Cisco Cisco 10 Gigabit Modules 白皮書
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Testing and Interoperability of 1 0 G B A S E -L R M O ptic al Interfac es
Introduction
Thi s a r t i c l e w i l l d i sc u ss so me o f t he i ssu e s i n t e st i ng 10 G B AS E -L R M o p t i c a l i nt e r f a c e s o v e r mu l t i mo d e f i b e r , a nd
w i l l o u t l i ne a me t ho d o l o g y f o r d o i ng so . The a r t i c l e w i l l a l so d e sc r i b e t e st r e su l t s f r o m a r e c e nt mu l t i -v e nd o r
i nt e r o p e r a b i l i t y t e st d e mo nst r a t i ng t he f e a si b i l i t y a nd r o b u st ne ss o f t he L R M i nt e r f a c e .
w i l l o u t l i ne a me t ho d o l o g y f o r d o i ng so . The a r t i c l e w i l l a l so d e sc r i b e t e st r e su l t s f r o m a r e c e nt mu l t i -v e nd o r
i nt e r o p e r a b i l i t y t e st d e mo nst r a t i ng t he f e a si b i l i t y a nd r o b u st ne ss o f t he L R M i nt e r f a c e .
Ba ck g round
M u l t i mo d e f i b e r c o mp r i se s t he ma j o r i t y o f t he i nst a l l e d b a se o f f i b e r p l a nt f o r d a t a c o mmu ni c a t i o ns. O l d e r
mu l t i mo d e f i b e r s i nst a l l e d i n t he e a r l y 1990 s e x hi b i t l a r g e a mo u nt s o f mo d a l d i sp e r si o n, ma k i ng f o r a c ha l l e ng i ng
t r a nsmi ssi o n c ha nne l , p a r t i c u l a r l y a t 10 G b / s d a t a r a t e s, a nd l i mi t i ng t he t r a nsmi ssi o n d i st a nc e si g ni f i c a nt l y . F o r
i nst a nc e , 10 G i g a b i t E t he r ne t 850 nm d e v i c e s f o r mu l t i mo d e f i b e r ( 10 G B AS E -S R ) a r e g u a r a nt e e d t o o p e r a t e u p t o
o nl y 26 m o n w o r st -c a se 62.5-µ m mu l t i mo d e f i b e r . 10 G B AS E -L R M i s a ne w c o st -e f f e c t i v e a nd sma l l f o r m f a c t o r
c o mp a t i b l e o p t i c a l l i nk so l u t i o n f o r e x t e nd e d r e a c h o n mu l t i mo d e f i b e r . L R M ha s b e e n sp e c i f i c a l l y d e si g ne d f o r
v e r t i c a l r i se r a p p l i c a t i o ns i n b u i l d i ng b a c k b o ne s, w hi c h r e q u i r e l o ng e r t r a nsmi ssi o n d i st a nc e s a nd w he r e ne w f i b e r
p u l l s a r e c u mb e r so me a nd c o st l y , t o e na b l e t he u p g r a d e t o 10 G i g a b i t E t he r ne t o f e x i st i ng o p t i c a l l i nk s b e t w e e n
d a t a c e nt e r sw i t c he s a nd w o r k g r o u p sw i t c he s. L R M i s st a nd a r d i ze d i n t he
mu l t i mo d e f i b e r s i nst a l l e d i n t he e a r l y 1990 s e x hi b i t l a r g e a mo u nt s o f mo d a l d i sp e r si o n, ma k i ng f o r a c ha l l e ng i ng
t r a nsmi ssi o n c ha nne l , p a r t i c u l a r l y a t 10 G b / s d a t a r a t e s, a nd l i mi t i ng t he t r a nsmi ssi o n d i st a nc e si g ni f i c a nt l y . F o r
i nst a nc e , 10 G i g a b i t E t he r ne t 850 nm d e v i c e s f o r mu l t i mo d e f i b e r ( 10 G B AS E -S R ) a r e g u a r a nt e e d t o o p e r a t e u p t o
o nl y 26 m o n w o r st -c a se 62.5-µ m mu l t i mo d e f i b e r . 10 G B AS E -L R M i s a ne w c o st -e f f e c t i v e a nd sma l l f o r m f a c t o r
c o mp a t i b l e o p t i c a l l i nk so l u t i o n f o r e x t e nd e d r e a c h o n mu l t i mo d e f i b e r . L R M ha s b e e n sp e c i f i c a l l y d e si g ne d f o r
v e r t i c a l r i se r a p p l i c a t i o ns i n b u i l d i ng b a c k b o ne s, w hi c h r e q u i r e l o ng e r t r a nsmi ssi o n d i st a nc e s a nd w he r e ne w f i b e r
p u l l s a r e c u mb e r so me a nd c o st l y , t o e na b l e t he u p g r a d e t o 10 G i g a b i t E t he r ne t o f e x i st i ng o p t i c a l l i nk s b e t w e e n
d a t a c e nt e r sw i t c he s a nd w o r k g r o u p sw i t c he s. L R M i s st a nd a r d i ze d i n t he
I E E E S t d . 80 2.3a q
TM
-20 0 6
se r i a l o p t i c a l
i nt e r f a c e st a nd a r d , p u b l i she d i n N o v e mb e r 20 0 6. L R M i s a 10 G se r i a l i nt e r f a c e t ha t u se s l o ng w a v e l e ng t h ( 1310
nm) o p t i c s a nd a r e c e i v e r w i t h a n a d a p t i v e e l e c t r o ni c e q u a l i ze r I C i n t he r e c e i v e c ha i n i n o r d e r t o t r a nsmi t u p t o
220 me t e r s o n l e g a c y mu l t i mo d e f i b e r . The a d a p t i v e e q u a l i za t i o n, k no w n a s E D C , i s u se d t o c o mp e nsa t e f o r t he
d i f f e r e nt i a l mo d a l d i sp e r si o n ( D M D ) p r e se nt i n l e g a c y f i b e r c ha nne l s.
nm) o p t i c s a nd a r e c e i v e r w i t h a n a d a p t i v e e l e c t r o ni c e q u a l i ze r I C i n t he r e c e i v e c ha i n i n o r d e r t o t r a nsmi t u p t o
220 me t e r s o n l e g a c y mu l t i mo d e f i b e r . The a d a p t i v e e q u a l i za t i o n, k no w n a s E D C , i s u se d t o c o mp e nsa t e f o r t he
d i f f e r e nt i a l mo d a l d i sp e r si o n ( D M D ) p r e se nt i n l e g a c y f i b e r c ha nne l s.
Issues w i th L R M testi n g o v er m ul ti m o d e f i b er a n d m a i n p a r a m eter s d ef i n i ti o n s
The mo st d i r e c t w a y t o v a l i d a t e L R M o p t i c a l i nt e r f a c e s i s si mp l y t o t e st o v e r a c t u a l mu l t i mo d e f i b e r , a s t hi s i s mo st
r e p r e se nt a t i v e o f t he a c t u a l a p p l i c a t i o n a nd i s t he o nl y w a y t o d e mo nst r a t e i nt e r o p e r a b i l i t y b e t w e e n t w o o p t i c a l
t r a nsc e i v e r s. H o w e v e r , t he r e a r e t w o si g ni f i c a nt d i f f i c u l t i e s i n r e p e a t a b l y a nd r e l i a b l y t e st i ng t r a nsmi ssi o n o v e r
mu l t i mo d e f i b e r .
r e p r e se nt a t i v e o f t he a c t u a l a p p l i c a t i o n a nd i s t he o nl y w a y t o d e mo nst r a t e i nt e r o p e r a b i l i t y b e t w e e n t w o o p t i c a l
t r a nsc e i v e r s. H o w e v e r , t he r e a r e t w o si g ni f i c a nt d i f f i c u l t i e s i n r e p e a t a b l y a nd r e l i a b l y t e st i ng t r a nsmi ssi o n o v e r
mu l t i mo d e f i b e r .
F i r st , mu l t i mo d e f i b e r s v a r y w i d e l y i n b a nd w i d t h a nd d i f f e r e nt i a l mo d e d e l a y ( D M D ) p r o f i l e s, so t ha t si g na l q u a l i t y
a nd t r a nsmi ssi o n r e su l t s w i l l a l so v a r y w i d e l y f r o m o ne f i b e r t o a no t he r ( se e F i g u r e 1, b e l o w ). I n t he p r o c e ss o f
p r o d u c i ng t he L R M st a nd a r d , t he I E E E L R M Ta sk F o r c e t o o k a st a t i st i c a l a p p r o a c h, mo d e l l i ng a nd t e st i ng a
nu mb e r o f f i b e r s t o d e f i ne t r a nsmi t a nd r e c e i v e r p a r a me t e r s t ha t w o u l d r e su l t i n e r r o r f r e e t r a nsmi ssi o n o v e r 99%
o f 220 m l o ng f i b e r s i n t he f i e l d ( t he ma j o r i t y o f d e p l o y e d f i b e r s a r e c o nsi d e r a b l y sho r t e r t ha n t hi s).
a nd t r a nsmi ssi o n r e su l t s w i l l a l so v a r y w i d e l y f r o m o ne f i b e r t o a no t he r ( se e F i g u r e 1, b e l o w ). I n t he p r o c e ss o f
p r o d u c i ng t he L R M st a nd a r d , t he I E E E L R M Ta sk F o r c e t o o k a st a t i st i c a l a p p r o a c h, mo d e l l i ng a nd t e st i ng a
nu mb e r o f f i b e r s t o d e f i ne t r a nsmi t a nd r e c e i v e r p a r a me t e r s t ha t w o u l d r e su l t i n e r r o r f r e e t r a nsmi ssi o n o v e r 99%
o f 220 m l o ng f i b e r s i n t he f i e l d ( t he ma j o r i t y o f d e p l o y e d f i b e r s a r e c o nsi d e r a b l y sho r t e r t ha n t hi s).
Tw o t e st p a r a me t e r s i n p a r t i c u l a r r e l a t e t o t he mo d e l l e d f i b e r t r a nsmi ssi o n c ha nne l a nd a r e b e l o w d e f i ne d .
– Tr a nsmi t t e r Wa v e f o r m D i sp e r si o n P e na l t y ( TWD P ). Thi s p e na l t y i s d e f i ne d a s t he d i f f e r e nc e ( i n d B )
b e t w e e n a r e f e r e nc e si g na l t o no i se r a t i o ( S N R ) a nd t he e q u i v a l e nt S N R a t t he sl i c e r i np u t o f a r e f e r e nc e
e q u a l i ze r r e c e i v e r f o r t he me a su r e d w a v e f o r m a f t e r p r o p a g a t i o n t hr o u g h a si mu l a t e d c ha nne l .
e q u a l i ze r r e c e i v e r f o r t he me a su r e d w a v e f o r m a f t e r p r o p a g a t i o n t hr o u g h a si mu l a t e d c ha nne l .
M e a su r i ng TWD P i nv o l v e s c a p t u r i ng a t r a nsmi t t e r w a v e f o r m a nd p r o c e ssi ng i t u si ng c o d e t o c a l c u l a t e t he
p e na l t y o f t ha t w a v e f o r m o n a r e f e r e nc e e q u a l i ze r (
p e na l t y o f t ha t w a v e f o r m o n a r e f e r e nc e e q u a l i ze r (
d e t a i l e d r e f e r e nc e a b o u t d e f i ni t i o ns a nd p r o c e ssi ng
).