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B gio dc v o to

Trng i hc bch khoa H ni------------------------

Lun Vn Thc s khoa hc

Qun tr mng tp trung trn nn WEB sdng cng ngh SNMP, CGI v CORBA cho hthng cung cp dch v Digital Subscriber Line

(DSL) ca Bu in H ni

Ngnh: X l thng tin v truyn thngM s:

TRN VNH THANH

Ngi hng dn khoa hc: TS. H QUC TRUNG

H ni 2006


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Lun vn thc s X l thng tin v truyn thng

- 1

LI CM N

Trc ht, xin c gi li cm n n thy gio hng dn ti l tin sH

Quc Trung, ngi gip ti trong qu trnh nghin cu hon thnh lun

vn ny.

Cho php ti gi li cm n n Trung tm tin hc Bu in H ni, c bit

l cc anh ch em ng nghip ti i iu Hnh Mng VNN, ni ti ang

cng tc tch cc cng tc, tham gia vo cc th nghim, tm hiu h thng

v to iu kin ti c th nghim cc gii php lin quan n ti.

Ti cng xin gi li cm n n cc bn cng hc trong kha o to thc s

chuyn ngnh X L Thng Tin V Truyn Thng 2004-2006 cung cp

cc ti liu cn thit trong qu trnh nghin cu v gip ti rt nhiu

trong qu trnh hc tp, chun b lun n.

Cui cng cho php ti cm n cc bn b, gia nh gip , ng h ti rt

nhiu trong ton b qu trnh hc tp cng nh nghin cu hon thnh lunvn ny.


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Lun vn thc s X l thng tin v truyn thng

- 1

LI CAM OAN

Ti xin cam oan lun vn ny l cng trnh nghin cu ca chnh bn thn.

Cc nghin cu trong lun vn ny da trn nhng tng h p l thuyt v hiu

bit thc t, khng sao chp.

Tc gi

Trn Vnh Thanh


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Mc lc

Mc lc ..................................................................................................................................1Danh sch cc thut ng v t vit tt ...................................................................................3Danh mc hnh v ..................................................................................................................5Danh mc cc bng................................................................................................................6Li ni u.............................................................................................................................7Chng I. TNG QUAN................................................................................................8

I.1. Mt s vn cbn .............................................................................................8I.2. L do chn ti ...................................................................................................9I.3. Cu trc ca lun n.............................................................................................13

Chng II. Giao thc SNMP..........................................................................................15II.1. Mt s vn cbn v SNMP ..........................................................................15

II.1.1. S ra i v pht trin ca SNMP ...............................................................16

II.1.2. M hnh SNMP............................................................................................18II.1.3. Cng dch v v dch v truyn ti phi hi p ...........................................22II.1.4. SNMP community .......................................................................................24

II.2. Cu trc thng tin qun tr (SMI) v csthng tin qun tr (MIB) ..................27II.2.1. Nhm h thng trong MIB II.......................................................................29II.2.2. Nhm cc t chc trong MIB-II ..................................................................31II.2.3. Nhm giao din (interface trong MIB-II)....................................................32

II.3. c t SNMP .......................................................................................................33II.3.1. Khun dng ca SNMP ...............................................................................34II.3.2. Cc lnh SNMP v trnh t thc hin..........................................................35II.3.3. Kin trc qun tr mng ...............................................................................36II.3.4. Nhng hn ch ca SNMP...........................................................................37

Chng III. Qun tr mng trn web vi CGI v CORBA..............................................39III.1. Chun CGI .......................................................................................................39

III.1.1. CGI - s mrng ca HTTP ......................................................................39III.1.2. Cc c trng ca CGI.................................................................................40III.1.3. M hnh quan h Client/Server s dng CGI ..............................................41III.1.4. Cch thc v phng php truyn d liu trong CGI..................................42III.1.5. Lp trnh CGI...............................................................................................44III.1.6. Ci t cc chng trnh CGI ......................................................................45III.1.7. M hnh qun tr mng ba bn s dng Web - CGI ....................................46

III.2. Chun CORBA ................................................................................................47III.2.1. Gii thiu chun CORBA............................................................................47III.2.2. Slc v lch s CORBA..........................................................................48III.2.3. Tng quan v kin trc CORBA..................................................................50III.2.4. B phn trung gian x l yu cu trn i tng (ORB) ............................51III.2.5. Ngn ngnh ngha giao din (IDL) .........................................................58III.2.6. M hnh bn bn gia Web client v server vi CORBA...........................60

III.3. Tm tt v CGI v CORBA.............................................................................62Chng IV. Xy dng h thng qun tr DSLAM qua web............................................65

IV.1. Kho st h thng mng cung cp dch v ADSL...........................................65IV.1.1. Gii thiu h thng mng cung cp dch v ADSL ca Bu in H ni...65


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IV.1.2. Cbn v thit b DSLAM..........................................................................66IV.1.3. H thng qun l mng xDSL .....................................................................67IV.1.4. Cng vic qun l mng ..............................................................................71IV.1.5. Chc nng qun l phn t mng ................................................................71

IV.1.6. Mng qun l truy cp .................................................................................75IV.1.7. Cu hnh Client Server NMS.......................................................................76IV.1.8. Kho st quy trnh cung cp dch v ADSL ................................................79

IV.2. Qun tr mng tp trung qua WEB s dng CGI.............................................85IV.2.1. Xy dng chng trnh trn CGI.................................................................90IV.2.2. Xy dng chng trnh gi nhn SNMP .....................................................94

IV.3. Qun tr mng tp trung qua WEB s dng CORBA....................................101IV.3.1. Xy dng ng dng vi VisiBroker ..........................................................102IV.3.2. Xy dng cng c qun tr mng xDSL s dng CORBA........................103

Chng V. Kt lun v hng pht trin .....................................................................110V.1. Cc kt qu t c.....................................................................................110V.2. Kt lun..............................................................................................................110

V.3. Kh nng mrng: ............................................................................................111V.3.1. Kt lun......................................................................................................112

Ti liu tham kho .............................................................................................................115


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Danh sch cc thut ng v t vit tt

ADSL Asymmetric Digital Subscriber Line

API Application Program Interfaces

ASN.1 Abstract Syntax Notation 1

ATM Asynchronous Transfer Mode

BOA Basic Object Adapter

BGP Border Gateway Protocol

CCITT International Telegraph and Telephone Consultative Comittee

CGI Common Gateway Interface

CORBA Common Object Request Broker Architecture

CSDL CSD Liu

DII Dynamic Invocation Interface

DNS Domain Name Service

DSI Dynarnic Skeleton Invocation

FTP File Transfer ProtocolHTML HyperText Markup Language

HTTP HyperText Transfer Protocol

IANA Internet Assigned Numbers Authority

IDL Interface Definition Language

IETF Intemet Engineering Task Force

IIOP Intemet Inter-ORB protocol

IOR Interoperable Object ReferenceIOS International Organization for Standardization

IOS Internetworking Operating System

IP Internet Protocol


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JAR Java ARchive

MTU Maxium Transfer Unit

NMS Network Management System NNM Network Node Manager

MIME Multipurpose Internet Mail Extensions

OID Object Identifier

OMG Object Management Group

PDU Protocol Data Unit

PPP Point-to-Point Protocol

RADIUS Remote Authentication Dial In User ServiceRDBMS Relational database management system

RFC Request For Comment

RMON Remote Monitoring

SGMP Simple Gateway Monitor Protocol

SHA Secure Hash Algorithm

SMB Server Message Block

SHDSL Symmetric High-speed Digital Subscriber Line

SMI Structure of Management Information

SNMP Simple Network Management Protocol

STDIN Standard Input

STDOUT Standard Output

TCP Transmission Control Protocol

UDP User Datagram Protocol

URL Uniform Resource Locator

USM User-based Security Model

WWW World Wide Web


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Danh mc hnh v

Hnh II-1 Cu trc nhm cc giao din trong MIB-II.........................................................33

Hnh III-1 Chu trnh thc hin mt CGI request ................................................................41Hnh III-2 M hnh web Client/Server ba bn s dng CGI ..............................................46Hnh III-3 M hnh gi yu cu qua Object Request Broker .............................................56Hnh III-4 M hnh client/server 4 bn trong ng dng CORBA SNMP...........................61Hnh IV-1 Cu trc qun l mng .....................................................................................68Hnh IV-2 M hnh tham chiu qun l mng....................................................................69Hnh IV-3M hnh h thng qun l DSLAM ca HUAWEI ti Bu in H ni...........70Hnh IV-4 M hnh h thng NMS Client/Server ..............................................................76Hnh IV-5 Giao din ha phn mm qun l thit b SIEMENS (ACI)........................77Hnh IV-6 Giao din ha phn mm qun l thit b HUAWEI (iManager N2000) ....78Hnh IV-7 Giao din ha phn mm qun l thit b UMAP (UltrAccess GUI) ..........78Hnh IV-8 Giao din ha phn mm qun l thit b ZTE ............................................79

Hnh IV-9 Cu trc phn lp ca SnmpVar .......................................................................88Hnh IV-10 Giao din ca DSLAMnet .............................................................................100Hnh IV-11 Lu xy dng h thng qun tr mng DSLAM vi VisiBroker .............103


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Danh mc cc bng

Bng II-1 Khun dng mt si tng............................. Error! Bookmark not defined.Bng II-2 Tn ca cc t chc v OlD ................................ Error! Bookmark not defined.Bng II-3 Mt snh ngha ca cc OID........................... Error! Bookmark not defined.Bng II-4 M t cc trng ca SNMP............................... Error! Bookmark not defined.Bng III-1 Cc bin mi trng chun.......................... Error! Bookmark not defined.


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Li ni u

Cuc cch mng Internet trong nhng nm gn y v s ln t ca cc dchv truy nhp internet qua ADSL trc cc dch v truy nhp truyn thng qua

Dial-up t ra nhiu bi ton ln cho cc nh cung cp dch v (ISP) trong

vic xy dng qun l mt s lng khng l cc thit b DSLAM phc v

lp t khp ni trong a bn cung cp.

Bn cnh , s bng n mnh m ca cc dch v Web v kh nng s dng

c web mi ni, mi lc, vo mi thi im m khng ph thuc vo h

thng nn hay khong cch a l to ra mt tro lu web ha cc loi hnh

dch v, k c cc loi dch v c tnh cht chuyn mn cao, xa nay vn gi

gn trong cc phng th nghim hay cc trung tm my tnh ln nh quan trc

v qun l cc dch v mng.

Trong lun vn ny, chng ti s cp n vn s dng cng ngh web

(CGI, CORBA) v cng ngh qun tr mng truyn thng (SNMP) theo di

v qun tr cc thit b cung cp dch v DSLAM vi mc ch xy dng mtcng giao tip trn nn WEB phc v cng tc qun tr cc thit b DSLAM

ca cc nh sn xut khc nhau hin ang c khai thc ti Bu in H ni.

V phng din l thuyt, lun n ny si vo tm hiu giao thc qun tr

mng SNMP v m hnh qun tr mng da trn giao thc ny; cng ngh

cng giao tip chung CGI trn WWW v CORBA cng sc gii thiu

cc kha cnh chnh, c lin quan n vic pht trin ng dng qun tr mng

trn nn web.


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Chng I. TNG QUAN

I.1. Mt s vn cbn

Giao thc qun tr mng SNMP c a ra t nhng nm 80 ca th k

trc nhng n nay vn c s dng rng ri trong lnh vc qun tr ca

cc mng TCP/IP. Mc d khi mi c a ra, SNMP chc thit k

nh mt gii php tm thi qun tr mng TCP/IP nhng do TCP/IP

qu ph bin v thnh chun giao tip de-factor ca th gii, SNMP cng tr

thnh mt chun ng vai tr cc k quan trng trong vic thit k cc phn

mm qun tr mng ca cc thit b cung cp dch v.

Common Object Request Broker Architecture (CORBA) c OMG (Object

Management Group) a ra nh l mt b khung kin trc chun cho cc

ng dng hng i tng trn mng. CORBA a ra nhiu xc lp quan

trng nh l trong sut ha tnh a phng ca cc i tng, gn kt ngn

ng bc cao cng nha ra cc phng thc gi hm ng.

Nh chng ta bit, cc trang web tnh s khng kh nng cung cp cc

thng tin cn c cht cp nht thng xuyn nh cc ng dng da trn

GUI (Graphical User Interface) ca windows. Cng ngh s dng

JavaApplet nhng trong cc trnh duyt khc phc c im yu ny, v

c kh nng cung cp y cc thng tin cp nht thi gian thc, k c

thng tin di dng ha. S dng Java trong cc trnh duyt trn thc t

m rng kh nng ca web ln nhiu ln, khin cho web tr thnh mtmi trng vn nng truyn ti thng tin khng b gii hn v khong cch

hay s khc bit v cu hnh h nn.


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I.2. L do chn ti

Dch v truy nhp Internet bng thng rng s dng cng ngh ADSL ln

u tin c Tp on Bu chnh Vin thng Vit nam (VNPT) th

nghim vo nm 2001 v c trin khai rng ri t thng 7 nm 2003 vitn thng hiu l MegaVNN. Dch v ny t khi ra i n nay c

nhng bc pht trin nhy vt, p ng c yu cu ca ngi dng v

bng rng, v dn dn thay th dch v truy cp Internet gin tip (Dial-up)

qua ng dy in thoi truyn thng.

L mt thnh vin ca VNPT, hin nay trn a bn thnh ph, Bu in TP

H ni ang cung cp 2 dch v chnh s dng cng ngh xDSL l dch vtruy nhp Internet bng rng qua ADSL v dch v dch v mng ring o -

MegaWan trn c 2 loi ng truyn ADSL v SHDSL.

c th cung cp dch v xDSL trn a bn thnh ph H ni, hin nay

Bu in H ni ang qun l mt h tng mng li bao gm mt h thng

phc v truy nhp hin i vi cc thit b DSLAM (Digital Subscriber Line

Access Multiplexer) phn b khp ni trn a bn thnh ph (hn 140im lp t, gn 200 DSLAM ) ca nhiu nh cung cp thit b ni ting.

Nhu cu s dng xDSL trn a bn vn ang tip tc pht trin rt nhanh,

s lng cc thit b DSLAM khai thc trn mng lin tc c u t mi

nhm p ng c nhu cu ca khch hng, mng li c mrng v

phc tp tng ln. n nay, trn a bn H ni hin c 8 chng loi thit b

ca 4 nh sn xut khc nhau Siemens, Huawei, Tailyn, ZTE vi cc

cng ngh khc nhau nh ATM DSLAM, IP DSLAM

H thng cc DSLAM thuc 4 hng sn xut ny c qun tr, gim st,

khai thc mng t xa bi 04 h thng qun l NMS (Network Management

System) t p trung do tng hng sn xut thit b cung c p. Cc h thng


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NMS ny u l mi trng ng, c thit k hng ti i tng l cc

k thut vin vn hnh mng nn khng cung cp giao din ra bn ngoi v

khng c mi lin h vi nhau.

Vi nhng hn ch trn, cng vi s pht trin ca mng li xDSL c v s

lng v chng loi thit b t ra mt thch thc ln i vi Bu in

H ni trong vic vn hnh, khai thc h thng; cng nhnh hng n

cht lng cc quy trnh cung cp dch v ca n v, c th nh sau:

Khng c chc nng cho php cc h thng h trbn ngoi giao tip

vi phn qun l mng

Do khng c chc nng giao tip vi cc h thng h trbn ngoi (v d h

thng qun l khch hng, h thng h trdch v.), qu trnh cung cp

dch v (ng mcng dch v, khi to dch v, tho hy dch v) u

phi chuyn n k thut vin khai thc mng thc hin bng nhn cng

thng qua h thng NMS ca mi hng; khng cho php kt ni, thc hin

tng ha dy chuyn sn xut, cng nh khng th xy dng v pht trin

thnh mt gii php tng th. iu dn n cc h qu tt yu sau:

Slng thao tc hng ngy tng ln theo s lng thu bao v dch

v: Mt ngy phi thc hin nhiu yu cu ng/m cng (khi c

khch hng mi ha mng, hu hp ng, n, tr ncc, vv). C

nhng ngy, s lng yu cu ln n hn 300; thi gian thc hin

trong t 7:00 cho n 21:00 vi cc quy nh cht ch v thi gian

hn ch ti a vic mt lin lc ca khch hng;

To mt sc p khng nhi vi qu trnh vn hnh v khai thc h

thng do phi s dng nhiu loi phn mm qun l NMS i vi

nhng cng vic hng ngy (kim tra thng s cng, ng, m, reset


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cng) . Thc t l c lc, cn b qun l mng phi ngi trc 04

mn hnh NMS v phi thao tc qua li gia 4 NMS ny;

Cng tc h trv chm sc khch hng gp nhiu kh khn:

V l do an ninh, bo mt nn phn qun l mng NMS nn k thut vin

ti b phn h trkhng c thng tin v trng thi thit b tr li v h

trkhch hng m phi hi thng tin t b phn qun l mng NMS, nh

hng khng tt n cht lng chm sc khch hng, tn nhiu nhn

lc v mt nhiu thi gian chi..

Kh khn trong vic tch hp ng dng, nng cao cht lng, ty bin

ca dch v:

Cc phn mm qun l thit b DLSAM c thit k cho cc nhu cu

qun l chung nn c nhiu im khng ph hp vi nhu cu s dng ca

Bu in H ni; khng tch hp vi cc CSDL hin c ca Bu in H

ni, do vy gp nhiu kh khn trong vic tch hp ng dng, nng cao

cht lng ca dch v.

Khng c mt gii php tng th cho ton h thng:

Khng c mt hng cung cp thit b DSLAM no c kh nng cung cp

mt gii php tng th tha mn cc yu cu trn, do gii php thit b

ca mi hng u khc nhau, cc hng ch c th c kh nng cung cp

gii php i vi thit b ca h khi c yu cu, m khng quan tm n

thit b ca cc hng sn xut khc. Thc t ti mng do Bu in H ni

qun l tn ti thit b ca 4 hng sn xut, trong khi s hng cung cp

thit b trn th trng Vit nam c tnh ln hn 10 hng.


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S pht trin ngy cng mnh m ca dch v xDSL vi xu hng nng cao

cht lng dch v m vn tit kim ngun nhn lc k thut cao i hi

phi c mt gii php gii quyt trit cc vn nu trn.

L mt cn b k thut ang cng tc ti mt n v cung cp dch v lnvi, ti c chi c tip xc vi nhng cng ngh tin tin ca th gii

cng nhc va chm nhiu vi cc vn ny sinh m mt nh cung cp

dch v phi i mt khi tin hnh cung cp dch v mng trn quy m rng,

c bit l vn qun tr mng v nhng rc ri ny sinh trong thc t khi

phi phi hp hot ng gia nhiu n v, s dng nhiu loi thit b ca

nhiu nh cung cp khc nhau. La chn ti Qun tr mng tp trungtrn nn WEB sdng cng ngh SNMP, CGI v CORBA cho h thng cung

cp dch v Digital Subscriber Line (DSL) ca Bu in H ni, chng ti

ang hng ti mc tiu tm hiu cng ngh qun tr mng da trn WEB v

xy dng mt gii php phn mm ng dng trong thc t ph hp vi m

hnh khai thc, qun l ni ti ang cng tc ni ring v c th p dng cho

cc nh nh cung cp dch v khc. Phn mm cn phi p ng cc yu cu

t ra vi cc kh nng:

Cho php tng ha cc thao tc khai thc hng ngy;

Cung cp giao tip cho php cc ng dng/dch v h trbn ngoi

c giao tip vi cc thit b DSLAM. C th theo di trng thi

thit b t xa, tu theo phn quyn ca cc n v tham gia khai thc

ph hp vi quy trnh qun l dch v ca nh cung cp dch v, to

tin tin ti thc hin cc chc nng qun l phc tp hn

Nht th ha giao din qun l, gip ngi s dng trnh vic phi

thao tc vi nhiu phn mm qun l khc nhau;


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Nhn thc c ngha quan trng ca vic tin hc ha, tng ha dn

cc thao tc n gin, gii phng ngun nhn lc c trnh cao khi cc

thao tc n iu, cng nh nng cao cht lng cung cp dch v, nhm

thc hin ti s c gng hon thnh ti hng ti kh nng p dngvo thc t khng chi vi n v mnh, m c th p dng vo cc n v

khc.

I.3. Cu trc ca lun n

Lun n c chia thnh 5 chng vi cc ni dung chnh sau:

Chng 1: Tng quan, trnh by nhng vn cbn sc trnh

by trong ti, l do la chn ti v trnh by squa v cu trc

lun n

Chng 2 s trnh by nhng vn c bn ca giao thc qun tr

mng SNMP v m hnh qun tr mng thng thng, s ra i v

pht trin ca ; cc vn lin quan n SNMP nh SMI, MIB, OID

cng nh cc chun c bn ca SNMP, cc hn ch ca SNMP v

khc phc

Chng 3 s trnh by nhng vn cbn ca CGI v CORBA. Cc

vn sc trnh by y l chun CGI, cc c trng ca CGI,

m hnh quan h Client/Server ba bn s dng CGI, m hnh qun tr

mng qua web, cbn v lp trnh CGI . Chng 3 cng s khi

lc v CORBA, gii php s dng CORBA lm mi trng xy

dng ng dng qun tr mng qua web. Cc vn sc trnh by

y l chun CORBA, tng quan v kin trc CORBA, b phn

trung gian x l cc yu cu trn i tng (Object Request Broker


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ORB), m hnh bn bn gia Web client, Web server, NMS Agent v

DSLAM trn CORBA.

Chng 4 p dng thc t h thng qun tr h thng cung cp dch

v xDSL ca Bu in H ni. Gii thiu h thng qun l mng

cung cp dch v xDSL ca Bu in H ni ang c trin khai

thc t v cc gii php xy dng cng c qun tr cc thit b

DSLAM thng qua giao thc SNMP da trn trn nn web bng CGI

v CORBA. Chng ny s trnh by nhng phn c bn lin quan

n xy dng gii php qun tr mng t p trung qua WEB s dng

CGI cng nh CORBA, gii thiu sb v gi phn mm VisiBrokerv trnh by c th phng php xy dng cng c qun tr mng

DSLAM s dng CORBA

Chng 5 Kt qu thc tin v p dng, trnh by nhng kt qut

c ca ti, mt s so snh gia hai cng c qun tr mng da

trn CGI v CORBA. Chng 5 cng s trnh by nhng kh nng

pht trin, m rng ca ti, c thng dng c nhiu hntrong thc t trong vic, c bit l p dng vo h thng qun tr

mng DSL ca Bu in H ni.


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Chng II. Giao thc SNMP

SNMP (Simple Network Management Protocol): l giao thc c s dng

rt ph bin gim st v iu khin thit b mng nh switch, router... Vi

nhng vn phng nh ch c vi thit b mng v t tp trung mt ni th c

l ta khng thy c li ch ca SNMP; Nhng vi cc h thng mng ln,

thit b phn tn nhiu ni, c bit l trong cc h thng mng ca cc nh

cung cp dch v vi m hnh qun l t p trung th vic s dng SNMP

dng nh l bt buc.

Giao thc SNMP c thit k cung cp mt phng thc n gin

qun l tp trung mng TCP/IP. Nu mun qun l cc thit b t 1 v tr tp

trung, giao thc SNMP s vn chuyn d liu t client (thit b m ang

gim st) n server ni m d liu c lu trong log file nhm phn tch

d dng hn. Cc phn mm ng dng da trn giao thc SNMP nh: MOM

ca Microsft v HP Openview vv

II.1. Mt s vn cbn v SNMP

Bn cht ca SNMP l tp hp mt s lnh n gin v cc thng tin m

lnh cn thu thp gip ngi qun tr thu thp d liu v thay i cu

hnh ca cc thit b tng thch vi SNMP.

V d, SNMP c th dng kim tra tc hay ra lnh shutdown mt cng

Ethernet, theo di nhit ca switch v cnh bo khi n ln qu cao.

SNMP c th qun tr rt nhiu thit b, t phn cng n phn mm nh

Web server hay csd liu, t thit bt tin nh routern mt s hub

r tin, hay cc h thng Unix, Window, cc my in, ngun in min l

cc thit b h trSNMP. Cc thit bc gi l h trhay tng thch


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SNMP tc l n c ci t mt phn mm c th thu thp mt s thng

tin v tr li cc yu cu ca ngi qun tr.

II.1.1. S ra i v pht trin ca SNMP

Giao thc Simple Netwok Management Protocol (SNMP) ra i vo nm

1988 p ng i hi cp bch v mt chun chung cho qun tr mng

Internet. SNMP cung cp cho ngi dng mt tp cc lnh n gin nht

c th qun trc cc thit b t xa.

c pht trin t giao thc Simple Gateway Monitoring Protocol (SGMP),

SNMP c m rng cho ph hp vi cc yu cu ca mt h thng

qun tr mng a dng. Ban u, SNMP chc xem nh l mt gii php

tm thi cho vic qun tr cc mng my tnh da trn nn TCP/IP trong khi

chi chuyn hn sang mt giao thc da trn kin trc mng ca OSI.

Tuy nhin, do s pht trin mnh m ca cc ng dng trn nn TCP/IP,

nht l t nm 1990, khin cho TCP/IP trthnh mt giao thc truy nhp

mng de factorca th gii. iu cng khin cho SNMP tr thnh giao

thc qun tr mng c s dng chnh v khng cn b xem l mt gii

php tm thi na [Stallings 96].

Cc hot ng v quy cch d liu ca SNMP c chnh da trn cc

tiu chun c a ra trong cc b RFC (Request For Comment) v hin

chng vn ang c pht trin. Trong s cc RFC xy dng nn chun

SNMP, c ba b tiu chun quan trng c dng lm c s cho SNMP.

Chng l:

RFC 1156 - Cu trc v nh danh ca cc thng tin qun tr ca

internet trn nn TCP/IP (Structure and Identification of Management

Information for TCP/IP based internets).


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RFC 1157 - A Simple Network Management Protocol (SNMP).

RFC 1213 C s thng tin qun tr mng cho Internet trn nn

TCP/IP (Management Information Base for Network Management of

TCP/IP-based internets: MIB-II)

Phin bn u tin ca SNMP (SNMPv1) ra i nm 1988 c quy nh

trong RFC 1157. phin bn u tin ny, tiu ch ca SNMP ng nh tn

gi ca n, l sn gin trong thc thi [Stallings 96] . l l do chnh

khin cho tnh bo mt trong SNMPv1 rt lng lo, ph thuc vo mt xu

chia s tng t nh mt khu dng thun vn bn gi l commutitiy

string. iu ny cho php tt c cc ng dng SNMP nu bit xu ny c

th truy cp thng tin qun tr trn thit b.

Mc d chun SNMPv1 thuc v qu kh (historical standard) nhng

hin nay n vn l phin bn m rt nhiu cc nh sn xut h tr.

Phin bn tip theo ca SNMP l SNMPv2 hay SNMPv2c. c quy nh

trong RFC 3416, RFC 3417 v RFC 3418, SNMPv2 thm cc khun dng

d liu, cc MIB v PDU mi, lm tng kh nng cho giao thc.

Tuy nhin hai phin bn u tin ny ca SNMP vn thiu cc tnh nng bo

mt, xc thc cn thit nn vn c th d dng b khai thc [Stallings 96] .

SNMPv3 l phin bn cui cng, ch yu tng cng bo mt trong qun tr

mng [Stallings 98] . Phin bn ny h trgiao thc xc thc mnh v knh

giao tip c m ha gia cc thc thc qun tr. Nm 2002, phin bn

ny c chuyn t bn tho sang thnh chun, bao gm cc RFC 3410,

RFC 3411, RFC 3412, RFC 3413, RFC 3414, RFC 3415, RFC 3416, RFC

3417, RFC 3418, v RFC 2576. V SNMPv3 l chun mi c cng b, do

vy ch c mt s hng ln nh Cisco mi h trSNMPv3. Tuy nhin vi


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nhu cu ngy cng cao ca bo mt trong qun tr mng, s c thm ngy

cng nhiu cc hng h trSNMPv3 trong cc sn phm ca mnh.

II.1.2. M hnh SNMP

Chun SNMP a ra mt m hnh c scho cc nh ngha d liu thng

qun tr v chun cho cc giao thc trao i thng tin .

Trong kin trc ca SNMP c hai loi thc th l manager v agent.

Manager l server chy mt phn mm c kh nng iu khin cc cng vic

qun tr cho mt mng. Manager thng c gi l trm qun tr - Network

Management Station (NMS). Trong mt mng, trm qun tr chu trch

nhim thm d (polling) v nhn cc trap t agent. Thm d l hnh ng

truy vn mt agent (router, switch, server Unix) yu cu mt s thng tin.

Cc thng tin ny c trm qun tr lu tr, phn tch v hin th. Trap cho

php agent thng bo cho trm qun tr nu c iu g vt khi phm vi

cho php xy ra. Khi nhn c trap, ty theo thng tin m trap cung cp,

trm qun tr s thc hin mt s thao tc c cu hnh t trc. Chng

hn, nu ng T1 kt ni ra Internet c s s, ngay lp tc router gi trapcho trm qun tr, khi trm qun tr c th thc hin hnh ng nh thng

bo li cho ngi qun tr.

Thc th th hai l agent, l mt phn mm nh chy trn thit bc qun

tr [SnmpFAQ]. N c th l mt chng trnh c l p nh mt tin trnh

daemon trong Unix, c th l thnh phn tch hp bn trong hiu hnh

nh IOS ca router Cisco hay l h iu hnh c p thp iu khin UPS.Agent cung cp thng tin v rt nhiu hot ng ca thit b. V d, agent

trong router c th theo di trng thi up/down ca cc interface. Trm qun

tr c th truy vn trng thi ca cc interface ny v thc hin cc hnh

ng tng ng nu interface down. Hoc l nu agent c cu hnh c


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kh nng nhn bit mt s s kin xu, agent c th gi trap n trm qun

tr, ni m cc tc v tng ng sc thc hin. Mt vi thit b. Hnh

II.1 minh ha mi quan h gia trm qun tr v agent.

Hnh II.1 Mi quan h gia manager v agent

Ch l trap v thm d c th xy ra ng thi. Khng c hn ch g v

thi im trm qun tr c th thm d agent v thi im agent gi trap

M hnh SNMP ca mt h thng qun tr mng bao gm b thnh phn

trng yu (cc thnh phn ny c m tHnh II.2):

Trm qun tr;

Thc th b qun tr (node hay Network Element - NE)

Csthng tin qun tr giao thc qun tr.

Vic qun tr mng c thc hin bi cc trm my tnh qun tr. Cc my

tnh ny s dng cc phn mm qun tr c nhim v qun l mt phn hoc

ton b cu hnh ca mng theo yu cu ca cc ng dng qun tr hoc cc

nh qun tr mng. Cc phn mm ny c th c giao din hc cho php

cc nh qun tr theo di trng thi ca mng v thc hin cc thao tc cnthit khi c yu cu.

Cc im qun tr (NE) c th l cc trm lm vic, cc thit b nh

tuyn, cu hoc chuyn mch hoc l bt k mt thit b no c kh nng


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trao i d liu v trng thi ca mnh vi th gii bn ngoi. c th thc

hin c cc chc nng b qun l, cc NE phi c c cc tnh nng c

bn ca mt SNMP agent, thc cht l mt modul phn mm c chc

nng lu tr v cp nht cc thng tin qun tr ca thit b cng nh c khnng gi cc thng tin n cho trm qun tr khi c yu cu.

Cu trc ca cc thng tin c xc nh bi thnh phn C s thng tin

qun tr (Management Information Base - MIB).

Mi mt h thng trn mng duy tr mt MIB phn nh cc trng thi ca

cc ti nguyn cn qun tr trong h thng .

Hnh II.2 Cc thnh phn c bn ca SNMP

Vic trao i d liu gia Manager v Agent c thc hin trn giao thc

SNMP [ietf]. Giao thc ny cho php cc thc th qun tr gi cc n Agent

cc truy vn v trng thi cc ti nguyn (cn gi l cc i tng). Cc itng ny c nh ngha trong MIB ca cc agent v c thc thay i

khi c yu cu. SNMP cung cp ba tc v cbn nh sau:


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Get: Trm qun l yu cu nhn gi tr ca mt hoc nhiu i tng

qun l (MO) t trm b qun l;

Set: Trm qun l yu cu thay i gi tr ca mt hoc nhiu i

tng qun l (MO) ti trm b qun l;

Trap: Trm b qun l gi thng tin v trng thi ca mt i tng

qun l khi c mt bin c c nh ngha trc xy ra

Theo quy nh ca giao thc SNMP, Get bao gm 2 tc vGetRequestv

GetNextRequest, trong :

GetRequest: ly gi tr ca mt hoc nhiu bin GetNextRequest: ly gi tr ca bin k tip

T phin bn SNMP v2, c thm mt tu chn na c a vo, l

GetBulkRequest. Cu lnh ny c su dng chnh ly mt lng ln d

liu dng ma trn

Bn cnh , SNMP cn nh ngha cc tc v khc nh:

GetResponse: tr v gi tr ca mt hoc nhiu bin sau khi pht lnh

GetRequesthoc GetNextRequest, hoc SetRequest.

InformRequest: Cho php cc trm qun tr gi thng tin dng trap

n cc trm qun l khc (t SNMP v2)

Trong mng TCP/IP, SNMP l mt giao thc hot ng tng ng dng v

s dng giao thc UDP. Do , SNMP l mt giao thc phi kt ni, tc lgia manager v agent khng c s duy tr kt ni trong sut qu trnh trao

i d liu.


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Hnh II.3 l mt minh ha ca giao thc SNMP v cc ng dng SNMP

trong kin trc mng, trong , network-dependent protocols c th l

Ethemet, FDDI hay X.25, vv

Hnh II.3 SNMP trong m hnh mng

II.1.3. Cng dch v v dch v truyn ti phi hi p

SNMP c thit k d dng trn cc dch v phi kt ni [SnmpFAQ].

Nguyn nhn dn n quyt nh ny l do SNMP c thit k c th

duy tr c lin lc trong cc trng h p xut hin li thit b hoc li

mng.

Nu SNMP s dng cc loi dch v hng kt ni (connection-oriented),vic mt kt ni s gim hiu nng trao i d liu ca SNMP. Chnh v l

do , SNMP s dng giao thc UDP (User Datagram Protocol) trong kin

trc TCP/IP. Trong m hnh OSI, SNMP cng c c h trbi dch v

truyn vn phi kt ni (Comectioless Transport Service). Cc phn on


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UDP c truyn i trong cc gi tin IP. UDP header c bao gm ca ch

ngun v a chch, cho php cc thc th SNMP nh danh a ch ca

nhau. Cc thc th SNMP ti p nhn cc gi tin n trn cng UDP 116

ngoi tr cc gi tin TRAP. Trm qun l nghe cc gi tin TRAP trncng 162.

Trong mi trng SNPM, cc gi tin khng nn c di vt qu 484 byte

[ietf]. Tuy nhin, cc thc th vn nn chp nhn cc gi d liu ln hn nu

nh h thng cho php.SNMP s dng User Datagram Protocol (UDP) lm

giao thc tng giao vn truyn d liu gia manager v agent v rt

nhiu l do. Th nht v UDP l giao thc n gin, khng lin kt nn :

Gi tin c kch thc header nh, thch hp vi truyn thng tin qun

tr;

Khng tn thi gian v cng sc thit lp, duy tr v ngt lin kt;

Khng tn bng thng ca mng;

Nhiu thit bc qun tr c ti nguyn CPU, b nh rt hn ch,nn ch c th ci t UDP lm giao thc tng giao vn.

Ngoi ra, UDP khng i hi tin cy. SNMP c thit k thng bo khi

c li xy ra v nu mng khng bao gili th ta cng khng cn thit phi

gim st. S l mt tng ti trong trng hp mng xy ra tc nghn hay

b li, ta li c gng truyn i truyn li m bo tnh tin cy nh ca

TCP. iu ny ch lm cho mng cng tc nghn hn.

Tuy nhin khng tin cy cng l mt vn ca UDP. iu ny i hi cc

ng dng SNMP phi x l trng hp gi tin b mt v truyn li nu cn.

Cng vic ny thng c thc hin mt cc n gin vi timeout. Trm

qun tr gi mt gi tin yu cu ti agent v chi tr li trong mt khong


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thi gian c thit lp trc gi l timeout. Nu sau thi gian timeout, trm

qun tr khng nhn c gi tin tr li t agent, n c th gi s rng gi

tin ny b mt v truyn li yu cu nu cn. S ln truyn li cng c th

c cu hnh trc. Ta c th thy rng khng tin cy khng phi l vn thc s ca UDP. Trong trng hp ti nht trm qun tr gi i mt yu

cu v khng bao ginhn c tr li. Tng t vi trap, nu agent gi i

mt trap v n khng n ni nhn, trm qun tr cng khng c cch no

bit c trap c gi i hay cha v agent cng khng th bit c

trap c n ch hay khng. Do vy thm ch agent cng khng cn truyn

li trap.

SNMP s dng cng UDP 161 truyn v nhn yu cu v cng 162

nhn trap t thit bc qun tr. Cc cng ny l mc nh, cc sn phm

SNMP thng cho php ngi s dng thay i cng v l do an ninh. V d

cng nhn trap ca manager c thi thnh 1999, khi agent cng phi

c cu hnh gi trap n ng cng ny.

II.1.4. SNMP community

SNMP s dng khi nim community l mt xu dng chung thit lp

mi quan h tin cy gia manager v agent. C ba loi community l : read-

only, read-write v trap. Nh tn gi ch ra, ba community ny cho php

gii hn thc hin ba cng vic. Read-only ch cho php c m khng c

thay i ni dng, chng hn ta c thc s lng gi tin truyn qua mt

cng ca router nhng khng c php thay i gi tr ny. Read-write cho

php c v thay i gi tr, do vy c thc gi tr mt bin m, thit lp

li gi tr ny, thm ch thay i bin trng thi ca mt interface hay thay

i cc cu hnh ca router. Community trap cho php manager nhn trap

t agent.


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V bn cht community chnh l mt khu, c manager v agent u s dng

ba xu ging nhau t tn cho 3 loi community ny. Hu ht cc hng

u s dng xu mc nh l public cho community read-only, private cho

community read-write. Theo gi tr mc nh ny, khi manager mun cgi tr ca mt bin, manager trnh xu public trong gi tin yu cu. Agent s

kim tra xu public v xc nh l trng vi community read-only, nh vy

manager c community cho php c gi tr. Tuy nhin agent cn phi thc

hin xc thc manager v xt n kh nng cho php truy cp da trn MIB

ca bin mi quyt nh l manager c th c gi tr ca bin hay

khng. V community c bn cht l mt khu nn cn thay i gi tr mc

nh. Khi cu hnh SNMP agent, ta phi cu hnh a ch ni nhn trap.

Thm vo , v SNMP community c gi i di dng thun vn bn, ta

nn cu hnh agent gi trap authentication-failure khi ai c gng truy vn

thit b vi mt community khng chnh xc.

Do s dng community nh l mt khu nn SNMPv1 l giao thc rt yu

v bo mt. Cc gi tin c gi i di dng thun vn bn nn khng

chng c kiu tn cng bng cch nghe ln sniffer.

SNMPv2 c gng gii quyt vn ny da trn cc cch tit cn cht ch

hn. Mt phin bn gi l SNMPv2 party-based tip cn theo hng: tuy

tng yu cu v xc thc v tnh mt m c th s dng cc knh khc nhau

trao i thng tin. Hnh 2.3. minh ha 3 knh vi cc yu cu v bo mt

khc nhau bng cch thay th community (chia s dng chung gia tt c

cc bn tham gia) bng party (chia thnh nhiu nhm, mi nhm trao i

theo cch thc ring). Knh th nht s dng truyn s liu khng quan

trng gia A v B, do vy s dng cp Party 1.A v Party 1.B c tnh cht

m- open. Knh th hai c v thay i cu hnh thng thng, yu cu


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c xc thc nn s dng cp Party 2.A v Party 2.B c tnh cht xc thc

authenticated. Knh th ba truyn cu hnh rt quan trng, yu cu phi bo

mt nn s dng c p Party 3.A v Party 3.B c tnh mt. Tuy nhin, vi

nhiu n lc tng cng bo mt trong SNMP dn ti ba phin bnkhng tng thch vi nhau l: SNMPv2p hay SNMPv2 party-based,

SNMPv2u hay SNMPv2 user-based v SNMPv2*. Cc phin bn ny

tht bi trong vic tm c s h trca cc nh sn xut v dng li bn

tho, ri chuyn sang qu kh. Cui cng, mt s tha hip c thc hin

v kt qu l chun SNMPv2c hay SNMP community-string-based. y l

mt bc tt li khi quay li s dng community nh SNMPv1, tuy nhin

chun ny li c h trca IETF cng nh cch nh sn xut. Trong ti

liu ny, khi ni n SNMPv2 l m ch SNMPv2c. Vn v bo mt ch

c gii quyt trit ch khi xut hin phin bn SNMPv3.

SMNPv3 ra i ch yu gii quyt vn bc xc v bo mt trong hai

phin bn trc [Stallings 98]. Phin bn ny khng c s thay i v giao

thc, khng c thm PDU mi, ch c mt vi quy chun mi, khi nim v

thut ng mi, cng khng nm ngoi vic lm tng tnh chnh xc

[Stallings 98]. Thay i quan trng nht trong SNMPv3 ny l s dng khi

nim SNMP entity thay cho c manager v agent. Mi SNMP entity gm

mt SNMP engine v mt hoc nhiu SNMP application. S thay i v

khi nim ny quan trng ch thay i v kin trc, tch bit hai phn ca

h thng SNMP, gip cho vic thc hin cc chnh sch bo mt. im quan

trng l SNMPv3 vn tng thch ngc vi cc phin bn trc.


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II.2. Cu trc thng tin qun tr(SMI) v csthng tin qun tr(MIB)

manager v agent c th trao i thng tin cho nhau th gia manager v

agent phi c nh ngha v khun dng d liu trao i chung.

Cu trc thng tin qun tr (Structure of Management Information-SMI)

c nh ngha trong RFC 1155 xc nh phng php cbn nh danh

cc i tng c qun tr v hnh vi ca chng [perkins]. Agent shu

danh sch cc i tng n gim st. Cc i tng ny c th l trng thi

hot ng (up/down/testing) ca mt interface ca router, s gi tin

truyn/nhn ca interface Danh sch ny cng cung cp thng tin m trm

qun tr c th s dng xc nh trng thi ca thit b cha agent.

Lu l SMI ch l c php nh ngha cc i tng c qun tr, cn

cc i tng c qun trnh ngha bng SMI gi l C s thng tin

qun tr (Management Information Base-MIB. MIB c thc coi l cs

d liu v cc i tng c qun tr m agent gim st. Tt c trng thi

hay thng tin thng k c th truy nhp bi trm qun tru c nh

ngha trong MIB.

Phin bn u tin ca SNMP a ra MIB-I nh ngha trong RFC 1066,

Phin bn tip theo (MIB II) c a ra vo nm 1991 (RFC 1213 ) cng

vi SNMPv2 b sung thm danh sch cc cc thng tin c bn, bt buc

phi c i v c chun ha trn mi thit b tng thch SNMP.

MIB c cu trc dng hnh cy [perkins]. Trong cu trc ny, tt c cc

bin SNMP hay cc i tng c m t di dng cnh v l v c t

tn theo kiu OBJECT IDENTIFIER (OID) ca ASN.1. Cc i tng qun

l c tp hp li thnh cc nhm lin h logic vi nhau tnh t gc (root).

Tim root, ta s c cc cnh tip theo mc 1: iso (l), ccitt (0) and joint-


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iso-ccitt (2), trong , iso nhnh theo quy nh ca t chc International

Organization for Standardization, ccitt l ca Intemational Telegraph and

Telephone Consultative Cornmittee, v joint-iso-ccitt ginh cho cc quy

nh c qun l bi c hai t chc ISO v CCITT [ietf].

Mt agent c th ci t nhiu MIB, nhng tt c cc agent u phi ci t

mt MIB c bit gi l MIB-II (RFC 1213). Chun ny nh ngha nhng

rt nhiu thng tin chung v h thng (v tr ca thit b, ngi lin h), v

s liu thng k ca interface ( tc , MTU, lng octet gi, lng octet

nhn). Mc ch ca MIB-II l cung cp cc thng tin qun tr chung v

TCP/IP. MIB-I l phin bn u tin nhng t khi MIB-II pht trin n, n khng cn c s dng na. c th gim st c nhng vn c

th lin quan n cc cng ngh mng khc nhau, cc tnh nng c bit ca

cc hng khc nhau th agent v manager phi c ci t cc MIB tng

ng. Chng hn, mt s bn tho v nghc a ra qun tr cc

cng ngh nh Frame Relay, ATM, FDDI v cc dch v nh email, DNS

:

ATM MIB (RFC 2515)

Frame Relay DTE Interface Type MIB (RFC 2115)

BGP Version 4 MIB (RFC 1657)

RDBMS MIB (RFC 1697)

RADIUS Authentication Server MIB (RFC 2619) Mail Monitoring MIB (RFC 2789)

DNS Server MIB (RFC 1611)


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Ngoi ra, mt im rt mna ca SNMP l cc hng sn sut v c nhn

u c thnh ngha cc MIB cho ring mnh. V d, mt agent trong mt

routerc ci t MIB-II (bt buc) v cc MIB cho cc loi interface m

n c (nh RFC 2515 cho ATM v RFC 2115 cho Frame Relay). Ngoi ra,router ny cn c thm mt s chc nng mi rt hu ch trong qun tr m

cha c cp n trong cc MIB chun no, do vy nh sn xut nh

ngha MIB ca ring mnh, ci t cc i tng c qun tr cho cc chc

nng mi ny. C rt nhiu cc li MIB, nhng mi agent chc h tr

mt s MIB, do vy trm qun tr ta cng ch cn ci t cc MIB cn

thit.

II.2.1. Nhm h thng trong MIB II

Thng tin trong nhm h thng c ngha rt quan trng trong qu tr mng.

Nh m t trong RFC 1213, nhm h thng a ra cc thng tin v h

thng qun tr. Nhm ny bao gm by i tng (xem Hnh II.4 NhmCu

trc ca MIB). Nu khng c cu hnh cha cc thng tin ny th agnt

s tr v gi tr di bng 0.


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Hnh II.4 NhmCu trc ca MIB

Bng II-1 Khun dng mt si tng

i tng Khun dng Truynhp

M t

SysDescr Displaystring(size 0 ... 255)

RO Tn, phin bn ca h thng

SysObjectID OBJECTIDENTlFIER

RO Tn nh sn xut, hoc nh danh ca nh qun trphn on mng

sysUpTime TimeTicks RO Thi gian tnh t khi phn qun tr mng c khing

syscontact Displaystring(size 0 ... 255)

RW Thng tin v ngi qun tr thit b

SysName Displaystring(size 0 ... 255)

RW Tn ca ngi qun tr

SysLocation Displaystring(size (0 ... 255) RW Vtr, n

i

t thit b

SysServices INTEGER(0 127)

RO M t cc dch v m thit b cung cp

* RW - c/Ghi (Read & Write) RO Chc (Read Only)


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II.2.2. Nhm cc t chc trong MIB-II

Trong hnh trn, chng ta thy nhm cc i tng t chc - enterprise

c xp di nhnh Private. Nhm Enterrprise c s dng cho

php cc t chc (nh sn xut) cung cc cc h thng mng c thng kcho cc sn phm ca mnh v cng b cc nh qun tr mng c th s

dng chng trong t chc mng ca mnh.

Cc cnh trong nhm enterrprise c s dng cho cc t chc ng k

cc OID theo mc ch ring ca t chc .

Nhiu t chc t to lp cho ring mnh mt MIB nh l Proteion, IBM,

CMU, Cisco vv

Bng II-2 Tn ca cc t chc v OlD

Tn ca t chc OIDD phng 1.3.6.1.4.1.0

Proteon 1.3.6.1.4.1.1Cisco 1.3.6.1.4.1.9 NSC 1.3.6.1.4.1.10 Novell 1.3.6.1.4.1 23

Sun Microsystems 1.3.6.1.4.1.42

Mi mt MIB ca cc t chc cng c nh ngha theo chun SMI v

ASN.1. V d: file nh dng CISCO-SMI.my ca hng Cisco System Inc c

dng nh sau:

ciscoProducts OBJECT IDENTIFIER ::= { cisco 1 )

-- OBJECT-IDENTIYStatus: mandatoryDescr:

ciscoProducts is the root OBJECT IDENTIFIER from which sysObjectIDvalues are assigned.Actual values are defined in CISCO-PRODUCTS-MIB.

local OBJECT IDENTIFIER ::= { cisco 2 )


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-- OBJECT-IDENTITYStatus: mandatoryDescr:

Subtree beneath which pre-10.2 MIBS were built.

II.2.3. Nhm giao din (interface trong MIB-II)

Cc thng tin quan trong c cha trong nhm giao din (interface) nh l

s lng cc giao din vt l, kiu, loi giao din c lp t trong thit b

cng nh s lng cc giao din ang hot ng (up) cng nh s lng cc

giao din ang tt (down).

Hnh II-1 minh ha cy OID bn di nhm giao din v cc nhnh, l bndi

Bng II-3 Mt snh ngha ca cc OID

i tng khung dng truy nh p M tIfNumber INTEGER RO S lng cc giao din mngIfTable sequence of

ifEntry NA Danh sch ccim vo ca giao din

Iflndex SEQUENCE NA im vo ca mt giao din c cha cc itng l cc giao din lp di

IfOutOctets Counter RO Tng s octes c chuyn qua giao

din, k c cc k t khung


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Hnh II-1 Cu trc nhm cc giao din trong MIB-II

II.3. c t SNMP

Theo RFC 1157, giao thc qun tr mng c nh ngha l mt giao tip

tng ng dng, thng qua theo di hoc thay i cc bin (i tng

iu khin) trong MIB ca cc Agent.

SNMP cung cp 03 tc v cbn l: GET, SET v TRAP, thng qua , ccthit b qun l mng c th yu cu nhn, thay i cc ci cc gi triu

khin ca Agent cng nhc thng bo v cc s kin bt thng xy ra

ti thit biu khin.


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II.3.1. Khun dng ca SNMP

Trong khun kh ca SNMP, lin lc gia cc thc thc thc hin thng

qua vic trao i cc thng ip SNMP c biu din di dng cc gi tin

UDP trn nguyn tc m ha cbn ca ASN.1. Cc thng ip mang theomnh thng tin v phin bn SNMP hin ang s dng, community name

c s dng xc thc v mt trong nm kiu d liu

(GetRequestPDU, GetNextRequestPDU, SetRequestPDU,

GetResponsePDU, TrapPDU)

(1) SNMP message:

Version Community SNMP PDU

(2) GetRequest PDU, GetNextRequest PDU, v SetRequest PDU:

PDUtype RequestID 0 0 variable-bindings

(3) GetResponse PDU:

PDUtype RequestID ErrorStatus Errorindex variable-bindings

(4) Trap PDU

PDUtype Enterprise AgentAddr GenericTrap specific Trap time stamp Variable-bindings

Bng II-4 M t cc trng ca SNMP

Tn M tCommunity c s dng nh l mt dng mt khu xc thc cc gi tin SNMP.

t kha public thng c s dng mc nhErrorStatus Gi tr nguyn c s dng thng bo v trng thi li xut hin khi

x l mt yu cu. Cc gi tr c th l: noError (0) tooBig (l) noSuchName (2) badVaIue (3) readOnly (4) genEn(5)

ErrorIndex Gi trc s dng khi ErrorStatus khc khng m t b sung cc


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thng tin v liGenericTrap Gi tr nguyn m t s kin xy ra thit b. Chng c th l:

ColdStart(0); WarmStart(1) LinkDown(2) LinkUp(3); AuthenticationFailure(4) EgpNeighborLoss(5) EnterpriseSpecific(6)

SpecificTrap S kin xy ra khng nm trong quy nh ca nh sn xut

II.3.2. Cc lnh SNMP v trnh t thc hin

Nh chng ta bit, SNMP c 5 lnh c bn l: Get, Get-Next, Get-

Response, Set v Trap. Tng ng vi nm lnh l nm gi tin:GetRequestPDU, GetNexRequestPDU, GetResponsePDU, SetRequestPDU

v TrapPDU.

Khun dng ca chng nh c m t trong phn trc. Phng thc

vn hnh ca chng c m thnh sau:


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Hnh II.5 Chu trnh SNMP

II.3.3. Kin trc qun tr mng

Hnh II.2 a ra mt m hnh n gin trong qun l mng ni b. Tham gia

vo m hnh ch c hai thc thn gin l Trm qun l v thit bc

qun l (Agent). Tt nhin l c hai thc thu phi dng giao thc qun

tr mng lin lc vi nhau (SNMP) v thng tin cn gi l cc gi tr ca


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cc bin trong MIB. S thng th ca m hnh tnh ton phn tn ko theo

phong tro phn tn ha vic qun tr mng [Mazumdar]. Mt h thng qun

tr mng phn tn thng thng s c mt s trm lm vic tng tc vi

nhau thng qua lin mng, trong , cc trm lm vic ny sng vai trqun tr mng ca phn on mng , hoc ca n v (thc th) . Trong

m hnh ny, chng ta ta cng s thy c mt trm qun tr chnh lm nhim

v tng tc vi trm qun tra phng v trch nhim qun tr chnh s

c giao cho cc trm qun tra phng ny. Tuy theo cu hnh v yu

cu c th m Trm qun l trung tm c th lm vic trc tip vi cc

Agent mc thp hn.

Hnh II.6 Kin trc qun tr h thng phn tn thng thng

II.3.4. Nhng hn ch ca SNMPSNMP c thit k theo hng n gin ha cc tc v nn c mt s cc

im hn ch:

Ch c mt gi thng tin i vi tng yu cu, khng ph hp vi cc

mng phc tp, c nhiu s liu cn phi kim tra [Stallings 96]


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SNMP l giao thc phi hi p, ngha l agent khng th chc chn l

cc gi tin trap do mnh gi i n c ch. Bn trong nm thng

ip ca SNMP l cc nghi thc hi-p n gin (my trm gi yu

cu, my agent phn hi kt qu) nn SNMP s dng giao thc UDP.iu ny ngha l mt yu cu t my trm c th khng n c

my agent v hi p t my agent c th khng tr v cho my trm.

V vy my trm cn ci t thi gian ht hn (timeout) v cch pht

li [Stallings 96].

Tnh bo mt km, tn cng ng (community) c s dng nh l

mt khu xc thc cc thng i p SNMP [Stallings 98]. Qun lmng da trn SNMP c mc bo mt thp. V d liu khng m ha

v khng c thit lp c th ngng bt k truy nhp mng tri php

no khi tn community name v a ch IP b s dng gi yu cu

gi mo ti agent. Do , SNMP ph hp vi m hnh quan trc hn

l vi m hnh iu khin.

Ch c cc cu d liu n gin. Khng ph hp vi cc yu cu vgi tr hay kiu ca i tng

Khng h trgiao tip t trm qun l n trm qun l

Khng h trcc lnh thc thi tc thi.

Qun l mng da trn SNMP c mc kh chuyn thp gia cc kin

trc khc nhau. V cu trc thng tin qun l ca SNMP ch h tr

gii hn cc kiu d liu.

Khng thn thin.

Nhiu nhc im ny c khc phc hoc gii quyt trong cc phin

bn tip theo ca SNMP (version 2, 3)


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Chng III. Qun tr mng trn web vi CGIv CORBA

III.1. Chun CGI

CGI l vit tt ca t ting anh Common Gateway Interface. CGI l mt

giao din chun cho php trao i thng tin gia phn mm Web Server vi

cc chng trnh (ng dng) bn ngoi [Weinman].

Nguyn thu, Web server ch l mt phn mm x l cc yu cu http n

thun nhn c v tr v cc trang html vi cc ni dung tnh. Do s pht

trin ca mng v nhu cu tng tc cao ca ngi s dng i vi ccngun thng tin trn web, thng tin c tnh cht ng nh truy vn cs

d liu

III.1.1. CGI - s m rng ca HTTP

Chun CGI c a ra v m t bi cc tc gi chnh ca HTTP server:

Tony Sander, Ari Luotonen, George Phillips v John Franks. Ban u dch

v ca cc HTTP server kh b gii hn v chng ch c th tr v cho cctnh duyt web cc ti liu HTML cnh (tnh). p ng cc yu cu

ngy cng tng v cc tnh nng ca web nh l cung cp cc thng tin cp

nht (ng) cho trnh duyt client, cc tc gi nu trn a ra mt phng

php mi, m rng cc dch v v nng lc t gc r ca cc Web server.

chnh l chun CGI [Weinman].

CGI l mt giao din n gin ginh cho vic chy cc chng trnh bnngoi (CGI script - cc kch bn CGI) bn di nn HTTP server. Khi c

mt yu cu ca khch hng c gi n n Web Server thng qua trnh

duyt Web, Web Server s gi ti CGI gateway. CGI s thc hin cng vic


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ca mnh v chuyn thng tin v cho Web Server di dng chun HTML

v Web server s gi tip cc thng tin ny v cho khch hng [Tittel96].

Sau y l tm lc bn bc x l ca CGI:

Bc 1: X l d liu c truyn t Client ti Server.

Bc 2: Server s hng cc yu cu m Client gi ti n cc

chng trnh CGI thc hin.

Bc 3: Gi li cc d liu v kt qu m chng trnh CGI thc hin

trli cho Server.

Bc 4: Server gi li d liu m n nhn t chng trnh CGI choClient.

III.1.2. Cc c trng ca CGI

CGI cho php bn m rng cc chc nng ca Web server, l mt phng

thc cho HTTP server trao i thng tin vi chng trnh ngi dng.

Trn quan im l thuyt: CGI s x l d liu a vo thng qua browser

v tr li thng tin cho ngi s dng [Tittel96].

Trn quan im thc hnh: CGI l trnh giao din cho php ngi lp trnh

vit chng trnh thc hin truyn thng vi Server [CGI201].

CGI cung cp cch gii quyt vn mt cch d dng v n gin.

Giao thc CGI c nh ngha theo mt chun, n cung c p cch

truyn thng vi Web server.

S dng CGI bn khng cn dng nhiu tri thc c bit, c th vit

chng trnh vi bt k ngn ng my tnh no thc hin giao tip

v truyn thng vi Web server [CGI201].


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S truyn t ca CGI l da trn cc chun vo ra.

III.1.3. M hnh quan h Client/Server s dng CGI

Thng thng, mt h thng khch/phc vc gi l h thng quan h

cp 2. Trong h thng ny, giao din ngi dng v cc quan h logic nm

v bn th nht. Cc chc nng phc v cng vic v d liu trn server

thuc v bn th hai. c thc xem l cc h nn (platform) v cc h

thng mng phn cng cng nh phn mm lin kt khch/phc vc gi

l cc trung gian.

Client Server

Operating System

External program

Internet

Yu cu Yu cu

Yu cu

Yu cu

Tr liTr liTr li

Tr li

Hnh III-1 Chu trnh thc hin mt CGI request

CGI to ra cu ni gia web server v cc dch v internet khc nh l cp

nht s liu cho cc server mng back-end hoc qun l my tnh khc trong

mng ng sau web server. Trong trng hp ny, CGI hot ng nh mt

trung gian (middleware) gia web server v csd liu bn ngoi hoc ccdch v thng tin khc [CGIPerl]. Vi s tham gia ca CGI, chng ta c

quan h tay ba trong kin trc Client/Serverc cu thnh bi c s d

liu bn ngoi v cc h thng dch v thng tin. Hnh III-2 m t kin trc

ba lp mi ny. Thng thng, lp u tin l mn hnh ca ngi s dng.


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Lp gia c to thnh bi cc i tng server, l cc d liu cnh v

cc khi logic thc thi. Lp th ba l cc dch v truyn thng thng thng.

Trong Hnh III-2 , lp gia l web serverc tng cng thm bi

dch vng dng CGI .

Cc nh cung cp dch v mng thng s dng cng ngh ny kt ni

cc trnh duyt web ca hn cc thc th qun tr theo di tnh trng

ca cc thit b. Cng ngh ny c ng dng trong web site ca Bay,

cho php cc trnh duyt c truy nhp vo cc ng dng qun l Optiviti.

III.1.4. Cch thc v phng php truyn d liu trong CGI

Vi vic s dng nhiu k thut khc nhau client c th truyn i s hoc

d liu ti chng trnh gateway thng qua HTTP server. Chng trnh

gateway thay v phi bt u vi mt chng trnh tnh (static program)

thi im hin ti th n sc thay th vi mt thc thng (dynamic

entity) tin hnh tr li ti ngi s dng cui cng.

C bn phng php ch yu server lin lc vi cc CGI script. Ba

phng php u tin l cch cc CGI script nhn c thng tin t

server v cch cui cng l cc CGI script gi thng tin cho server.

Sau y, chng ta s ln lt xem xt cc phng php : phng php

bin mi trng (Enviroment variables), tham s dng lnh (Command

Line) bng hoc bng dng nhp chun (Standard input).

III.1.4.1 Phng php thnht - Bin mi trng

Cc bin mi trng l cc bin c thit lp bi phn mm server v c

thc truy nhp t cc chng trnh bn ngoi. Cc bin ny cha ng

cc thng tin v server, chng trnh bn ngoi v yu cu ca khch hng.

Xem bng


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Bng III-1 Cc bin mi trng chun

Tn bin M tAUTH_TYPE kiu xc thc truy nhpCONTENT-LENGTH ln ca cc d liu (thc th) tnh theo byteCONTENT-TYPE nh kiu MIME ca thc th: application/octet-stream,

text/pain, GATEWAY-INTERFACE

Phin bn CGI ca server

HTTP_(string) D liu header ca khchPATH-INFO ng dn mrng cc CGI scrript bin dchPATH-TRANSLATED nh x to n ng dn thc trong h thng fileQUERY-STRING Xu tm kim c vit di dng chun URLREMOTEADDR a ch IP ca pha a ra yu cuREMOTEHOST Tn min y ca pha a ra yu cuREMOTEINDENT D liu phn bit v pha kt ni n server

REMOTE-USER nh danh ngi dng do pha client giREQUEST_METHOD Yu cu ca pha client (GET hay l POST)SCRIPT-NAME Univeral Resource Identifier (URI) - ng dn nhn bit

mt CGI script.SERVER-NAME Tn server, phn tn my ch trong URI hoc DSNSERVER-PORT Cng dch v nhn yu cuSERVER-PROTOCOL

Tn v phin bn ca giao thc yu cu

SERVER-SOFWARE Tn v phin bn ca phn mm phc v tr li yu cu

III.1.4.2 Phng php thhai Dng lnh

Phng php ny thng c s dng cho cc truy vn HTML ISINDEX.

Thng tin c thc chuyn cho cc chng trnh bn ngoi thng qua cc

tham s dng lnh khi chng trnh c gi ( chy).

III.1.4.3 Phng php ba dng dliu vo chun (standard input)

Khi pha client s dng phng php POST hoc PUT gi cc yu cu

n cc chng trnh bn ngoi, thng tin sc server chuyn cho cc

chng trnh bn ngoi thng qua dng nhp chun (standard input). Nu s

dng GET, d liu s c a vo bin mi trng QUERY_STRING.

Server cng s thit l p bin CONTENT_TYPE v CONTENT_LENGTH


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tng ng vnh dng kiu d liu MIME v ln ca d liu (tnh bng

byte).

III.1.4.4 Phng php dng dliu ra chun (standard input)

Khi chng trnh bn ngoi sau khi thc hin yu cu, thng tin s gi d

liu ngc li cho web server ( web server chuyn ti p cho trnh duyt

client) thng qua dng d liu ra chun (standard output). Cc d liu ny

phi c vit khun dng HTML.

III.1.5. Lp trnh CGI

Chng trnh CGI gateway c th vit bng mt ngn ng lp trnh no ,

chng hn nh C/C++, Visual Basic, Perl y l mt chng trnh thc hin

c (executable). Mi khi c yu cu thc hin CGI t pha khch hng th

my ch (server) s to mt tin trnh (process) mi cho gateway v truyn

thng tin t khch hng cho tin trnh ny.

Khi lp trnh CGI, c hai nguyn tc sau cn phi c tun th:

1. Kt qu tr v cho Client (d liu hay text) phi c ghi ra dng d

liu ra chun (Standard output, STDOUT);

2. Cc d liu ra cn phi c bt u bng chui Content-type v

mt dng trng

Sau y l mt v d v mt on m chng trnh CGI bng C:

#include

void main(void)

{

printf(Content-type: text/html\n\n);

printf(Hello World!);

}


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Nh cp phn trc, chng trnh chn gin gi thng i p ra

STDOUT theo ng yu cu ca CGI: mt dng nh kiu MIME type:

text/html v tip theo l mt dng trng.

III.1.6. Ci t cc chng trnh CGI

Sau y l mt s bc cbn ci t mt chng trnh CGI trn server

v cch thc hin chng

Yu cu u tin l ngi s dng phi c quyn truy nhp web server v c

quyn ghi vo th mc c tn l cgi-bin, ni t cc chng trnh cgi. Cc

chng trnh CGI s c web server gi ra thc hin t ng khi web

server nhn c yu cu t pha ngi s dng.

Th hai, chng trnh CGI cn phi chy c v c th truy nhp t pha

ngi dng bnh thng.

i vi cc chng trnh dng ngn ng Perl, phn mm Perl cng phi

c ci t trong mng [Tittel96].

i vi cc chng trnh s dng Java, trong th mc cgi_bin cn phi cmt file thc thi vi dng lnh:

java ProgramFileName

trong ProgramFileName l tn ca java class. Trong cc h thng unix,

file ny c thc vit di dng ngn ng kch bn (shell script). i vi

h windows, file ni trn c th l mt file batch. Trong mi trng hp,

phn mm h trjava phi c ci t trong cng mt th mc [CGI2].

Trn y l cc bc cn thit ci t cc chng trnh CGI. Sau cc

bc ci t cn thit, cc chng trnh CGI sc gi ngay khi c yu

cu t cc applet code trong trnh duyt client.


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III.1.7. M hnh qun tr mng ba bn s dng Web - CGI

Trn Hnh III-2 l s tng tc ca mt h thng qun tr mng qua web

s dng CGI. Nh cp phn trc, web server s chuyn cc thng

tin cho cc chng trnh CGI back-end thng qua cc bin mi trng, dngnhp d liu chun v s yu cu thc hin cc chng trnh (thng l cc

chng trnh SNMP server) ny ty theo yu cu c th. Cc chng trnh

ny c khi chy v sc cc d liu t dng nhp d liu chun. Sau

, chng trnh ny s lin h vi cc SNMP agent ly cc thng tin cn

thit. Sau khi hon thnh, chng trnh s tr thng tin li cho web server

di dng m HTML thng qua giao din STDOUT. Cui cng, web server

s tr li file HTML ny cho Client.

Hnh III-2 M hnh web Client/Server ba bn s dng CGI


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III.2. Chun CORBA

CORBA l vit tt ca cm t Common Object Request Broker Architecture

- c a ra bi t chc qun l i tng (Object Management Group -

OMG) vi mc ch to ra mt mi trng (khung) lm vic chung cho cc

ng dng hng i tng [Rosenberger]. Chun ny nhm ti mt mi

trng tnh ton phn tn khng ng nht v to ra mt c ch lin lc

chun gia cc i tng trong mi trng khng ng nht

[Rosenberger].

III.2.1. Gii thiu chun CORBA

CORBA c a ra nhm gii quyt hai vn cbn nht m ngnh cng

nghip phn mm phi i mt ngy hm nay, l nhng kh khn trong

vic pht trin cc ng dng Client/Server v cch thc tch h p cc h

thng sn c (k tha chng) cng nh yu cu tng thch ngc ca

cc h thng s pht trin .

Tng t nh cc RFC (Request For Comments) ca IETF (Intemet

Engineering Task Force, OMG cng a ra cc yu cu kin ngh (Request

For Proposals - RFP) i vi CORBA. T "Common" trong COBRA th

hin s h p nht ca hai kin ngh API quan trng. Mt kin nghn t

HyperDesk and Digital, h tr API ng; kin ngh khc do Sun v HP

(Hewlett Packard) h trAPIS tnh. Kt qu l CORBA c tinh chnh v

tha hng c hai tnh nng ca hai kin ngh nu trn [CORBA14] .

Theo OMG, CORBA l gii php cho vicphi c c kh nng tng tc

gia cc h thng phn cng phn mm ang ngy cng pht trin c vs

lng v chng loi ngy nay ("to the need for interoperability among the

rapidly proliferating number of hardware and software products available

today" [OMG].


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III.2.2. S lc v lch s CORBA

OMG l mt t chc chuyn ngnh v v li, do 8 cng ty quc t thnh lp

thng 5 nm 1989, trong ng k l Hewlett-Packard v SUN. OMG p

ng ng nhu cu chung v c mt phng php lm vic kh khch quan,nn c hng ng mnh m. T ch ch c tm thnh vin ban u,

n nay OMG pht trin ln ti hn 800 thnh vin chnh thc.

Hot ng ca OMG nhm mc ch cung cp mt khung lm vic chung

cho cc ng dng hng i tng nhm thit lp mt khung cnh khi

nim chung v hng tip cn s vt phn tn, c th cho php cc h p

dng hng s vt, v sc pht trin trn nhng hiu hnh v thitb khc nhau, c th trao i vi nhau. Thnh tu ln nht ca OMG l

thit lp c kin trc qun l i tng (Object Management Architecture

- OMA) m CORBA l mt phn trong . Ni mt cch ngn gn, OMA

bao gm cc b phn trung gia x l yu cu trn i tng (Object Request

Broker - ORB), cc dch v vi tng (cn gi l cc dch v CORBA),

cc tin ch chung, cc giao din min (domain Interface) v cc i tng

ng dng. Vai tr ca CORBA trong OMA l qun l vic thc hin cc

chc nng ca ORB [OMG].

Ra i t thng 5/1989, CORBA c nhiu bc pht trin mnh m,

trong ng ch nht l hai phin bn 1.0 v 2.0 vi cc tnh nng t

ph.

CORBA 1.0

y l phin bn u tin ca CORBA, c gii thiu vo thng 12/1990,

tc l ngay sau khi t chc OMG c thnh lp. u nm 1991, phin bn

1.1 ra i, trong c a ra khi nim v ngn ngnh ngha giao din

(Interface Definition Language - IDL) v cc cng c API gip cho cc ng


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dng c th giao tip c vi cc ORB. Mt thi gian ngn sau, OMG

cng b phin bn 1.2 vi mt sc tnh b sung so vi cc phin bn

trc . C th coi cc phin bn 1.x l bc khi im quan trng cho

kh nng tng tc gia cc thnh phn i tng, cho php cc i tngtrn nhiu my c kin trc khc nhau, c vit bng cc ngn ng khc

nhau c th trao i c vi nhau.

CORBA 2.0

Cc phin bn 1.x cn thiu hon chnh v cha a ra c nhng quy nh

y v s tng tc gia cc thnh phn i tng. Mc d chng cng

a ra c cc chun cho ngn ng IDL v cho vic truy nhp ORB

thng qua mt ng dng nhng chng li mc phi mt hn ch cbn l

cha quy nh c cc giao thc chun cc ORB c th trao i c

vi nhau [TL_CORBA].Chnh v c hn ch ny m CORBA ORB ca mt

nh cung cp ny khng th trao i c vi CORBA ORB ca mt nh

cung cp khc, t thu hp kh nng tng tc gia cc i tng trong

mi trng phn tn. khc phc hn ch trn, thng 12/1994, phin bn CORBA 2.0 ra i.

Trong phin bn ny, OMG a ra Giao thc chung gia cc ORB

(Internet Inter-ORB Protocol - IIOP) - y l giao thc chun gip cho cc

ORB ca cc nh cung cp khc nhau c th trao i c vi nhau. Chun

mi ny c ng dng trn cc mng c s dng giao thc TCP/IP. OMG

cng quy nh r rng tt c cc nh cung cp mun sn phm ca mnhhot ng c trong kin trc CORBA u phi ci t giao thc IIOP.

Ti p sau phin bn 2.0, OMG tip tc cng b mt s phin bn k tip:

CORBA 2.1 (12/1997), CORBA 2.2 v 2.3 (1998). Cc phin bn sau ny

tng bc pht trin v mrng cc u im ca phin bn 2.0 trc .


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CORBA 3.0

Corba 3.0 c chnh thc ra mt vo thng 10/2002. Mc d c thit k

khc gn nh, CORBA 3.x khng phi l mt tiu chun n m thc

cht l mt h cc tiu chun c thm vo chun 2.x [CORBA3.0]

V cbn, CORBA l mt cng ngh tch hp cc ng dng tnh ton phn

tn. Ht nhn ca cc h thng CORBA ORB che du cc chi tit

thnh phn mc di v h thng nh platform, mng, cho php cc

nh lp trnh tp trung chnh vo gii quyt cc vn ca mnh thay v vic

phi pht trin mt h thng h tng tnh ton phn tn [CORBA3.0].

Cng nh cc tiu chun cng ngh khc, CORBA cng phi t mnh pht

trin p ng c cc yu cu ngy cng cao ca nhu cu. Vic b sung

thm ba tnh nng chnh ca CORBA trong phin bn 3.0 nh Portable

Object Adapter - POA, CORBA Messaging, v Objects By Value cho php

p dng CORBA cho nhng lnh vc m trc y cn cha ph hp.

III.2.3. Tng quan v kin trc CORBA

Trong phn ny, chng ta s cp n cc thnh phn chnh ca CORBA:

B phn trung gian x l cc yu cu trn i tng (Object Request

Broker ORB): cu trc ca phn ct li ca kin trc CORBA.

Ngn ng nh ngha Giao din (Interface Definition Language

IDL) thnh phn cbn ca kin trc CORBA.

M hnh truyn thng trong kin trc CORBA (CORBAcommunication model) l gii cch thc hot ng ca cc i

tng CORBA trong kin trc mng my tnh.


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M hnh i tng trong kin trc CORBA, bao gm cc tham chiu

i tng v cc B iu hp i tng c bn (Basic Object

Adapters BOAs).

Khi nim v vai tr ca cc thc th Client v Server trong kin trc

CORBA.

Khi nim v vai tr ca cc client stubs v server skeletons trong

vic xy dng cc ng dng trong kin trc CORBA.

III.2.4. B phn trung gian x l yu cu trn i tng (ORB)

B phn trung gian x l cc yu cu trn i tng (Object Request Broker ORB) chnh l b phn cn bn cu thnh kin trc CORBA, cn c

bit n nh l object bus hoc th vin cc i tng o (main object

library) [OMG_ARCH] Sau khi c ORB, cc thnh phn khc khi mun trao

i thng tin vi nhau th khng cn phi kt ni trc ti p. Thay vo ,

chng ch cn giao tip vi ORB thng qua cc hm API ca CORBA. Cc

giao tc tip theo s do CORBA m nhn. C th, khi mt thnh phn ng

dng mun s dng mt dch vc cung cp bi mt thnh phn ng

dng khc, trc tin n cn c c mt s tham chiu ti i tng cung

cp dch v. Sau khi c c s tham chiu ny, n c quyn gi cc

phng thc ca i tng c tham chiu n v c th truy cp vo cc

dch v m n mong mun do i tng cung cp. Chc nng u tin

ca CORBA l gii quyt cc yu cu v tham chiu i tng, cho php

cc thnh phn i tng c th thit lp kt ni vi nhau (Hnh III.1)[OMG_ARCH]


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Hnh III.1 ORB gii quyt cc yu cu vi tng

d theo di, ty trv sau chng ta s quy c gi thnh phn ng

dng c yu cu s dng dch v l Client, cn pha cung cp dch vc

gi l Server.

Sau khi c c s tham chiu ti i tng cung cp dch v cn s

dng, Client c th bt u gi cc phng thc trn i tng ny. Thng

thng, cc phng thc trn i tng u cn c cc tham su vo v

tr v cc k quu ra nn chc nng tip theo ca ORB l nhn cc tham

su vo t pha Client, i chng sang mt khun dng ph hp c th

truyn ti c i tng c tham chiu xa thng qua mng my tnh.

Qu trnh ny c gi l tp h p (marshal). Sau , ORB li c trch

nhim thc hin mt s chuyn i ngc: n nhn cc gi tr tham su

ra c tr v v chuyn chng sang mt khun dng m pha Client c th

hiu c. Qu trnh ny c gi l phn tch (unmarshal). Xem HnhIII.2.


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Hnh III.2 Qu trnh marshal v unmarshal

Ton b qu trnh marshal v unmarshal c thc hin m khng cn c s

can thip ca ngi lp trnh. Pha Client ch vic a ra yu cu v mt

phng thc t xa v s nhn c cc kt qu tr v ging nh khi thc

hin cc phng thc trong lng n vy. Tt c cc cng vic u do ORB

m trch v trong sut i vi pha Client [OMG].

Nh vy, cc qu trnh marshal v unmarshal gip cho vic giao tip gia

cc thnh phn ng dng trong mng tr nn c lp i vi mi trng

(platform-independent). iu c ngha l mt ng dng chy trn h

Macintosh c th gi cc phng thc trn mt ng dng khc chy trn h

UNIX. Khng ch c vy, nhng s khc bit v phn cng cng khng gy

trngi g bi l ORB s tng thc hin cc s chuyn i nu thy cn

thit. C th ni mi s khc nhau v mi trng ca cc ng dng u

c ORB x l v gii quyt [CORBA].


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Mt ln na xin c nhc li rng ton b qu trnh marshal v unmarshal

u hon ton c thc hin bi ORB v hon ton trong sut i vi c

pha Client v pha cung cp dch v (Server). Ngi lp trnh cng tuyt i

khng c lin quan g ti cc qu trnh trn.

Nh vy, c th thng k tm tt cc chc nng ca ORB nh sau:

Nhn mt tham chiu i tng t pha Client, thay mt Client xc

nh v tr ca Server tng ng l ni s thi hnh dch v m Client

yu cu. (Lu rng vic lm th no c c tham chiu i

tng l thuc trch nhim ca pha Client).

Khi xc nh c v tr ca Server, ORB phi m bo rng pha

Server sn sng nhn yu cu.

B phn ORB pha Client c trch nhim nhn cc tham su vo

t Client, sau thc hin qu trnh marshal.

B phn ORB pha Server thc hin qu trnh unmarshal cc tham

s v chuyn chng cho Server x l. Trong trng hp c cc tham s tr v, ORB li tin hnh cc qu

trnh marshal v unmarshal ging nh trn.

Vai tr trung gian ca ORB c thc minh ha bng hnh v di y:

Hnh III.3 Vai tr trung gian ca ORB


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thy c li ch c c khi s dng ORB, chng ta hy xem xt

trng hp c N thnh phn Client/Server trong mi trng ng dng. Nu

khng s dng ORB, ta s cn phi nh ngha N2 giao din chng c th

lm vic c vi nhau (hnh a). Trong khi , s dng ORB, s giao dincn phi nh ngha ch l N. Cha k l khi khng c ORB, cc giao din

phi c ng b v ngn ng cng nh v h nn (platform)

Hnh III.4 Tng tc gia cc thnh phn qua ORB v khng qua ORB

Bn cht ca ORB l mt thnh phn phn mm chy gia cc my tnh

Client Server v cung cp cch lin lc gia chng [CORBA14]. ORB c

02 chc nng chnh:

Cung cp tham chiu n cc i tng m client yu cu

marshals v unmarshals cc tham si/n cc i tng

Trong CORBA, chng ta s dng tham chiu i tng xc nh i

tng trong ORB. C th xem ORB hot ng nh mt b su tp cc i

tng v ti nguyn mng, lin quan n cc phn mm ng dng, cho phpcc ng dng ny nh v v s dng chng trong mi trng ORB.


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Hnh III-3 M hnh gi yu cu qua Object Request Broker

Hnh III-3 minh ha mt yu cu c gi bimt client n mt i tng

thc thi thng qua mt ORB. Thc th Client gi mt yu cu thc hin

mt tc v trn i tng m khng cn phi bit n v tr ca i tng

cng nh cch thc thc hin tc v. ORB s c nhim v tm i tng

s thc hin yu cu, tp hp cc tham s cn gi n i tng cng nh

phn tch cc kt qu gi v ti tng .

Nh trnh by trn, marshallingl qu trnh dch cc tham s t pha

Client thnh khun dng ca d liu s c truyn i trong mng.

Unmarshalling l qu trnh ngc li ca marshall: chuyn i s liu t

mng sang khun dng m pha client c th hiu c [Rosenberger 98].

Trong CORBA, Client c th gi yu cu n server qua nhiu con ng:

thng qua IDL (Interface Definition Language) tnh hoc qua DII (Dynamic

Invocation Interface) Giao din yu cu ng. Ngoi ra, client cn c th

gi yu cu trc tip n ORB nh m t chi tit Hnh III.5


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Hnh III.5 Cu trc ca ORB

Cc IDL stub cung cp cc giao din tnh cho cc i tng phc v v ph

thuc vo i tng (tu theo loi i tng c th). Ni mt cch n

gin, IDL stub l mt on m nh c bin dch cng vi phn mmclient to cho client kh nng truy cp server.

Dynamic Invocation Interface (DII) cung cp phng thc pht hin ng

cc giao din server v c th yu cu truy cp cc i tng m thm ch

client cn cha c bit n (hoc cha tn ti) ngay t khi bin dch phn

mm client. Gi phi tr cho c tnh ny l mc phc tp b tng ln

ng k.V pha server, ni cha cc i tng thc thi, cng c cc thnh phn

(c gi l b khung - skeleton) tng ng vi hai giao din trn. l

static IDL skeletons v Dynamic Skeleton Invocation (DSI) tng ng vi

IDL stub v DII ca pha client.

Cc server skeleton ny cng l cc on m lnh nhc sinh ra khi bin

dch cc c t giao din IDL. Chng cung cp cc giao din tnh cho tngdch v, c server cung cp (export).

x l mt yu cu, on m thc thi i tng c th gi cc Object

Adapter v giao din ORB cho cc dch v thng qua ORB. Object Adapter


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qun l cc lo hnh dch v nh l sinh ra v thng dch cc tham chiu i

tng cng nh cc phng php yu cu [OMG_ARCH] .

qun l c cc i tng thc thi, server c th truy cp vo hai cs

d liu: interface repository (kho cha giao din) v implementation

repository (kho cha cc phng thc). Interface repository cung c p cc

i tng bn vng (persistent) c c ty v chnh l cc thng tin

IDL trong ton b tin trnh (run-time).

Implementation repository cha cc thng tin cho php ORB nh v v

kch hot cc phng thc ca i tng.

III.2.5. Ngn ngnh ngha giao din (IDL)

Ngn ngnh ngha giao din IDL (Interface Definition Language) l mt

thnh phn khc ca CORBA v c s dng nh ngha kiu ca cc

i tng bng cch c tc cc giao din ca n. L ngn ngc s

dng m t cc giao din gia cc i tng CORBA nhng IDL khng

phi l 1 ngn ng lp trnh theo ng ngha ca n m ch t gii hn

mc nh ngha cc giao din.

IDL khng phi l ngn ng th tc, n ch c thnh ngha cc giao tip

khng c phn ci t. N tng t nh phn header ca cc class trong

C++, phn header khng cha bt k ci t ca lp no nhng m tc

lp v giao din ca lp.

IDL hon ton khng ph thuc vo ngn ng s dng, ni cch khc IDL

c thc thc thi trong mt s ngn ng c tn ti nh x ngn ngn

n, v d nh Java, C, C++ v mt s ngn ng khc.

IDL hon ton ch l ngn ng m t nn cc chng trnh pha Client

khng nht thit phi vit bng IDL m c thc vit bng ngn ng bt


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k, nhng ngn ng phi c nh x vo IDL. IDL s c trch nhim

chuyn i d liu, kiu d liu mt cch tng thch gia cc ngn ng

khc nhau [TL_CORBA] .

Mt giao din bao gm mt nhm cc tc vc t tn (cc hm hoc l

phng thc) v nh, cc client c th yu cu chng c phc v.

IDL l mt loi ngn ngc t, n h trchnh t C++ cho khai bo hng,

kiu bin v tc v. Tuy nhin nh ni trn, IDL khng c cu trc th

tc v bin, t, n khng c cc cu lnh iu khin r nhnh nh if-else,

while

IDL c vit theo phong cch ca C++, h trnaming space, tin x l,

tha kn v a tha k (multiple inheritance) v tt nhin l c thm

mt s t kha h trm hnh tnh ton phn tn.

module tng t nh cc Java package

interface giao din ca CORBA, tng t nh Java interface

exception - tng t nh Java exception

attribute Cc bin thnh vin c to tng khi to(get i vi

cc thuc tnh chc (readonly attributes), get v set cho cc thuc

tnh bnh thng)

operations - tng t nh method trong cc ngn ng lp trnh khc

Cc kiu dliu n gin nh l short, unsigned short, char, ...

Cc kiu d liu c cu trc nh mng, array, sequence, struct,

enum

Sequence l kiu d liu tng t nh mng nhn cc thnh vin ca n c

kch thc khng ging nhau v c th thay i c trong qu trnh thc


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thi. Nh vy, seqquense c th xem l tng t nh bin kiu vector ca

Java, c mt s khc bit l cc thnh vin phi l cng c mt kiu, trong

khi Java cho php thnh vin l cc i tng c kiu khc nhau.

Sau khi khai bo xong file IDL, ngi s dng c th da vo b tin x

l (precompiler) bin dch cc file IDL sang ngn ngc s dng

hon thnh qu trnh thc hin.

on m sau y minh ha mt v d v file IDL

module Bank {

interface Account{

float balance();

};

interface AccountManager {

Account open( in string name);

};

};

V d trn a ra mt nh ngha v giao din Account v AccountManager.

T kha trong phng thc open c ngha l bin name s phi c

chuyn t pha client n server. Theo nh ngha ca IDL, cc tham s

trong cc phng thc phi c m ty l chng c chuyn t ph

client n server (in) hay l ngc li (out) hay l theo c hai hng (inout).

l mt s khc bit so vi C v Java.

III.2.6. M hnh bn bn gia Web client v server vi CORBA

Chng ta tham kho vai tr ca CGI trong m hnh ba bn Client/Server

s dng CGI v thy c cc nhc im ca CGI: ng vi mi mt

yu cu t pha client, web server phi to ra mt tin trnh hon ton mi

bt k yu cu l g.


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phn trc, chng ta cng bit ORB ca CORBA cng cp cc tham

chiu n cc i tng v chuyn i, tr li cc tham s t client n cc

i tng. Trong phn ny, chng ta s tm hiu cch thc thc hin ca

CORBA trong mi trng client/server ba bn.

Hnh III-4 M hnh client/server 4 bn trong ng dng CORBA SNMP

Hnh III-4 minh ha mt ng dng quan trc mng s dng kin trc

Clent/server ba bn s dng CORBA ca VisiBroker.

(1)Trn hnh minh ha, ta thy pha web client gi yu cu n web

server thng qua HTTP;

(2)Web client dowwnload trang html (trong c mt Java applet v

mt file Jar). Vic ny cng c thc hin qua HTTP;

(3)Web browser ti applet v file Jar vo b nhca my client v bt

u chy applet;

(4)Sau khi ngi s dng click vo 1 nt bm trong ca s ca applet

yu cu nhn thng tin v mng, yu cu c gi n gatekeeper

(chy trn web server thng qua ORB/IIOP)


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(5)VisiBroker Gatekeeper cho php applet c lin lc vi SNMP

server thng qua mi trng mng nh l mt cng giao tip t pha

client n i tng server nm pha bn kia ca mng

(6)SNMP server s giao tip vi cc Agent trong mng ni b thc

hin cc yu cu ly thng tin

(7)SNMP server gi tr kt qu v cho Gatekeeper trn web server

(8)Gatekeeper tng chuyn tip kt qu v pha Web client thng qua

ORB/IIOP.

(9)Kt quc np v trnh by cho ngi s dng trnh duyt web.

III.3. Tm tt v CGI v CORBA

Chun CGI cho php Web server lin lc vi cc chng trnh bn ngoi,

tin hnh thc hin cc nhim v ring bit. S khc nhau chnh gia cc

chng trnh ng dng l hiu hnh n m bo yu cu v tc hot

ng ca chng trnh.

Trong mi trng Unix, d liu t cc from gi ti chng trnh bn ngoithng qua chun vo. Mt vi tham s c thc dng yu cu cc

tham s truyn qua cc bin mi trng. Server s gi cc d liu ra ca

chng trnh bn ngoi hng ti client. Do i hi cc chng trnh bn

ngoi phi sinh ra thng tin header cho client. Mt trong cc thnh phn ht

sc qua trng ca header l trng Content-type. Chnh nhn m client s

bit x l nh th no vi d liu.

Trong mi trng Window, file-base truyn ti chng trnh bn ngoi ,

tng t, d liu ca chng trnh c a vo trong file cho serverc.

Tt c d liu c lu vo trong file ring profile.


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T nhng xem xt trn, chng ta thy rng cc chng trnh CGI sc

gi thc hin mi khi c yu cu t pha khch hng. Mi ln nh vy, my

ch (server) s to mt tin trnh (process) mi cho gateway v truyn thng

tin t khch hng cho tin trnh ny thng qua cc bin mi trng v dngnhp d liu chun. Sau khi chng trnh CGI c thc hin xong, kt qu

sc gi ngc li cho phn mm web server thng qua dng d liu ra

chun. Nh vy, i vi mi mt yu cu t pha Client, my ch web

server s phi to ra mt tin trnh (process) hon ton mi, tiu tn kh

nhiu ti nguyn h thng. Cng c nhiu yu cu ca khch hng, cng c

nhiu tin trnh CGI do my ch to ra; iu dn n s chim dng ti

nguyn, gy chm tr cho h thng. Mt khc, kh nng tng tc vi ngi

s dng ca CGI cng c nhng hn ch [Mazumdar].

Tuy nhin, CGI cng c u im l c th ci t trn cc hiu hnh v

cc Web server khc nhau, giao din c chun ha v p ng c cc

yu cu cbn.

T nhng phn tch trn, chng ta c th tm rt ra mt s nhn xt v skhc nhau gia cc ng dng CORBA v cc ng dng da trn CGI nh

sau:

(1)Trong ng dng CGI, web server phi to mt tin trnh hon ton

mi ng vi mi mt yu cu, tiu tn nhiu ti nguyn h thng

cng nh thi gian thc hin. Ngoi ra, ton b thng ip gi gia

client v serverc thc hin trn HTTP, dn n phi c c nhiubc x l (overhead)

(2)Trong ng dng CORBA, web server v HTTP chc s dng

truyn trang HTML v Java applet vo lc bt u ca tin trnh. Sau

th client v i tng server thit lp v trao i thng tin vi


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nhau thng qua IIOP, nh, gim c khc nhiu overhead so vi

HTTP [Mazumdar] .

(3)i vi cc ng dng CORBA, serveri tng ch chy bn trong

trong (ng sau) web server v ch cung cp cc dch v thng qua

cc giao din c quy nh cho cc client. Phin lm vic gia

applet v serveri tng sc s gi trong ton b tin trnh v

ton b cc thng tin trng thi sc gi cho n khi mt trong hai

pha ngt kt ni.

(4)CORBA bo m s trong sut v v tr (ni b hay xa) i vi cc

phng thc truy vn dch v, ngha l i vi client, cng vic c

thc hin nh nhau d serveri tng nm mng khc, trn cng

mt mng hay trong cng mt my tnh [CORRBA14].

(5)Vi m hnh h tng kin trc phn tn cc i tng, CORBA cho

php cc Java applet lin lc vi cc i tng c vit bng cc

ngn ng lp trnh khc thng qua mng.


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Chng IV. Xy dng h thng qun trDSLAM qua web

IV.1.Kho st h thng mng cung cp dch v ADSL

IV.1.1. Gii thiu h thng mng cung cp dch v ADSL caBu in H ni

T thng 7-2003, mt dch v mi c trin khai rng kh p trn mng

VNN l dch v truy c p qua ng dy thu bao s xDSL, bao gm cc

cng ngh ADSL, SHDSL v VDSL (gi tt l xDSL). Cc dch v xDSL ra

i mang li kh nng truy cp Internet bng rng gi r cho khch hng.

Ti thi im hin ti ch tnh ring ti a bn H ni c khong trn

35.000 khch hng (cng truy cp) s dng dch v xDSL.

c th cung cp dch v xDSL trn a bn thnh ph H ni, hin nay

Bu in H ni ang qun l mt h tng mng li bao gm mt h thng

phc v truy nhp hin i vi cc thit b DSLAM (Digital Subscriber Line

Access Multiplexer) phn b khp ni trn a bn thnh ph (hn 140

im lp t, gn 200 DSLAM ) ca nhiu nh cung cp thit b ni ting.

n nay, trn a bn H ni hin c 8 chng loi thit b ca 4 nh sn xut

khc nhau Siemens, Huawei, Tailyn, ZTE vi cc cng ngh khc nhau

nh ATM DSLAM, IP DSLAM

H thng cc DSLAM thuc 4 hng sn xut ny c qun tr, gim st,

khai thc mng t xa bi 04 h thng qun l NMS (Network Management

System) t p trung do tng hng sn xut thit b cung c p. Cc h thng

NMS ny u l mi trng ng, c thit k hng ti i tng l cc

k thut vin vn hnh mng nn khng cung cp giao din ra bn ngoi v

khng c mi lin h vi nhau.


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Tuy khc nhau v chng loi thit b, nh sn xut, phn mm qun l,

nhng tt c cc h thng NMS u c thit k vi cc thnh phn chnh

nh sau:

1. H thng DSLAM:

Thit b ca hng Siemens: XpressLink Standard, XpressLink Mini,

XpressLink M200 v M1200 (IP DSLAM)

Thit b ca hng Huawei: MA5100 v MA5600V3 (IP DSLAM)

Thit b ca hng Tailyn: UMAP 2100

Thit b ca hng ZTE:ZTE 8203

2. H thng BRAS (BoardBand Remote Access System): ERX 1410 ca

hng Juniper

3. H thng my ch phc v vn hnh khai thc v qun l: ACI server,

FTP server, DHCP server, NMC-RX Server, SDx server,

4. H thng my ch cung cp dch v: Radius, Billing server, VoD server,

Catching server, TV server,

5. H thng bo v Firewall, log server,

6. Mng truyn dn: truyn dn STM-1 v E1

7. Mng truy cp cs: s dng i dy cp ng in thoi sn c t nh

thu bao n cc tng i in thoi.

IV.1.2. C bn v thit b DSLAM

H thng ghp knh truy nhp ng thu bao s DSLAM (Digital

Subscriber Line Access Multiplexer) l im giao tip gia ngi s dng

u cui v nh cung cp dch v bng rng.


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Trong mng qun l DSLAM, chng ta c th phn bit theo vai tr ca

chng trong mng: DSLAM-HUB v DSLAM (stanalone, sub-DSLAM):

DSLAM-HUB th c hot ng vi vai tr l thit b ghp knh cp 1,

kt ni ln BRAS bng lung STM-1 v c cc DSLAM cp 2 kt ni

vo.

DSLAM thng l cc thit b ghp knh cp 2 c kt ni ln

DSLAM cp 1 hoc BRAS m khng c cc DSLAM th cp. u ra

ca n c kt ni v cc DSLAM chnh. Sub-DSLAM chu s qun

l ca DSLAM chnh (Main DSLAM).

Kt ni gia gia MainDSLAM vi SubDSLAM, hoc MainDSLAM

SubDSLAM vi mng IP bng cc loi giao tip sau:

n X Ethernet 100/1000 (cho lu lng IP).

155Mbps SDH.

34Mbps PDH.

n X 2Mbps.

IV.1.3. H thng qun l mng xDSL

H thng qun l mng NMS (Network Management System) s lm vic

theo khuyn ngh ca ITU: G.992.1, G.992.2, G.997.1 v IETF RFC 2662.

NMS l h thng m, kt hp vi tiu chun cu trc qun l mng vin

thng TMN c xc nh bi khuyn ngh M.3010 ca ITU.

H thng ADSL sc qun l bi mt h thng qun l tp tru

LV co CORBA

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