I HC QUC GIA TP. H CH MINH TRNG H CNG NGH THNG TIN

----------

TIU LUN

MNG TRUY NHP QUANG TH NG PON

Gio vin hng dn: Th.S Chu Tin Dng

Nhm SV thc hin: 1. Phan Nguyn Tn Hu 2. Trng Chu Tun 3. L Minh Diu

Nha Trang, 09/2015

Phn 1: MNG TRUY NHP QUANG TH NG PON

1. Gii thiu chung

PON, vit tt t tn Passive Optical Network, ngha l "mng quang th ng", l mt hnh thc truy cp mng cp quang, kiu mng kt ni im - a im (P2M), cc si quang lm c s to kin trc mng. Mi khch hng c kt ni ti mng quang thng qua mt b chia quang th ng v khng cn ngun cp, v vy khng c cc thit b in ch ng trong mng phn chia v bng thng c chia s t nhnh n ngi dng, cho php mt si quang n phc v nhiu nhnh c s, thng l t 16-128. PON bao gm mt thit b u cui dy quang (OLT - Optical Line Terminal) ti vn phng trung tm ca nh cung cp dch v v cc thit b mng quang hc (ONUs - Optical Network Units) ni gn ngi dng cui. Cng ngh PON lm gim yu cu s lng dy dn v thit b ti vn phng trung tm so vi cc kin trc im - im.

Tn hiu ng xung c truyn chia s n tt c cc nhnh si c s. Tn hiu download c ti cc h gia nh, tn hiu ny c m ha c th ngn nga b "cu mc" trm. Tn hiu upload c kt hp bng vic s dng giao thc a truy nhp phn chia theo thi gian (TDMA). OLT s iu khin cc ONU s dng cc khe thi gian cho vic truyn d liu ng xung.

2. Tng quang v cng ngh PON

Mng quang th ng PON (hnh 2.1) s dng phn t chia quang th ng trong phn mng phn b nm gia thit b ng truyn quang (OLT) v thit b kt cui mng quang (ONU). Hot ng ca mng PON c iu khin bi giao thc truy nhp theo a ch MAC (lp 2)

a)

Hnh 2.1: M hnh mng quang th ng

Cc phn t th ng ca PON u nm trong mng phn b quang (hay cn gi l mng quang ngoi vi) bao gm cc phn t nh si quang, cc b tch /ghp quang th ng, cc u ni v cc mi hn quang. Cc phn t tch cc nh OLT v cc ONU u nm u cui ca mng PON. Tn hiu trong PON c th c phn ra v truyn i theo nhiu si quang hoc c kt hp li v truyn i trn mt si quang thng qua b ghp quang, ph thuc tn hiu i theo hng ln hay xung ca PON.

2.1 B tch / ghp quang

Mt mng quang th ng s dng mt thit b th ng tch mt tn hiu quang t mt si quang sang mt vi si quang v ngc li. Thit b ny l Coupler quang. n gin, mt Coupler quang gm hai si ni vi nhau. T s tch ca b tch c th c iu khin bng chiu di ca tng ni v v th n l hng s.

I O2

O3

I O2

I O2

I O3

` Hnh 2.2: Cu hnh c bn cc loi Coupler

Hnh 2.2a c chc nng tch tia co thnh 2 tia u ra, y l Coupler Y.Hnh 2.2b l Coupler ghp cc tn hiu quang ti hai u vo thnh mt tn hiu

ti u ra. Hnh 2.2c va ghp va tch quang v gi l Coupler X hoc Coupler phn hng 2x2. Coupler c nhiu hn hai cng vo v nhiu hn hai cng ra gi l Coupler hnh sao. Coupler NxN c to ra t nhiu Couper 2x2.

a) Coupler 4 ngn 8x8

b) Coupler 3 ngn 8x8 Hnh 2.3: Coupler 8x8 c to ra t nhiu

Coupler Coupler c c trng bi cc thng s sau:

Splitting loss (tn hao tch): Mc nng lng u ra ca Coupler so vi nng lng u vo (db). i vi Coupler 2x2 l tng, gi tr ny l 3dB. Hnh 2.3 minh ho hai m hnh 8x8 Coupler da trn 2x2 Coupler. Trong m hnh 4 ngn (hnh a), ch 1/6 nng lng u vo c chia mi u ra. Hnh (b) a ra m hnh hiu qu hn gi l mng lin kt mng a ngn. Trong m hnh ny mi u ra nhn c 1/8 nng lng u vo.

Insertion loss(tn hao chn): Nng lng tn hao do s cha hon ho ca

qu trnh x l. Gi tr ny nm trong khong 0,1dB n 1dB.

Directivity (nh hng): Lng nng lng u vo b r r t mt cng u vo n cc cng u vo khc. Coupler l thit b nh hng cao vi thng s nh hng trong khong 40-50dB.

Thng thng, cc Coupler c ch to ch c mt cng vo hoc mt Combiner (b kt hp). i khi cc Coupler 2x2 c ch to c tnh khng i xng cao ( vi t s tch l 5/95 hoc 10/90). Cc Coupler loi ny c s dng tch mt phn nng lng tn hiu, v d vi mc ch nh lng. Cc thit b nh th ny c gi l tap coupler.

2.2 Cc u cui mng PON

Optical Line Terminal (OLT thit b ng truyn quang ): OLT cung cp giao tip gia h thng mng truy cp quang th ng EPON v mng quang ng trc ca cc nh cung cp dch v thoi, d liu v video. OLT cng kt ni n mng li ca nh cung cp dch v thng qua h thng qun l EMS(Element Management System).

Optical Network Unit (ONU: thit b kt cui mng quang): ONU cung cp giao tip gia mng thoi, video v d liu ngi dng vi mng PON.

M hnh cy vi reunant trunk (d)

M hnh bus s dng tapcoupler(b) M hnh cy ( s dng splitter 1:N)(a)

Chc nng c bn ca ONU l nhn d liu dng quang v chuyn sang dng ph hp vi ngi dng nh Ethernet, POST,T1...

Element Management System (EMS :h thng qun l ): EMS qun l cc phn t khc nhau ca mng PON v cung cp giao din n mng li ca cc nh cung cp dch v. EMS c chc nng qun l v cu hnh, c tnh v bo mt.

2.3 M hnh PON

C mt vi m hnh thch hp cho mng truy cp nh m hnh cy, vng hoc bus. Mng quang th ng PON c th trin khai linh ng trong bt k m hnh no nh s dng mt tapcoupler quang 1:2 v b tch quang 1:N.

M hnh vng (c)

Ngoi nhng m hnh trn, PON c th trin khai trong cu hnh Redundant nh l vng i hoc cy i hay cng c th l mt phn ca mng PON c gi l trung k cy.

Hnh 2.4: Cc m hnh mng PON

Tt c s truyn dn trong mng PON u c thc hin gia OLT v cc ONU. PLT ti tng i (Central Office), kt ni truy nhp quang n mng ng trc (c th l mng IP, ATM hay SONET). ONU ti u cui ngi s dng (trong gii php FTTH_Fiber To The Home, FTTB_Fiber To The Building) hoc ti Curb trong gii php FTTC_Fiber To The Cur v c kh nng cung cp cc dch v thoi, d liu v video bng rng.

Tu theo im cui ca tuyn cp quang xut pht t tng i m cc mng truy nhp thu bao quang c tn gi khc nhau nh si quang n tn nh FTTH, si quang n khu dn c FTTC...

3. WDM v TDM PON

hng xung (t OLT n ONU), mng PON l mng im-a im. OLT chim ton b bng thng hng xung. Trong hng ln, mng PON l mng a im-im: nhiu ONU truyn tt c d liu ca n n mt OLT. c tnh hng ca cc b tch ghp th ng l vic truyn thng ca mt ONU s khng c nhn bit bi cc ONU khc. Tuy nhin cc lung d liu t cc ONU khc nhau c truyn cng mt lc cng c th b xung t. V vy trong hng ln, PON s s dng mt vi c ch ring bit trong knh trnh xung t d liu v chia s cng bng ti nguyn v dung lng trung k.

Mt phng php chia s knh hng ln ca ONU l s dng ghp knh phn chia theo bc sng WDM, vi phng php ny th mi ONU s hot ng mt bc sng khc nhau. Gii php WDM yu cu mt b thu iu khin c hoc l mt mng b thu OLT nhn cc knh khc nhau. Thm ch nhiu vn kh khn cho cc nh khai thc mng l kim k tng bc sng ca ONU: thay v ch c mt loi ONU, th c nhiu loi ONU da trn cc bc sng Laser ca n. Mi ONU s s dng mt laser hp v rng ph iu khin c cho nn rt t tin. Mc khc, nu mt bc sng b sai lch s gy ra nhiu cho cc ONU khc trong mng PON. Vic s dng Laser iu khin c c th khc phc c vn ny nhng qu t cho cng ngh hin ti. Vi nhng kh khn nh vy th WDM khng phi l gii php tt cho mi trng hin nay.

Mt s gii php khc da trn WDM cng c xut nhng gi c kh cao. Do vy, TDM PON ra i. Trong TDM PON, vic truyn ng thi t vi ONU s gy ra xung t khi n b kt hp. ngn chn xung t d liu, mi ONU phi truyn trong ca s (khe thi gian) truyn ca n.

Hnh 2.5: Mng PON s dng mt si

Mt thun li ln ca TDM PON l tt c cc ONU c th hot ng cng mt bc sng, OLT cng ch cn mt b thu n. B thu pht ONU hot ng tc ng truyn, thm ch bng thng c th dng ca ONU thp hn. Tuy nhin, c tnh ny cng cho php TDM PON t hiu qu thay i bng thng c dng cho tng ONU bng cch thay i kch c khe thi gian c n nh hoc thm ch s dng ghp knh thng k tn dng ht bng thng c dng ca mng PON.

Trong mng truy cp thu bao, hu ht cc lung lu lng ln v xung khng phi l Peer to Peer (user to user). V vy iu ny dng nh l hp l tch knh ln v xung. Mt phng php tch knh n gin c th da trn ghp knh phn chia khng gian(SDM) m n tch PON c cung cp theo hng truyn ln xung. tit kim cho si quang v gim chi ph sa cha v bo qung, mt si quang c th c s dng cho truyn theo hai hng. Trong trng hp ny, hai bc sng c dng l: hng ln 1=1310nm, hng xung 2=1550nm. Dung lng knh mi bc sng c th phn phi linh ng gia cc ONU.

Ghp knh phn chia theo thi gian l phng php c u tin hin nay cho vic chia s knh quang trong mng truy cp khi m n cho php mt bc sng n hng ln v b thu php n OLT lm cho gii php ny c u th hn v chi ph u t.

Phn 2:PHN LOI MNG QUANG TH NG

I. TNG QUAN V CNG NGH QUANG TH NG GIGABIT GPON

1.1. Tng quan v cng ngh G-PON

Hnh 1: Mng truy nhp quang th ng GPON

Tc d liu: 1,244/2,488 Gbit/s hng xung v 0,155/0,622/1,244/ 2,488

Gbit/s hng ln

Bc sng: 1260 - 1360nm ng ln; 1480 - 1500nm ng xung

a truy nhp hng ln: TDMA

Cp pht bng thng ng DBA (Dynamic Bandwith Allocation)

Loi lu lng: d liu s

Khung truyn dn: GEM

Dch v: h tr y cc dch v hin c (Ethernet, TDM, POTS, )

T l chia ca b chia th ng: ti a 1:128

Gi tr t l bit li (BER) ln nht: 10 - 12

Phm vi cng sut s dng lung xung: -3 n +2 dBm (10 Km ODN) hoc +2

n +7 dBm (20 Km ODN)

Phm vi cng sut s dng lung ln: -1 n +4 dBm (10 Km v 20 Km ODN)

Loi cp: Tiu chun ITU-T Rec. G.652

Suy hao ti a gia cc ONU:15 dB

C ly cp ti a: 20 Km vi lade DFB lung ln, 10 Km vi Fabry-Perot

a. Kh nng cung cp bng thng

Hng xung

Tc hng xung GPON = 2,488 Mbit/s hiu sut 92% = 2289 Mbit/s.

Trong ng dng nhiu nhm ngi s dng (MDU: multiple-dwelling-unit), vi

t l chia l 1:32, GPON c th cung cp dch v c bn bao gm truy cp

Internet tc cao (100 Mbit/s trn mi thu bao vi t l dng chung 20:1) v

Voice (tc 100 Kbit/giy) n 32 ONU, mi ONU cung cp cho 8 thu bao.

Hng ln

Tiu chun ny ngoi vic a ra b cc yu cu v h thng mng cn a ra

b cc yu cu QoS ring cho lp PON vt ra ngoi cc phng thc Ethernet

lp 2 v phn loi dch v (CoS) IP lp 3 m bo vic phn pht cc dch v

thoi, video v TDM cht lng cao qua mi trng chia s trn nn TDMA.

Tuy nhin, cc c ch CoS lp 2 v lp 3 ch c th t mc ti a l QoS

lp truyn ti. Nu lp truyn ti c tr v dung sai ln th vic phn chia

mc u tin dch v khng cn ngha. i vi TDMA PON, vic dung lng

cung cp QoS hng ln s b hn ch khi tt c cc ONT ca PON s dng ht

bng thng hng ln v u tin ca n trong TDMA. Hng ln GPON c

thng lng n 1,25 Gbit/s cao hn 20% so vi GEPON l mt s khc bit

ng k gip cho c ch QoS c th hot ng tt hn.

GPON s dng bng thng ngoi bng cp pht bn vi khi nim khi

lu lng (T-CONT) cho hng ln. Khung thi gian hng ln v hng

xung s dng khung tiu chun vin thng 8 kHz, v cc dch v c ng

gi vo cc khung theo nguyn bn ca n thng qua qu trnh m hnh ng

gi GPON (GEM). Ging nh trong SONET/SDH, GPON cung cp kh nng

chuyn mch bo v vi thi gian nh hn 50 ms.

iu c bn lm cho GPON c tr thp l c nhiu lu lng hng ln TDMA

t nhiu ONU c ghp vo cng mt khung 8 KHz (125 s). Mi khung

hng xung bao gm mt bn cp pht bng thng hiu qu c gi qung

b n tt c cc ONU v c th h tr tnh nng tinh chnh cp pht bng thng.

C ch ngoi bng ny cho php GPON DBA h tr vic iu chnh cp pht

bng thng nhiu ln m khng cn phi sp xp li ti u ha tn dng bng

thng.

Bng thng

Cng ngh GPON h tr 1,25 Gbit/s hoc 2,5 Gbit/s hng xung, v hng ln

c th x dch t 155 Mbit/s n 2,5 Gbit/s.

Hiu sut bng thng t ln hn 90%.

b. Kh nng cung cp dch v

Khong cch OLT - ONU

Gii hn c ly ca cng ngh GPON hin ti c quy c trong khong 20 km

vi h s chia tch/ghp quang ln ti 1:128 (hin ti thng s dng t l

1:32).

Chi ph trn mi khch hng

Hin ti gi thit b GPON cn tng i cao. Tuy nhin vi vic xut hin cc

b tch/ghp quang c h s tch/ghp quang ln s gip gim chi ph trn mi

khch hng. Ngoi ra khi lu lng s dng ln th chi ph trn mi Mbps s r

hn so vi cng ngh GEPON.

Kh nng h tr cu trc xp chng CATV

GPON c kh nng h tr cu trc mng xp chng dch v CATV, p ng

c i hi cho dch v hng xung tc cao. Cc h thng ny u s

dng bc sng 1490 nm hng xung v 1310 nm hng ln, bc sng 1550

nm c dnh ring cho CATV.

c im dch v

GPON c trin khai p ng t l dung lng dch v/chi ph khi so snh

vi mng cp ng/DSL v mng HFC c dung lng nh v cc mng

SDH/SONET cng nh gii php quang Ethernet im im c chi ph cao. V

vy n ph hp vi cc h gia nh, doanh nghip va v nh, chnh ph v cc

c quan cng s.

- Cc dch v dnh cho h gia nh

- Dnh cho doanh nghip va v nh

- Dnh cho Chnh ph, Gio dc v Y t

Hnh 2: M hnh mng GPON in hnh

Cc ng dng c bn

- GPON c ng dng trong cc mng truy nhp quang FTTx cung cp cc

dch v nh IPTV, VoD, RF Video (chng ln), Internet tc cao, VoIP,

Voice TDM vi tc d liu/thu bao c th t 1000 Mbps, h tr QoS y

.

Mng IP

Mng ATM

Mng TDM

CO

B chia

OLT

C quan chnh ph Trng hc

Bnh vin

H gia nh

Khu bit th

Khu cng nghip Doanh nghip

- Thng tin lin lc Cc ng thoi, thng tin lin lc, Truy cp internet,

intranet tc cao, Truy cp internet khng dy ti nhng a im cng cng,

ng bng thng ln (BPLL) v lm backhaul cho mng khng dy

- Bo mt - Camera, Bo chy, bo t nhp, Bo ng an ninh, trung tm iu

khin 24/7 vi kh nng gim st, backup d liu, SANs

- Gii tr - CATV, HDTV, PPV, PDVR, IPTV H thng ng ln Video hon

thin cho modem DOCSIS v dch v Video tng tc, truyn hnh v tinh; tt

c cc dch v trn cp quang GEPON

- Nh thng minh, Gim st trong nh & BMS Nc, in v gim st x l

cht thi, khm sc khe ti nh, iu khin n t xa, iu khin t xa cc thit

b t ng trong nh.

1.2. Tnh hnh trin khai cng ngh G-PON

Hin nay hai cng ngh GPON v GEPON ang c trin khai ng thi trn th gii. Trong GPON ch yu c trin khai Chu , Chu M v Chu u. Ti y v c bn cc nh cung cp dch v FTTH s dng kin trc ca GPON ca ITU. V ang tin hnh tng bc xy dng cc mng quang th ng G-PON, song song xy dng cc mng truy nhp quang th ng XG-PON, hng n xy dng cc mng truy nhp quang th ng 40G-PON trong tng lai gn.

Hnh 3: Tnh hnh trin khai GPON trn th gii.

1.2.1.1. Tnh hnh trin khai trn Th gii

- Huawei l nh cung cp hng u trong c hai lnh vc cung cp gii php

GPON v sn xut thit b Port, xp sau l Alcatel-Lucent v ZTE.

- Chu -Thi Bnh Dng vn l th trng pht trin GPON si ng tip n

l Chu u, Bc M v Trung ng, Chu Phi.

a. Khu vc Chu u:

- Cc mng 2,5 GPON hin c cc cng ty vin thng France Telecom v

Deutsche Telekom xy dng Ty u theo m hnh FTTH/GPON ca ITU.

- Hin ton Chu u c khong 5 triu thu bao FTTH/GPON. Phn ln lng

thu bao tp trung ti Ty u v Bc u (nh Thy in, Thy S, Php v an

Mch).

b. n v Trung ng

- n : Hin c 5 nh cung cp dch v bng rng chnh ti n : BSNL,

Bharti Airtel, MTNL, Hathway Cable, Tata Communications. Cng ngh truy

nhp DSL vn l cng ngh truy nhp ph bin n . Cc thu bao

FTTH/FTTB/GPON mi ch c mt ti mt s thnh ph ln v c khong 60

nghn thu bao.

- Cc nh trin khai GPON chnh trong khu vc l Alcatel-Lucent, Huawei, ZTE

v Etisalat t Cc tiu Vng Quc Rp.

c. Khu vc Bc M :

Verizon, bt u tin hnh trin khai mng quang truy nhp quang th ng FTTP/GPON ti M vi tn FiOS vo nm 2007, hin nay c mt ti 18 bang trn ton nc M, h tr tc d liu ti a 150 Mbit/s hng xung v 35 Mbit/s hng ln.

Dch v qua mng quang th ng FiOS:

- FTTP hay FTTH bt u cung cp t nm 2006.

- Verizon VoiceWing hay dch v Thoi IP VoIP hay Verizon FiOS internet bt u

t 31/03/2009.

- FiOS Video hay FiOS TV vi hn 500 knh, 180 knh ca nhc, hn 95 knh truyn

hnh nt cao v hn 10.000 video theo yu cu.

Thng k thng 08/2011 ca y ban truyn thng Lin bang M, mng FiOS hin c

mt trn 16,5 triu gia nh M, c thm 735.000 kt ni FiOS internet ln 4,8 triu thu bao internet FiOS v 701.000 kt ni FiOS Video ln 4,2 triu thu bao FiOS Video.

d. Chu Thi Bnh Dng:

Top 15 th trng dch v bng rng c nh : Australia, Trung Quc, Hong Kong,

n , Indonesia, Nht Bn, Malaysia, New Zealand, Pakistan, Philippines,

Singapore, Hn Quc, i Loan, Thi Lan v Vit Nam.

Theo nh mt bo co nghin cu th trng dch v bng rng vo cui nm

2011 : Khu vc Chu -Thi Bnh Dng c khong 187 triu thu bao bng rng

c nh,

DSL vn l cng ngh truy nhp dch v bng rng c s dng ph bin nht,

Nht Bn : l mt trong cc quc gia thuc khu vc Chu c tc tng trng

dch v bng rng t mc hai con s hng nm. Tnh n cui nm 2009 c

31,7 triu thu bao.

Hin Nht Bn s dng ch yu l cng ngh FTTH/FTTB theo cng ngh truy nhp quang th ng EPON, song cng c s quan tm nghin cu th nghim v trin khai GPON.

Hn Quc : Nm 2007, Hanaro Telecom a vo trin khai gii php mng truy

nhp quang th ng GPON Alcatel-Lucent ti Hn Quc, h thng ny h tr

phn phi cc dch v bng rng tin tin nh IPTV, truyn hnh nt cao HDTV,

truyn hnh theo yu cu VoD qua HanaTV, cc dch v Internet tc cao v cc

dch v truyn hnh tng tc, khi u h thng h tr c 110.000 thu bao.

Hin cc dch v bng rng FTTH/FTTB/GPON l dch v chim th phn ch yu

ti Hn Quc, FTTH/GPON chim 70% s kt ni dch v bng rng

i Loan : Chunghwa Telecom bt u tin hnh trin khai FTTH/FTTB da trn

cng ngh GPON vo nm 2007. Hin nay dch v bng rng s dng

FTTH/FTTB/GPON l dch v chim th phn ln nht i Loan chim 30% kt

ni dch v nm 2009,

Trung Quc : Cc nh cung cp dch v bng rng ln nht hin nay ca Trung

Quc l China Mobile, China Telecom, China Unicom tin hnh hp tc cng

vi cc Cng ty, Tp on cng ngh l Huawei, ZTE, Alcatel-Lucent, Ericsson

trin khai GPON ti Trung Quc. Cc dch v bng rng truyn qua GPON c

mt ti Bc Kinh, An Huy, Qung ng, Thm Quyn, Hin nay Huawei v

ZTE tr thnh nhng nh cung cp gii php trin khai GPON hng u th

gii. Nhng cc dch v bng rng ti Trung Quc vn c truyn ch yu qua

DSL vi hn 120 triu thu bao (2009) nhng cc dch v FTTH/GPON cng ang

pht trin vi tc pht trin thu bao vo khong 20-50% mi nm.

e. Cc khu vc khc nh Nam M v Chu Phi :

- Khu vc Nam M : Hin c Argentina, Chile l c nhng ng thi quan tm

nghin cu v th nghim GPON.

- Khu vc Chu Phi : Nc u tin v duy nht hin nay trin khai GPON ti

khu vc ny l Kenya qua nh cung cp KDN vi s h tr t ITU v Alcatel-

Lucent.

1.2.1.2. Tnh hnh trin khai ti Vit Nam

Tnh n cui nm 2009, Vit Nam c khong 3 triu thu bao dch v bng rng vi 3 nh cung cp dch v internet ln nht l VNPT, Viettel v FPT. D kin n nm 2015 s c khong 4 triu thu bao vi doanh thu nm 2015. DSL vn l cng ngh c s dng ph bin ti Vit Nam. Dch v bng rng da trn cng ngh truy nhp quang th ng GPON bt u c trin khai ti Vit Nam vo u nm 2011, hin c 3 nh cung cp dch v FTTH/GPON l Netnam, VNPT v CMC, cc dch v ny hin mi ch c trin khai ti hai trung tm kinh t ln ca t nc l TP.H Ni v TP. H Ch Minh. Hin c khong 12 nghn thu bao dch v FTTH/GPON.

1.2.1.3. Nhn xt v tnh hnh trin khai cng ngh GPON trn th gii v ti Vit

Nam

Qua nghin cu tm hiu thc trng trin khai cng ngh GPON c th thy cng

ngh GPON hin ang c trin khai kh ph bin v s tr thnh xu hng

cng ngh pht trin mnh trong tng lai; l loi hnh truy nhp bng rng ch

yu cung cp cc dch v truy nhp bng rng.

Cng ngh ny hin c cc nh cung cp dch v trong nc trin khai theo

m hnh truy nhp FTTx cung cp cc dch v bng rng vi nhiu chng loi

thit b ca nhiu hng cung cp thit b khc nhau

2.1.1. Tnh hnh chun ha G-PON ca ITU-T

G-PON c ITU-T chun ha theo h khuyn ngh G.984.x, m rng t h khuyn ngh BPON G.983.x.

ITU-T G.984.1 ( 03/2008) G-PON: General characteristics: Pht trin cc

phn trong khuyn ngh ITU-T G.984.2 v k tha cc c tnh c t h khuyn

ngh G.983.x (BPON)

ITU-T G.984.2 (03/2003) G-PON: PMD layer specification: Cc ch tiu k

thut v cc yu cu i vi lp PMD (Physical Media Dependent) trong mng

truy nhp quang OAN (Optical Access Network).

ITU-T G.984.3 (03/2008) G-PON: TC layer specification: M t lp hi t

truyn dn (Transmission convergence TC) cho cc mng G-PON.

ITU-T G.984.4 (02/2008) G-PON: ONT management and control interface

specification: Cung cp chi tit k thut giao din iu khin (OMCI) v qun l

ONT (qun l cu hnh, qun l li, qun l hiu nng) cc h thng GPON

ITU-T G.984.5 (09/2007): G-PON: Enhancement band a ra di bc sng

dnh cho cc tn hiu dch v p dng cho WDM trong mng quang th ng G-

PON.

ITU-T G.984.6 (03/2008): G-PON : Reach Extension, b sung thm cc

nghin cu mi v bc sng quang v tc chia tch

ITU-T G.984.7 (07/2010): Long reach, a ra b cc yu cu lp PMD v lp

hi t truyn dn i vi h thng G-PON c c ly truyn dn t 20km n 40km.

2.2. Tnh hnh tiu chun ha G-PON ti Vit Nam

Hin ti Vit Nam cha c cc tiu chun c th no v mng truy nhp quang th ng. B Thng tin Truyn thng v Tp on Bu chnh vin thng Vit Nam mi ch tin hnh nghin cu thng qua cc ti nghin cu cp b cng nh cp tp on nh:

Nghin cu phng n trin khai cng ngh quang th ng Gigabit (GEPON v GPON) ph hp vi yu cu mng VNPT giai on 2007-2010 Tp on Bu chnh vin thng Vit Nam nm 2008.

023-2011-T-KHCN&CN Tiu chun k thut cho cp si quang trong nh/ngoi

tri s dng trong mng FTTx nm 2011 ca Tp on Bu chnh Vin thng Vit Nam (TCCS-VNPT).

2.3. Nhn xt v tnh hnh tiu chun ha GPON trn th gii v ti Vit Nam

- Hin cng ngh GPON c ITU hon chnh thnh b khuyn ngh ITU-T

G.984.x. S hon thin ca b khuyn ngh ny l mt s c quan trng cho vic

la chn tiu chun tham chiu nhm hng n xy dng b tiu chun quc gia

v h thng truy nhp quang th ng GPON ti Vit Nam

- Cng ngh GPON v ang c trin khai ti Vit Nam nhng vic cha c tiu

chun quc gia no v cng ngh GPON ti Vit Nam t ra yu cu cn sm xy

dng tiu chun v cng ngh GPON ti Vit Nam.

- Khuyn ngh G.984.2 (03/2003) l mt khuyn ngh nm trong b khuyn ngh

G.984.x ca ITU vi hai sa i b sung gn nht G.984.2 Amendment 1 (02/2006)

v G.984.2 Amendment 2 (03/2008) m t y v r rng v cc yu cu k

thut cho phn lp tin ch truyn ti vt l PMD. y l s cc cho vic xut

xy dng tiu chun h thng truy nhp quang th ng G-PON Phn tin ch

truyn ti PMD

II. MNG TRUY CP QUANG TH NG ETHERNET EPON

1.Gii thiu chung

Vic vt tri v kh nng truyn d liu ca mng quang th ng PON l khng

ph nhn, nhng khai thc ti a kh nng ca n th cn tu thuc vo cng

ngh c la chn trong truyn ti. Chng ny trnh by s kt hp cng ngh

Ethernet trong mng truy nhp quang th ng gi tt EPON, v a ra nguyn

l truyn,li ch ca n v EPON vi kin trc IEEE 802, giao thc iu khin

a im MPCP(Multi Point Control Protocol)

1.1 Li ch ca mng truy cp quang th ng Ethernet _ PON

EPON l s kt hp gia mng truy cp quang th ng PON v k thut

Ethernet nn n mang u im ca c hai cng vic ny. Vic trin khai EPON

mang li li ch rt to ln bao gm:

Bng thng cao hn: EPON s cung cp bng thng cao nht cho ngi dng

trong bt k h thng truy cp quang th ng no. Tc lu lng hng

xung l 1Gbps v lu lng ln t 64 ONU c th vt qu 800 Mbps. Vi kh

nng cung cp bng thng rt ln nh vy, EPON c mt s li ch sau:

o S lng thu bao trn mt mng PON ln.

o Bng thng trn mi thu bao nhiu.

o Kh nng cung cp video.

o Cht lng dch v tt hn.

Chi ph u t thp hn: H thng EPON ang khc phc gia chi ph v hiu

sut bng si quang v cc lnh kin Ethernet. EPON cung cp cc chc nng v

c tnh si quang vi gi c th so snh c vi DSL v cp ng T1s. Hn

na, vic gim chi ph t c nh kin trc n gin, hiu qu hot ng cao v

chi ph bo dng thp. EPON chuyn giao nhng c hi gim gi sau:

o Loi tr nhng phn t ATM v SONET phc tp v c .

o Cc lnh kin quang th ng sng lu gim c chi ph bo dng.

o Nhng giao din Ethernet chun loi tr nhu cu cho DSL v

Modem cp b sung.

Nhiu li nhun hn: EPON c th h tr ng thi cc dch v thoi, d liu

v video, cho php nh cung cp nng cao dch v bng rng v linh hot.

Ngoi ra, n cng cung cp cc dch v truyn thng nh POST, T1, 10/100 Base-

T, h tr cc dch v trn nn ATM, TDM(Time Division Multiplexing) v

SONET.

1.2 Mng truy cp quang th ng EPON

EPON l mng da trn mng PON m n mang lu lng d liu c

ng gi vo khung Ethernet. N s dng chun m ng truyn 8b/10b (8 bit

ngi dng c m ho nh 10 bit ng truyn ) v hot ng tc chun ca

Ethernet.

1.2.1 Nguyn l hot ng

Chun IEEE 802.3 nh ngha hai cu hnh c bn cho mt mng Ethernet.

Mt cu hnh trong cc trm s dng chung mi trng truyn dn vi giao thc

a truy cp sng mang c pht hin xung t (CSMA/CD) v cu hnh cn li, cc

trm s giao tip vi nhau thng qua mt chuyn mch s dng cc tuyn kt ni

im- im v song cng. Tuy nhin, EPON c mt s c tnh m khin cho n

khng th trin khai trn mt trong hai cu hnh ny m thay vo ta phi kt hp

c hai.

hng xung, EPON hot ng nh mt mng qung b. Khung Ethernet

c truyn bi OLT qua b chia quang th ng n tng ONU ( vi N trong

khong t 4 n 64). ONU s lc b cc gi tin khng phi l ca n nh vo a

ch

MAC(Media Access Control) trc khi truyn cc gi tin cn li n ngi

dng. Hnh 4.1.

hng ln, v c tnh nh hng ca b kt hp quang th ng, khung d

liu t bt k ONU no ch n OLT v khng n cc ONU khc. Trong trng

hp , hng ln: c tnh ca EPON ging nh kin trc im- im. Tuy

nhin, khng ging nh mng im - im tht s, cc khung d liu trong EPON

t cc ONU khc nhau c truyn ng thi vn c th b xung t. V vy,

hng ln (t ngi dng n mng), ONU cn s dng mt vi c ch trnh xung

t d liu v chia s dung lng knh quang hp l. y, lung d liu hng

ln c phn b theo thi gian. Hnh 4.2

Hnh 4.2: Lu lng hng ln trong EPON

Nu khng c khung no trong b m in vo khe thi gian th 10 bit c

tnh rng s c truyn. S sp xp nh v khe thi gian hp l c th nh v tnh

(TDMA c nh) hot ng da vo hng i tc thi trong tng ONU (thc hin

thng k ). C nhiu m hnh nh v nh l nh v da vo quyn u tin ca d

liu, da vo cht lng dch v QoS hay da vo mc dch v cam kt

(SLAs:Service Level Agreements).

1.2.2 Giao thc iu khin a im MPCP(Multi Point Control Protocol)

h tr vic nh v khe thi gian bi OLT, giao thc MPCP ang c nhm

IEEE 802.3ah pht trin. MPCP khng xy dng mt c ch phn b bng tn c

th, m thay vo , n l mt c ch h tr thit lp cc thut ton phn b bng

tn khc nhau trong EPON. Giao thc ny da vo hai bn tin Ethernet: Gate v

Report. Bn tin Gate c gi t OLT n ONU n nh mt khe thi gian

truyn. Bn tin Report c ONU s dng truyn t cc thng tin v trng thi

hin ti ca n (nh mc chim d ca b m) n OLT, gip OLT c th phn b

khe thi gian mt cch hp l. C hai bn tin Gate v Report u l cc khung iu

khin MAC (loi 88-08) v c x l bi lp con iu khin MAC.

C hai m hnh hot ng ca MPCP: t khi to v hot ng bnh thng. Trong

m hnh t khi to c dng d cc kt ni ONU mi, nhn bit tr

Round-trip v a ch MAC ca ONU . Trong m hnh bnh thng c dng

phn b c hi truyn dn cho tt c cc ONU c khi to.

T nhiu ONU c th yu cu khi to cng mt lc, m hnh khi to t ng

l mt th tc da vo s cnh tranh. lp cao hn n lm vic nh sau:

OLT ch nh mt khe khi to, mt khong thi gian m khng c ONU khi to

trc no c php truyn. Chiu di ca khe khi to ny phi ti thiu l:

+ - ;

vi l chiu di ca ca s truyn m mt ONU khng khi

to c th dng.

OLT gi mt bn tin khi to Gate bo hiu thi gian bt u ca khe khi to

v chiu di ca n. Trong khi chuyn tip bn tin ny t lp cao hn n lp

MAC, MPCP s gn nhn thi gian c ly theo ng h ca n.

Ch cc ONU cha khi to mi p ng bn tin khi to Gate. Trong lc nhn bn

tin khi to Gate, mt ONU s thit lp thi gian ng h ca n theo nhn thi

gian n trong bn tin khi to Gate.

Khi ng h trong ONU n thi gian bt u ca khe thi gian khi to (cng

c phn phi trong bn tin Gate), ONU s truyn bn tin ca chnh n (khi

to Report). Bn tin Report s cha a ch ngun ca ONU v nhn thi gian

tng trng cho thi gian bn trong ca ONU khi bn tin Report c gi.

Khi OLT nhn bn tin Report t mt ONU cha khi to, n nhn bit a ch

MAC ca n v thi gian Round-trip. Nh c minh ha hnh 4.3, thi gian

Round-trip ca mt ONU l thi gian sai bit gia thi gian bn tin Report c

nhn OLT v nhn thi gian cha trong bn tin Report.

Hnh 4.3: Thi gian Round-trip

T nhiu ONU cha khi to, c th p ng cng bn tin khi to Gate, bn tin

Report c th xung t. Trong trng hp , bn tin Report ca ONU b xung t

s khng thit lp bt k khe no cho hot ng bnh thng ca n. Nu nh

ONU khng nhn c khe thi gian trong khong thi gian no , n s kt lun

rng s xung t xy ra v n s th khi to li sau khi b qua mt s bn tin

khi to Gate ngu nhin. S bn tin b c chn ngu nhin t mt khong thi

gian gp i sau mi ln xung t.

Di y chng ta m t hot ng bnh thng ca MPCP: 1. T lp cao hn

(MAC control client), MPCP trong OLT a ra yu cu truyn bn tin Gate

n mt ONU c th vi cc thng tin nh sau: thi im ONU bt u truyn

dn v thi gian ca qu trnh truyn dn (hnh 4.4).

2 Trong lp MPCP (ca c OLT v ONU) duy tr mt ng h. Trong khi

truyn bn tin Gate t lp cao hn n lp MAC, MPCP s gn vo bn tin

ny nhn thi gian c ly theo ng h ca n.

3 Trong khi tip nhn bn tin Gate c a ch MAC ph hp (a ch ca cc

bn tin Gate u l duy nht), ONU s ghi ln cc thanh ghi trong n thi gian

bt u truyn v khong thi gian truyn. ONU s cp nht ng h ca n

theo thi gian lu trn nhn ca bn tin Gate nhn c. Nu s sai bit

vt qu ngng c nh trc th ONU s cho rng, n mt s ng

b v s t chuyn vo mode cha khi to. mode ny, ONU khng c

php truyn. N s ch n bn tin Gate khi to tip theo khi to li.

4 Nu thi gian ca bn tin Gate c nhn gn ging vi thi gian clu trn

nhn ca bn tin Gate, ONU s cp nht ng h ca n theo nhn thi gian.

Khi ng h trong ONU ch n thi im bt u ca khe thi gian truyn dn,

Hnh 4.4: Giao thc MPCP-hot ng ca bn tin Gate

ONU s bt u phin truyn dn. Qu trnh truyn dn ny c th cha nhiu

khung Ethernet. ONU s m bo rng khng c khung no b truyn gin on.

Nu phn cn li ca khe thi gian khng cho khung tip theo th khung ny s

c li cho khe thi gian truyn dn tip theo v trng mt phn khng s

dng trong khe thi gian hin ti.

Bn tin Report s c ONU gi i trong ca s truyn dn gn cho n cng vi

cc khung d liu. Cc bn tin Report c th c gi mt cch t ng hay

theo yu cu ca OLT. Cc bn tin Report c to ra lp trn lp iu khin

MAC (MAC Control Client) v c gn nhn thi gian ti lp iu khin MAC

(Hnh 4.5). Thng thng Report s cha di yu cu cho khe thi gian tip theo

da trn di hng i ca ONU. Khi yu cu mt khe thi gian, ONU cng c

tnh n c cc phn mo u bn tin, l cc khung mo u 64 bit v khung mo

u IFG 96 bit c ghp vo trong khung d liu.

Khi bn tin Report c gn nhn thi gian n OLT, n s i qua lp MAC

(lp chu trch nhim phn b bng tn). Ngoi ra, OLT cng s tnh li chu trnh

i v v vi mi ngun ONU nh trong hnh 3.8. S c mt s chnh lch nh ca

Hnh 4.5: Giao thc MPCP-hot ng ca bn tin Report

RTT mi v RTT c tnh t trc bt ngun t s thay i trong chit sut ca

si quang do nhit thay i. Nu s chnh lch ny l ln th OLT s c

cnh bo ONU mt ng b v OLT s khng cp phin truyn dn cho ONU

cho n khi n c khi to li.

Hin nay giao thc MPCP vn ang tip tc c xy dng v pht trin bi

nhm 802.3ah ca IEEE. y l nhm c nhim v pht trin v a ra cc gii

php Ethernet cho cc thu bao ca mng truy nhp.

1.2.3 EPON vi kin trc 802

Kin trc IEEE 802 nh ngha hai phng thc: Share Medium v song cng.

Trong phung thc chia s trung gian (Share Medium), tt c cc trm c kt

ni n min truy nhp n, phn ln mt trm c th pht ti mt lc v tt

c cc trm c th nhn bt c lc no. Trong phng thc song cng, l s kt

ni PtP kt ni hai trm v c hai trm c th pht v nhn ng thi. Da vo

nh ngha , cc cu khng bao gi chuyn tip khung quay tr li cng vo ca

n. Ni khc, n cho rng tt c cc trm c kt ni n cng mt cng ca cu

v c th truyn thng vi nhau m khng cn thng qua cu. Phng thc ny

to ra kh nng cc ngi dng c kt ni n cc ONU khc nhau trong cng

mng PON v c th truyn thng vi nhau m d liu khng cn x l lp 3

hoc lp cao hn.

gii quyt vn ny v m bo thch hp vi cc mng Ethernet khc, cc

thit b gn lin vi EPON s c lp con thm vo, da trn cu hnh ca n s

chn Share Medium hoc Point to Point Medium. Lp con ny c xem nh l

lp con Share Medium Emulation (PtPE). Lp con ny phi di lp MAC

m bo hot ng ca Ethernet MAC hin ti c nh ngha trong chun P802.3

ca IEEE. Hot ng ca lp Emulation da vo tagging ca Ethernet vi tag duy

nht cho mi ONU( hnh 4.6). Nhng tag ny c gi l LinkID v c t vo

trong mo u trc mi khung.

Hnh 4.6: Trng LinkID c nhng trong mo u

bo m s duy nht cho LinkID, OLT s n nh mt hoc nhiu tag cho mi ONU trong sut qu trnh ng k lc u.

1.2.4 Point to Point Emulation

Trong m hnh ny, OLT phi c N cng MAC, mt cng cho mt ONU( hnh

4.7a). Khi mt khung c gi xung (t OLT n ONU), lp con PtPE trong

OLT s chn LinkID kt hp vi cng MAC c th vo khung d liu. Cc khung

s c chia s cho tng ONU nhng ch mt lp MAC ca n. lp MAC ca

cc ONU cn li s khng nhn c khung ny. Trong kh nng ny, n s xut

hin nu ch khi khung c gi theo kt ni PtP ch cho mt ONU.

Chn LinkID kt

hp vi cng MAC

Chp nhn khung nu LinkID ph

hp

Hnh 4.7 a): Hng xung trong PtPE

T chi khung nu LinkID khng ph hp

hng ln, ONU s chn LinkID c n nh ca n vo mo u ca mi khung c

chuyn. Lp con PtPE trong OLT s tch khung nhn bit cng MAC chnh xc da vo

LinkID duy nht cho mi ONU.(hnh 4.7b).

Tch khung theo

cng trong LinkID

Chn LinkID c

n nh cho ONU

Hnh 4.7 b): Hng ln trong PtPE

Hnh 4.8: Cu gia cc ONU trong PtPE

Cu hnh PtPE thch hp vi cu khi mi ONU c kt ni n mt cng c lp

ca cu. Cu c t trong OLT s chuyn tip lu lng vo trong ONU gia cc

cng ca n.

1.2.5 Share Medium Emulation

Trong SME, bt k mt Node no (OLT hay ONU) s chuyn khung d liu v s

c nhn tt c cc Node (OLT v ONU). Trong hng xung, OLT s chn

mt LinkID qung b m mi ONU u chp nhn (hnh 4.9a). m bo hot

ng Share Medium cho hng ln, lp con SME trong OLT phi nhn nh tt c cc

khung tr li hng xung tt c cc ONU nhn chnh khung d liu ca n th

lp con SME ONU ch tha nhn khung nu LinkID ca khung khc vi LinkID

ca n.

Chn

Link ID qung b

Chp nhn tt c cc

khung ngoi tr khung

ca n Hnh 4.9a) Hng truyn xung trong SME

Chp nhn tt c cc khung v phn hi li

hng xung

Khi truyn khung, chn

LinkID

Khi nhn khung, t chi

LinkID ca chnh n

Hnh 4.9 b): Hng truyn ln trong SME

SME ch yu cu mt cng MAC trong OLT. Chc nng vt l ca lp ny (lp con

SME) l cung cp truyn thng ONU n ONU, khng cn cu lin kt.

Kt lun

Ni dung trn cho thy c s kt hp gia mng truy nhp quang th ng

PON v cng ngh Ethernet to ra mt khuynh hng mng trin vng cho mng

truy nhp th h sau. EPON l mt bc pht trin trong tin trnh cp quang ho

mng truy nhp th h sau xy dng mng truy nhp bng rng. Vi s quan tm

c bit n mng EPON, mng truy nhp th h sau s ging nh mt m hnh kt

hp Ethernet im-im v im-a im, ti u ho cho truyn ti d liu IP cng

nh cc dch v thoi v video theo thi gian thc. Nhng cht lng ca mng l

iu ct li.