TIU LUN MN HCTruyn ti IP quang
CU TRC KHUNG VC-4
Ging vin hng dn: PGS.TS Bi Trung Hiu Sinh vin : Bi Th Hng Lp :
CH10DT3
H
i 4-10-2011
Mc lc1. Cu trc khung VC-4
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3 1.1 Cu trc POH (Path
Overhead)........................................................................................
3 1.2 Ghp TUG -3 vo VC-4
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5 2. Con tr AU-4
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6
Tiu lun truyn ti IP quang
Cu trc khung VC-4
Cu trc khung VC-4
1. Cu trc khung VC-4Cu trc c 9 dng x 261 c t ngha l khung c 9
dng mi dng ghp 261 byte, mi byte ghp 8 bit, vy s gm 2340 byte d liu
v 9 byte POH. Gm 2 phn chnh: Phn th nht ghp cc byte POH t dng qun
l, gim st tuyn mc cao. Phn th 2 l phn ti trng ghp cc lung nhnh PDH,
vi khung VC-4 c ghp t dng n dng 9 thu c c t 2 n c t 261. n dng 9
thu c c t 1 dng cho
Trnh t truyn cc byte trong khung l t tri sang phi v t trn xung
di. Trnh t truyn cc bit trong m t byte l bit c trng s ln nht truyn
i trc v bit c trng s b nht truyn sau cng. Nguyn tc ny p dng cho mi
loi khung tn hiu trong SDH. 9 byte POH261
9
C-4
Hnh 1: Cu trc VC-4
1.1 Cu trc POH (Path Overhead) POH c ghp cp VC v ch c x l khi
giao tip vi cc lung cn ng b hoc c x l bi cc trm truyn dn thc hin
vic tch ghp cc VC. Ti cc trm truyn dn, cc POH c th khng cn phi gii
ghp khi cc VC. Tu theo phn cp ca VC m POH c phn chia ra hai kiu l
POH bc cao v POH bc thp.
Bi Th Hng-CH10DT3
3
Tiu lun truyn ti IP quang
Cu trc khung VC-4
-
POH ca VC-41c t
9 hng
Hnh 2: Cu trc POH ca VC-4 Chc nng ca cc byte Byte J1: Nhn dng ng
truyn VC-4 Mi ng truyn c gn m t nhn, c nhim v thng bo ng m d liu s
c truyn n. Ngoi ra byte ny cn c chc nng nh v cho con tr ( PTR) ch
ra im bt u ca cc VC-4 trong STM-1. Byte B3 : BIP-8 ca VC-4 Byte n y
c s dng tnh ton v gim st li ng truyn ti cc trm u cui. S kim tra ng
ng ti giai on n y c tin hnh trn ton b VC sau lu tr v truyn trn byte
B3 ca VC tip theo. Byte C2: Nhn tn hiu c s dng ch th thnh phn v cch
sp xp ti trng trong khung VC-4. Byte G1: Ch th li u xa Byte G c s
dng chuyn ti thng bo v trng thi v cht lng cui tuyn (u vo trm u xa)
ti trm gc. Chc nng cc bit ca G c quy nh nh sau: Bit n bit 4 ch th
li u xa khi kim tra byte B3. Chn gi tr u ca 4 bit ch th t khng c li
(0000) n 8 li (1000). By gi tr cui ca 4 bit ch th u xa khng c li.
Cc bit b5, b6, b7 ch th u xa khng hon ho, mt tn hiu VC-4, mt khung.
Khi xy ra cc s c th c i t b5 b6 b7 = 101 v chuyn v trm gc. Byte F2:
Knh iu hnh mngBi Th Hng-CH10DT3 4
Tiu lun truyn ti IP quang
Cu trc khung VC-4
Byte F2 c dng nh m t knh trao i thng tin gia cc ngi khai thc mng
tc l trao i d liu gia hai my tnh. Byte H4: S th t khung trong a
khung C chc nng ch th s th t ca khung trong trng hp d liu thng tin
c b tr trong a khung gm nhiu container cp thp (nh TU-12). Byte
Z3,Z4,Z5: L cc byte d phng, hin nay cha s dng. 1.2 Ghp TUG -3 vo
VC-4 Ghp cc TUG-3 c to th nh t
x TU-3 vo VC-4
VC-4 = 3 x TUG-3 + 18 byte chn c nh nh hnh 3 Ghp cc TUG-3 c to
th nh t 7 x TUG-2 vo VC-4 VC-4 = 3 x TUG-3 + 18 byte chn c nh nh
hnh 4261 = (86 x 3) + 2 c t chn +1 POH
VC-4
P O H261
3 x TU-3
9
Con tr PTR Cc bit chn c nh
9 TUG-3
86
Hnh 3 : Ghp cc TUG-3 c to thnh t 1 x TU-3 vo VC-4
Bi Th Hng-CH10DT3
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Tiu lun truyn ti IP quang
Cu trc khung VC-4
261 = (86 x 3 ) + 2 c t chn +1 POHN P I
NP I
NP I
VC-4
P O H
21 x 3 = 63
9
261N P I
21
N P I
N P I
9
TUG-3
Hnh 4: Ghp cc TUG-3 c to thnh t 7 x TUG-2 vo VC-4 Ba khung c
TUG-3 ghp vo khung VC-4. V 3 khung TUG-3 ch c 258 c t, nn trong khi
VC-4 chn thm 18 byte c nh (2 c t) vo c t th hai v th ba, ghp 9 byte
VC-4 POH to thnh khung VC-4 c 261 c t 9 hng.
86
2. Con tr AU-4 Cu to ca AU-PTR nh sau9 ByteH1 Y Y H2 H3 H3 H3
H3
Hnh 5: Cu to ca AU-4 PTR + Byte Y = 1001 SS11 + Byte = 1111 1111
+ Cc byte H H2 H3 l cc byte c trng cho hot ng ca con tr, gi tr H2
H3 nh sau6
ca AU-PTR v qu trnh ng chnh ph thu c vo cc byte ny. Cu to cc
byte HBi Th Hng-CH10DT3
Tiu lun truyn ti IP quangH1N N N N S S I D I D I
Cu trc khung VC-4H2D I D I D
3 x H3...
C d liu
Dng AU
Gi tr con tr
Cc byte ng chnh m
Hnh 6: Cu trc ca cc byte H1, H2, H3 ngha cc bit Bit n bit 4 (bit
N) trong con tr mang NDF (New data flag), cho php gi tr DF c ch th
bi o con tr thay i nu s thay i l do ti trng thay i. Hot ng bnh thng
c ch th bi t m 0110 trong 4 bit N. C s liu mi gi tr 4 bit N thnh
1001. DF c din gii l c kh nng khi c ti thiu 3 bit ph
hp vi mu 00 . DF c din gii l khng c kh nng khi c ti thiu 3 bit
ph hp vi mu 0110. Hai bit SS l 2 bit ch th loi con tr (AU-4 PTR c
SS = 10). Ba byte H3: Bnh thng 3 byte H3 khng mang thng tin, khi
chn m cc byte H3 b xo ghp v o 3 byte ti trng ca cc lung nhnh. Cc
bit D (Decrement) l gim v cc bit I (Increment) l tng: L cc bit cha
gi tr PTR n c to bi 2 bit cui cng ca byte H1 v 8 bit ca byte H2 (cc
bit t 7 n 16) 10 bit gi tr PTR ny gm 5 bit I v 5 bit D c s dng ch
ra byte u tin ca VC-4. Do c m ho 10 bit cho nn n c th to ra 210 =
1024 gi tr. Mc khc trong VC-4 li c ti 261 x 9 = 2349 byte. V vy c
th nh s c tt c cc byte, ngi ta t c 3 byte lin tip nhau th nh nhm
tng ng vi m t gi tr ca PTR. Do s nhm trong VC-4 l 2349: 3 = 783
nhm. Tng ng vi s nhm ny gi tr PTR cng c nh s t 0 cho n 782, bt u t
byte u tin.
Thng bo ng chnh m khi 5 bit D b o ngc trng thi v a ch s b gim
trong con tr AU-4 k tip (a ch -1). Thng bo ng chnh dng khi 5 bit I
b o ngc trng thi v a ch s tng trong con tr AU-4 k tip (a ch
+1).
Bi Th Hng-CH10DT3
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