giao trinh to chuc mvt

7/29/2019 Giao Trinh to Chuc MVT

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MC LCChng 1: Tng Quan V Mng Vin Thng......................4

1.1, Cc khi nim c bn trong lnh vc vin thng................................................................4

1.2,Cc thnh phn c bn ca mng vin thng........................................................................7

1.3, M hnh cc dch v vin thng...........................................................................................8d) Dch v truyn thng a phng tin ...............................................................................12

Chng 2, Mng Li Truyn Thng Cng Cng............142.1. Khi nin, phn loi v iu kin kt cu...........................................................................14

2.1.1, Khi nim....................................................................................................................14

2.1.2, Phn loi mng li truyn thng v iu kin kt cu...............................................14

2.2, Mng chuyn mch v in thoi.......................................................................................15

Chng 3...............................................................................18

Cc k hoch c bn xy dng mng vin thng...............183.1, Gii thiu chung.................................................................................................................183.2, Trnh t thc hin qu trnh lp k hoch..........................................................................19

3.2.1, Xc nh mc tiu xy dng mng..............................................................................20

3.2.2. Lp k hoch di hn..................................................................................................22

3.2.3. K hoch trung hn.................................................................................................... 22

3.2.4. D bo nhu cu.......................................................................................................... 23

3.3. D bo nhu cu..................................................................................................................23

3.3.1. Khi nim...................................................................................................................24

3.3.2. Tng trng nhu cu..................................................................................................253.3.3. Cc bc xc nh nhu cu........................................................................................26

3.3.4. Cc phng php xc nh nhu cu............................................................................28

3.4. D bo lu lng...............................................................................................................30

3.4.1. Khi nim...................................................................................................................30

3.4.2. Cc bc xc nh lu lng....................................................................................30

3.4.3. Cc phng php xc nh d bo lu lng.............................................................31

3.5. K HOCH NH S.....................................................................................................34

3.5.1. Gii thiu....................................................................................................................35

3.5.2. Cc h thng nh s .................................................................................................353.5.3. Cu to s ...................................................................................................................35

3.5.4. Cc th tc cho vic lp k hoch nh s .................................................................36

3.6. K HOCH NH TUYN...........................................................................................39

3.6.1. Gii thiu ...................................................................................................................39

3.6.2. Cc phng php nh tuyn.......................................................................................40

3.7. K HOCH TNH CC ...............................................................................................41

3.7.1. Gii thiu chung..........................................................................................................41

3.7.2. Cc tiu ch cho vic tnh cc ..................................................................................42

3.7.3. Cc h thng tnh cc ...............................................................................................423.8. K HOCH BO HIU...................................................................................................45

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3.8.1. Gii thiu ...................................................................................................................45

3.8.2. Phn loi bo hiu.......................................................................................................46

3.9. K HOCH NG B................................................................................................... 47

3.9.1.Gii thiu chung...........................................................................................................47

3.9.2. Cc phng thc ng b mng .................................................................................47

3.9.4. Mng ng b Vit Nam.............................................................................................513.10. K hoch cht lng thng tin.........................................................................................52

3.10.1. Cht lng chuyn mch..........................................................................................52

3.10.2. Cht lng truyn dn..............................................................................................52

3.10.3. n nh.................................................................................................................53

Chng 4, Quy hoch mng vin thng .............................544.1. Quy hoch v tr tng i....................................................................................................54

4.1.1.Gii thiu.....................................................................................................................54

4.1.2. Phng php qui hoch v tr tng i.........................................................................54

4.1.3. Chi ph thit b............................................................................................................564.2. Quy hoch mng truyn dn...............................................................................................57

4.2.1. Gii thiu....................................................................................................................57

4.2.2. Cu hnh mng truyn dn..........................................................................................58

4.2.3. Cc dng c bn ca truyn dn..................................................................................60

4.2.5. V d cu hnh mng truyn dn..................................................................................61

4.2.6. NH TUYN................................................................................................................61

4.2.6. TO NHM KNH...................................................................................................62

4.3. Quy hoch mng li thu bao..........................................................................................63

CHNG 5, QUN L MNG VIN THNG ..............645.1. Tm quan trng ca cng tc qun l mng vin thng.....................................................64

5.2. Mng qun l mng vin thng TMN................................................................................64

5.2.1. Gii thiu v TMN..................................................................................................... 64

5.2.2. Cc chc nng qun l ca TMN...............................................................................65

CHNG 6, MNG A DCH V TCH HP S ISDN.....................................................................................................72

6.1. c im ca mng vin thng khi cha c ISDN.............................................................72

6.2. Khi nim v ISDN............................................................................................................72

6.2.1. ISDN...........................................................................................................................72

6.2.2. Mc ch ca ISDN.....................................................................................................72

CHNG 7, MNG TH H MI NGN....................767.1. S ra i ca NGN.............................................................................................................76

7.2. Cu trc mng....................................................................................................................79

7.2.1. M hnh phn lp chc nng ca mng NGN........................................................80

7.2.2. Phn tch.................................................................................................................81

7.3. Dch v trin khai trong NGN........................................................................................887.3.2. Nhu cu NGN i vi cc nh cung cp dch v.........................................................89

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7.3.3. Yu cu ca khch hng..............................................................................................91

7.3.4. Dch v NGN..............................................................................................................91

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Chng 1: Tng Quan V Mng Vin Thng1.1, Cc khi nim c bn trong lnh vc vin thng

Gn y, my tnh pht trin nhanh, kh nng lm vic nhanh v gi thnh gim

n ni chng ng dng khp mi ni trn th gii v xm nhp vo mi lnh vc. Do

s a dng v tinh vi ca my tnh v s pht trin nhanh ca cc trm lm vic, nhucu v mng vin thng truyn ti thng tin khng ngng pht trin. Cc mng ny

kh nng cung cp cc ng truyn thng chuyn cc s liu trong lnh vc cng

ngh, khoa hc k thut v m bo p ng cc loi ng dng phong ph khc nhau

t gii tr cho ti cc cng vic phc tp. Cc mng ny cn c kh nng truyn ti

thng tin vi tc khc nhau t vi k t trong mt giy ti hng Gbit/s. Theo mt

ngha rng hn, cc mng ny cung cp chc nng truyn ti thng tin mt cch linh

hot. Thng tin truyn ti vi tc khc nhau, an ton v tin cy cao. im

ny khc xa so vi kh nng ca mng in thoi c hnh thnh truyn ti tn

hiu ting ni vi tc c nh 64Kbit/s, an ton v tin cy khng ng b. im

quan trng y l cc thit b trn mng vin thng cng c s tho thun v vic

trnh by thng tin di dng s v cc th tc trn cc ng truyn. Tt c cc quy

c, tho thun v cc quy tc nhm xc nh thng tin s trao i vi nhau gi l cc

giao thc thng tin (communication protocol). S kt hp (marriage) gia hai cng

ngh hng u vin thng v my tnh l mt thch thc mi cho cc nh khoa hc, k

s v cc nh thit k.Truyn thng l vic truyn thng tin t mt im ti mt im khc, gm c truyn

thng c hc (bu chnh) v truyn thng in (vin thng) bi v n pht trin t

dng c hc (my mc) sang dng in/quang v ngy cng s dng nhng h

thng in/quang phc tp hn.

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Hnh 1.1: Vin thng

T l phn truyn thng c hc (th t, bo ch) ang c xu hng gim trong khi

t l phn truyn thng in/quang, c bit l truyn song hng, li gia tng v s

chim th phn ch o trong tng lai. V vy, ngy nay nhng tp on bo ch cng

ang tp trung v hng ti truyn thng in/quang, coi l c hi kinh doanh tng

lai ca mnh.

Vin thng chim phn ch o trong truyn thng.

Vin thng (Telecommunication) l qu trnh trao i cc thng tin cc dng

khc nhau (ting ni, hnh nh, d liu...) vi c ly xa nh vo cc h thng truyn dn

in t (truyn dn cp kim loi, cp quang, vi ba, v tinh).

Mng vin thng (Telecommunications Network) l tp hp cc thit b (Devices),

cc k thut (Mechanisms) v cc th tc (Procedures) cc thit b kt cui ca

khch hng c th truy nhp vo mng v trao i thng tin hu ch. Cc yu cu tra cho mng vin thng l phi c kh nng cung cp cc ng truyn tc khc

nhau, linh hot, c tin cy cao p ng cc loi hnh dch v khc nhau.

Mng vt l & Mng logic (physical and logical networks)

Mng vt l bao gm cc h thng truyn dn, chuyn mch nh: mng cp ni

ht, mng vi ba s, mng SDH, mng thng tin v tinh, mng li cc tng i. Cc h

thng c thit lp nhm to ra cc ng dn tn hiu gia cc a ch thng qua cc

nt mng. Mng vt l ng vai tr l c s h tng ca vin thng, n phc v chung

cho lin lc in thoi, truyn thng d liu v cc dch v bng rng khc.

5

Cc

mng

ringVIN

THNG

Hai hng

Truyn thng n

hng

C

KH

IN

in thoi Ccmng

s liuTelex

in

Bo

Bu chnh

Bo ch

Pht thanh TV

Truynhnh

cp


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Trn c s h tng cc mng logic c to ra nhm cung cp cc dch v vin

thng tho mn nhu cu ca x hi. Mng in thoi, mng TELEX, mng Radio

truyn thanh l cc mng logic truyn thng. Ngy nay, ngoi cc mng trn cn c c

thm cc mng khc c th cng tn ti trong mt khu vc, nh l mng in thoi

cng cng (PSTN), mng d liu chuyn gi cng cng (PSPDN), mng nhn tin(Paging network), mng in thoi di ng, mng my tnh ton cu (INTERNET),

mng s a dch v tch hp (ISDN) vv...Cc mng trn cung cp hng lot dch v

vin thng tho mn nhu cu ca khch hng.

H thng truyn thng (Communication System): l cc h thng lm nhim v x

l v phn phi thng tin t mt v tr ny n mt v tr khc v cn gi l h thng

thng tin. Mt h thng thng tin bao gm cc thnh phn sau: b m ho, b pht,

mi trng truyn dn, b thu, b gii m.

Hnh 1.2: M hnh h thng truyn thng

Trong h thng truyn thng chng ta cn quan tm: khun dng thng tin, tc

truyn dn, c ly truyn dn, mi trng truyn dn, k thut iu ch, th tc pht

hin v sa li.

Cc phng thc truyn tn hiu trong h thng truyn thng:

- n cng (Simplex): Thng tin ch truyn trn mt hng, b thu khng th trao

i thng tin vi pha pht.

- Bn song cng (Half- Duplex): Thng tin truyn trn hai hng nhng khng

cng thi im.

- Song cng (Full-Duplex): Thng tin truyn trn hai hng ng thi .

6

B m ha B

phtMi trng

truyn dnB

thu

B gii mThng tin Thng tin


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1.2,Cc thnh phn c bn ca mng vin thng

M hnh tng qut ca cc h thng vin thng

a. Gii thiu chung v mng vin thng .

Khi xt trn quan im phn cng, mng vin thng bao gm cc thit b u cui,

thit b chuyn mch v thit b truyn dn.

b. Thit b u cui

Thit b u cui l cc trang thit b ca ngi s dng giao tip vi mng

cung cp dch v. Hin nay c nhiu chng loi thit b u cui ca nhiu hng khc

nhau ty thuc vo tng dch v (v d nh my in thoi, my fax, my tnh c

nhn...). Thit b u cui thc hin chc nng chuyn i thng tin cn trao i thnh

cc tn hiu in v ngc li.

c. Thit b chuyn mch

Thit b chuyn mch l cc nt ca mng vin thng c chc nng thit lp

ng truyn gia cc cc thu bao (u cui). Trong mng in thoi, thit b chuyn

mch l cc tng i in thoi.Tu theo v tr ca tng i trn mng, ngi ta chia thnh tng i chuyn tip

quc t, tng i chuyn tip lin vng v tng i ni ht.

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My Fax

Thit b

chuyn mch

u cui d

liu

in thoi

V tinh truynthng

Thit b

u cui

in thoi

ng truyn

dn Thit b

chuyn mch

Thit b

u cui

My Fax

My tnh

Hnh 1.3: Cc thnh phn ca mng vin thng

: Nt chuyn mch

Hnh 1.4:Cu trc mng in thoi c v khng c thit b chuyn

mch

: Thu bao


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d. Thit b truyn dn

Thit b truyn dn c s dng ni cc thit b u cui hay gia cc tng

i vi nhau v truyn cc tn hiu mt cch nhanh chng v chnh xc.

Thit b truyn dn phn loi thnh thit b truyn dn thu bao, ni thit b ucui vi tng i ni ht, v thit b truyn dn chuyn tip, ni gia cc tng i. Da

vo mi trng truyn dn, thit b truyn dn c th phn loi s lc thnh thit b

truyn dn hu tuyn s dng cp kim loi, cp si quang v thit b truyn dn v

tuyn s dng khng gian lm mi trng truyn dn. Thit b truyn dn thu bao c

th s dng cp kim loi hoc sng v tuyn (radio). Cp si quang s dng cho cc

ng thu ring v mng s lin kt a dch v, yu cu dung lng truyn dn ln.

1.3, M hnh cc dch v vin thng

Khi nim dch v vin thngKhi nin dch v vin thng lun gn lin vi cc khi nim mng vin thng.

Mi mng vin thng s cung cp mt vi loi dch v c bn c trng cho mng

vin thng v mng ny c th cng h tr vi mng khc cung cp c mt

dch v vin thng c th.

Dch v vin thng l dch v truyn k hiu, tn hiu, s liu, ch vit, m

thanh, hnh nh hoc cc dng khc ca thng tin gia cc im kt cui thng qua

mng vin thng.

Hnh 1.5. Dch v vin thng

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Ni mt cch khc, chnh l dch v cung cp cho khch hng kh nng trao i

thng tin vi nhau hoc thu nhn thng tin qua mng vin thng (thng l mng cng

cng nh mng in thoi chuyn mch cng cng, mng in thoi di ng, mng

internet, mng truyn hnh cp,) ca cc nh cung cp dch v v nh cung cp h

tng mng.Hnh 1.6. M hnh cc dch v vin thng

Cc loi hnh dch v c bn v yu cu ca chng v cht lng dch v

Cc dch v vin thng c bn thng c cp l dch v thoi, dch v s liu, dchv thu knh vin thng v dch v truyn thng a phng tin. Ngoi ra, c rt nhiu dch vvin thng c bn khc v vn cn tn ti ti ngy nay, tuy nhin khng c ph cp rng

ri nh 4 dch v ny.

a) Dch v thoi/telex/Fax/nhn tin

Dch v thoi

in thoi l dch v vin thng c pht trin rng ri nht, l dch v cung cp khnng truyn a thng tin di dng ting ni hoc ting ni cng hnh nh (nh trng hpin thoi thy hnh - videophone) t mt thu bao ti mt hoc nhm thu bao.

Dch v thoi c bn nht l dch v in thoi c nh do mng PSTN (mng in thoi

chuyn mch cng cng) cung cp. Dch v ny cp cho khch hng ng truyn ti tn nhring, kt ni ti tng i in thoi c nh, cho php khch hng thc hin c cuc githoi i ti cc khch hng khc.

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Hnh 1.7. Dch v thoiNgoi dch v in thoi truyn thng, cn c nhiu dch v thoi khc nh dch v in

thoi dng th (cardphone), in thoi di ng tc thp (in thoi di ng ni vng -

cityphone), in thoi i ng, in thoi v tinh v hng hi v.v.

s dng dch v in thoi dng th, khch hng mua trc mt tm th vi mt

gi tin xc nh trc ti cc i l bu in. Khi s dng th ny, khch hng c th gi

in ni ht, lin tnh hoc quc t. Khi cn gi, khch hng a th vo cc my in dng

th cng cng t trn ng ph. Cc ph m thoi s c tr v ghi nhn vo tm th

ty theo thi gian m thoi v loi hnh dch v ca cuc gi. C th dng nhiu th cho

mt cuc gi hoc mt th cho nhiu cuc khc nhau. Dch v ny c u im ln nht l

thun tin cho vic qun l lng s dng ca khch hng. Tuy nhin mt my in thoidng th cng cng phi cao, ph hp vi cc khu dn c ng, kinh t pht trin, du lch,

ngh mt.

Dch v in thoi di ng l dch v thng tin v tuyn c thit lp nhm m bo

lin lc vi cc my in thoi u cui di ng. Mt thu bao in thoi c nh c th gi cho

mt thu bao di ng hoc ngc li hoc c hai u l thu bao di ng. Bn cnh vic cung

cp kh nng trao i thng tin di dng ting ni, cc thu bao in thoi di ng cn c

th s dng cc dch v khc nh dch v bn tin ngn, hp th thoi, FAX hoc truyn s

liu.... Ti Vit nam, hin nay c su nh khai thc dch v vin thng c chnh ph cp giyphp cung cp dch v in thoi di ng: VINAPHONE (trc y l VPC), VMS, VIETTEL,

SPT, EVN v HANOITELECOM. n cui nm 2004, tng s lng thu bao in thoi c

nh v di ng Vit Nam l khong 10 triu, n gia nm 2006 con s ny ln n khong

17 triu.

Dch v Telex

Dch v Telex l dch v cho php thu bao trao i thng tin vi nhau di dng ch bng

cch g vo t bn phm v nhn thng tin trn mn hnh hoc in ra bng giy. Dch v ny

s dng cc ng truyn tc thp, da trn mt mng kt ni ring, c cch nh s thu

bao khc vi cc thu bao in thoi thng thng.

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Hnh 1.8. My Telex

Dch v Fax

Dch v Fax l dch v cho php truyn nguyn bn cc thng tin c sn trn giy nh chvit, hnh v, biu bng, s ... gi chung l bn fax t ni ny n ni khc thng qua h thngvin thng.

Hnh 1.9. Dch v Fax

Dch v fax bao gm fax cng cng v fax thu bao. Dch v fax cng cng l dchv m ti cc c s Bu in chp nhn, thu, truyn a, giao pht cc bc fax theo nhucu ca khch hng. Dch v fax thu bao cung cp cho cc t chc hoc c nhn c nhu culin lc vi cc thit b u cui khc qua mng vin thng. Thit b fax thu bao c uni vi tng i in thoi cng cng bng ng cp ring hoc chung vi thit b inthoi.

Dch v nhn tinNhn tin l dch v cho php ngi s dng tip nhn cc tin nhn. Mun s dng

dch v ny, khch hng cn mua hoc thu mt my nhn tin ca Bu in. My nhn tin

c kch thc nh gn, c th cho vo ti hay t gn trong lng bn tay. Ngi cn nhn

gi in ti trung tm dch v ca bu in yu cu chuyn tin nhn ti ngi nhn l thu bao

nhn tin. Dch v ny rt tin li cho nhng ngi thng xuyn di chuyn m vn nhn c

thng tin vi chi ph khng ln. Trc y ti mt s thnh ph ln nh H ni, Thnh ph H

Ch Minh, nng u c cc trung tm cung cp dch v nhn tin. Ngoi ra dch v nhn tin

Vit nam 107 cho php ngi dng c th nhn c tin nhn trong phm vi ton quc song

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n nay dch v ny ngng hot ng. Hin nay, dch v nhn tin thng c thc hin

thng qua in thoi di ng v c nh.

b) Dch v thu knh vin thng (leased line)

Dch v thu knh ring l dch v cho thu knh truyn dn vt l dng ring kt ni v

truyn thng tin gia cc thit b u cui, mng ni b, mng vin thng dng ring ca khchhng ti hai a im c nh khc nhau.

Dch v ny p ng c cc nhu cu kt ni trc tip theo phng thc im ni im

gia hai u cui ca khch hng. Vit Nam cc i l Bu in i din pha nh cung cp

dch v (i vi VNPT), cung cp cc dch v thu knh sau:

+ Knh thoi ng di

+ Knh in bo

+ Knh pht thanh v truyn hnh

+ Knh truyn s liu

c) Dch v s liu

Dch v truyn s liu l dch v truyn ti hoc cc ng dng truyn ti thng tindi dng s liu trong mng vin thng. Dch v truyn s liu thch hp vi cc kho thngtin d liu ln nh ngn hng, th vin, thng k, iu khin t xa thng qua thit b ucui...

Hin nay trn mng vin thng Vit Nam, Cng ty VDC c coi nh cung cp dch

v truyn s liu ln nht vi cc sn phm dch v nh: truyn s liu X25, Frame relay...d) Dch v truyn thng a phng tin

Dch v vin thng bng rng cung cp cho khch hng kh nng truyn ti thng tinvi rng bng tn ln ln ti vi chc Mbit trn giy (Mbit/s) (trn nn mng ISDN -Mngs a dch v tch hp). Bng tn ny cho php truyn ti ng thi nhiu dng thng tinkhc nhau vi cc yu cu v bng tn cng rt khc nhau trn cng mt knh lin lc. Mytnh, my fax, in thoi v k c in thoi thy hnh u c th c phc v thng quamt knh lin lc duy nht. Bng tn ny c s dng v phn b gia cc dch v khc

nhau mt cch mm do, ti u v p ng ti a yu cu v cht lng dch v ca khchhng. Ti thit b thu bao, khi cc dch v vin thng khc nhau, s dng nhiu mi trngthng tin khc nhau nh ting ni, hnh nh, m thanh hay s liu u c tch hp vo mtthit b duy nht, khi ta c c dch v thng tin a phng tin (multimedia). Lc lin lc s c thc hin thng qua nhiu mi trng thng tin trong cng mt thi im vcng n gin nh thc hin mt cuc gi in thoi thng thng.

Hnh 2.9 l mt v d in hnh ca dch v a phng tin: Dch v Truyn hnh hi ngh(Video conference).

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Hnh 1.10. Dch v truyn hnh hi ngh

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Chng 2, Mng Li Truyn Thng Cng Cng2.1. Khi nin, phn loi v iu kin kt cu

2.1.1, Khi nimMng li truyn thng cng cng l tp hp cc thit b vin thng, chng c

ni ghp vi nhau thnh mt h thng dng truyn thng tin gia cc ngi sdng v thc hin cc dch v vin thng tng ng.

2.1.2, Phn loi mng li truyn thng v iu kin kt cuMng li truyn thng c th c nh ngha l mt h thng chuyn thng tin.

Cc mng li truyn thng in hin nay ang c s dng x l cc loi thng

tin khc nhau bao gm mng li in thoi, mng li in tn, v mng li truyn

s liu. Ngoi ra, ISDN l mt mng li c kh nng x l tch hp cc loi thng tin

trn. V kha cnh loi cuc gi v cc dch v, cc mng li truyn thng c thc phn chia thnh mng truyn thng cng cng, mng truyn thng chuyn dng

v mng truyn thng di ng. Da vo phm vi cc dch v truyn thng c a

vo hot ng, cc mng truyn thng c th c phn loi tip thnh mng truyn

thng ni b, mng truyn thng ni ht, mng truyn thng lin tnh, mng truyn

thng quc t. Nu chng ta phn loi chng v x l chuyn mch, ta c th c mng

truyn thng tc thi v mng truyn thng nhanh. Nh ni trn, cc mng truyn

thng c th c phn ra nhiu hn na ty theo nhu cu v i hi ca ngi s

dng. V cn bn, mng truyn thng bao gm mt h thng chuyn mch nh rng ni cuc gi theo yu cu ca thu bao v mt h thng truyn dn truyn

thng tin gi n ngi nhn. V cn bn, n phi p ng nhng iu kin sau:

1, C kh nng kt ni cc cuc gi c gi t tt c cc thu bao ch gi c

ng k trong h thng n thu bao b gi vo bt c lc no hoc vo thi gian

nh trc.

2, C kh nng p ng cc yu cu v nhng c tnh ca truyn dn.

3, S ca thu bao b gi phi c tiu chun ha.

4, C kh nng thc hin vic truyn tin mt cch cn thn v tin cy cao.

5, Cn c mt h thng ghi ha n hp l.

6, Hot ng ca n cn phi va tit kim va linh hot.

thc hin c nhng iu trn, mng tng i phi c thit k, sau a

vo hot ng mt cch ng n bng cch xem xt cht lng cuc gi, kh nng x

l cuc gi, chi ph lp t v chi ph vn hnh, mi lin h gia h thng truyn dn

v h thng chuyn mch. Cc mc c nu ra trn y c th c tng hp thnh

s kt ni cuc gi v tiu chun truyn dn, k hoc nh s, tin cy v h thngghi ha n.

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2.2, Mng chuyn mch v in thoi

V cc thu bao ng k trong h thng ri rc, nn v cn bn m ni th h

thng ny phi c kh nng x l tt c cuc gi ca h mt cch tit kim, tin cy v

nhanh chng. t c mc ch ny, cc c tnh v nhng yu cu i hi ca

thu bao phi c xem xt m bo cc dch v thoi cht lng cao. Mt mngni ht vi mt hoc hai h thng chuyn mch c th c thit lp nu cn thit. i

vi cc thu bao sng trong mt vng ring bit c th ch cn mt h thng tng i.

Nhng nu s thu bao trong mt vng ring bit vt qu mt gii hn no , c th

lp t nhiu tng i. Ni chung, cc mng li ng dy c th c lp ra nh

minh ha hnh 2.1. Mng li mc ni tip trong hnh (a) c lp ra bng cch ni tt

c cc mng li dy ca tt c cc vng theo kiu ni tip. Tri li, mng li vng

trong hnh (b) c thit lp theo kiu trn. Nh c n t trong hnh (c), mng hnh

sao c tp trung vo mt im chuyn mch. Trong hnh (d) trng hp mng cmc theo kiu li cc ng ni cc pha vi nhau c thc hin. Cng vy, nu

c yu cu, mng li ghp c th c lp t nh hnh (e).

Hnh 2.1, Cc kiu mng li ng dy

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Hnh 2.2, Thit lp tng i

Bt c mng li no c cp trc y c th c lp t p ng nhng

nhu cu v yu cu ca thu bao. Trong trng hp c mt vng rng ln cn nhiu h

thng chuyn mch, thng thng th mng mc theo hnh li c thit lp. i vi

nhng vng nng thn hoc nhng vng xa xi nh nng tri hoc cc lng chi c

mt gi thp, ngi ta s dng mng hnh sao. Cc phng php ni mng c th

dung cho cc mng li ng dy c phn no phc tp hn. Thng thng vic ni

mng c thc hin theo 4 mc nh minh ha trong hnh 2.2; trung tm ni ht, trung

tm lin tnh, trung tm khu vc, trung tm vng. Trong mng li phn cp c cc

mc nh trn, vic to hng thay th bao gm cc hng c mc s dng cao v cchng thay th c s dng. Nu mt cuc gi c pht sinh, hng c mc s

dng cao s c tm u tin. Cuc gi ny c ni vi bn b gi thng qua hng

thay th ca tng i mc cao k tip.

Mng in thoi

Khi nim:

- Mng in thoi l tp hp cc thit b, tng i, h thng truyn dn, h

thng thu bao v cc thit b ph tr khc, chng c kt ni cht ch vinhau m bo thng tin thoi gia cc thu bao v cc dch v thoi

- PSTN (Public Switching Telephone Network): mng chuyn mch thoi

cng cng: L mng c quy m quc gia c t chc, qun l, phn nh r

rng t trn xung di. L mt b phn c s h tng quc gia p ng nhu

cu trao i thng tin thng xuyn ca ngi dn, phc v pht trin kinh t

v an ninh quc phng

- PA(B)X (Private Automatic (Branch) Exchange: mng in thoi ring

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S dng tng i ring lp t mt mng in thoi cho ni b mt c

quan, hoc mt khu vc no . C cc ng trung k kt ni vi mng

in thoi cng cng.

H thng truyn dn trong mng in thoi

L mi trng truyn dn tn hiu trong mng in thoi m bo suyhao cho php v tho mn cc yu cu v:

Dung lng thu bao v tc pht trin thu bao

- iu kin a l, kh hu thi tit

- Cc yu t v quy hoch th

- Thun tin cho bo dng, sa cha

- Tit kim chi ph

Tu theo s lng thu bao hay tc pht trin thu bao chia thnh:- Mng in thoi khng phn vng

- Mng in thoi phn vng

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Chng 3

Cc k hoch c bn xy dng mng vin thng3.1, Gii thiu chung

Vic lp k hoch trong mng vin thng ni chung v trong mng in thoi niring c nh qun l vin thng a ra phi rt r rng v mang tnh cht tng th.

Tt c mi vn c xem xt k cng, c th nh vic s dng cc thit b ang tn

ti, s pht trin dn s trong cc khu vc v s pht trin ca nn kinh t ni chung

hay s chuyn ho sang cc cng ngh mi. Trong vn lp k hoch th yu t thi

gian ph hp vi cc k hoch ny l rt quan trng, ph hp vi vic u t hay

d bo di hn. Trong mng vin thng, cc thnh phn trn mng (thit b chuyn

mch , thit b truyn dn, thit b ngoi vi) m nhim nhng chc nng ring ca n

nhng m nhim chc nng ca mt mng th cn phi c s kt hp hi ho gia

chng. Cc k hoch c bn nhm phi hp cc thit b trn m bo thc hin chc

nng mng.

Hnh 1.3. Cc thnh phn trong mng vin thng

Cc k hoch c bn (cc quy tc c bn cho thit k mng) sau c coi l

nn tng cho vic xy dng mng vin thng.

+ Cu hnh mng dng t chc mng vin thng.

+ K hoch nh s qui nh vic hnh thnh cc s (quc gia v quc t ) v cc

chc nng ca tng thnh phn.

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+ K hoch to tuyn quy nh vic chn tuyn gia cc nt mng cho truyn ti

lu lng thng tin m bo hiu qu v kinh t cng nh k thut.

+ K hoch bo hiu quy nh cc th tc truyn cc thng tin iu khin gia

cc nt mng thit lp, duy tr v gii to cuc thng tin.

+ K hoch ng b quy nh th tc phn phi tn hiu ng h gia cc nt

mng sao cho chng hot ng ng b vi nhau.

+ K hoch tnh cc xy dng c s tnh cc cho cc cuc thng tin.

+ K hoch truyn dn quy nh cc ch tiu v cc tham s k thut cho qu trnh

truyn dn tn hiu trn mng.

+ K hoch cht lng thng tin ch ra mc ch cho vic t chc khai thc v bo

dng trn mng.

3.2, Trnh t thc hin qu trnh lp k hoch

Khi tin hnh lp k hoch, phng hng c bn c quyt nh bi cc mc

tiu qun l ca chnh ph m chng s tr thnh i tng xy dng mng li.

Thng qua xc nh cc nhu cu khch hng da trn cc mc tiu qun l v cc nh

gi v nhu cu v lu lng, xc nh c cc mc tiu lp k hoch v thit lp

c chin lc chung. Tng ng vi mc tiu , mt khung cng vic v mng

li c bn v di hn c thit lp. Sau mt k hoch thit b r rng c d

tnh tng ng vi cc thit b.S chui cng vic ca qu trnh lp k hoch mng

Hnh 3.1. S chui cng vic ca qu trnh lp k hoch mng

19

Xc nh nhu cu

Lp k hoch mng ti u

Lp k hoch ngn hn

Lp k hoch trung hn

Lp k hoch di hn

Xc nh mc tiu

Mc tiu qun l


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3.2.1, Xc nh mc tiu xy dng mngKhi lp k hoch mng li, chin lc chung nh l cp ca dch v c a ra,

khi cc dch v bt u vi u t l bao nhiu, v cn bng li nhun vi chi ph

nh th no cn phi c xem xt ph hp vi chnh sch ca chnh ph. Nhng vn

ny cn phi c xc nh mt cch r rng nh l mc tiu ca k hoch.

3.2.1.1, Cc iu kin ban u

xc nh mc tiu, yu cu cc nhn t sau y:

- Mc tiu qun l: thit lp k hoch v dch v c a ra mt cch r

rng.

- Chnh sch quc gia: bi v mng li c mt nhn t cng cng quan trng,

nn n c quan h cht ch vi chnh sch quc gia.

- D bo nhu cu v s phn b ca n.

- D bo lu lng.y l cc nhn t chnh quyt nh cu hnh c bn ca mng li, v cng l

khng th thiu c cho u t thit b hiu qu.

Xu hng cng ngh v iu kin ca mng li hin ti cn nh hng n vic

xc nh cc mc tiu.

3.2.1.2, Nhng yu t cn c xem xt trong khi xc nh mc tiu

Cc mc tiu sau cn c xc nh:

(1) Cc yu cu v dch v

i vi vic xc nh cc yu cu v dch v, vic xem xt cn tp trung vo loidch v, cu trc ca mng li cho vic m dch v, v mc ch ca dch v.

(a) Loi dch v

Cc yu cu i vi cc dch v vin thng ang ngy cng tng ln bao gm tnh

a dng, cc chc nng tin tin, cc vng phc v rng hn, v tin cy cao hn.

Hn na, s tin b ca cng ngh gn y cho php a ra c cc dch v nh vy.

Tuy nhin, loi dch v c a ra l rt khc nhau trong tng nc v ty theo cp

pht trin vin thng hin ti. V th, i vi vic xc nh mc tiu k hoch, c

th cn n mt cuc kim tra y xc nh dch v c a ra.

(b) Cu trc mng cho vic m dch v

Vic xc nh cu trc mng li cho vic m ra cc dch v l cn thit. Thng

thng c cc kh nng sau:

- Thc hin s dng mng hin ti.

- Thc hin s dng mng hin ti v mng li.

- Thc hin s dng mng li.

- Thc hin bng cch cung cp cc u cui vi cc chc nng hin i hn.

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Hin nay, mng a ra cc chc nng lu tr thng tin v cc chc nng

chuyn i phng tin, ngoi cc chc nng kt ni c bn. Tuy nhin, s pht trin

gn y trong thit b bn dn nng cp cc chc nng v gim chi ph cho cc thit

b u cui. V th, cc u cui ny c th x l mt s chc nng m tng c

a ra bi mng li.[S chuyn giao chc nng gia u cui v mng li]

- Kinh t: nu nhu cu ln, mng li nn c cc chc nng trn. Trong trng

hp ny, vic a ra cc chc nng bi cc thit b mng li s kinh t hn. Nu nhu

cu nh, vic a ra cc chc nng bi cc u cui l kinh t hn.

- Cp dch v: nu mng li a ra cc chc nng, cc dch v a ra c th

c s dng dng chung v th s rt d dng cung cp cho cc nhu cu ang tng.

Nhng p ng nhanh chng cho cc nhu cu mi v tha mn cc yu cu cao

cp ring l, tt nht l ci t cc chc nng ny cho u cui.- Vn hnh: nu cc chc nng c ci t cho mng li, cc h thng bo

hiu iu khin kt ni tr nn phc tp. Nu cc chc nng c ci t cho u

cui, mi u cui c cc chc nng iu khin ring ca n, s cho php vn hnh tt

hn.

- Bo dng: nu cc mng li c nhiu chc nng, n c th nhanh chng qun

l cc li. Tuy nhin, nu cc chc nng c tn ti cc u cui, c th bo dng

ngay lp tc. Tuy nhin, cc tc ng ca li thng c gii hn trong u cui.

(2) Xc nh cc mc tiu vng dch v

Cc mc tiu c nh ngha cho mt vng dch v bao gm ton b cc qu ca

chnh ph cho lp k hoch mng li, cc yu cu x hi i vi dch v, ph tn v

li nhun nh gi i vi vic a ra cc dch v, v phm vi ca vng hnh chnh.

V c bn, mt vng dch v c xc nh da vo vic xem xt li nhun v chi ph

c nh gi t nhu cu ca vng, song song vi cc mc tiu di hn. Thm ch

ngay c khi doanh thu d tnh rt nh so vi chi ph, n vn c th c xc nh l

mt vng dch v trong trng hp c mt cc nhn t quan trng nh l tnh x hii vi dch v, s hn ch bi vng hnh chnh, s ph hp vi cc chnh sch quc

gia v kinh t a phng.

(3) Xc nh cc mc tiu cho cht lng thng tin

Khi xc nh cc mc tiu cht lng thng tin, chng ta phi xem xt Khuyn

ngh ITU-T, cc lut v quy nh lin quan trong quc gia, mc tha mn ngi s

dng, cc tc ng x hi, tnh kh thi v mt k thut, v chi ph. Nu c cc mng

hin ti, phi chp nhn s iu chnh gia cc mng hin ti v mi. Vi cc gi thit

ny, chng ta c th xc nh cht lng chuyn mch, cht lng truyn dn, v chtlng n nh.

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Mi mc tiu cht lng c xc nh s dng cc t l gi tr sau:

- Cht lng chuyn mch: mt kt ni v tr kt ni.

- Cht lng truyn dn: LR(t l tp m)

- Cht lng n nh: t l li.

3.2.2. Lp k hoch di hnK hoch di hn l khung cng vic c bn ca lp k hoch mng li. K

hoch di hn c th bao trm mt giai on l 20 hoc 30 nm. K hoch ny bao

hm cc phn m rt kh thay i nh l cu hnh mng li, v tr tng i, v k

hoch nh s. Cc phn ny c ln k hoch theo cc mc tiu c xc nh trong

phn trn.

(1) Cu hnh mng li

u tin, thit k s lc cc trm chuyn mch ni hatj v cc trm chuyn mch

toll cho nhu cu, lu lng, v vng dch v ca chng, v xc nh cp mng li.Sau xc nh cc tuyn ti u, lu tm n cu hnh mng li.

(2) K hoch nh s

Cn i nhu cu v cu hnh mng li, xc nh dung lng, vng, v c cu

nh s ti u nht.

(3) K hoch bo hiu

Xem xt loi dch v v cu trc mng li, xc nh nhn t yu cu cho h

thng bo hiu.

(4) K hoch cc

Xem xt loi dch v, h thng gi cc, cu trc mng li, v k hoch nh s,

xc nh h thng cc ti u.

(5) K hoch v tr tng i

Xem xt nhu cu, lu lng, cu trc mng li, v h thng gi cc, xc nh v

tr ca mi tng i v vng dch v ca n cho chi ph thit b l thp.

3.2.3. K hoch trung hn

K hoch trung hn thng bao trm ti a l 10 nm. Thm ch n cn bao hmc k hoch thit b cho cc giai on ngn hn. K hoch trung hn c da trn cc

kt qu ca k hoch di hn. So vi k hoch di hn, k hoch trung hn yu cu

chnh xc cao hn khi ti u ha u t, v nh gi v quy m v dung lng ca

thit b.

(1) Tnh ton cc mch

Xem xt cc v tr tng i, lu lng, vng dch v, v s n nh v cht lngdch v, xc nh s mch ti u.

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(2) K hoch mng ng truyn dn

Xem xt s mch gia cc tng i, v cu hnh mng, xc nh h thng truyn

dn ti u m a ra mc tho mn c v kinh t v tin cy.

(3) K hoch mng ng dy thu bao

Xem xt nhu cu, v tr tng i, vng dch v, v mc n nh cht lng dch v,

chia mng ng dy thu bao thnh mt vi vng phn b. Khi chia, to ra s kt

hp ti u ca cc vng phn b v vy mi vng c th phc v hiu qu nht cc

thu bao ca n.

3.2.4. D bo nhu cu

D bo nhu cu l nh gi s lng thu bao kt ni n mi im ca mng

li, v xu hng pht trin trong tng lai.

Cc nhn t sau s c nh hng n d bo nhu cu:

- Cc nhn t kinh t: tc pht trin kinh t, tiu th c nhn, khai thc v sn

xut cc sn phm cng nghip.

- Cc nhn t x hi: dn s, s h gia nh, s dn lm vic.

- Gi cc: gi thit b, cc c bn, cc kt ni, cc ph tri.

- Chin lc marketing: chin lc v sn phm v qung co.

Cc s liu trn phi c thu thp d bo nhu cu v phn b. Thc hin mt

d bo n gin ch bng vic nhn vo xu hng tng lai gn l cch tip cn

th ng, l khng th chp nhn c. Lp k hoch nn bao gm cc loi tip

cn tch cc, v d, tha nhn s gia tng trong nhu cu c ch dn bi chin

lc kinh doanh.

D bo nhu cu thc t, phng php thch hp nht nn c la chn trong mtvi phng php ty theo iu kin ca mi quc gia v mi vng, v ty theo s

ph cp ca vin thng.

3.3. D bo nhu cu

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D bo l khu quan trng khng th thiu c trong cng vic ra quyt nh. N d

bo cc xu hng tng lai v tr thnh iu cn bn lp k hoch kinh doanh c kinh t

v c hiu qu.

- Lnh vc dch v Vin thng c nh hng ln n cuc sng con ngi v cc hot

ng kinh t v n l mt ngnh c quy m ln vi cc thit b i hi lin tc u t rtnhiu. Bi vy, iu c bit quan trng vi ngnh ny m rng kinh doanh n nh v u

t thit b c hiu qu phi da vo d bo nhu cu di hn. Trong phn ny s trnh by cc

bc v phng php d bo nhu cu.

3.3.1. Khi nim

Theo ngha rng, d bo nhu cu khng ch bao gm vic d bo m l c vic thu

thp v x l s liu, v vic iu chnh d bo nh hnh 3.1 sau y. Ba bc ny c

lin quan cht ch vi nhau. Thu thp v x l s liu cung cp nhng s liu c bn

cho hai bc kia. iu chnh d bo phn hi nhng phn tch c c kt qu d

bo nhu cu. Ni chung, ba bc ny c nh ngha nh sau:

(a) Thu thp v x l s liu

Chui s liu v nhu cu in thoi (yu t ni sinh) v thng k v dn s, s h

gia nh, cc ch s kinh t... (yu t ngoi sinh) c thu thp v x l theo yu cu.

(b) iu chnh nhu cuNhng khc bit gia gi tr d bo v gi tr thc phi c phn tch v gi tr

d bo s c iu chnh theo kt qu ca s phn tch ny.

(c) D bo nhu cu

Nhu cu tng lai c d bo hoc c tnh ton. y l cng vic d bo

chnh v c gi l d bo theo ngha hp. Ngoi cc phng php truyn thng, cc

s liu nhn c t hai bc kia phi tn dng xc nh v nh gi cc gi tr dbo.

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Hnh 3.1, Khi nim v cng vic d bo

3.3.2. Tng trng nhu cu

Mng in thoi thng phn chia thnh 3 pha nh trong hnh 5.2 sau y:

- Pha bt u: tc tng trng chm.

- Pha tng trng nhanh: tc tng trng rt nhanh hay gi l giai on tng

tc.- Pha bo ha: tc tng trng gim.

mi pha, cc iu kin v kinh t v x hi l khc nhau. Khi chn la mt

phng php d bo, iu quan trng phn tch la chn l phi xc nh c

mng hin ti ang nm pha no.

(1) Pha bt u

Pha bt u lin quan n giai on tng trng chm ca mng, vi mt in

thoi mc thp.

Trong pha ny, nhu cu in thoi ch yu l dnh cho nhu cu sn xut kinh

doanh. Nhu cu ny ph thuc vo cc ngnh cng nghip v cc ngnh cng cng.

Bi vy, mt mng c bn c lp t cng vi s pht trin cng nghip. Khng c

mng c bn ny pht trin cng nghip s b cn tr.

Nhu cu c nhn b hn ch trong pha ny. in thoi vn l th hng ha xa x

i vi ngi tiu dng ni chung v khng th c xem nh l hnh ha cn thit

25

D bo theo ngha hp

D bo nhu cu

iu chnh nhu cu Thu thp v x l s liu

D liu phn tch

Kt qu d

bo

S liu c bn

S liu


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cho cuc sng. Cc hng ha tiu dng khc v thc phm vn c u tin hn l

in thoi. V vy, d bo nhu cu in thoi cho sn xut kinh doanh phi da vo

phn tch s pht trin kinh t ca a phng v quc gia.

(2) Pha tng trng nhanh

pha ny, kinh t pht trin. Trong lnh vc cng nghip, cn thit phi ci

tin mng vin thng p ng dch v cht lng cao hn. iu ny ph hp khi

mc sng ngi dn tng ln v nhu cu hng ha v in thoi ni chung l tng ln.

Trong giai on tng trng nhanh ny, nhu cu ca dn c tr nn ln hn cung.

Thm ch khi nhu cu hin ti c p ng, vn ny sinh nhiu nhu cu hn na.

Tnh trng ny tip tc din ra cho n khi mng tng trng n mt qui m hp l.

Pha ny tng xng vi giai on thit lp mng. Cng vic d bo trong giaion ny l rt quan trng v mt lot nhng sai st trong d bo c th dn n nhng

sai xt trong vic lp k hoch v chi ph.

(3) Pha bo ha

pha ny, mt in thoi dn c t ti 80% hoc hn th v c in thoi

dn c v sn xut kinh doanh u pht trin tng ng.

Sau pha ny, nhu cu s thay i v c cu l nhu cu v cc dch v mi, vdoanh thu cng s thay i theo c cu nhu cu chng hn nh doanh thu v in thoi

th 2.

Nhng nhn nh trn khng phi lun l ng mt vi khu vc thm ch ngay

c trong mt quc gia. Tuy th, vic xc nh c mi pha l vn rt cn thit v

phng php d bo s c p dng cho mi pha.

3.3.3. Cc bc xc nh nhu cuCc bc d bo nhu cu c th hin nh sau:

Bc 1: Xc nh cc mc tiu d bo

Bc u tin ca cng vic d bo l phi xc nh r cc mc tiu d bo. Cc

mc tiu d bo bao gm nhu cu ca dn c v nhu cu cho sn xut kinh doanh.

Vng mc tiu d bo l ton b vng trong nc hoc vng tng i,... Giai on d

bo c th l 5 nm, 10 nm hoc 15 nm.

Bc 2: X l cc iu kin ban u

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D bo theo chui thi gian c th c thc hin theo cch nh sau mi lin

quan gia nhu cu v cc yu t quyt nh nhu cu qu kh v c bn l khng thay

i so vi tng lai. Bi vy, cc yu t ni sinh nh h thng cc v c cu cc v

cc yu t ngoi sinh nh cc k hoch pht trin vng phi c xem xt.

Bc 3: Cc s liu cn thu thp

Trong bc ny phi xc nh c yu t no nh hng n cc mc tiu d bo

v nhng s liu no nn thu thp. Tip theo, cc s liu thu thp c phi c phn

loi sao cho vic phn tch chng c d dng.

Cc s liu lin quan n d bo nhu cu in thoi nh sau:

- Nhu cu in thoi, mt in thoi.

- Dn s, s h gia nh.

- S cc c quan.

- T l tng thu nhp.

- Tc tng trng kinh t.

- Cc k hoch pht trin th.

Cc s liu trn c sp xp theo thi gian, theo cc nhn t (nh nhn t ngoi

sinh v ni sinh) v theo cc vng tng i.

Bc 4: Tip cn v phn tch xu hng nhu cu

Xu hng nhu cu cn c phn tch theo quan im nh sau:

- Cc gi tr qu kh.

- C cu th trng in thoi.

- Ngun nhu cu.

- Mt in thoi.

- Cc c im ca vng nghin cu.

- So snh vi cc vng khc v cc quc gia khc.

Bc 5: Nghin cu cc k thut d bo v tnh ton gi tr d bo.

Cc phng php d bo c phn loi theo 3 phng php sau:

- Phng php chui thi gian.

- Phng php m hnh ha.- Cc phng php khc.

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Mt phng php d bo c xc nh thng qua cc s liu thu thp. Tuy nhin,

cho gi tr d bo m bo chnh xc cao hn, iu quan trng l nn chn

phng php kh thi nht v chn cc gi tr ti u.

Bc 6: Xc nh cc gi tr d bo

T vic phn tch kt qu nhn c bc 2 v bc 4, cc gi tr ti u s cquyt nh.

3.3.4. Cc phng php xc nh nhu cu3.3.4.1, Phng php chui thi gian

(1) Khi qut

i vi phng php chui thi gian, xu hng trong qu kh s c p dng

d bo cho tng lai.V d, gi s thi gian l t v bin d bo (nhu cu hoc lu

lng) l y, hm biu din mi quan h c dng y=f(t). Phng php ny thng

c s dng cho d bo ngn hn. Hn ch ca phng php ny l cc bin v chnhsch nh cc v mc dch v khng c tnh n v nh vy th n khng c tnh

thuyt phc. Nhng phng php ny d thc hin nht v n gin v ngoi cc s

liu cn c nh nhu cu v mt in thoi ra th khng i hi thm s liu no

khc. Chnh v l do m phng php ny c s dng rng ri trong d bo dn

s, d bo kinh t,

(2) iu chnh s liu bin thin

Thng thng, s liu chui thi gian bao gm 4 dng sau: bin thin xu th, bin

thin chu k, bin thin theo ma, bin thin bt thng. Bi vy cn phi chuyn cc

bin thin khc nhau v dng bin thin d liu xu th bng phng php bnh qun

thng, phng php nhn cng

Phng php bnh qun thng c gii thch ngn gn nh sau: Phng php ny

l phng php n gin nht trong cc phng php c tnh s bin thin theo ma

v n cng c gi l phng php bnh qun theo chu k. Phng php ny c p

dng khi bin thin xu th - mt trong cc nhn t ca chui thi gian xut hin nh

bin thin l mt gi tr xu hng ca cc ng thng v cho php tm s bin thinca s liu bng cch tnh n gin hn.

Gi s rng trong chui thi gian chu k theo thng ca n nm, i thng l x ij, Mi l

gi tr trung bnh, M0 l bnh qun gi tr trung bnh.

Mi=xij/n

M0=xi/12 (5.1)

Ch s ma (SI) c tnh nh sau:

SI=Mi/M0*100 (5.2)

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chuyn dng d liu ma, s dng ch s ma nh m hnh (5.2) v nhn vi

100.

(3)Cc biu thc s dng cho d bo

Biu thc thch hp c la chn phi da trn nn tng ca xu hng nhu cu

trong qu kh. thi im ny, cc c im ca mi biu thc phi c xem xty . l, biu thc v giai on d bo phi c xc nh xem nhu cu s thay

i nh th no.

i vi d bo bng phn tch chui thi gian th ch thi gian l yu t gii thch

bin nhu cu. Cc yu t khc nh nhng thay i c cu khng c gii thch.

Nhng phi ch rng, phng php ny ch ng trong trng hp mi lin quan

gia cc yu t quyt nh nhu cu hin ti v nhu cu qu kh s khng thay i c

bn trong tng lai. Nu bt k s thay i c cu no c xem l s nh hng ln

n nhu cu th nguyn nhn v mc nh hng ca n phi c phn tch klng v phng php d bo phi c iu chnh.

Sau y l cc biu thc c dng cho phn tch chui thi gian. Phng trnh

tuyn tnh v phng trnh bc 2 kh l ph hp vi d bo ngn hn. Hm m v hm

logistic ph hp vi d bo di hn. Hm logistic nhn c t vic nghin cu vn

tng dn s c bit ph hp trong d bo li ch cng cng ca hng ha c tiu

th lin tc.

(4)Xc nh hng s ca m hnh d bo

Vi mi phng php c xc nh da vo xu th nhu cu trong qu kh th

hng s ca mi mt phng trnh phi c tnh ton. Phng php ph bin

nht l phng php bnh phng nh nht.

(a) Phng php bnh phng nh nht

Phng php ny c ngha l tm ra c mt phng trnh sao cho tng din

tch khc bit gia gi tr thc t v gi tr d bo nh nht.

(b) Xc nh gi tr ti hn (mc bo ha)

Gi tr ti hn K trong hm logistic v hm m iu chnh l gi tr da vos liu qu kh thi im d bo. Gi tr K khng nht thit phi l hng

s. Khi nn kinh t pht trin, gi tr K tr nn ln hn. Sai s ln s khng

xut hin thm ch nu K c coi nh l mt hng s cho n khi ng cu

tin gn n K.

Gi tr K l khc nhau khng ch vi cc quc gia v cc vng m cn khc

nhau ty theo trnh kinh t v cc iu kin ca dn c. N thng c xc

nh da trn cc yu t kinh t v cc yu t chnh tr, tham kho s liu cacc quc gia khc v s liu ca cc khu vc ln cn.

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3.3.4.2, Phng php hi quy

(1) Khi qut

Trong m hnh hi quy, mi quan h ca nguyn nhn v kt qu gia nhu cu

v cc yu t quyt nh n c m hnh ha d bo. u tin, cc yu t

tm c tm kim bao gm mi lin quan ph thuc ln nhau hoc mi linquan gia nguyn nhn v kt qu trong qu kh. Nhn chung, cc yu t kinh t

v cc yu t x hi u lin quan n nhu cu.

Trong nhng nhn t ny, mt vi nhn t l m hnh c nh hng ln n nhu

cu v gi tr tng lai ca n c th l d bo. Vi nhng m hnh ny nhu cu

l d bo.

(2) Xc nh cng thc hi quy

(a) S tng quanTrc khi xc nh cng thc truy hi, cn phi tm mt nhn t an xen vi

nhu cu. Biu hin cng ca s lin h l khi nim ca s tng quan.

(3) Cc phng php khc

3.4. D bo lu lng

3.4.1. Khi nim

D bo lu lng l nh gi tng s lng xy ra ti mi im ca mng li.

Cc nhn t nh hng n d bo lu lng: kt qu d bo lu lng, cc dao ngc bn, dch v.

3.4.2. Cc bc xc nh lu lng

Lu lng thng c d bo theo cc bc sau y:

Bc 1: Xc nh mc ch v i tng d bo. Xc nh mc tiu ca d bo,

lu lng v nm c d bo.

Bc 2: Thu thp s liu v xc nh gi thit

Xc nh cc gi thit ca d bo (v d: h thng gi v cc d n pht trin a

phng c th c). La chn v phn tch s liu biu th xu hng ca nhu cu lu

lng.

Bc 3: Nghin cu xu hng lu lng

Ghi chp v phn tch cc c tnh lu lng. Gm c: xu hng chui thi gian

ca lu lng, phn tch xu hng lu lng ni ht v ng di trong nc, cc

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nhn t chnh nh hng n lu lng (v d: cu thu bao), mi lin h gia s pht

trin vng v lu lng, s phn b lu lng theo thi gian.

Bc 4: La chn phng php d bo. Phng php thch hp nht c la

chn qua vic xem xt cc c tnh ca lu lng v cc nhn t dao ng.

Bc 5: Tnh ton lu lng c bn

Tnh ton lu lng trung bnh hng nm cho nm tham kho.

Bc 6: D bo lu lng

D bo thc hin bng cch s dng phng php chui thi gian, hoc nhn t l

tng lu lng vi lu lng c bn.

Bc 7: nh gi / xc nh d bo

Xem xt cc c tnh ca cc nhn t dao ng s dng trong d bo, d bo so

snh xu hng lu lng ton cu v s liu lu lng ca tng nc.

Bc 8: Tnh ton lu lng tham kho

Lu lng tham kho c tnh theo gi thit v s dao ng trong d bo (lu

lng trung bnh hng nm).

Bc 9: Bin son cc bo co

Cc bo co m chng ta a ra cc s liu c s cho d bo lu lng (lu lng

tham kho v s thu bao), d bo, cc gi thit cho d bo, v c s nh gi / xc

nh d bo c son tho.

Bc 10: Hon thin d bo

Bng vic tip tc so snh d bo vi cc s liu thc t, ci tin phng php d

bo t c chnh xc cao hn.

3.4.3. Cc phng php xc nh d bo lu lng

Cc phng php d bo khc nhau c chn la theo lng thoongn tin sn c

l bao nhiu (ngha l ch c s liu cho mi trm hoc s liu cho ton quc gia l sn

c). Trong phn ny, chng ti s miu t hai trng hp: (1) s liu lu lng sn c

v (2) s liu lu lng khng sn c.

3.4.3.1, Khi s liu lu lng sn c

Khi mt vi s liu lu lng c sn, s dng cc phng php sau y:Phng php chui thi gian.

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Phng php hi quy.

D bo ton cu xem xt cc iu kin ca tng a phng.

D bo n gin t l tng lu lng im im.

Mi phng php s c miu t di y:

(1) Phng php chui thi gian

Phng php ny xc nh xu hng chui thi gian da trn s liu qu kh, v

d bo tng lai bng cch m rng xu hng.

(2) Phng php hi quy

Phng php ny xc nh cc nhn t to ra cu lu lng, v m t s dao ng

lu lng s thay i ca cc nhn t ny. M hnh d bo cng thc (4.1) da

trn m hnh n hi. Cng thc ny c s dng tnh ton t l tng lu

lng.

Y=aX1.X2...Xn

,,... : Bin thin

a: hng s

y: t l tng lu lng

X1 ,X2,... Xn: Bin s miu t

Trong hu ht cc trng hp, lu lng c lin quan cht ch vi s lng thu

bao. Tuy nhin, v s lng cuc gi l khc nhau gia cc thu bao kinh doanh

v thu bao dn c nn hoc l s thu bao dn c hoc l s thu bao kinh doanh

c chuyn i ln nhau. Kt qu ny gi l s thu bao chuyn i v c nh

ngha l bin s miu t.

Phng php ny thu c ng xu hng theo tng quan gia lu lng v s

thu bao bin i. S dng ng xu hng ny, lu lng c d bo bng

cch c tnh s thu bao chuyn i.

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Hnh 6.2. D bo tng quan s dng gia lu lng v s thu bao

(3) D bo ton b c xem xt n cc iu kin ton ccM hnh d bo ton b, c p dng trong khu vc rng ln, c th s

dng tng i nhiu s liu thng k hn nh ch s kinh t. Tuy nhin,

lu lng d bo cho mi khu vc tng i l khng d, bi v s liu thng

k cho cc khu vc nh nh vy thng c hn. V vy, t l tng lu lng

ca khu vc c tnh ton t t l tng lu lng ton b c xem xt n

iu kin pht trin cc b ca vng. S dng cng thc sau y:

y=K.X

=ym.(X/xm)

(4.2)trong

y: t l tng lu lng ca khu vc lien quan.

x: t l tng thu bao ca khu vc lien quan(s dng l bin i din th

hin s pht trin ca khu vc).

: l hng s.

K=ym/Xm

ym: t l tng lu lng ton b.Xm: t l tng thu bao ton b

(4)D bo n gin t l tng lu lng im - im

d bo lu lng gia cc khu vc, chng ta cn s liu pht trin d n

v xu hng nhu cu cho cc khu vc. V lu lng ph in thoi ng

di chuyn tip my tnh trn ton quc nn n chu tc ng ca nhiu xu

hng kinh t x hi. Cc xu hng ny khng o c vi mt n v

nh nh mt khu vc. Cng cn xt nhng nh hng ca iu kin c

nhng vng khi u v kt thc lu lng.

Bi vy, lu lng gia cc trm c d bo tng th theo quy trnh sau

y. Vng lu lng d bo thng l vng tnh cc lien tnh (TA).

(a) thu c t l tng lu lng, xem xt cc nhn t chung vi khu vc

rng ln hn, trong xc nh khu vc s d bo (d bo ton b).

(b)S dng d bo ton b nh l mt ch s nhn t nh cc ch s kinh t,

GNP, vv ph bin vi cc vng ln [quc gia v cc thnh ph chnh],

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lu lng khi u c bn c on trc qua xem xt iu kin cc b

(nhng d n pht trin vng v bin ng dn s).

(c) T l tng lu lng ca khu vc c d bo da trn t l tng lu

lng ca u v cui vng tnh cc lin tnh.

(d)Lu lng gia hai vng c d bo bng vic nhn t l tng lulng vi lu lng c bn gia hai vng.

y=y1.y2

y: t l tng lu lng gia TA1 v TA2

y1: t l tng lu lng ca TA1.

y2: t l tng lu lng ca TA2.

3.4.3.2, Khi s liu lu lng khng c sn

(1) D bo tng lu lng khi u

Khi mt in thoi thp, nhiu ngi s dng mt s lng in thoi c

hn. V vy tng lu lng khi u cho mi in thoi l tng i ln. Nhng

khi mt in thoi tng, s thu bao vi t l s dng thp cng tng ln.

Bng cch ny, tng lu lng khi u cho mi in thoi gim.

(2) D bo u ra lu lng thoi ng di

D bo u ra lu lng thoi ng di s dng th a ra hnh 6.4.

th ny th hin mi quan h gia s lng dn c v t l lu lng ng

di. N d trn nhng quan im sau y:

T l u ra lu lng thoi ng di trong tng i lu lng khi u

ph thuc vo hot ng kinh t x hi cc th. Nu th nh v hot

ng kinh t - x hi ph thuc ln vo cc vng ngoi , t l lu lng thoi

ng di s cao. V vy, di cc iu kin kinh t x hi ging nhau, th c

dn c t hn s c t l lu lng in thoi ng di cao hn.

Da vo t l lu lng thoi ng di thu c hnh 6.4, c th d bou ra lu lng thoi ng di.

3.4.3.3. M hnh trng trng (d bo lung lu lng gia cc tng i)

i vi mng ni ht khng c sn s liu, cng thc m hnh trng trng

c s dng tnh lung lu lng. Phng php ny ph thuc vo khong

cch gia cc tng i. Nhn chung, khi khong cch gn, lng ngi nhiu

hn, lu lng in thoi s tng ln.

3.5. K HOCH NH S

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3.5.1. Gii thiuK hoch nh s c thit lp phi locgic v mm do. Cc con s khng ch

c s dng nh nhng iu kin phn chia gii hn cho cc im ni iu khin

gia cc thu bao v mng li m cn c s dng cho vic tnh cc cc cuc

gi.Khi lp k hoch nh s cn quan tm n cc vn sau:- K hoch nh s phi n nh trong mt thi gian di, s lng cc con s phi

p ng cho nhu cu pht trin dung lng trong 50 nm cng nh khi pht trin

dch v mi.

- Trn ton mng quc gia cc con s phi c dng chung c thit lp mt

cuc gi m khng quan tm ti v tr thu bao ch gi.

- K hoch nh s phi n gin v d s dng cho cc thu bao. S lng cc

con s cng t cng tt sao cho khng vt qu nhng quy nh m ITU-T a ra cho

s quc t.

- V vn chuyn mch, k hoch nh s phi m bo sao cho th tc bin

dch, to tuyn v tnh cc n gin.

3.5.2. Cc h thng nh s3.5.2.1. H thng nh s ng

H thng nh s ng l h thng nh s khi ton mng li c coi nh

mt vng nh s, cc con s c gn cho cc thu bao trn mng theo mt khun

dng chun . Trong h thng ny, mi thu bao c a ch ring v s lng cc con

s l c nh.

3.5.2.2. H thng nh s m

Trong h thng nh s ng, khi lng thu bao tng ln v mng ln ln th

mi s thu bao phi tng thm s lng cc con s nhng khi quay s vi nhiu s

con s nh vy th khng thun tin. Do , trong h thng nh s m, mng cxy dng da trn tp hp cc vng nh s ng. Trong h thng ny, thu bao thuc

vng nh s ng khc nhau c u ni vi nhau nh vic thm vo cc con s

tin t trung k v cc m trung k trc s ng. H thng ny cn cho php u ni

cc thu bao trong mt vng, cng tnh , vi cc s ngn hn.

3.5.3. Cu to s3.5.3.1.S quc gia :

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ITU-T quy nh rng con s 'O' lm s tin t trung k

- M vng c th bao gm mt hay vi con s .

- Mi mt tng i ni ht trong mt vng c gn mt m ring.

3.5.3.2.S quc t

+ i vi nhng quc gia nh a ra cc dch v gi quc t ITU-T quy nh '00'

l s tin t quc t.

+ M quc gia c th c t 1 ti 3 con s . ITU-T a ra bng m quc gia ca

cc nc .

+ S kt hp gia m quc gia v s quc gia to thnh s quc t .

* ITU-T khuyn ngh rng con s quc t khng nn vt qu 12 con s . Do

s lng cc con s trong s quc gia phi l (12-n).

{trong n l s con s trong m quc gia (country code)}.

Ch : ITU-T khuyn ngh rng s lng con s ISDN quc t c chiu di ti a

l 15 con s . Gi s rng, c vi mng in thoi v ISDN trong mt quc gia, ITU-T

m rng k hoch nh s cho in thoi t 12 s ln 15 s nhn dng c cc

mng khc nhau.

3.5.4. Cc th tc cho vic lp k hoch nh sThng thng, k hoch nh s thit lp da trn cc bc sau y:

* Xc nh dung lng s

D bo nhu cu pht trin s lng thu bao quyt nh s lng cc con s.

La chn s ch s

* Phn vng nh s- Xem xt s ph hp gia a gii hnh chnh v vng tnh cc.

36

M tng iM vngTin t trung k S thu bao+++

S thu bao

S quc giaHnh 2.5 :Cu to s quc gia

S thu baoM tngi

M vngM quc giaTin t quc t + +++

S quc giaS quc t

Hnh 2.6 :Cu to s quc t


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- S ph hp gia vng t thu bao v vng t trung tm chuyn mch s cp.

* Cu to s

- Xem xt s kt hp gia h thng nh s ng v nh s m

- Quy nh chiu di cc s thu bao l thng nht.

3.5.4.1 Quyt nh dung lng nh s

3.5.4.1.1 Chu k cu k hoch nh s

Mi ln mt k hoch nh s c thit lp, cc thay i trong k hoch xy ra

sau thng gy ra nhiu kh khn. iu l khng trnh khi, v th vic a ra

cc ch s v cc thng s khc phi cn c vo vic d bo nhu cu in thoi chnh

xc trnh vic thiu s. Do vy, khi d bo nhu cu in thoi phi lu tm ti spht trin trong tng lai. Trn thc t vic thc hin d bo nhu cu di hn l rt kh

khn. Tuy nhin, k hoch nh s nn trin khai bng cch mi ln em p dng vo

thc tin th i hi khng c thay i trong vng 50 nm

3.5.4.1.2 Cc ch s v dung lng s

Dung lng s ph thuc vo vic c bao nhiu ch s c s dng cho vic

nh s. Dung lng nh s tng trng cho gii hn cao hn v tng s thu bao

v /hoc thit b u cui m c th c cung cp trong mt vng thch hp. V d,nu 4 ch s c s dng cho vic nh s th l thuyt n s to thnh 10.000 s c

th s dng c, ln xung t 0000 n 9999. C ngha l kh nng nh s

y s l 10.000 s. Tuy nhin, khng phi tt c cc s ny u s dng cho vic

nh s, bi v c mt gii hn c quy nh cho cc tn t trung k v quc t v

cc m dch v c bit.

3.5.4.1.3 La chn cc ch s

Vic la chn cc ch s phi quan tm ti nhu cu nh s thu bao m bao

gm c cc dch v c bit cng nh khi cc m ny c n nh ti cc thu bao.

V d, chng hn ta gi s nhu cu nh s trong tng lai l 9 triu s, th cc ch

s c la chn theo cch sau:

a. Cc iu kin tin quyt:

- Ch s 0 nn c s dng cho tin t trung k

- H thng nh s 1XY nn c s dng cho cc s ca cc dch v c bit- M quc gia nn s dng 3 ch s

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b. Cc gii hn trong vic s dng s:

- 9 ch s t 1 n 9 khng bao gn ch s 0 c s dng cho ch s u tin

ca m tng i

c. Thc hin php tr i 3 ch s i vi m quc gia t tng s 12 ch s ch cn

li 9 ch s. Nh vy chng ta c th s dng n 9 ch s cho s quc gia

- Gi s vi 8 ch s, th kh nng nh s s l: 9 x 8 x 10 6 = 72.000.000 s

Do vy, p ng c nhu cu nh s l 9 triu s th nn s dng 8 ch s.

Hn na, cn phi quan tm n tn tht khi phn tch trong dung lng nh

s lin quan ti vic thit lp mt vng nh s. minh ho khi nim tn tht phn

tch, chng ta hy so snh mt vng c phc v bi mt tng i in thoi duy

nht vi mt vng c phc v bi 2 tng i in thoi khc nhau.

a. Nu l vng c phc v bi mt tng i in thoi duy nht

- Ch s 2 s c n nh cho m tng i

- Nu s ca mt thu bao gm 4 ch s th kh nng nh s l 10.000 s, do

s p ng nhu cu trong tng lai l 8000 s. Ly 10.000 s ca kh nng nh s tr

i 8000 s ca nhu cu tng lai th cn 2000 s l dung lng khng dng n.

b. Nu vng c phc v bi 2 tng i in thoi khc nhau

- Vng dch v ni ht ny c chia thnh vng A v vng B.

- i vi vng A, gi s nhu cu trong tng lai l 5000 s, ch s 5 c n nh

cho m tng i.

- i vi vng B, gi s nhu cu trong tng lai l 3000 s, ch s 6 c n nh

cho m tng i.

- S thu bao c quy nh c 4 ch s. Kh nng nh s l 10.000 s s c

n nh cho mi vng A v B. Nh vy, tng kh nng nh s cn c l 20.000 s.

38

S: 2-XXXX

Nhu cu in

thoi: 8000

S: 5-XXXX S: 6-XXXX

Nhu cu: 5000 Nhu cu:

3000

a. nh s vi mt tng i

duy nht

b. nh s vi hai tng i

khc nhau


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Ly 20.000 s ny tr i 8.000 s ca nhu cu tng lai cn 12.000 s l dung lng

khng dng n.

Dung lng khng dng n l qu cao trong trng hp (b) cho vng nh s

l khng thch ng. V d c trch dn trn c th l trng hp c bit. Tuy

nhin n li minh ho cho kh nng m cc m trung k v/hoc cc m tng i c

th thiu nu khng la chn s lng ch s hon chnh cho ton b dung lng nh

s.

3.5.4.2 La chn vng nh s

Qua v d trn cho thy ccc vng nh s nn c la chn cn c vo nhu

cu tng lai, theo vic thiu kh nng nh s s khng xy ra.Nu kh nng nh

s thiu th cc s ny c th c s dng t cc vng s khc.

la chn vng nh s ng n th cn phi m bo tnh nht qun i vi

kh nng nh s, gia cc vng dch v ni ht v cc vng tnh cc. Nu khng

m bo tnh nht qun s dn ti cc vn sau:

- Cc mc gi khc nhau c p dng cho cc vng c cng m trung k v

nh vy th ngi s dng s khng th hiu ni h thng tnh cc

- Khi cc vng cung cp ca trung tm c s ging ht cc vng tnh cc th

tng i c th to ra mt ch s tnh cc bng cch nhn dng m trungk. Nu c bt k s khng nht qun no gia cc vung dch v ni ht v

cc vng tnh cc th tng i phi nhn dng m tng i t mi nhn

dng vng tnh cc. iu ny dn ti s phc tp trong hot ng ca tng

i.

Cc vng nh s nn c la chn cho ton b kh nng nh s theo ng

h thng phn vng nh a ht qun l m nhng ngi s dng thng tho.

3.6. K HOCH NH TUYN

3.6.1. Gii thiu

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Thng thng mt cuc gi c thc hin qua nhiu tng i khc nhau. nh

tuyn l qu trnh chn mt ng i (tuyn) qua cc nt mng ti ch mt cch

ti u nht v mt k thut cng nh v mt kinh t.

Mt s yu cu t ra:

. Qu trnh chn tuyn v cc th tc iu khin phi n gin.

. m bo s dng knh & cc thit b mt cch hiu qu.

. m bo thit k v qun l mng d dng

3.6.2. Cc phng php nh tuyn3.6.2.1. nh tuyn c nh :

nh tuyn c nh l phng php quy nh mt s tuyn c nh cho vic

chuyn lu lng gia hai tng i. Do phng php ny yu cu phn iu khin rt

n gin nn n c ng dng trong cc h thng chuyn mch c in. Tuy nhin,

phng php ny rt hn ch trong vic chn tuyn dn n khng linh hot khi c

knh no b li.

3.6.2.2.nh tuyn lun phin:

Phng php nh tuyn lun phin c t r trong hnh v di y. Gia bt

k hai nt mng no cng c nhiu hn 1 tuyn. Nguyn tc nh tuyn lun phin nh

sau: khi tt c cc mch thuc tuyn u tin bn th tuyn th hai c chn. Nutuyn th 2 bn th tuyn th 3 c chn v c nh vy cho ti khi tm c tuyn

ri hoc s mt cuc gi .

Hnh 2.7. Nguyn tc nh tuyn lun phin

Phng php ny rt hiu qu trong vic ti u ho s dng cc knh trung k vthng c p dng gia cc tng i in t s SPC.

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3.6.2.3.nh tuyn ng

nh tuyn ng l mt kiu c bit ca nh tuyn lun phin nh trn, mt

im khc bit l tng linh hot v gim thi gian chn tuyn gia hai nt mng

cn c vo tnh trng ca mng hoc theo thi gian nh trc. Kiu nh tuyn ny c

th c s dng gia cc tng i in t s hoc gia cc nt trn mng s liu hin

nay.

3.7. K HOCH TNH CC

3.7.1. Gii thiu chungHng nm trn mng vin thng, cc nh cung cp dch v vin thng phi

u t nhiu cho vic vn hnh, bo dng cng nh pht trin, qun l mng, do

cc thu bao phi tr cc cho cc dch v m h s dng. xc nh mc cc m

thu bao phi tr cho cc dch v vin thng v cc tiu ch cho tnh cc vic lp k

hoch tnh cc a ra cc loi cc, s tin v phng php tnh ton ph hp l

rt cn thit. m bo xy dng c h thng tnh cc ph hp nh trn th k

hoch tnh cc phi tho mn mt s yu cu sau y:

- Quy tc tnh cc phi cng bng, d hiu i vi khch hng v n gin cho

nh qun l.

- H thng tnh cc ring phi ph hp vi cu trc tnh cc chung.

- H thng tnh cc phi khuyn khch nhu cu s dng dch v thu bao hay

dch v mi.

- Cc thit b v k thut cho vic tnh cc phi tin cy chnh xc.

Cc c phn chia thnh 3 loi :

- Chi ph lp t ban u (Installation fee) khi pht trin thu bao mi th cc c

quan ch qun phi u t cho lp t dy cp, do thng thng khi mi lp t

th ngi s dng phi tr mt khon tng i ln.

- Chi ph cho ng k dch v (Subscription fee) y l mt khon chi ph c nh

duy tr hot ng ca ng dy v cc thit b lin quan.

- Cc cho cuc thng tin (Call charge) hai kiu trn th c nh v khng yu cu

mt thit b hay mt cch tnh no nhng i vi vic tnh cc cho cc cuc thng tin

th phc tp hn ph thuc vo thi gian, khong cch.

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3.7.2. Cc tiu ch cho vic tnh cc3.7.2.1. Tnh cc da trn s lng cuc gi

Phng php ny ch quan tm n s lng cuc gi, khng cp n thi

gian duy tr cuc gi. u im l n gin ho cc thit b tnh v lu cc, nhng

nhc im l cc cuc gi c th din ra lu.3.7.2.2. Tnh cc da trn thi gian duy tr cuc gi

Thi gian duy tr cuc gi c tnh t khi thu bao b gi nhc my tr li cho

ti khi cuc gi c gii phng. Trong phng php ny c li khi m cuc gi din

ra di.

3.7.2.3. Tnh cc da trn thi gian duy tr cuc gi v khong cch

Thng thng cc cuc gi ng di cn s dng nhiu thit b hn so vi cc

cuc gi ni ht nn cc s cao hn. Do khong cch l tiu ch quan trng cho

vic tnh cc cho cc cuc gi ng di cng vi thi gian duy tr cuc gi. Khong

cch y cp ti khong cch gia tng i ch gi v tng i b gi. phc v

cho vic tnh cc, mng quc gia c chia thnh nhiu vng cc khc nhau mi

vng c quy nh mt mc cc c nh.

3.7.2.4. Tnh cc ph thuc vo khi lng thng tin

Trong thng tin s liu th vic tnh cc c th da trn khi lng thng tin c chuyn.

Kiu tnh cc ny th rt d hiu i vi ngi s dng. i vi thng tin s

liu, v d trong chuyn mch gi cc c tnh ph thuc s lng gi c chuyn

i.

* Ngoi ra cn c phng php tnh cc ph thuc vo tng thi im trong

ngy. V d tnh cc cho bui m, cui tun hay vo nhng dp l. Khi m lu

lng thp th c th gim gi tng nhu cu s dng dch v.

3.7.3. Cc h thng tnh cc

3.7.3.1. H thng tnh cc u (Flat - Rate System)

y l cch tnh cc n gin nht, khng quan tm ti s lng cuc gi

cng nh thi gian duy tr cuc gi. Mt mc cc c nh c t ra cho ngi s42

Khi lng thng tin (bit) = Tc bt * thi gian truyn


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dng trong mt khong thi gian thng thng l mt thng. Tuy nhin phng php

ny c mt s u nhc im.

. u im : - Khng yu cu thit b lin quan ti tnh cc .

- Cng tc qun l rt n gin .

- Ngi s dng bit trc c mc cc m h phi tr .

- Khuyn khch vic s dng dch v vi cc thit b c sn.

. Nhc im: - H thng khng cng bng i vi ngi s dng.

- Hn ch vic ng k thu bao mi.

- Thu bao khng iu chnh c mc m h phi tr.

3.7.3.2. H thng tnh cc da trn cuc thng tin (Measured - Rate System)

Trong cc h thng tnh cc theo cuc gi th thng tin cc c th ph thuc

vo thi gian duy tr cuc gi v khong cch thng tin. Nu mc cc cho mt c ly

c nh trong khong thi gian T l a th mc cc cho mt cuc thng tin c th tnh

theo cng thc sau:

Mc cc = a * t/T

Trong :

a : l mc cc cho mt c ly nht nh trong khong thi gian T

t : l thi gian duy tr cuc thng tinT: Chu k tnh

Tu thuc vo s thay i ca chu k tnh hay t gi trn mt n v o m

chng ta c th c hai cch tnh cc.

a. Phng php tnh cc theo chu k c nh

Chu k T l c nh, gi tr a thay i theo khong cch ca cuc thng tin.

i vi cc thao tc nhn cng , phng php ny rt ph bin do thit b n gin

(gm ng h o v cch tnh n gin). Chu k y thng thng c chn l 3

pht khi cuc gi bt u v sau l mt pht.

i vi cc h thng chuyn mch khng iu khin theo nguyn tc SPC th t

gi a thay i nh vic thay i ca s lng cc xung o c theo tng khong

cch. Do s lng cc vng cc tng ln v cc thit b rt phc tp.

V d

43

Vng B

Vng AVng C

20 Km 70Km

Hnh 2.14 : V d vic tnh cc theo chu k c nh


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Gi s mt cuc gi din ra khong 5 pht 30 giy gia thu bao thuc vng A,

B v C. Trong trng hp ny th t gi trn mt n v o lng c tnh nh bng

sau .

Bng 2.2: Tnh cc theo chu k c nh

Khong cch T 1 ti 3 pht

u

Mi pht sau

< 40 Km 60 20

41 - 60 Km 90 30

61 - 80 Km 120 40

* i vi cuc gi t vng A ti vng B

* i vi cuc gi t vng A ti vng C

b. Phng php o cc xung theo chu kTi kiu tnh cc ny th t gi trong mt n v o lng a l c nh v chu

k T s thay i phc thuc vo khong cch. Trong trng hp ny ngay c khi s

lng cc vng cc tng ln th khng nh hng n thit b v ch cn thay i gi

tr T. Bi vy thit b tnh cc trong tng i non- SPC khng b phc tp. Tng t

nh v d trn khi mt cuc gi din ra trong khong 5 pht 30 giy cho 3 vng A,B

v C i vi phng php tnh cc m c chu k thay i th c minh ho theo

hnh v v bng sau.

44

60

0 3 4 5 6

20

20

2

0

Pht

Tng120

1

206

00 3 4 5 6

4

004

04

00

Pht

Tng

240


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Bng 2.3: Tnh cc theo chu k thay i

C li thng

tin

Chu k vi mc cc trn mt n v o lng

l 10

< 40 Km 30 s

41 60 Km 20 s

61 80 Km 15 s

5 pht 30 giy = 330 giy

* i vi cuc gi A B: 10 * 330/30 = 110

* i cuc gi A C: 10 * 330/15 = 220

. Qua hai v d trn ta thy rng mc cc c tnh cho thu bao l khc nhau,

tu thuc vo nh qun l la chn kiu no v tng i SPC c th cung cp cc chc

nng trn.

3.7.3.3. H thng tnh cc hn hp

H thng tnh cc hn hp c s dng khc phc cc nhc im v tn

dng cc u im ca c hai h thng tnh cc trn. Trong h thng ny, ngoi mc

cc tnh theo cuc thng tin nh trn th khch hng phi tr thm mt mc cuc

c nh tu thuc vo tng dch v c th cho vic bo dng cc thit b kt cui. Hthng tnh cc hn hp c mt s c im sau y :

* Mc cc c nh cho cc thu bao cho cc dch v nh vy l kh cng bng

* Khi khng c cuc thng tin no din ra th nh cung cp dch v vin thng vn

c th p ng vic cp ngun nui cho cc thit b.

* Cn thit cc thit b cho vic tnh cc

3.8. K HOCH BO HIU

3.8.1. Gii thiu

45

Vng

B

Vng AVng C

20 Km 70Km

Hnh 2.15 : V d vic tnh cc theo chu k thay i


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Bo hiu l qu trnh trao i cc thng tin iu khin lin quan n vic thit

lp duy tr v gii to cuc thng tin v qun l mng gia cc thit b u cui v cc

thit b chuyn mch hay gia cc thit b chuyn mch.

Bo hiu l mt chc nng quan trng m bo s kt ni gia cc tng i,

ng truyn v cc thit b u cui mng li. Khi p dng mt h thng bo hiu,

n s nh hng ln v lu di ti chc nng mng li. V vy, bo hiu phi c tnh

mm do sao cho d thch nghi vi s m rng mng li trong tng lai.

3.8.2. Phn loi bo hiuBo hiu trong mng in thoi c chia thnh bo hiu thu bao, l bo hiu

gia thit b u cui v tng i ni ht v bo hiu lin i, bo hiu gia cc tng

i.

Hnh 2.8: Phn loi bo hiu trong mng in thoi

Bo hiu thu bao l qu trnh trao i cc loi tn hiu bo hiu gia thu bao

v tng i ni ht v ngc li.

Bo hiu lin i gm bo hiu knh kt hp v bo hiu knh chung. i vi

h thng bo hiu knh kt hp, cc tn hiu thu v pht trn cng mt ng vi tn

hiu ting ni. Trong khi bo hiu knh chung tn hiu bo hiu thu v pht qua

mt ng dnh ring cho bo hiu khc vi knh ting ni. H thng bo hiu lin

i c phn chia thnh 2 h thng chnh l : Bo hiu knh kt hp (CAS) v Bo

hiu knh chung (CCS). H thng bo hiu knh chung CCS c u im hn so vi

bo hiu knh kt hp nh: dung lng cao, linh hot, gim phn cng v tin cy cao.

Trong mng in c nhiu h thng bo hiu khc nhau c s dng nh bo

hiu MFC,CCITT No 5, CCITT No 6... Tuy nhin nhu cu ca khch hng v cc dch

v ngy cng cao m cc h thng bo hiu c khng c kh nng p ng cc dch vny do hn ch v tc , dung lng v cht lng. Do cn mt h thng bo hiu

46

Tng i Tng i

Thit b

u cuiThit b

u cui

Bo hiu thu

bao

Bo hiu thu

bao

Bo hiu lin

i


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mi c kh nng p ng cc loi hnh dch v v tn dng ti u kh nng ca tng

i SPC.

Xut pht t yu cu v mt h thng bo hiu mi, gn y c mt vi h

thng bo hiu knh chung c a vo p dng. Nm 1968 ITU-T a khuyn

ngh v h thng bo hiu knh chung s 6 c thit k ti u cho lu lng lin lc

a, s dng trn cc ng trung k Analog, tc thp 2,4 Kbps. Vo nhng nm

80, ITU-T gii thiu h thng bo hiu knh chung s 7 (CCS7) thit k ti u cho

mng quc gia v quc t s dng trung k s, tc t 64 Kbps.

Hin nay trn mng vin thng Vit Nam s dng c hai loi bo hiu: R2 v

C7. Mng bo hiu s 7 (C7) a vo khai thc ti Vit Nam theo chin lc trin khai

t trn xung theo tiu chun ca ITU (khai thc th nghim u tin t nm 1995 ti

VTN v VTI). Cu trc mng bo hiu C7 xy dng da trn c s cu trc mng

chuyn mch quc gia nhm chuyn ti an ton v hiu qu cc bn tin bo hiu CCS7

gia cc vng lu lng chia thnh 5 vng bo hiu tng ng vi 5 vng lu lng

thoi. Cho n nay mng bo hiu s 7 hnh thnh vi mt cp STP (im chuyn

tip bo hiu) ti 3 trung tm (H Ni, Nng, TP. H Ch Minh) ca 3 khu vc

(Bc, Trung, Nam), s dng loi STP tch hp t ti cc tng i chuyn tip quc

gia. i vi STP quc t cng l im chuyn tip lu lng bo hiu SCCP cho cccuc gi Roaming quc t.

3.9. K HOCH NG B

3.9.1.Gii thiu chungTrong mng lin kt s (IDN), vic truyn dn v chuyn mch cc tn hiu s

trn mng li c iu khin bi ng h vi mt tn s ring. Nu cc ng h ti

cc tng i hot ng c lp vi nhau th tn s ca chng s b sai lch, hay l hin

tng trt , gy ra li thng tin nh hng n cht lng cc dch v . Do k

hoch ng b c a ra xy dng v t chc mng ng b m bo s ng b

trn mng. S trt cc dng bt b nh hng khc nhau n cc dch v thoi, d liu

hay truyn hnh.

3.9.2. Cc phng thc ng b mngng b mng l mt khi nim chung m t phng thc thc phn phi tn

hiu ng h (common time and frequency) ti tt c cc phn t trn mng sao cho

chng hot ng ng b vi nhau.

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3.9.2.1. Phng thc cn ng b (Plesiochronous Synchronization Method)

Trong phng thc cn ng b, cc tng i trn mng lp t cc b to dao

ng c lp nhau cung cp tn hiu ng h iu khin cho qu trnh lm vic ca

tng i . H thng ny dng cho mng vin thng quc t v c nh gi nh

sau :

u im : - Linh hot trong vic m rng, sa i v ti s dng mng .

- Khng yu cu mt mng phn phi tn hiu ng h .

Nhc im :

- Ti cc tng i trn mng yu cu cc ng h c n nh cao.

- Yu cu cu hnh d phng cho cc ng h ny.

- Gi thnh cho vic ng b mng cao.

3.9.2.2. Phng thc ng b ch t (Master - Slaver Synchronization Method)

Trong phng thc ng b ch t, trn mng ng b ti mt nt no trang

b mt ng h c n nh cao gi l ng h ch. Thng qua mng phn phi tn

hiu ng b (Synchronization Network) , ng h ch s phn phi tn hiu ng h

ti cc ng h ca tng i khc trn mng, cc ng h ca cc tng i ny gi l

ng h t. Ti y tn hiu ng h c ti to li lm ngun ng h tham kho

cho tng i t thc hin iu khin to ra tn hiu ng h ng b vi tng i ch

trn mng.

u im: khng cn yu cu ng h ti mi tng i trn mng c n nh cao

(ch yu cu ng h ch) .

Nhc im :

- Yu cu mt mng phn phi tn hiu ng h ng b (cc ng truyn

dn thng thng dng cho mng ny ).

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Hnh 2.9 : Phng thc cn ng b


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- Khi xy ra sai li trn ng truyn, tn hiu ng b lm nh hng ti

tng i t trn mng.

3.9.2.3. Phng thc ng b tng h

Trong phng thc ng b ny cc ng h khc nhau c lp t ti cc

tng i trn mng v iu khin tng h ln nhau to ra ngun ng h b chung

cho mi ng h trn mng.

nh gi phng thc ng b tng h:

u im :

- Khng yu cu ng h c n nh cao cho cc tng i trn mng.

- Cc tng i khng cn phn cp (khc vi h thng ng b ch t).

Nhc im :

- Khi mt ng h ti tng i trn mng b li, th ton mng b nh hng.

- Cc ng phn phi tn hiu ng h ng b hnh thnh theo kiu mch vng

do vic cch ly li ra khi h thng kh khn hn.

3.9.3. ng h v cc tham s lin quan

49

~ ~

~

Hnh 2.13 : Phng thc ng b tng h

~

~ ~

~

~ ~

~

ng

h ch

ng

h

t

ng

h

tHnh 2.10 :Phng thc ng b ch - t


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Vic ng b ho mng li c bn l vn gi cho cc ng h trn mng

lm vic khng sai lch nhau v tn s cng nh v pha. ng h c nh ngha nh

l mt ngun tn s, ni ti b chia hay b m. N to ra mt gc thi gian kim

sot vic nh thi cho trng chuyn mch ca tng i s (to ra cc xung nhp iu

khin cc mch s ni chung) .

3.9.3.1. Cc tham s tiu biu ca ng h

Hai tham s quan trng nht c lin quan n cht lng ng h l n nh

v chnh xc. (Stability & Accuracy).

+ chnh xc (A): l mc tng ng tn s ca n vi mt tn s chun

(tn s danh nh )

A: chnh xc; F d : Tn s danh nh; F ra : Tn s ra

+ n nh (S): l mc m cn c vo mt ng h s to nn cng mt

tn s trong khong thi gian chy lin tc ca n.

F d : Tn s danh nh; F ra : Tn s ra; S : n nh

50

A= F d - F raF

d

=

Fd - F ra*

1

F

d

T1- T0

S


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3.9.3.2. Mt s loi ng h tiu biu

C hai ngun ng h nguyn t v tinh th thch anh u dng to dao

ng trong cc b to xung. Mt s im khc nhau gia hai loi ny l, ngc li vi

ngun ng h nguyn t, tn s ca cc ng h thch anh n nh, s thay i tn sca chng (do lu ngy) rt n nh v cc din bin tnh cht ca n c th on trc

mt cch an ton. Din bin c d bo trc nn c th dng lp li chnh xc

tn s. Cc ng h in t gm hai loi : loi dng tia Cesium chun gi l ng h

Cs, loi dng pin cha kh Rubilium gi l ng h Rb.

3.9.4. Mng ng b Vit NamMng ng b Vit Nam hot ng theo phng thc ch t c d phng.

Mng ng b ca VNPT bao gm 4 cp l: cp 0, cp 1, cp 2, cp 3.Trong :

- Cp 0: l cp ca cc ng h ch quc gia. S dng ng h c n nh tn

s,1.10E-11 (ng h Cesium).

- Cp 1: l cp trc ng b trc tip t ng h ch (PRC) ti cc tng i nt

chuyn tip quc t, chuyn tip quc gia v cc ng h th cp.

- Cp 2: l cp mng ng b t ng h ca cc nt chuyn tip quc t hoc

chuyn tip quc gia hoc ng h th cp ti cc tng i HOST v cc tng i c

trung k vi cc nt chuyn tip quc t v chuyn tip quc gia.

- Cp 3: l cp mng ng b t ng h ca cc tng i HOST v t cc tng

i c trung k vi cc nt chuyn tip quc t v chuyn tip quc gia ti cc thit b

thuc phn mng cp thp hn.

ng b cho cc mng ni ht

Mng ni ht c tuyn truyn dn SDH quc gia(1):+ Tn hiu ng b ly t tuyn trc SDH quc gia ng b cho tng i Host

(tng i Host phi c trang b cng ng b 2MHz)

+ Trong trng hp Host cha trang b cng ly tn hiu ng b 2MHz th ly tn

hiu trc tip t lung E1 c lu lng.

Mng ni ht ch c tuyn truyn dn PDH(2):

+ Tn hiu ng b ly trc tip t lung E1 ng b cho Tng i Host.

- u tin 1: Ly tn hiu ng b t cc tuyn truyn dn cp quang.

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- u tin 2: Ly tn hiu ng b t cc tuyn truyn dn viba.

Cc tuyn truyn dn SDH ni tnh phi ng b theo tn hiu ng b ca tuyn

trc truyn dn quc gia thng qua b phn phi tn hiu ng b SASE.

Cc tng i v tinh v c lp ng b theo tng i Host theo tn hiu ng b

ly t tuyn truyn dn ni tnh theo phng thc m t (1) v (2) tng ng.

Cc thit b khi a vo khai thc hot ng trn mng vin thng ca VNPT phi

m bo yu cu khng lm tng cp mng ng b.

3.10. K hoch cht lng thng tin

3.10.1. Cht lng chuyn mchi vi cc dch v vin thng, Nhiu ngi s dng phi chia s quyn s

dng thit b trn mng li. Do , khi lu lng m cao th mt s cuc gi c th

khng thc hin kt ni c. Cht lng m lin quan n qu trnh u ni cung

cp dch v vin thng c gi l cht lngchuyn mch, c ngha l cht lng

chuyn mch trong qu trnh k t khi thu bao ch gi quay s cho ti khi kt ni

c vi b gi hoc l khi mt thu bao t my gii phng cuc thng tin cho ti khi

gii phng hon ton cc thit b lin quan n cuc thng tin .

Cht lng chuyn mch lin quan cht ch n cht lng ca thit b v lu

lng thng tin. Ngi ta quy nh cht lng chuyn mch ny da trn iu kin lkhi lu lng mc trung bnh v thit b hot ng tt. Cht lng chuyn mch c

th tm chia thnh tn tht u ni v tr u ni. Tn tht u ni c ngha l mt

cuc gi b tn tht khi m cc mch trung gian cho cuc gi ang trng thi bn

hay thit b bn hoc l thu bao b gi bn hay khng nhc my tr li. Do tnh

tn tht u ni ny ngi ta s dng tham s gi l xc sut tn tht. Trong khi

tr u ni l khong thi gian t khi thu bao ch gi nhc my khi xng cuc gi

cho ti khi nhn c m mi quay s (tr m mi quay s), hay l khong thi gian

t khi quay s cho ti khi nhn c hi m chung (tr quay s) hay l khong thi

gian t my gii phng cuc thng tin cho ti khi cc thit b lin quan tr v trng

thi ri. tr ny thng c biu th qua tham s thi gian tr trung bnh.

3.10.2. Cht lng truyn dnTrong dch v in thoi, nghe hiu phi c m bo trong sut qu trnh

m thoi t pha pht n pha thu. Do , nghe hiu c a ra thng qua cht

lng m thoi tng th bao gm cht lng pht, truyn dn v thu.

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Cht lng thu ting ni m t r nt ca mch thu iu ny ph thuc vo

kh nng nghe ca ngi nghe, ting n trong phng v cc thnh phn khc.

Cht lng pht ting ni m t r nt ca mch pht v n cng ph thuc

vo ting ni ca ngi ni, ting n trong phng v ngn ng vv.

Cht lng truyn dn ting ni m t mc truyn dn chnh xc trn cc

ng truyn dn bao gm c thit b thu bao v tng i. Cht lng truyn dn

c quy nh da trn nhy ca my in thoi, tn tht trn ng truyn, Nhiu

v s hn ch v bng tn. Cht lng pht v thu ting ni cn ph thuc vo kh

nng nghe hiu, pht m ca ngi ni, nghe v trng thi truyn dn ting ni.

3.10.3. n nhNgy nay thng tin lin lc c coi l c s h tng quan trng ca mt x hi

ho thng tin. Do tin cy ca cc thit b trn mng nh tng i v cc ng

truyn dn phi m bo. iu ny c ngha l tin cy c th cung cp cac dch

v cn thit trong iu kin lu lng khng bnh thng do li thit b hay t mt

l do no . Cht lng n nh ( n nh) a ra cc mc bo dng cn thit

cho cc dch v thng thng.

n nh cng cao th cng tt tuy nhin tin cy m vt qu mt ngng

no th gi thnh s tng rt cao. Do , mc tt nht c chn da trn s cn igia gi thnh c th chp nhn c v vn k thut. Gi tr c chn ny phi

tho mn mt s iu kin khc nh thit k mng, bo dng mng v.v. Cc tai nn

hay thin tai gy ra c coi l cc nh hng khch quan khng tnh trong n nh

ca h thng. Khi mt mng vin thng c thit k th cn ch vic lp t cc

tuyn truyn dn v vic phn b ri rc cc tng i. tin cy ca thit b, h thng

bo dng c coi nh l cc nhn t bn trong. Do chng ta cn quan tm nh

cu hnh ca thit b d phng v cng ngh bo dng mng .

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Chng 4, Quy hoch mng vin thng4.1. Quy hoch v tr tng i

4.1.1.Gii thiuV thit b vin thong thu bao chim phn ln v chi ph mng vin thng,

thit k nhng thit b nh vy l rt quan trng. Trn ht, qui hoch v tr tng

i l iu rt quan trng nh l nn tng ca qui hoch.

Qui hoch v tr tng i ni ht bao gm vic xc nh khi no, u, v

trm tng i rng bao nhiu s c lp t.

C th c nhiu phng thc a dch v theo yu cu ti cc thu bao trong

mt vng. Chng hn, bn c th chia vng thnh s vng nh hn, trong trng

hp khc mt vng c th c cung cp dch v bi tng i n. C th c

nhiu k hoch i vi vic t v tr ca cc tng i v ranh gii ca cc vngdch v. Trong bt k trng hp no, cc thu bao c th c cung cp cht

lng dch v tha mn gi tr nht nh. Tuy nhin, tng chi ph mng ph

thuc rt ln vo cc gi tr c to ra. V vy, mc ch ca qui hoch v tr

tng i l tho mn nhu cu v gi tr nht nh ca cht lng dch v, v

thit lp cu hnh ca cc tng i theo gim ti thiu tng chi ph mng.

4.1.2. Phng php qui hoch v tr tng i

4.1.2.1. Phn chia vng4.1.2.1.1. Vng tng i

Vng tng i l vng m tng i nhm cho php cc dch v n cc

thu bao ca tng i. Khu vc ny s c qui hoch c tnh ti phn c im

a l v phn b mt nhu cu cng nh chi ph tng i v thit b ngoi vi.

4.1.2.1.2. Khi n v

Khu vc trm tng i c chia thnh cc khi n v. Cc khi n v ny

l n v nh nht nhm khai thc thit b thu bao c tnh ti cc iu kinca mi trng khai thc tng lai. Khi n v l c s ca vic d bo nhu

cu.

4.1.2.2. Khi nim v qui hoch v tr tng i

a) Thnh phn ca vic qui hoch v tr tng i

Trong vic pht trin qui hoch v tr tng i, iu quan trng l xem xt

phm vi ca tng i (tc l, s lng thu bao yu cu dch v), kch thc khu

vc tng i v v tr ca tng i a ra hnh 12.2.

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Hnh 4.1. Thnh phn ca vic qui hoch v tr tng i ni ht

b) Nhng xem xt trong vic trin khai qui hoch v tr tng i ni ht

Nhng mc sau s c xem xt trong vic trin khai qui hoch v tr tng i.

Nhng iu kin ca mi trng tng lai

- D bo v nhu cu tng lai.

- Qui hoch thnh ph (cc ng ph, cng vin, ng xe la,).

Quan h qua li

- Quan h qua li vi khu vc tng i gn bn cnh.

Tho manc vi cht lng dch v bt buc

- Tn hoa ng dy.

4.1.2.3. X l trng thi ban u

Trong vic xc nh vng dch v vi mi tng i, cc yu t sau s c xem xt

nh cp on trc.

- Nhng qun huyn hnh chnh.- c im a l.

- Nhng ng st v nhng ng chnh

- Nhng khu kinh t v cc vng dn c.

- Nhng khu vc tnh cc.

- Tng i s t ti hoc gn cc khi n v c mt nhu cu cao, a ra

vic xem xt hnh thc v phn b mt nhu cu ca khu vc tng i.

4.1.2.4. Phn b mt nhu cu

55

Phm vi ca tng i Kch c ca tng i V tr tng i

Nhu cu

Chi ph tng i

di cc ng thu bao

Chi ph cc ng thu bao

Tng chi ph


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in thoi l cng c c tnh kinh t v x hi i vi vic lien lc. Mc d, mt

nhu cu i vi in thoi c s phn b m n th hin mt cao ti cc trung

tm ca thnh ph v gim dn pha ngoi , tng t vi s phn b v cc hot ng

x hi v kinh t.

Phn loi cc ng cong phn b mt nhu cuCc ng cong phn b mt nhu cu tha nhn c nhiu dng ph thuc vo

c im a l v tnh trng pht trin ca thnh ph. Cc ng cong c chia

thnh hai loi: Cc ng cong phn b ng dng v cc ng cong phn b c hm

m.

4.1.3. Chi ph thit bChi ph thit b ti khu vc dch v c chia ra mt cch gn nh ugns nh sau:

Ch ph thit b Chi ph cho cc ng dy thu bao

Chi ph trm tng iChi ph cc ng trung k ni ht

Chi ph cc ng dy thu bao

Chi ph cc ng dy thu bao c c tnh da trn chng loi cp s dng v

tng chiu di ca chng.

(1) Chi ph u tin theo chng loi cp c tnh theo cc thng s sau:

(a) S cp i

(b) S cc/km(c) S ng cp trung bnh /km

(d) T l t/khng gian

(e) Xy dng ngm (cc ming cng, cc l, cc ng hm,)

(2)Chi ph theo tng chiu di ca cc ng dy thu bao c quyt nh theo t

hp cp c ng knh tha mn hn ch mt mt ng dy v in tr ng dy,

tng ng vi di ng dy thu bao.

Chi ph cc ng trung k ni ht

Chi ph cc ng trung k ni ht ph thuc vo s ng trung k, khong cchgia cc tng i, chng loi cp v tnh trng lp li. Vic lp t s lng tng i

loi ln ti mt vng s lm tng s ng trung k, nh vy kt qu l chi ph cao

hn, nhng chi ph cc ng trung k ni ht ni chung c tnh nh hn phn tng

chi ph thit b.

Chi ph ca cc tng i

Chi ph ca cc tng i gm c nh sau:

- Chi ph ca cc tng i

+ Chi ph thit b tng i

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