TM HIU V MNG FTTx TRN NN CNG NGHGPONPosted: Thng Mi Hai 12, 2011
inUncategorized 01.Gii thiu chung.Trong bi vit ny chng ta s xem xt
quy trnh trin khai mng . Quy trnh bt u t vic la chn cng ngh (APON,
BPON, GPON hay EPON) n qu trnh trin khai mng core, mng truy
nhp.2.La chn cng ngh .Theo phn tch xu hng pht trin hin nay , PON l
cng ngh truy nhp tin tin c th h tr tc rt cao, p ng cc yu cu dch v
triple-play cho ngi dng m li tit kim chi ph do vic dng chung OLT v
ng cp quang phn phi ti cc b tch/ghp spliter, cc thu bao ch cn chy
dy ring ti cc b Spliter cc u ph. Ngoi ra do thit b l th ng khng yu
cu in nn chi ph lp t bo tr thp. im yu cng ngh v chi ph u t ban u
cao c th gim bt bng cch lai ghp gia mng cp quang FTTx v cp ng VDSL2
nh hnh sau :
Hnh 1. Lai ghp gia mng cp quang FTTx v cp ng VDSL23.Kin trc mang
truy nhp quang,3.1 Kin trc mng .3.1.1 FTTB ( Fiber to the Building
).Dch v mng quang n ta nh bao gm hai trng hp: dnh cho khu vc chung
c MDU (multi-dwelling units) v dnh cho khu vc doanh nghip. Mi trng
hp ny li bao gm cc tiu ch dch v nh sau: FTTB cho MDU :Bao gm cc dng
dch v nh sau:- Dch v bng rng khng i xng (dch v broadcast s, video
theo yu cu, download file ) Dch v bng rng i xng (broadcast ni dung,
email, trao i file, o to t xa, khm bnh t xa, chi game trc tuyn) .-
Dch v in thoi truyn thng v ISDN: mng truy nhp phi h tr mt cch linh
hot cung cp cc dch v in thoi bng hp. FTTB cho doanh nghip:Bao gm cc
dng dch v nh sau:- Dch v bng rng i xng (broadcast ni dung, phn mm
nhm, email , trao i file)- Dch v in thoi truyn thng v ISDN: mng
truy nhp phi h tr mt cch linh hot cung cp cc dch v in thoi bng hp.-
ng thu knh ring: mng truy nhp phi h tr mt cch linh hot cung cp dch
v thu knh ring vi cc mc tc khc nhau.
Hnh 2. Cp quang ko n nh cao tng FTTB.3.1.2 FTTC v FTTCab(Fiber
To The Curb):Bao gm cc dng dch v nh sau:- Dch v bng rng khng i xng
(dch v broadcast s, video theo yu cu, download file ) Dch v bng rng
i xng (broadcast ni dung, email, trao i file, o to t xa, khm bnh t
xa, chi game trc tuyn)- Dch v in thoi truyn thng v ISDN: mng truy
nhp phi h tr mt cch linh hot cung cp cc dch v in thoi bng hp.- Cc
dch v mng trc xDSL.
Hnh 3. Cp quang ko n khu dn c FTTC.3.1.3 FTTH ( Fiber to the
Home ).Bao gm cc dng dch v nh sau:- Dch v bng rng khng i xng (dch v
broadcast s, video theo yu cu, download file ) .- Dch v bng rng i
xng (broadcast ni dung, email, trao i file, o to t xa, khm bnh t
xa, chi game trc tuyn).- Dch v in thoi truyn thng v ISDN: mng truy
nhp phi h tr mt cch linh hot cung cp cc dch v in thoi bng hp.
Hnh 4. Cp quang ko n h gia nh FTTH.3.2 Cu hnh mng tham chiu
.3.2.1 Giao din nt dch v SNI (Service Node Interface ).
Hnh 5. V tr giao din SNI v UNI.Giao din nt dch v SNI l giao din
gia mng truy nhp v mt nt dch v. Nu pha mng truy nhp-giao din nt dch
v v nt dch v-giao din nt dch v khng cng mt a im th kt ni t xa gia
mng truy nhp v nt dch v c th c s dng bi ng truyn ti trong sut.
Trong thit b OLT s bao gm giao din .
Bng 1.V d giao din nt dch v SNI v cc dch v3.2.2 giao din mng ngi
dng UNI (User Network Interface ).Thit b ONU/ONT bao gm giao din
UNI v thit b OLT bao gm giao din SNI nh ch ra trong bng 9. Giao din
UNI ty thuc vo dch v do nh khai thc mng cung cp. V d v giao din UNI
c ch ra trong bng sau
Bng 2.V d giao din nt dch v UNI v cc dch v3.2.3 Thit b u cui i
trm OLT,b chia SPLITTER, ONT/ONU.a/ Thit b OLT (Optical Line
Termination ).Thit b u cui ng dy OLT (optical line terminal) c kt
ni ti mng chuyn mch qua cc giao din chun. V pha mng phn phi, OLT
bao gm cc giao din truy nhp quang theo tiu chun GPON v tc bit, qu
ng truyn, jitter, OLT gm ba phn chnh sau y: Chc nng giao din cng
dch v (service port Interface Function); Chc nng u ni cho
(cross-connect function); Giao din mng phn phi quang (ODN
interface)Cc khi chc nng chnh ca OLT c m t trong Hnh 26 S khi chc
nng OLT.
Hnh 6. S khi chc nng OLT.- Khi li PON (PON core shell)Khi ny gm
hai phn, chc nng giao din ODN c m t trong mc sau v chc nng ni t
truyn dn (PON TC Transmission Convergence) bao gm khung tn hiu, iu
khin truy nhp phng tin, OAM, DBA v qun l ONU. Chc nng PON TC bao gm
khung tn hiu, iu khin truy nhp phng tin, OAM, DBA v qun l ONU. Mi
PON TC la chn mt phng thc truyn dn nh ATM, GEM hoc c hai.- Khi u ni
cho (cross-connect shell)Khi u ni cho cung cp ng truyn gia khi PON
v khi dch v. Cng ngh kt ni ph thuc vo cc dch v, kin trc bn trong
OLT v cc yu t khc. OLT cung cp chc nng u ni cho ty thuc vo phng thc
truyn dn la chn (GEM, ATM hay c hai).- Khi dch v (service shell)Khi
thnh thc hin chuyn i gia cc giao din dch v v giao din khung TC ca
phn mng PON.Chc nng chnh OLT:-Thit b kt ni u cui quang OLT (Optical
Line Terminal) .-OLT l thit b kt cui quang tch cc t ti nh trm
(CO).-OLT l thit b thuc lp access ca mng MANE. Giao din a dch v kt
ni vi mng li. Tp trung lu lng.-OLT cung cp kt ni quang P2P v
P2MP.-OLT giao tip vi cc ONT, MxU, mini DSLAM ca mng PON.-OLT thc
hin truyn thng tin i v n nhiu ngi s dng qua mt tuyn si quang.-OLT c
th thc hin chc nng chuyn mch to cc cng dch v cho ng ln hoc ng
xung.
Hnh 7.Mt s loi OLT in hnh .Control board:SCUL SCUBService
board:GPBC OPFAEthernet service subtending board:ETHAUplink
interface board:GICF/G GICD/E X1CA X2CA TOPAPower interface
board:PRTGUniversal interface board:CITAb/ Thit b u cui mng
ONU/ONTHu ht cc khi chc nng ca ONU tng t nh cc khi chc nng ca OLT.
Do ONU hot ng vi mt giao din PON (hoc ti a 2 giao din khi hot ng ch
bo v), chc nng u ni cho (cross-connect function) c th c b qua. Tuy
nhin, thay cho chc nng ny th c thm chc nng ghp v tch knh dch v (MUX
v DMUX) x l lu lng. Cu hnh tiu biu ca ONU c th hin trong Hnh 6 S cc
khi chc nng ONU. Mi PON TC s la chn mt ch truyn dn ATM, GEM hoc c
hai.
Hnh 8. S khi chc nng ONU.-L thit b u cui t pha ngi s dng-Cung cp
cc lung d liu vi tc t 64 Kb/s n 1 Gb/s.-Giao din ng ln c tc v giao
thc hot ng tng thch vi cng xung ca OLT.-ONU c dung lng va v nh v c
cung cp a dch v nh POST, ADSL, VDSL, LAN
Hnh 9.Mt s loi ONU in hnh .C/ B chia SPLITTER. Dng chia tn hiu
quang t mt si truyn i trn nhiu si v ngc li . Thc hin chia cng sut
quang ti si quang u vo u vo ti N si quang u ra. T l chia c nhiu cp
khc nhau: 1/8;1/16;1/32; 1/64;1/128 ty thuc ng dng s dng. H s chia
cng sut quang ph thuc vo cp chia. Suy hao tn hiu quang t u vo ti u
ra t l vi h s chia . Phn b b chia ph bin trn mng theo t l chia 1: 2
ti t quang phi cp 1 v t l chia 1: 32 ti t quang phi cp 2. Ti nhng
im c nhiu thu bao d bo c nhu cu bng thng ln nh khu vc nhiu ngn hng
c th t b chia 1:32 sau ny nng cp bng thng d dng.
Hnh 10.M hnh chia v thc t .Ngoi ra cn c mt s loi :
Hnh 11. Mt s loai thit b u cui khc.4.Cc c tnh c bn ca GPON.4.1
tc bit.V c bn, GPON hng ti tc truyn dn ln hn hoc bng 1.2 Gbit/s.
Tuy nhin, trong trng hp dch v xDSL khng i xng cho FTTH hoc FTTH th
khng cn thit n tc cao nh vy. GPON nh ngha 7 dng tc bit nh sau: ng
ln 155 Mbit/s, ng xung 1.2 Gbit/s; ng ln 622 Mbit/s up, ng xung 1.2
Gbit/s; ng ln 1.2 Gbit/s up, ng xung 1.2 Gbit/s; ng ln 155 Mbit/s
up, ng xung 2.4 Gbit/s; ng ln 622 Mbit/s up, ng xung 2.4 Gbit/s; ng
ln 1.2 Gbit/s up, ng xung 2.4 Gbit/s; ng ln 2.4 Gbit/s up, ng xung
2.4 Gbit/s.4.2 khong cch logic.Khong cch logic l khong cch ln nht
gia ONU/ONT v OLT ngoi tr khong vt l. Trong mng GPON, khong cch
logic ln nht l 60 km.4.3 khong cch vt l.Khong cch vt l l khong cch
vt l ln nht gia ONU/ONT v OLT. Trong mng GPON, c hai ty chn cho
khong cch vt l v 10 km v 20 km. i vi vn tc truyn ln nht l 1.25
Gbit/s th khong cch vt l l 10 km.4.4 T l chia.i vi nh khai thc mng
th t l chia cng ln cng tt. Tuy nhin t l chia ln th i hi cng sut
quang pht cao hn h tr khong cch vt l ln hn. T l chia 1:64 l t l l
tng cho lp vt l vi cng ngh hin nay. Tuy nhin trong cc bc pht trin
tip theo th t l 1:128 c th c s dng.5.Thng s k thut . Bc sng
1260-1360nm ng ln ,1480-1500nm ng xung . a truy cp hng theo TDMA.
Cp pht bng thng ng DBW (Dynamic Bandwith Allocation). Loi lu lng :d
liu s. Khung truyn dn GEM. Dch v y : (Ethernet,TDM,POST ). T l chia
th ng :ti a l 1:128. Gi tr BER ln nht :. Phm vi cng sut lung xung :
-3 n 2 dBm (10km ODN), T 2 n 7 dBm (20km ODN ). Loi cp tiu chun
ITU-T Rec.G625 . Suy hao ti a gia cc ONU l :15 Db. C ly cp ti a
:20km DFB laser lung ln, 10km vi Fabry-perot.
Hnh 11. TDMA GPON.GPON s dng TDMA c cc u im : Cc ONU c th hoat
ng cng bc sng . Cc OLT cng ch cn mt b thu. Gim chi ph u t ,bo dng .
dng lp t thm cc ONU nu c nhu cu m rng mng.Yu cu s dng khi dng k
thut TDMA :ng b lu lng trnh xung t d liu khi c hai gi d liu n b
nghp cng mt thi im.6.2 phng thc ghp knh.Phng thc ghp knh l ghp knh
song hng .Hin nay cc h thng GPON u s dng ghp knh phn chia khng gian
.N thc hin nh s dng nhng si ring bit cho truyn dn ng ln v ng xung
.u im :-tng c qu cng sut trong mng .-vic s dng hai si quang lm cho
vic thit k mm do hn.-kh nng m rng trong tng lai.-chi ph gim do s
dng cng bc sng ,b pht v b thu.Nhc im : cn gp i s lng si, connector
.7.Phng thc ng gi d liu.GPON nh ngha hai phng thc ng gi d liu ATM v
GEM (GPON Encapsulation Metho).Phng thc ng gi GEM s dng ng gi qua
mng GPON, cung cp kh nng ng gi tng t ATM.H tr nhiu dch v khc nhau
,khch hng ATM c sp xp trong sut vo khung GEM s dng th tc ng gi GEM
.Lu lng d liu bao gm cc khung Ethernet ,gi tin IP,IPTV ,VoiIP , v
cc loi khc gip cho truyn dn khung GEM hiu qu v n gin .8. nh c v phn
nh bng tn ng.a. Th tc nh c . mt ONU c th hot ng trong mng PON n phi
c ranging (xc nh c ly gia OLT v ONU ) .C ly ranging ti a l 20km .Th
tc ranging c chia lm 2 pha . pha th nht ng k s sri cho UNU cha ng k
v cp pht ONU-ID cho ONU thc hin .S ID phi l duy nht ng thi ONU-ID c
s dng iu khin ,theo di v kim tra ONU.
Hnh 12. GPON ranging pha 1Cc pha trong bc th nht :B1.OLT xc nh
tt c cc ONU ang hot ng cho ngng qu trnh truyn dn ((1)ONU halt).B2 .
OLT xc nh tt c cc ONU cha c ID yu cu truyn s serial ((2)
Serial_number request).B3. Sau khi nhn c yu cu truyn s serial ,ONU
khng c ID s truyn sri ( (3) SN- transmission ) sau khi ch mt khong
ti a l 50ms.B4.OLT ch nh mt ONU-ID ti mt ONU cha ng k m OLT nhn c
seri ((4) assign ONU-ID).Trong pha tip theo RTD c o cho mi ONU ng k
mi ,pha ny cng p dng cho cc ONU b mt trong qu trnh thng tin.
Hnh 13. GPON ranging pha 2.Cc bc trong pha th hai bao gm :B5.
OLT xc nh tt c cc ONU ang hot ng cho ngng qu trnh truyn dn ((5) ONU
halt).B6.S dng cc s seri ,OLT xc nh mt ONU nht nh v ch cho ONU c
truyn cho qu trnh tr ((6) ranging request ).B7. ONU c cng s sri vi
OLT c xc nh cho qu trnh tr ((7) ranging tranmssion ) ,bao gm c
ONU-ID trong pha 1.B8. OLT o RTD ph thuc vo thi gian m tn hiu s dng
cho php o tr c thu .Sau khi s sri v ONU-ID l ng ,OLT thng bo tr cn
bng ((9)Equalization Delay ) ti ONU ((8)- ranging_ time message
).B9.ONU lu gi tr tr cn bng v to tr nh thi cho chui d liu lung ln
vi gi tr ny .b. phng php cp pht bng thng .
Hnh 14. Bo co v phn b bng thng trong GPONTh tc cp pht bng thng
:B1. ONU lu d liu thu bao cho lu lng hng ln vo b m.B2. Khi d liu
trong b m c bo ti OLT nh mt yu cu ti mt thi im OLT quy nh .B3.OLT
xc nh thi gian bt u truyn dn v khong thi gian truyn cho php (1/4 ca
s truyn dn ) ti ONU nh mt s cp php .B4ONU nhn s cp php v truyn khi
d liu xc nh .
Hnh 15 .Th tc cp pht bng thng trong GPON.9.Bo mt v m ha sa li.a.
bo mt :Do mng GPON l mng im a im nn d liu hng xung tt v cc ONU u c
th nhn c d liu nn cn dng chun mt m AES (Avanced Encrytion
Standard).Nu l lin kt im- im th khng cn bo mt.b. m ha sa li :Cng
ngh GPON ang s dng phng php sa li tin FEC (Forward Error
Correction) .FEC tng qu ng truyn ln 3-4 Db.V vy cho php tng tc bt v
khong cch gia OLT v ONU.FEC c ty chn c hng nn v hng xung ,thng dng
m RS (255,239 ).10.Kt lun chng 3.Chng ny chng ta a ra nhng u im ca
mng GPON , chng minh ti sao hin nay trn th gii v ti Vit Nam cng ngh
ny li ang c trin khai rng ri nht .Qua tm hiu v cc thit b u cui ,cc
ng dng ,c tnh ni bt ,,,,,,6.K thut truy nhp v phng thc ghp knh.6.1
k thut truy nhp. K thut truy nhp ph bin l TDMA . TDMA l k thut chia
bng tn thnh cc khe thi gian k tip nhau.Nhng khe ny c th n nh trc
cho mi khch hng .Lm Vn T
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