c gn mt b nhn dng s duy nht thng qua

cc th tc bo hiu ca mt phng iu khin. S ny c th l b nhn dngng 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 mt phng

qun l. Qun l mt phng chu trch nhim v cc chc nng nh bo hiu trao

i v dng thng tin OAM iu khin cc thtc bo hiu (ngha l bo hiu

Lp AAL

Lp ATM

Lp Datalink

Lp vt l

Chuynmch

Dnknh

nhtuyn

Qun ltc nghn

AAL 1 AAL 2AAL3/4

AAL 5

Lp con hi

t truyn

Lp con hi

t truynLp con phthuc mi

trng vt l

Lp con ph thuc mi trng vt lCc giao din

SDH SonetCp quang100Mbps

Lp cao hn


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cho bo hiu). Chng ta cn knh ny v bo hiu trong cc mng bng rng phc

tp v rng hn bo hiu knh D trong N-ISDN.

Thng tin v OAM c dng gim st cht lng mng v qun l lu tr

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 1.1

Q

U

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.


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n

l

l

p

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

L

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.

Lp con

ng

truynvt l(PM)

ng b bit.

Thu,pht s liu.

Bng 1.1: Chc nng ca cc lp trong B-ISDN

1.3.2.Lp vt l

S khc nhau ca lp vt l ATM vi lp vt l trong m hnh OSI l trong

m hnh OSI ti lp ny cng vic ca n lin quan n vic truyn ti cc phn t

b nht l cc bits t im ny n im khc. Cn trong ATM phn t b nht


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li l cc t bo. V vy chc nng chnh ca lp vt l trong ATM l ti cc t bo

v chc nng ny c thc hin bi lp con hi t truyn 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 truynvt 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 i quang in.....

Lp con hi t truyn (TC) thc hin cc chc nng nh chn

hoc tch cc t bo trng, to v x l m iu khin li tiu ,

nhn bit gii hn t bo, khun dng t bo, phi hp tc ti

trng ca cc khun dng vn chuyn 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 u t bo

khng c li. Vic kim tra li mo u t bo c thc hin lp con TC. Theo

hng ngc li, t lp ATM ti lp vt l, lung t bo ATM c ghp thmthng tin phn tch t bo v thng tin v khai thc v bo dng (OAM) lin quan

n lung t bo ny.

1.3.2.1.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 v nu cnthit 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 dung cc loi m ng truyn khc

nhau.

Cc t bo ATM c truyn i theo nguyn tcsau: cc Bytes trong t bo

c gi i theo th t t 153, ngha l trng tiu c gi trc, cc bits

trong Byte c gi i theo th t t bit th 8 n bit th 1.Cc t bo c truyn

l mt chui lin tc. m bo phn Payload c phn bit vi phn Header,


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Payload c pht i di dng i tn. Tu theo phng php 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 t bo

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 cng c chn khi

khng c t bo ATM c truyn i. Cc t bo lp vt l c chn 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 OAM ca lp vt l. S lng t

bo OAM c chn ph thuc v cc yu cu v OAM. Tuy nhin trong mt

chng truyn dn nhiu nht l sau 26 v t nht l sau 512 t bo, phi c mt t

bo OAM.

1.3.2.2.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 HECc 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 Bytes u vi x8cho a thc sinh

x8+x

2+x+1. Qu trnh pht hin vsa li c m t trong hnh

1.6.


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Hnh 1.6: C ch pht hin v sa li HEC

Phn thuhot 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 sang ch pht

hin li.

Nu h thng tip tc pht hin ra li th t bo vn b hy d li l li nhay 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 1.7.

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)


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Hnh 1.7: 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 hin kim tra cho t bo tip

theo. Nu sau

ln khng pht hin li th h thng chuyn sang trng thi ng bSYN, 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 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

Trng thitm ng b

(HUNT)

Trng thitin ng b(PreSYN)HEC sai

HEC ng

Trng thing b

(SYN)

Kim tra tng t bo

Kim tra tng t b

Kim tra tng bit

HEC sailin tip

ln

HEC nglin tip

ln


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thng cdng 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 trm thu 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.

1.3.3.Lp ATMLp ATM lthnh 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) n lp 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 oVC(Virtual Channel) l knh thng tin cung cp kh

nng truyn n hng cc t bo ATM .

ng oVP(Virtual Path) l s kt hp c tnh cht logic hoc

ca mt nhm cc knh o thnh mt b m n c cng mtc 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 ngkt ni o. Hnh 1.8 m t qu trnh kt

hp cc VCs, VPs v ng truyn.

VC

VP

VC

VP

VC

VP

VC

VP

VC

VP

VC

-ng truyn dn

VP


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Hnh 1.8: 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 ngha ca

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 dinUNI.

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 hiu trao 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 dng VCI(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.


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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 cao

thnh 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, 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/VCINu 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 tbo.

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 kt ni c th.

Khi t bo n nt chuyn mch, gi tr ca VPI hoc c gi tr VPI, VCI u c

thay i cho phhp vi chng tip theo. Thit b chuyn mch ch da trn gi trVPI 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 lchuyn mch VChoc chuyn mch ATM.


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Hnh 1.9 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, D2l cc b ni

xuyn, ni ch thay i gi tr VPI, a i, xi, yil cc gi tr VCI, VPI tng ng.

Hnh 1.9: Cuc ni knh o thng qua cc nt chuyn mch v b ni xuyn

Hnh 1.10 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 vothnh 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 c gi khng i.

Hnh 1.10 Nguyn tc chuyn mch VP

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

VCI1

VCI2

VCI3

VCI4

VCI5

VCI6

VPI1

VPI2

VPI3

VPI4

VPI6

VPI5

VCI3

VCI4

VCI1

VCI2

VCI5

VCI6

Chuyn mch VP


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Khc vi chuyn mch VP, chuyn mch VC l im cui ca cc lin kt

knh o v ng o. V vy trong chuyn mch VC, gi tr ca VCI v VPI u

thay i. V trong chuyn mch VC bao gm c chc nng chuyn mch VP nn

chuyn mch VC c th thc hin chc nng ca mt chuyn mch VP. Hnh 1.11

gi thch nguyn l chuyn mch VC.

Hnh 1.11: Nguyn l chuyn mch VC

1.4. T bo ATM

Nh trnh by trn t bo ATM l n v dng truyn thng tin trong

ATM. Tuy nhin khng phi tt c cc t bo ATM u c s dng truyn

thng tin mbn cnh cn tn ti nhiu loi t bo khc nhau nh s trnh by

diy.

1.4.1.Phn loi t bo ATM

T bo ATM c th c phn loi theo lp cu thnh v chc nng. Trc

ht t bo ATM c chia thnh t bo lp ATMv t bo lp vt l. T bo ATM

c to ra trong lp ATM cn t bo lp vt l c to ra trong lp vt l. T bo

lp ATM c phn chia thnh t bo c gnv t bo khng c gn. Cn t

bo lp vt l c chia thnh t bo rng, t bo hp l v t bo khng hp l.

VCI1

VCI2VPI4 VPI5

VPI1 VPI3

VPI2

VCI1

VCI2 VCI3

VCI4

Chuyn mch VP

Chuyn mch VC

VCI1

VCI2

VCI1

VCI2


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c im ca loi t bo nh sau:

T bo rng: L t bo c lp vt l xen vo/tch ra lung t

bo danh gii gia lp ATM v lp vt l c tc ph hp vi tc

ca ng truyn.

T bo hp l: L cc t bo c mo u khng c li hoc c li n

c sa bi chu trnh sa li HEC.

T bo khng hp l: L t bo c nhiu li khng th sa c (b

loi b ti lp vt l). T bo rng, t bo hp l v t bo khng hp

l ch tn ti lp vt l.

T bo c gn: L cc t bo mng thng tin dch v s dng cho

cc dch v lp ATM.

T bo khng gn l t bo khng c s dng, khng mang thng

tin dch v. T bo c gn v t bo khng c gn l cc t bo

lp ATM.

Hnh 1.12 ch ra cc loi t bo.

Hnh 1.12: Phn loi t bo

1.4.2. Cu trc t bo ATM

Nh ta bit c im chnh ca ATM l hng lin kt. Do khc vi

mng chuyn mch gi, a ch ngun v ch, s th t cc gi l khng cn thit

SAP

T bo c gn T bo c gn

T bo khng gn T bo khng gn

T bo hp l

T bo khng hp l

T bo rng

T bo bloi b

T bo rng

Lp ATM

Lp vt l

SAP : im truy nhp dch v


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trong ATM. Hn na do cht lng ca ng truyn cao nn cc c ch chng li

trn c s t lin kt n lin kt c b qua. Ngoi ra cng khng cung cp cc

c ch iu khin lung gia cc nt mng do c cu iu khin cuc gi ca n. V

vy chc nng c bn cn li ca phn tiu trong t bo ATM l nhn dng cuc

ni o.

T bo c th c truyn trn giao din gia ngi s dng vi mng UNI

(User-Network Interface) hay gia cc nt chuyn mch NNI(Network-Network

Interface). Cu trc ca cc t bo trong hai c mt s im khc nhau. Hnh 3.13

trnh by cu trc ca t bo ATM trong hai giao din, giao din NNI (hnh 3.13.a)

v giao din UNI (hnh 3.13.b).

Bit

8 7 6 5 4 3 2 1 Byte

s

VPI 1

VPI VCI 2

VCI 3

VCI PT CL

P

4

HEC 5

Phn d liu (48 Bytes)

....

Hnh 1.13.a : Khun dng t bo ATM ti giao din NNI


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Bit

8 7 6 5 4 3 2 1 Bytes

GFC VPI 1

VPI VCI 2

VCI 3

VCI PT CLP 4

HEC 5

Phn d liu (48 Bytes)

....

Hnh 1.13.b: Khung dng t bo ATM ti giao din UNI

c im ca cc trng trong cu trc t bo nh sau:

1.4.2.1.S hiu nhn dng knh oVCI (Virtual Channel Identifier)

VCI c dng nh danh cho mt knh o VCtrn mt ng truyn

dn.

Do mng ATM c c im hng lin kt nn mi cuc ni c gn mt shiu nhn dng VCI ti thi im thit lp. Mi gi tr VCI ch c ngha ti tng

lin kt t nt ny n nt khc ca mng. Khi cuc ni kt thc, VCI c gii

phng dung cho cuc ni khc. Trng VCI c di 16 bits (trong c hai giao

din NNI v UNI).

1.4.2.2.S hiu nhn dng ng o VPI (Virtual Path Indentifier)

S hiu nhn dng ng oVPI c tc dng nh danh cho mt ng

truyn otrong mt ng truyn vt l.

Mi mt ng o c mt gi tri VPI ring bit. VPI gip cho cc chuyn

mch c th xc nh ng i cho cc t bo mt cch d dng. Kch thc ca

trng VPI tu thuc t bo c truyn qua giao din UNI (8 bi ts) hay NNI (12

bits).

T hp ca VPI v VCI to thnh mt gi tr duy nht cho mi cuc ni. Tu

thuc vo v tr i vi hai im cui ca cuc ni m nt chuyn mchATM s


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nh ng da trn gi tr VPI v VCI hay ch da trn gi tr VPI. Tuy vy c n

ch rng VCI v VPI ch c ngha trn tng chng lin kt ca cuc ni. Khi

qua nt chuyn mch VCI v VPI s nhn cc gi tr mi ph hp vi on tip

theo.

1.4.2.3.Kiu t bo PT(Payload Type)

Trng PT cho bit kiu ca t bo ang c truynqua mng, l t bo

mang thng tin ca ngi s dng hay cc t bo mng cc thng tin gim st, vn

hnh, bo dng OAM (Operation-Administration-Maintenance). Trng PT c

kch thc l 3 bits v c cc c im chnh nh sau: T bo mang thng tin ca ngi s dng nu bit u tin ca trng

PT l 0 cn nu l 1 th t bo mang cc thng tin qun l mng

OAM.

Bit th hai l bit bo hiu tc nghn trn mng.

Bit cui cng c chc nng bo hiu cho lp tng thch ATM AAL

(ATM Adaptation Layer).

Hnh 3.14 v bng 3.2 trnh by cu trc trng PT

Hnh 1.14: Khun dng trngPT trong t bo mng thng tin ngi s dngKhun dng Chc nng

100 T bo OAM lp F5 c lin quan n lin kt

101 T bo OAM lp F5 c lin quan n u cui

110 T bo OAM qun l ti nguyn

111 Dnh s dng cho tng lai

Bng 1.2: Cu trc trng PT vi t bo OAM

0 0/1 0/1

T bo ca ngis dng

Bit bo hiu tc nghn"1" nu c tc nghn

Bit bo hiu lp AAL


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1.4.2.4.CLP(Cell Loss Priority)

Bit CLP c tc dng xc nh u tin gi cc t bo trong trng hp cc ti

nguyn trong mng khng cn ti u na (chng hn trong trng hp qu ti).

Trong trng hp ny, nhng t bo c u tin cao hn c truyn trc, cn

nhng t bo c u tin thp hn s b loi b hoc truyn dn sau.

Nu CLP=0 : u tin cao.

CLP=1 : u tin thp.

u tin gi t bo c nh gi theo hai tiu chun: u tin v mt thi gian

hoc u tin v mt ni dung

- Nhng t bo c u tin v mt thi gian thp hn s c tr

truyn ln hn.

- Nhng tbo c u tin v mt ni dung cao hn s c kh

nng b loi b thp hn.

Ngoi ra, mc u tin cn c th c nh gi trn c s cuc ni hoc trn c

s loi t bo. Trong trng hp nh gi mc u tin da vo cuc ni th nhng

t bo c truyn trn cng mt knh o hoc mt ng o c cng mc u tin.Cn trong trng hp nh gi mc u tin da vo loi t bo th nhng t bo

c truyn trn cng mt knh o hoc ng o s c cc mc u tin khc nhau.

1.4.2.5.HEC(Header Error Control)

HEC l trng iu khin li cho phn Header ca t bo. Kch thc ca

HEC l 8 bits, HEC cha m d vng CRC (Cyclic Redundary Code). Sau mi

chng, phn Header ca t bo ATM li b thay i, HEC s tnh ton v kim trali CRC vi mi chng. a thc sinh c dng l :

x8+x

2+x+1.

1.4.2.6.GFC(Generic Flow Control)

Gia hai kiu t bo truyn trong mng ATM c s khc bit trng thng

tin ny. Trng thng tin ny (chim 4 bits) ch c trong t bo ti giao din UNI

gi l trng iu khin dngchung.


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C ch hot ng ca GFC cho php iu khin lung cc cuc ni ATM

giao din UNI. N c s dng lm gim tnh trng qu ti trong thi gian ngn

c th xy ra trong mng ca ngi s dng. C ch GFC dng cho c cc cuc ni

t im ti im v t im ti nhiu im.

Khi kt hp mng ATM vi cc mng khc GFC c dng bo hiu cho

cc mng ny lm th no hp knh cc t bo ca cc cuc ni khc nhau. Thc

cht GFC l mt b cc gi tr chun nh ngha mc u tin ca ATMi

vi cc quy lut truy cp vo cc mng khc nhau.

Tuy nhin vic s dng 2 loi t bo khc nhau ti hai giao din khc nhau l

nhc im ca ATM. V nh vy trong mng khng s dng cc giao thc ng

nht nn khng th lp t cc thit b ti bt c v tr no trong mng.


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Chng 2: Cc c im k thut ATM

2.1.Lp tng thch ATM (AAL)

2.1.1. Tng quan

Nh trong m hnh tham chiu giao thc ATM lp AAL v cc lp caohn

cung cp cc giao tip v dch v cho cc ng dng u cui nh chuyn tip

khung, dch v d liu chuyn mch Gigabit, giao thc Internet v cc giao din

chng trnh ng dng.

Thc t phn ln cc t bo l mang thng tin ca ngi s dng, th nhng cc

thit b my tnh, ni sn sinh ra cc d liu ny li khng trc tip to ra hoc sinh

ra t bo m d liu cn phi chuyn qua mng phi tng thch vi mng ATM.

iu ny c ngha l pha pht phi to ra c n v d liu c di thch hp

v chuyn cc t bo ny qua mng. Pha thu phi thc hin chc nng to li d

liu ban u t cc t bo.

Trong thc t d liu to ra thng ln hn 48 Bytes, do nhiu ngun ng dngkhc nhau vi nhiu khun dng thng tin c trng cho cc ng dng ny. Do vy

mng ATM phi cung cp cc dch v vn chuyn. Mi th tc chun b cho cng

vic ny l rt phc tp v do lp cao nht trong giao thc ATM m nhim, l

lp tng thch ATM gi l AAL.

Chc nng v phn loi AAL

Nhim v ca lp AAL l tora s tng thch gia lp ATM v cc dch v

cc lp cao hn, n n c truyn t u cui pht n u cui thu v trong

sut i vi mng. C ngha l mng ATM khng x l phn thng tin ti trng ca

ngi s dng v n cng khng bit cu trc can v d liu.

Cc chc nng bn trong AAL l quy nh ngi s dng gi lung d liu n

cc lp cao hn ti pha thu trong c ch n nh hng do cc lp ATM sinh

ra.


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Trong lp ATM, lung d liu c th b sai lch do sai li trong truyn dn hoc

t bo b tr do tr ca cc b nh m b thay i hoc do tc nghn trong

mng. T , t bo c th b mt hoc phn pht nhm a ch. Cc giao thc AAL

c s dng gii quyt cc vn ny. V i vi mi loi yu cu cht lng

dch v khc nhau th c nhng AAL tng ng khc nhau. c nghin cu k

hn v cc loi AAL ta c th xem xt chng thng qua vic nghin cu AAL trong

B-ISDN.

Thng qua AAL cc n v d liu giao thc PDU (Protocol Data Unit) cc

lp cao hn c chia nh v a xung trng d liu ca t bo ATM. AAL

c chia nh thnh hai lp con l lp con phn on v ti hp SAR

(Segmentation And Reassembly) v lp con hi t CS (Convergence Sublayer).

Chc nng chnh ca SAR l chia cc PDU ca lp cao hn thnh cc phn

tng ng vi 48 Bytes ca trng d liu trong t bo ATM ti u pht. ti u

thu SAR ly thng tin trong trng d liu ca t bo ATM khi phc li cc

PDU hon chnh.

Lp con SC ph thuc vo loi dch v. N cung cp cc dch v ca lp AALcho cc lp cao hn thng qua im truy nhp dch v SAR (Service Access Point).

gim thiu cc th tc ca AAL, khuyn ngh I.362 ca ITU-T chia AAL thnh

4 nhm khc nhau tu thuc vo c im dch v ca chng. Vic phn loi cc

lp AAL ch yu da trn 3 tham s l

Mi quan h v mt thi gian.

Tc bit.

Dng truyn (hay kiu lin kt).

Vic phn chia c trnh by trong bng 2.1.


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Tnh cht Loi dch v

Loi A Loi B Loi C Loi D

Mi quan h

thi gian gia

ch v ngun

Yu cu thi gianthc Khng yu cu thi gian

thc

Tc truyn C nh Bin i

Kiu kt ni C kt ni Khng kt

ni

Loi AAL AAL1 AAL2 AAL3/4 AAL5,

AAL3/4

Bng 2.1: Phn loi cc nhm AAL

Loi A: Phc v cc dch v yu cu thi gian thc, tc truyn khng i,

kiu hng lin kt. Cc dch v thuc v loi ny thng l ting ni 64 Kbps v

tn hiu video c tc khng i. Cn gi l AAL kiu 1(AAL1).

Loi B: L cc dch v thi gianthc, tc truyn thay i, kiu hng lin

kt. Cc dch v ca n thng l tn hiu Audio v Video c tc thay i (c s

dng nn) cn c gi l AAL2.

Loi C: L cc dch v khng yu cu thi gian thc, tc truyn thay i,

kiu hng lin kt. V d ca dch v ny l chuyn File, cc dch v mng d liu

trong u ni c thit lp t trc khi truyn d liu.

Loi D: Bao gm cc dch v khng yu cu thi gian thc, tc thay i,

kiu khng c hng. V d cho loi dch v ny l chuyn cc Datagrams, cc pdng ca mng truyn d liu m khng thit lp u ni trc khi truyn d

liu. C AAL3/4 v AAL5 u c th s dng cho dch v loi ny.

Cc chc nng ca lp AAL c th rng (khng c) nu nh lp ATM

p ngc cc yu cu ca mt dch v vin thng c th no . Trong trng

hp ny khc hng c th s dng tt c 48 Bytes ca trng thng tin. Dung lng

ca trng thng tin t bo c chuyn trc tip v trong sut ln lp cao hn.

Trng hp ny c gi l cc chc nng ca AAL0.


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Hnh 2.1 m t qu trnh hnh thnh t bo.

Hnh 2.1: Qu trnh hnh thnh t bo

Trong : SDU (Service Data Unit) khi s liu dch v.

PDP (Protocol Data Unit) khi s liu giao thc.

SAP (Service Access Point) im truy nhp dch v.

AAL-SDU

Thng tinCS-SDUPhn uCS-PDU

Phn cuiCS-PDU

CS-SDU

Phn onCS-PDU

Phn uSAR-PDU

Phn cuiSAR-PDU

Thng tin SAR-SDU

AAL-SAP

ATM-SAP

ATM-SDU

Trng thng tin t boMo ut bo

T bo

PL-SAP

Lp vt l (PL)

Lp ATM

Lp AAL

SAR

CS


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2.1.2.AAL1

AAL1 dng truyn cc ng dng c tc khng thay i qua mng B -

ISDN, v n to ra ti my thu tn s xung ng h ca my pht. iu ny i hi

cc thng tin lin quan n tn s xung ng h phi gi n ni thu cng vi Data.

Cc dch v c cung cp bi AAL1 l:

Truyn ti v phn pht cc khi SDU vi tc bit c nh.

Truyn ti cc thng tin v ng b gia bn pht v bn thu.

Truyn ti cu trc thng tin gia bn pht v bn thu.

Khi cn thit, ch th cc thng tin b mt hoc li m AAL1 khng c

kh nng sa.

Ngoi ra AAL1 c th thc hin mt s chc nng khc lin quan n cc dch v

c lp ATM cung cp nh:

Phn tch v ti to li cc thng tin khc hng.

X l tr t bo, x l tr t hp thng tin ti t bo.

X l cc t bo mt v nhm a ch.

Ti to li ng h v cu trc d liu ti u thu.

Kim tra v x l thng tin iu khin giao thc AAL (PCI) dng cho

cc li bit.

Kim tra v c th x l li bt ca trng thng tin.

2.1.2.1.Lp con SAR

Data pht i c ng vo khi 47 Bytes. Sau mi khi ny c gn

thm mt Header c chiu di 1 Byte. Header ny chc cc thng tin nh: Tn sxung ng h ca dng bit c pht i. Tip theo cc khi ny c t vo trong

vng thng tin ca t bo ATM v n c xem nh SAR-PDU.

n v d liu SAR-PDU gm 48 Bytes. Bytes u tin l trng thng tin

iu khin. PCI bao gm 4 bits ch th t SN (Sequence Number) v 4 bits phng

v s th t SNP (Sequence Number Protection). Trng SN c chia ra thnh bit

bo hiu lp con hi t CSI (Convergence Sublayer Indication) v 3 bits m s th


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t SC (Sequence Number). Cu trc ca AAL1 c ch ra trong hnh 4.2. Gi tr

SC to ra kh nng pht hin cc t bo b mt hoc truyn nhm. Bit CSI c th

c s dng truyn thng tin ng b hoc cc thng tin v cu trc d liu.

Trng SNP cha m CRC l tng kim tra cho phn SN dng a thc sinh

x3+x+1, bit cui cng l bit P (Parity) dng kim tra chn l cho c 7 bits u ca

PCI.

Hnh 2.2: Cu trc AAL1

Khi AAL1 c dng truyn Data c cu trc (d liu c ly mu tn

s 8Khz) th dng s liu l cc dng Data lin tc. y cc gii hn cu trc c

xc nh bng con tr. V vy thng tin ca SAR-PDU c con tr khc vi thng tin

ca SAR-PDU khng c con tr. Vi Data c cu trc Byte u tin trong vng

thng tin ca cc SAR-PDU c s th t chn c dng lm con tr.

2.2.1.2.Lp con CS

Cc chc nng ca lp con CS hon ton ph thuc vo dch v, bao gm

mt s chc nng c bn nh x l gi tr tr t bo, x l cc t bo b mt hoc

chn nhm, sa li theo c ch sa li ca HEC, khi phc li ng h theo phng

php nh du thi gian d ng b SRTS (Synchronous Residual Time Stamp).

Trong phng php STRT mc thi gian RTS (Residual Time Stamp) c s dng

CSI SC CRC EPB

1 2 3 4 1 2 3 4

4bits 4bits

Mo ut bo

SN SNP Thng tin SAR-PDU

Phn uSAR-PDU

47 Bytes

SAR-PDU(48 Bytes)

SN : S th t SC: m th tSNP: Bo v s th t EPB: Kim tra bit chnCSI: Ch th lp ph hi t CRC: Cc bits kim tra


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o c v mang thng tin v mc khc nhau gia ng h ng b chung ly

trong mng v ng h ca thit b cung cp dch v.

2.1.3.AAL2

AAL loi 2 c thit k cho cc dch v truyn Data c tc thay i

nhng cn c s tng quan v thi gian gia my pht v my thu. Nh vy c

ngha l thng tin ca my pht phi c truyn n my thu. Lp tng thch

AAL2 vn cha c xc nh mt cch chi tit. Ch c cc dch v v chc nng

di y c d kin trc.

Cc dch v c cung cp l: Cc SDUs xut pht t mt ngun c tc bit bin thin c trao

i gia AAL v lp cao hn.

Thng tin ng b ho c truyn ti gia ngun v ch.

Bo tin v cc li m chng khng c sa bi AAL2.

Cc chc nng c thc hin:

Phn on v ghp li cc thng tin ca ngi s dng.

iu khin s bin thin tr t bo.

X l cc t bo b mt hoc chn nhm.

Khi phuc ng h ngun ti my thu.

Kim tra AAL-PCI php hin cc li bt v x l cc li ny.

Kim tra trng thng tin ca ngi s dng php hin cc li bit

v tin hnh cc hot ng sa li nu c th.

2.1.4.AAL 3/4

AAL3/4 c pht trin t AAL3 (phc vcho cc dch v loi C) v AAL4

(phc v cho cc dch v loi D). Ngy nay hai kiu AAL trn hp li lm thnh

AAL3/4, AAL3/4 tho mn cc dch v loi C,D. Hnh 2.3 l cu trc ca AAL3/4.

Lp con CS ca AAL3/4 c chia nh thnh hai lp con l:

CPCS (Common Part Convergence Sublayer): Lp con hi t chung

SSCS (Service Specific Convergence Sublayer): Lp con ph thuc dch v


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Hnh 2.3: cu trc ca AAL3/4

Cc gi Data c chiu di thay i c m thm mt s bits tr thnh

mt s nguyn ln 32 bits, sau cng thm vo phn Header v Trailer to thnh

CS-PDU. Cc CS-PDUs ny c ct thnh cc on c chiu di 44 Bytes v li

c cng thm Header v Trailer na ri a n lp ATM di dng cc SAR-

PDUs 48 Bytes.

C hai m hnh hot ng c nh ngha cho AAL3 l ch kiu thng

ip (Message Mode) v kiu dng bit (Streaming Mode).

Ch kiu thng ip cho php truyn cc AAL-SDUs c chiu di thay

i cng nh chiu di c nh trong mt AAL-SDU tng ng vi mt AAL-

IDU (Interface Data Unit).

Khng ging nh kiu thng ip. Ch kiu dng bit gi mt AAL-SDU

trong mt hoc vi AAL-IDU v vic truyn cc AAL-SDUs ti cc ch qua giao

din AAL khng y s b loi b.

C hai m hnh kiu thng ip v kiu dng bit u cung cp hai hot ng

truyn dn l hot ng m bo v hot ng khng m bo. Hot ng m bo

trc ht dng cho m hnh kt ni Point to Point. H thng s pht li cc SDU b

mt v s cung cp cc chc nng iu khin thng tin. Hot ng khng m bo

khng c chc nng ny. Vic truyn Data trn lp con CPCS lun lun l hot

ng khng c m bo.

2.1.4.1.Lp con SAR

SSCS

CPCSCS

SAR

AAL3/4,5

SAR


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Ni chung cc CS-PDUs c di thay i, v vy SAR-PDU bao gm 44

Bytes l d liu ca CS-PDU, 4 Bytes cn li c dnh cho trng thng tin iu

khin.Cu trc ca SAR-PDU nh hnh 2.4.

Hnh 2.4: Cu trc SAR-PDU ca AAL3/4

ngha cc trng trong SAR-PDU nh sau:

Trng kiu on ST (Segment Type) c di 2 bits, n ch ra loi ca CS -

PDU c cha trong SAR-PDU: nh phn u ca SAR-PDU BOM (Beginnig of

Message), phn cui EOM (End of Message) v cc CS-PDU n SSM (Single-

Segment Message). Trng ch th di LI (Length Indicator) ch ra s Bytes ca

CS-PDU c cha trong trng d liu ca SAR-PDU. LI c di 6 bits. Ngoi ra

trong SAR-PDU cn c trng s th t gi SN (Sequence Number) di 4 bits. Mi

khi nhn c SAR-PDU thuc v mt cuc ni, gi tr SN li tng ln 1 n v.

Chc nng th hai ca lp con SAR l pht hin li. Trng kim tra li CRC

c di 10 bits thc hin vic kim tra li bit trong cc SAR-PDUs. Gi tr

CRC c tnh trong trng tiu , trng d liu v trng LI. Lp con SAR cn

c kh nng pht hin cc gi b mt hoc chn nhm.

Chc nng th ba ca SAR l ng thi phn knh v hp knh cc CS-PDUs

ca cc cuc ni n mc ATM. Chc nng ny s dng trng d liu nhn

Mo ut bo

Thng tin SAR-PDUPhn u

SAR-PDU

SAR-PDU(48 Bytes)

SN : S th t (4bits)SN: Loi phn on(2bits)MID: Ch th ghp knh(10bits)LI: Ch th di(6bits)CRC: Cc bits kim tra(10bits)

Kt cuiSAR-PDU

2Bytes 44 Bytes 2Bytes

ST SN SNP LI CRC


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dng hp knh MID (Multiplexing Indetifier) di 10 bits. Cc SAR-PDUs vi d

liu nhn dng knh MID khc nhau s thuc v cc CS-PDUs ring bit. Vic phn

knh/ hp knh phi c thc hin trn c s t u cui n u cui.

Nh ta bit lp con CS c chia lm hai phn l phn chung CPCS v

phn ph thuc dch v SSCS. Chc nng v cu trc ca SSCS hin ti vn cha

c r rng, n i hi phi nghin cu thm. Phn CPCS truyn cc khung d

liu ca ngi s dng vi di bt k trong khong 165535 Bytes. Cc chc

nng ca CPCSnm trong 4 Bytes phn tiu (Header) v 4 Bytes phn ui

(Trailer).

Hnh 2.5: Cu trc CPCS-PDU ca AAL3/4

Cu trc ca CPCS-PDU nh hnh 4.5 trong trng ch th phn chung CPI

(Common Part Indicator) c s dng qun l phn cn li ca phn tiu v

phn ui. Trng nhn hiu bt u Btag (Beginning Tag) v nhn hiu kt thc

Etag (Ending Tag) cho php to nn s lin kt mt cch chnh xc gia phn tiu

v phn ui ca khung. Trng kch thc b m cung cp BASize (Buffer

Alocation Size) bo hiu cho u thu kch thc b m ti a cn thit nhn

CPCS-PDU. Trng m PAD (Padding) m bo sao cho trng d liu ca

CPCS-PDU l mt s nguyn ln 4 Bytes do n c di t (0 3) Bytes.

CPI Btag BAsize AL Etag Length

Phn uCPCS-PDU

Thng tin CPCS-PDU

CPCS-PDU

CPI: Ch th phn chung (1Byte)AL: ng b (1Byte)Btag: nh du im u (1Byte)Etag:nh du kt thc (1Byte)BAsize: Kch thc b m(2Bytes)PAD: Phn cng thm (1n 3 Bytes)Length: di thng tin CPCS-PDU(2Bytes)

Kt cuiCPCS-PDU

PAD


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Trng ng chnh AL (Alignment) c s dng ng chnh phn ui 32 bits

ca CPCS-PDU. Trng di Length ch ra di ca trng d liu.

2.1.5.AAL5

AAL5 phc v cho cc dch v c tc thay i, khng theo thi gian thc.

Cng ging nh AAL 3/4, AAL5 c s dng ch yu cho cc nhu cu v truyn

s liu. Mc d mi loi AAL c s dng ti u cho mt kiu lu lng ring

bit, cng khng h tn ti iu kin l AAL c thit k ti u cho mt loi lu

lng ny li khng c s dng cho mt loi lu lng khc, nhng hin nay

trong thc t nhiu nh cung cp sn xut thit b ATM u s dng AAL5 htr cho mi loi lu lng.

Tuy nhin cc th tc trong AAL5 n gin hn rt nhiu so vi cc th tc

trong AAL3/4. V d y khng c chc nng phn/ hp knh cho cc t bo. Tt

c cc t bo trong AAL5 c pht i thnh dng t bo c s th t c th

Gi Data c chiu di thay i (165535 Bytes) trc ht c thm vo

mt s bits tr thnh mt s nguyn ln 48 Bytes, sau c cng thm mt

Trailer ( y khng c phn Header) to thnh cc CPCS-PDUs. Cu trc ca

CPCS-PDU nh hnh 4.6.

Hnh 2.6: Cu trc CPCS-PDU ca AAL5

Thng tin CPCS-PDU

CPI: Ch th phn chung (1Byte)PAD: Phn cng thm (0n 47 Bytes)Length: di thng tin CPCS-PDU(2Bytes)CRC: Kim tra (4Bytes)CPCS-UU: Ch th CPCS gia khch hng v khch hng (1B

Length CRCCPCS-UU CPI

PADKt cui

CPCS-PDU

8 Bytes


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2.1.5.1.Lp con SAR.

Lp con SAR chp nhn cc SDUs c di l mt s nguyn ln ca 48

Bytes c gi xung t cc CPCSs. N s khng b xung thm cc trng thng

tin iu khin (nh phn tiu v phn ui) vo cc SDUs va nhn c. SAR

ch thc hin chc nng phn on u php v to li cc gi u thu.

4.1.5.2.Lp con CS

nhn bit c im bt u v kt thc ca SAR-PDU, AAL5 s dng

trng kiu ti tin PT trong phn Header ca t bo.

PT1: Cui ca mt SAR-PDU.

PT0: u/ gia ca mt SAR-PDU.

AAL5 c hai m hnh hot ng l : Message Mode v Streaming Mode. C

hai m hnh ny u c hai c ch truyn dn l : truyn dn m bo v truyn dn

khng m bo. S khc bit gia AAL3/4 v AAL5 l AAL5 ch c mt cu hnh

ng truyn im -im (Point to Point) khng c cu hnh ng truyn im -a

im (Point to Multipoint).

Hot ng ca AAL5 c m t nh hnh 2.7.

Hnh 2.7: Hot ng ca AAL5

AAL Service Data Unit

CPCS-PDU Payload

SAR-PDU

CPCS-PDU

SAR-PDU

ATM Cells

Bytes

1: 65535 Bytes

PAD CPCS-UUCPI Length CRC

1 1 2 4

AAL-SDUAAL5-SAP

CPCS-PDU Trailer

SAR-PDU SAR-PDU

PayloadHeader PayloadHeader PayloadHeaderATM SAP

Payload Type=AAL_Indicate


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2.2. Chuyn mch ATM

2.2.1.Tng quanCc h thng chuyn mch pht trin cho cc mng in thoi v s liu

khng th p dng trc tip cho cc h thng chuyn mch bng rng. Cc yu cu

chnh nh hng n vic xy dng cc h thng chuyn mch bng rng bao gm:

Cc giao din tc cao (50 Mbps n 2.4Gbps), vi tc chuyn

mch n 80 Gbps.

C kh nng thng k cc lung ATM qua cc h thng chuyn

mch ATM.

Trong ATM c hai thit b thc hin cc chc nng chuyn mch cc t bo,

l chuyn mch ATM (chuyn mch VC) v cc b ni xuyn (chuyn mch VP).

Cu trc chuyn mch ATM c chia lm hai phn l phn cng v phn

mm. Phn cng gm giao din cc nt chuyn mch c tc dng lm cho dng

thng tin i vo li chuyn mch tng thch v tc v dng t bo. Phn li

thc hin chc nng chuyn mch cc t bo.Phn mm iu khin nt chuyn mch ATM, n gm ba nhm chc nng: X

l lu lng qua nt chuyn mch, thc hin cc chc nng vn hnh v bo dng

v cc chc nng qun l h thng.

2.2.2.Chc nng ca nt chuyn mch ATM

Mt chuyn mch ATM hoc mt nt ni xuyn thc hin hai chc nng sau

y:

Thay i VPI/VCI.

Chuyn ti t bo t u vo n mt u ra tng ng ca n.

Do nhng yu cu nghim ngt v thng lng, tr v s mt mt t bo i

vi mt nt chuyn mch, nn ch c c cu chuyn mch vi nhng kin trc song

song mc cao mi c th p ng cc yu cu .


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Chuyn mch ATM thc hin cc chc nng chuyn mch da trn nguyn

l chung c m t trong hnh 4.8.

Hnh 2.8: Nguyn l chuyn mch ATM

Chuyn mch ATM mang hai c tnh: chuyn mch gi do tnh cht tng t

bo ATM c truyn ti trong mng mt cch ring bit v chuyn mch c kt

ni do cc kt ni gia hai u cui phi c thit lp trc khi truyn ti t bo.Khi cc nt chuyn mch ATM s truyn ti cc t bo t cc tuyn ni n

(Incoming Link) n cc tuyn ni i (Outgoing Link) trn c s cc thng tin nh

tuyn nm trong phn mo u t bo v cc thng tin lu gi tng nt chuyn

mch trong giai on thit lp kt ni. Qu trnh thit lp kt ni ti tng nt chuyn

mch thc hin hai chcnng sau:

1. i vi tng kt ni, xc nhn gi tr nhn dng kt ni (VCI) ca

tuyn ni n, nhn dng tuyn ni v to gi tr VCI ca tuyn ni i

2. Thit lp bng nh tuyn ti tng nt chuyn mch xc nh mi

quan h gia cc tuyn ni n v tuynni i ca tng kt ni.

VCI v VPI l thng tin nhn dng kt ni trong cc t bo ATM. c th xc

nh chnh xc tng kt ni, mi VP trong tng chng ng truyn c mt gi tr

VPI ring v mi VC trong tng VP c mt gi tr VCI ring. Bc u tin thit

lp kt ni gia hai u cui l xc nh ng ni gia thit b ngun v thit b

Bngthng dch/

nh tuyn

I1I2

I8

O1O2

O8

Mo uvo

Mo ura

X GX

Z VN

C AB

Mo u D liu

T bo

F BA


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ch. Qu trnh ny kt thc vi kt qu l xc nh c chui cc chng ng

truyn dng trong kt ni v cc gi tr nhn dng ca chng. Trong trng hp ch

c chuyn mch VC, cc thng tin gia cc nt chuyn mch k tip nhau s c

trao i qua ng ni thit lp gi tr lin quan n kt ni ca bng nh tuyn.

Gi tr ny iu khin vic chuyn i VCI ca tuyn ni n thnh VCI ca tuyn

ni i. Cc t bo s c tuyn ti khi tt c cc bng nh tuyn thuc ng ni

c thit lp. Ti cc nt chuyn mch, gi tr VCI cng vi tuyn ni n s c

s dng xc nh tuyn ni i v gi tr VCI mi ca tng t bo n.

i vi chuyn mch VC/VP quy trnh xy ra cng tng t nh trong chuyn

mch VC, khc nhau ch yu lin quan s lng cc bng nh tuyn dng cho mt

kt ni.

Trong c hai trng hp, nt chuyn mch c cc gi tr nhn dng mo

u t bo v thc hin x l i vi bng nh tuyn xc nh tuyn ni n v

gi tr nhn dng kt ni , nhn dng kt ni s c thay th bng gi tr mi v t

bo c chuyn mch t tuyn ni n ra tuyn ni i.

Trong mng ATM, cc ng dng khc nhau c th yu cu cc dng kt nikhc nhau. V d dch v thoi c th thc hin gia hai im kt cui khch hng,

trong khi s c nhiu khch hng hn cng s dng dch v in thoi hi ngh.

Nhng nhnh chung c 4 dng kt ni nh sau:

1. Kt ni im -im: l kt ni c thit lp gia hai u cui. Phn

ln cc dch v hin nay nm trong dng kt ni ny.

2. Kt ni im- a im: l kt ni trong lung t bo c khi to

t nt ngun c phn chia n hai hoc nhiu im kt ni khc.

V d c trng ca dng kt ni ny l vic phn b tn hiu Video,

trong my Video ch c dng phc v nhiu u cui khc

nhau.

3. Kt ni a im-im: l kt ni trong tn hiu c khi to t

nhiu nt khc nhau v cng c gi ti mt im cui. V d ca

kt ni ny l trung tm thuthp d liu ca h thng ngn hng.


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4. Kt ni a im-a im: l kt ni trong thng tin c khi to

v trao i ng thi gia mt nhm nhiu khch hng. in thoi

hi ngh l mt v d ca kt ni ny.

2.2.3. Cu to chung ca cc phn t chuyn mch

Phn t chuyn mch l n v c bn nht trong cu trc ca h thng chuyn

mch. Ti u vo, cc thng tin v chn ng (c lin quan ti VCI/VPI) c

phn tch, cn c trn kt qu phn tch m cc t bo c a ti u ra thch

hp. Ni chung cc phn t chuyn mch bao gm mt mng lin kt gia u ra v

u vo, b iu khin u vo IC (Input Controller) ti mi cng vo v b iukhin u ra OC (Output Controller) ti mi cng ra. trnh vic mt mt cc t

bo khi xy ra ng bn trong do hai hoc nhiu t bo cng tranh chp mt u

ra, phn t chuyn mch cn phi c cc b m

Cc t bo ti phn t chuyn mch c ng b vi ng h bn trong

thng qua b iu khin u vo IC. OC c nhim v chuyn cc t bo m n nhn

c t mng lin kt u vo u ra ti u ra cho trc. IC v OC lin kt vi

nhau thng qua mng lin kt u vo-u ra. Ngi ta phn loi phn t chuyn

mch theo cu trc mng lin kt u vo-u ra v cch thc t chc b m. Cc

phn t chuyn mch ATM c th chia lm hai loi: phn t chuyn mch phn chia

theo khng gian v phn t chuyn mch phn chia theo thi gian. Cc loi phn t

chuyn mch khc nhau s ln lt c xem xt.

2.2.4.Phn t chuyn mch phn chia khng gian (hay phn t chuyn mch

theo kiu ma trn)


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Trong phn t chuyn mch theokiu ma trn mng lin kt u vo-u ra

c cu trc ma trn hnh ch nht, ma trn ny cho php ni gia mt u vo v

mt u ra bt k (Hnh 2.9).

Hnh 2.9: Phn t chuyn mch kiu ma trnVic ni u vo vi u ra c thc hin da trn cc thng tin lin quan

n nh tuyn nm trong phn mo u ca t bo ATM. Phn t chuyn mch

theo kiu ma trn li c chia ra thnh ba loi vi cch t chc b m khc nhau

B m u vo.

B m u ra.

B m ti giao im ca ma trn.

2.2.4.1.B m u vo

Trong phn t chuyn mch dng b m u vo, b m t bo c t

b iu khin u vo (Hnh 2.10). Nu s dng m kiu vo trc ra trc FIFO

(First In First Out), ng s xy ra nu hai hoc nhiu t bo u hnh i

cng tranh chp mt u ra. Trong trng hp ny tr mt t bo c quyn i ti

u ra , tt c cc t bo cn li s b tc nghn. Hu qu ko theo l cc t bo

nm sau t bo tc nghn u hng cng s b tc nghn. khc phc nhc

IC

IC

IC

OCOCOC

1

2

b

1 2 b

IC: B iu khin u vo(Input ContrOC: B iu khin u ra(Output Cont


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im ny c th thay b nh FIFO bng b nh truy nhp ngu nhin RAM. Nu t

bo u tin b nghn , nhng t bo sau vn c th truyn ti mt u ra ri cho

trc. Tuy vy vic s dng RAM yu cu cc c ch qun l b nh phc tp hn

m bo tm ra nhng t bo c chn ti cc u ra ri cng nh m bo th

t truyn cc ti cng mt u ra. Ngoi ra c th truyn cc t bo ti cng mt

b m ng thi ti cc u ra khc nhau th cc b m phi c nhiuu ra hoc

thi gian truy nhp gim xung.

Hnh 2.10: Phn t chuyn mch kiu ma trn c b m u vo

2.2.4.2.B m ti u ra

Trong chuyn mch kiu ny (Hnh 2.11). Tc nghn ch c th xy ra khi

tc vn hnh ca ma trn chuyn mch bng vi tc ca dng t bo u vo.

Nhc im ny c th c khc phc bng vic gim thi gian truy cp b m

v tng tc hot ng ca ma trn chuyn mch. Tuy vy nu yu cu tc

hot ng cao s dn n gii hn v mt kch thc ca phn t chuynmch.

||||

||||

||||

1

2

b

1 2 b


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Hnh 2.11: Cu trc phn t chuyn mch ma trn vi b m u vo

2.2.4.3.B m ti giao im ca ma trn chuyn mch

B m cng c th nm ti giao im ca ma trn chuyn mch (hnh 2.12).

Cu trc ca phn t chuyn mch loi ny cho php cc t bo i ti cc u ra

khc nhau khng nh hng ln nhau. Nu cc t bo nm nhng b m khc

nhau c cng mt u ra th logic iu khin cn phi chn xem b m no s

c phc v u tin. Cu trc phn t chuyn mch kiu ny c nhc im l b

m giao im c kch thc nh v khng chia s c b m.

Hnh 2.12: Cu trc phn t chuyn mch kiu ma trn c b m ti giao im

|

|

|

|

1 2 b

|

|

|

|

|

|

|

|

1

2

b

||||

1 2 b

1

2

b

||||

||||

||||

||||

||||

||||

||||

||||


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2.2.5.Phn t chuyn mch phn chia thi gian

2.2.5.1.Phn t chuyn mch dng kiu BUS(Bus-Type Switching Element)

Cc phn t chuyn mch dng kiu Bus s dng mng lin kt u vo- u

ra l cc Bus ghp knh theo thi gian tc cao (hnh 2.13). Tc nghn khng xy

ra ch khi tng dung lng ca knh truyn ln hn tng dung lng ca tt c cc

u vo. m bo yu cu ny, phn t chuyn mch kiu Bus s dng phng

php truyn ti bit theo kiu song song. Thut ton truy nhp Bus p dng y

cho php Bus truyn c chia s cho mi b m theo mt chu k cho trc. Mi

b iu khin u vo c th truyn tbo ti mt u ra trc khi nhn t bo k

tip. Phn t chuyn mch kiu Bus cn c b m u ra phng trng hp

c vi t bo cng ti mt u ra trong khi ti mt thi im ch c th a ra ngoi

mt t bo.

Hnh 2.13: Phn t chuyn mch kiu BUS

2.2.5.2.Phn t chuyn mch kiu vng

Phn t chuyn mch kiu vng c cu trc c minh ho nh hnh 2.14.

Tt c cc b iu khin u vo v u ra c ni vi nhau thng qua mng hnh

vng. Mng lin kt u vo-u ra hot ng theo nguyn lphn khe thi gain

vi dung lng ca vng phi ln hn hoc bng tng dung lng ca tt c cc

IC IC IC

OC OC OC

Bus Ghp knh thi gian tc cao

1 2 b

1 2 b


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u vo. Trong thc t thng hay s dng phn t chuyn mch vng Orwell trong

mt vi vng c s dng song song m bo yu cu v tc .

Hnh 2.14: Cu trc phn t chuyn mch kiu vng

2.2.5.3.Phn t chuyn mch s dng b nh trung tm

Trong phn t chuyn mchs dng b nh trung tm, cc b iu khin

u vo v u ra u s dng mt b nh chung duy nht (hnh 2.15). S liu t tt

c cc u vo u c ghi vo b nh ny, s liu c c ra bi u ra bt k

b nh chung cn c th c t chc thnh cc b m logic u vo, u ra. Bi

v cc b m cng chia s mt b nh chung duy nht nn dung lng b nh yu

cu trong trng hp ny nh hn nhiu so vi trng hp phn t chuyn mch

dng cc b m ring r. Cc phn t chuyn mch loi ny thng lm vic theo

nguyn tc t nh ng. Mt khc cng cn lu rng phn t chuyn mch c

b nh trung tm phi c t chc thnh cc tng song song m bo tn sut

truy nhp b nh khng ln hn tc cho php ca b nh.

Hnh 2.15: Cu trc phn t chuyn mch s dng b nh trung tm

IC OC

IC OC

1

b

1

b

IC OC

IC OC

1

b

1

b

B nhtrung tm


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2.2.6.So snh cc cu trc chuyn mch

Phn t chuyn mch kiu ma trn c chia lm ba loi vi cc t chc b

m khc nhau: b m u vo, b m u ra, b m ti giao im ca ma trn.

B m u vo s trnh c hin tng nghn u vo v tng tc thc t ca

dng d liu i qua chuyn mch. B m ti giao im ca ma trn chuyn mch

do dng chung b m gia u vo v u ra cho nn hiu qu s dng b m

cao, lng t bo phi ch trung bnh gim, nhng nhc im ca n l b m

giao im c kch thc nh, khng chia s c v vic qun l b m ti giao

im ma trn chuyn mch phc tp hn rt nhiu nn trong thc t b m ny t

c s dng. Cc phn t chuyn mch kiu ny c tc chuyn mch thp

(bng tc ca tng lung) kh c kh nng p dng k thut Multicast, kh iu

khin u tin v t l s dng b nh thp. Tuy nhin v mt iu khin tng

i n gin.

Cu trc chuyn mch Bus v nguyn l kh n gin, d ngdng. Tuy

nhin, cu trc ny c hn ch l chuyn mch Bus ch cho ta mt ng ni cho

mt tp hp cc phn t gn vo n nn di thng cho mi phn t ph thuc nhiuvo s lng phn t gn vo Bus. Di thng ny khng th tng ln qu gii hn

do ph thuc tn s ng h h thng v di thng ng truyn. Nu ta tng tn

s ng h th yu cu b vi x l mnh hn v iu ny cng ch c gii hn.

Cu trc chuyn mch vng c u im so vi chuyn mch Bus l mt khe

thi gian c nhiu cng vo s dng trong mi vng. Tuy nhin thc hin vic

ny ta phi thm phn cng v cng kh xy dng cc h thng chuyn mch ln

nh cu trc Bus.

Cu trc chuyn mch b nh dng chung c u im l tit kim c b

nh nht do tt c cc cng u s dng chung mt b nh, k thut nhn bn

Multicast thc hin d dng. Thm na do chuyn i ni tip-song song nn trong

chuyn mch tc x l ch cn bng mt phn ca tc dng s liu thc t.

Nhc im ca loi ny l b m nh, iu khin b m phc tp.


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2.2.7.Cuc ni o c nh PVC (Permanent Virtual Connection)

Cng nh bt k mng chuyn mch gi no trong ATM ngi ta cng nh

ngha cuc ni o c nh (PVC). Vic ny c thc hin thng qua mt vi hnh

thc yu cu dch v. H thng qun l s t cu hnh nh tuyn cho cc thit b

quy nh cc gi tr ca VCI/VPI trc. Cu hnh cng c t sn trong bng

ni ng ti cc nt chuyn mch. Ngi s dng c th nhn dch v ATM theo

hai cch:

1. Thit lp mt knh oc nh.

2. Thit lp mt chuyn mch knh o (hay cuc ni o tm thi).

PVC ging nh ng ring, trong ngi s dng gi ngi cung cp dch

v yu cu mt ng ring t im An im B. ngi cung cp dch v ci t,

khai bo mt knh da vo dung lng m khch hng yu cu. Hp ng PVC

thng ko di vi nm. Ngi s dng phi tr tin thu knh ngay c khi khng

s dng knh.

Th tc thit lp PVC.

1. Ngi s dng yu cungi cung cp dch v cp cho PVC.2. Ngi s dng c thng bo a ch b gi, yu cu bng thng

trung bnh hay tc v khong thi gian knh PVC.

3. Ngi iu hnh thm nhp knh thng tin t my iu khin

thit lp ng. Bc ny ph thuc vo thi gian thc cng nh

ngi s dng trong mng thoi yu cu u ni.

4. Knh c thit lp theo yu cu.

5. Ngi s dng tr tin thu knh theo thng v thi gian s dng

knh. Nu knh khng s dng th ch tr tin thu theo thng.

PVC c u im v thi gian thc, bng thng theo yu cu, khng cn th tc

thit lp gi, u ni bng lnh, knh tn ti lin tc gia cc im, d m rng v

c th ct u ni knh nu khng s dng.


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2.2.8.Cuc ni o tm thi SVC (Switched Virtual Channel)

Kiu ni o tmthi cho php u cui c th c th gi c cc u cui

khc mt cch linh ng.

SVC hot ng ging nh cuc gi in thoi quay s trc tip. Khi thit lp

gi, bng thng c phn nhim ng bng 64 Kbps v knh c phn nhim

cho ngi s dng ngay khi cuc gi c thit lp v ngi s dng phi tr tin

cho cho thi gian gi cho d c chuyn thng tin i hay khng. Th tc bao gm:

thit lp gi, chuyn d liu, ct u ni, tnh cc.

i vi kiu ni o tm thi mt knh o c t ng thng qua mt giao

thc bo hiu khng yu cu thit lp bng tayging nh thit lp PVC. Hnh 2.16

m t vic thit lp SVC thng qua bo hiu.

Hnh 2.16: Thit lp SVCs thng qua bo hiu

Bo hiu trong ATM c khi u bi mt thit b ATM cui cng mong

mun c thit lp mt kt ni thng qua mng ATM. Cc gi bo hiu c gi

thng qua mt knh o c nh c VPI 0, VCI 5 . Knh ny c dnh ring

truyn bo hiu. Tt c cc ntchuyn mch u c cu hnh trc c th

thu c bt c mt gi bo hiu no v gi n n b x l bo hiu c tch

hp trong nt chuyn mch. Bn cch knh o ny cn c mt s knh o khc

END SystemA

END System B

ATM SwitchConnect to B

Connect to B

Connect to B

Connect to B

OK

OK

OK

OK


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c dng truyn cc tn hiu bo hiu v iu khin khc. trong thc t tt c

cc knh o c VCI32. Bo hiu ny c truyn

dn trong mng t nt chuyn mch ny n nt chuyn mch khc thit lp cc

gi tr nhn dng kt ni m n phi i qua. Vic ny c lp li cho n khi n

ch cui cng. Cc gi tr nhn dng kt ni (VPI/VCI) cho mt kt ni c th

c ch r bi nt mng nhn c yu cu kt ni. Cc gi tr nhn dng kt ni

lun lun c ch r mi chiu ca kt ni, nhng cc thng s mi chiu c

th khc nhau, c bit bng thng mt chiu c th l 0.

2.2.9.X l phn tiu ca t bo trong h thng chuyn mch

Nt chuyn mch c hai nhim v chnh l c v thay i cc gi tr VCI/VPI

v truyn cc t bo t mt u vo n mt u ra cho trc. H thng chuyn

mch c hai cch thc hin vic :

Phng php t nh ng.

Phng php dng bng iu khin.

2.2.9.1.Phng php chuyn mch t nh ng (Self- Routing Switching

Element)

Khi phn t chuyn mch t nh ng, s hiu nhn dng VPI/VCI c c

v dch u vo mng chuyn mch. Sau khi c c v bin dch, mi t bo

c b xung thm phntiu m rng dng ring khi truyn bn trong mng

chuyn mch, tiu ny nm trc tiu ca t bo. Nh vy do kch thc ca

t bo c m rng vy tc yu cu ca mng cng phi tng theo. Hnh 2.17

minh ho c ch x l phn m rng tiu ca t bo trong mng chuyn mch

c xy dng trn c s cc phn t chuyn mch t nh ng


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Hnh 2.17: C ch x l u khung trong h thng chuyn mch t nh ng

Trong chuyn mch c k tng, phn tiu m rng c k trng con. Trng

con th i cha a ch u ra ch ca phn t chuyn mch tng con th i. Vi

cu trc ny ta c th sp xp nhng phn t chuyn mch chng ln nhau thnh

hng ct, khi c th tng c cng ra. Do c th m rng dung lng ca

nt chuyn mch mt cch tu .

i vi cc mng chuyn mch nhiu tng dung lng ln phng php

chuyn mch t nh ng rt c a chung do n gim nh mc phc tpkhi iu khin. Vic tng tc chuyn mch hon ton c th thc hin c

trong trng hp ny.

2.2.9.2.Phn t chuyn mch dng bng iu khin (Table-Controlled

Switching Element)

S hiu nhn dng VPI/VCI trong phng php dng bng iu khin c

thay i ti mi phn t chuyn mch trong h thng, do kch thc ca t boc gi nguyn. Hnh 2.18 trnh by qu trnh x l tiu t bo trong mng

chuyn mch s dng phn t chuyn mch c bng iu khin. Ni dung ca bng

iu khin c cp nht trong giai on thit lp cuc ni, mi phn t ca bng

bao gm gi tr VPI/VCI mi v u ra tng ng ca mi t bo ti mi tng

chuyn mch.

A

A B,m,n

Bng

c vthay i

tiu ca

t bo

Phnt

chuynmch

tchn

ng

Phnt

chuynmch

tchn

ng

B nB n m B

T bo ATM

VPI/VCI

c v thay i phn tiu ca t bo u vo

Gi tr VPI/VCIc

Gi tr VPI/VCI mi + phtiu m rng

m n


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Hnh 2.18: C ch x l tiu ca phn t chuyn mch dng bng iu khin

2.3 Cc mng chuyn mch:

2.3.1 Phn loi :

Hnh 2.19: Phn loi cc mng chuyn mch

A BC

T bo ATM

VPI/VCI

c v thay i phn tiu ca t bo mi tng

Gi tr VPI/VCI cGi tr VPI/VCI mi + ph

tiu m rng

m n

A C,m

Bng

Phn tchuynmch

C B,n

Bng

Phn tchuynmch

Ma trn chuyn mch mrng

Ma trn chuyn mch hnh phu

Ma trn chuyn mch trn

Ma trn chuyn mch mt ng

Ma trn chuyn mch a ng

Ma trn chuyn

Ma trn chuyn

Cc mng chuyn mch


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Sau khi nghin cu cc loi phn t chuyn mch c bn, phn ny s xem

xt ti cc h thng mng chuyn mch khc nhau c xy dng t phn t

chuyn mch c bn. Hnh trn th hin s phn loi cc mng chuyn mch.

2.3.2 Mng chuyn mch n tng:

Trong mng chuyn mch n tng, cc u vo v u ra c ni vi nhau

bi mt tng n cc phn t chuyn mch.

2.3.2.1 Ma trn chuyn mch m rng:

y l mt th d ca ma trn chuyn mch m rng c to thnh t cc

phn t chuyn mch khch thc b*b. Tuy vy khi s dng trong ma trn chuyn

mch m rng, cc phn t chuyn mch cn phi c b sung b u vo hoc b

u ra. Tn hiu c a tiu vo ca ct phn t chuyn mch k tip thng

qua cc u ra b sung. u ra thng ca cc phn t chuyn mch c ni vi

u vo b sung ca cc phn t chuyn mch hng di n trong cng mt ct.

u im ca ma trn chuyn mch m rng l tr qua mng chuyn mch nh do

mi t bo ch c a vo b m mt ln khi qua mng. Khi s u vo tng ln

th s phn t chuyn mch cng phi tng ln, iu ny gii hn kch thc ca ma

trn chuyn mch m rng gi tr u vo, u ra l 64*64 v 128*128.

h h h h

h h h h

h h h h

h h h h

h h h h

h h h h

h h h h

h h h h

u vob sung

u ra b sung

u ra

Hnh 2.20: Ma trnchuyn mch mrngu vo


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2.3.2.2 Mng chuyn mch hnh phu:

Hnh 2.21: Mng chuyn mch hnh phu

Trong mng chuyn mch khng tt nghn trn hnh, cc phn t chuyn

mch c ni vi nhau theo mt cu trc ging nh hnh phu. Tt c phn t

chuyn mch u c 2b u vo v b u ra. C th coi mi phu l mt ma trn

ch nht c N u vo v b u ra. Nh vy, trong mng chuyn mch N u vo

v N u ra s c tng cng N/b phu mc song song vi nhau. Cu trc chuyn

mch hnh phu cng ch c p dng vi cc mng chuyn mch c kch thc

nh c khong 32*16 hoc 128*128.

2.3.2.3 Mng chuyn mchtrn:

Nguyn tc lm vic ca mng chuyn mch trn da trn s trn hon v

cc phn t chuyn mch tng n. C ch phn hi c p dng trong mng

chuyn mch trn ni mt u ra bt k vi mt u vo cho trc. Nh vy t

bo c th i qua li mt vi ln trong mng trn trc khi i ti u ra cho trc.

Ti u ra ca phn t chuyn mch, b iu khin u ra cn phi xem xt xem

cn phi a t bo vo ng phn hi hay n c th ra khi mng trong trng

hp u ra l u ra cho. Mngchuyn mch trn c u im l s phn t

SE

*

SE

*

SE

*

SE

*

SE

*

SE

*

Phu th Phu th

b u

2b u

N u


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chuyn mch t, tuy vy tr trong mng ln v ph thuc vo s ln t bo i qua

phn t chuyn mch .

Hnh 2.22: Mng chuyn mch trn

2.3.3 Mng chuyn mch a tng:Mng chuyn mch a tng c xy dng t vi tng ca phn t chuyn

mch cc tng ny c ni vi nhau theo mt vi dng cho trc. Ty theo s

ng mt t bo c th i t u vo ti u ra trong mng m mng a tng c

chia thnh hai nhm con l mng mt ng v mng a ng.

2.3.3.1 Mng mt ng:

Trong mng mt ng ch c mt ng duy nht ni mt u vo ti mtu ra cho trc. Cc mng ny cn gi l mng chuyn mch Banyan. Bi v ch

c mt ng ni gia u vo v u ra cho nn vic nh ng s rt n gin.

Nhc im ca mng Banyan l tt nghn bn trong c th xy ra khi nhiu t bo

cng ng thi yu cu mt ng ni. Mng Banyan li c chia nh thnh vi

nhm chnh c trnh by di y.

Trong mng Banyan mc L (mng Banyan c L tng), ch c cc phn t

chuyn mch nhng tng tip gip nhau l c ni vi nhau. Mi ng ni s

u u

n hn


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i qua mt tng L nh trc. C hai loi mng Banyan mc L l mng Bayan

thng thng v mng Banyan bt quy tc. Mng Banyan thng thng c xy

dng t cc phn t chuyn mch cng loi trong khi mng Banyan bt quy tc

c xy dng t cc loi phn t chuyn mch khc nhau.

2.3.3.2 Mng a ng:

Trong mng a ng, c th c rt nhiu ng lin kt c ni t u

vo ti mt u ra cho trc. V vy mng a ng c u im l chng lm gim

hoc thm ch loi b hn tc nghn xy ra bn trong mng chuyn mch.

Trong phn ln cc mng a ng, vic chn ng lin kt bn trong cthc hin trong giai on thit lp cuc ni. Tt c cc t bo thuc v cng mt

cuc ni u dng chung mt ng lin kt bn trong. Nu cc phn t chuyn

mch s dng m theo kiu FIFO th s khng cn dng cc c ch bo ton

th t cc t bo.

Cc mng a ng li c phn loi thnh mng gp vng (Folder

Network) v mng khng gp (Unfolder Network) .

Hnh 2.23: Mng chuyn mch gp vng ba tngTrong mng gp vng, tt c u vo v u ra u nm v mt bn ca h

thng chuyn mch, cc ng lin kt bn trong u hot ng theo hai chiu vo

b/2

b/2

b/2

b/2 b/2

b/2 b/2

b/2

b/2

b/2

b/2

b/2 b/2

b/2

b/2

bb/2

b

b

b

1

1 1 1

1

1 1

b/2 b/2 b/2b

b/2 b/2 b/2


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Mt loi mng khc c to thnh t s kt hp gia mng sp xp, mng

gi t bo v mng chuyn mch Banyan.Mng sp xp c nhim v sp xp cc t

bo i vo trong mng thnh mt dng n ph thuc vo th t v a ch ch ca

chng. Mng gi t bo s cn c vo u ra ca tng t bo m cho php ch mt

t bo c i ti mng banyan, cc t bo cn li c mng gi t bo phn hi

tr v mng sp xp. Nhng t bo quay tr li mng sp xp s c mc u tin cao

hn nhm m bo th t khng i. Cc t bo i vo mng Banyan c a ti

u ra m hon ton khng s xy ra tc nghn.

Ngoi hai loi mng trn cn c mng a ng c xy dng t vi mng

chuyn mch Banyan kt hp li, cc mng Banyan ny c sp xp trn cc mt

phng nm song song vi nhau. Tt c cc t bo ca mt cuc ni s c truyn

trn cng mt mt phng. Mt t bo i vo h thng chuyn mch c chuyn ti

mt phng thch hp nh nhng b phn phi c lp mi u vo. Ti u ra

ca h thng chuyn mch, cc b ghp knh s thu thp cc t bo t tt c cc mt

phng. Hnh trn minh ha cu trc mng Banyan song song.


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Chng 3: Mng ATM

3.1 Cu trc mng vin thng ATMThnh phn quan trng cu thnh nn mng ATM l chuyn mch ATM.

Chuyn mch ATM gm cc loi sau:

Chuyn mch ATM dung trn mng xng sng: l loi chuyn mch c dunglng ln nht trn mng. hin nay tt ccc hng u a ra thtrng loi cdung lng t10 n 160Gbit/s.

Chuyn mch ATM c th s dng trn c mng xng sng v mng truy nhp.

Chuyn mch ATM dung cho mng truy nhp: thng thng l loi c dung lngnh nht trn mng.

Ngoi ra cn c thit b qun l mng OAM. Nhiu tp on vin thng sn xutthit b OAM ring bit vi chuyn mch ATM, nhng cng c tp on nhNORTEL th li b phn qun l mng nm trong chuyn mch ATM.

Hnh

Su y ta tm hiu v h tng i ATM ca NEC v s dng n xydng cu trc mng vin thng ATM.

Tng i ATOMNET-M20: l tng i dung lng chuyn mch ln c kchthc chun 1800x880x880mm. dung lng chuyn mch nh nht 10Gbit/s, lnnht l 40 or 160Gbit/s. dng lm tng i xng sng ca mng ATM cng cng.

Tng i ATOMNET-M7: l tng i chuyn mch ctrung bnh, kchthc dng t550x435x450mm. dung lng ln nht 10Gbit/s nh nht 5Gbit/s.loi ny dng lm tng i xng sng trong mng dng ring.


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Tng i ATOMIS-5E: c dung lng chuyn mch nh nht trong hATM. Loi ny c kch thc 435x165x420mm dng hp bn v c dng lmthnh phn ca thit b nhm.

Thit b qun l mng ATONET-NMS: bao gm hai server u song song vmt my ch WS. H thng ny u vo mng ATM qua router.

Mng vin thng ATM s dng cc chuyn mch ATM cung cp cc dchv B-ISON gm hai loi mng: mng cng cng v mng dng ring. Trn c stng i ATM ca NEC ta c cu trc mng vin thng ATM nh hnh

Hnh 3.1: Cu trc mng vin

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