willnerobsglobecom7.ppt

8/16/2019 willnerobsglobecom7.ppt

1/31

Optical Burst Switching (OBS):Issues in the Physical Layer

University of Southern California

Los Angeles, CA

A. E. Willner


2/31

O-E-O

Offseti!e

Switch

i!e Scale in OBS

"#ntr#l

Pac$et

Burst

Generally, ….• Offset ti!e %etween c#ntr#l pac$et & %urst is '- !icr#secs

• Burst ranges in ti!e fr#! ' !icr#sec t# ' !illisecs

• "#ntr#l pac$et has a l#wer %it rate than the *ata payl#a*


3/31

Outline

1. Degradations Due to Physical-Layer

Impairments

2. Fast Monitoring of a Burst

3. Fiber-Loop Buffers for OBS Efficiency


4/31

Signal Degradation due to Chromatic Dispersion

0 1 0 01 1time f carrier freq.

Vi

V j

VkFourier

• Information Bandwidth of Data

• Temporal Spreading → f (distance, (bit rate)2)→ (ps/nm)/km

time Fiber time

Photon Velocity (f) = See! of Light in Vacuu"

#n!e$ of %efraction(f)


5/31

Chromatic Dispersion Effects on Payload and

Control Packet

• Control Packet (C.P.), not payload, is regeneratedat every node

• C.P. has lower bit-rate (CD effect∝ (bit-rate)2 )

There is higher chance for payload to be degraded

Node

Node

Node

Node

t

t t

t

Payload C.P.


6/31

Offset Time Affected by Wavelength Skew:

Uncompensated Systems (2.5 Gbit/s Payload?)

t

t

30 nm400 km of Fiber

(CD=17 ps/(nm.km))

t

t

C.P.

Payload

Offset time change ~ 1 µs

C.P.

Payload

Skew

Offset

Offset


7/31

+alue #f una%le ,ispersi#n "#!pensati#n

( %it/s Payl#a*)

Distance (km)

0

1

2

3

4

5

0 20 40 60 80 100 120 140 160

OC-768

No Compensation

TunabeCompensato!(500-2100 ps"nm)

#i$e% 80 km Compensato!

& ' e

c o s u ! e

e n a t ' ( % )

A tuna%le *ispersi#n c#!pensat#r all#ws f#r a wi*e

range #f trans!issi#n *istances at %it/s.


8/31

P#lari0ati#n-relate* I!pair!ents in 1igh-

Perf#r!ance Syste!s

P#lari0ati#n-!#*e-*ispersi#n (P2,)

P#lari0ati#n *epen*ent l#ss (P,L)

,egra*ati#n %ase* #n

n#n-catastr#phic

e3ents

4an*#! p#lari0ati#n

c#upling

Statistically

3aries with ti!eBit-rate an*

wa3elength

*epen*ent

P#lari0ati#n state

generally un$n#wn

an* wan*ers


9/31

P#lari0ati#n 2#*e ,ispersi#n (P2,)

cross section

Elliptical Fiber Core

side view

0 10 20 30 40 500 10 20 30 40 50

0.111050

Probability of Exceeding a Specific DGD (%

Differential Gro!p Delay (p"

#ax$ellian

di"trib!tion

tail

0 10 20 30 40 50

0.111050

Probability of Exceeding a Specific DGD (%

Differential Gro!p Delay (p"

#ax$ellian

di"trib!tion

tail

• P#D ind!ce"

rando%ly c&angingdegradation".

' ritical li%itation at

≥ 10 Gbit)" payload

data rate".

he 5 p#lari0ati#n !#*es pr#pagate at *ifferent spee*s.

'st-#r*er P2, 6 ,,


10/31


11/31

7i%er 8#nlinearities

15001000500 20000

6

5

4

3

2

1

0

50-ps uses

04 ps"nm"km

-02 ps"nm"km

008 ps"nm"km

9ink Dispe!sion

Dispersion

Variation

~ 4%

Di"tance (,%

4×10 b"s

C!omatic %ispe!sion canes te e++ects o+ noninea!it'

e+!actie in%e$ %epen%s on +!e*uenc' an% poe!

n(ω-P

Chromatic Dispersion Power

P o $ e r P

e n a l t y ( d .

' /"olation of nonlineareffect" i" ery diffic!lt' /t i" al"o diffic!lt to

%onitor and co%pen"ate


12/31

E,7A ain

Deployed EDFA cross saturation causes gain transients

due to:

• Channel turn-on

• Channel re-routing• et!or" recon#iguration• $in" #ailures

%i&e scale o#

gain saturation

and reco'er( is

) *s to &s

InputChannels

Dropped

Channels

EDFA

EDFA

OutputChannels


13/31

15 Chs droppedP#wer #f t16 ch S ste15 Chs added 15 Chsadded

1ayee9LarSing15 Chdroppe

' %/s Si!ulati#n 4esults7i%er 8#nlinearit Penalt


14/31

0 2 4 6 8 10 12

# of EDFAs

T i m e (

s )

Recip

rocal

Time(

s -1)

10

7.5

5.0

2.5

0.0

1.0

0.75

0.5

0.25

0.0

1 dB power excursion for surviving channels

4 channels dropped4 channels survive

Time Response

Zyskind, OFC’96 PD-31


15/31

Outline


Impairments




16/31

Win*#w #f Opera%ility in OBS• Win*#w #f #pera%ility is shrin$ing as syste!s %ec#!e !#re c#!ple=

• Ensuring a l#ng-ter! sta%le an* healthy netw#r$ is tric$y

bit !ate

poe!

noninea!ities

%ispe!sion

numbe! o+

cannes

poa!i:ation

e++ects

+o!mat


17/31

Monitoring in OBS Systems

• 2#nit#ring ti!e scale c#rresp#n*s t# that #f OBS (µs > !s)

• ,yna!ic !#nit#ring c#3ers the wi*e range #f %#th!ulti-wa3elength payl#a*s an* c#ntr#l pac$ets

• 2#nit#ring inclu*es?- P#wer

- Wa3elength - Optical signal-t#-n#ise rati# - ,ist#rti#n: ",9 P2,9 n#nlinearities


18/31

Impact of Monitoring on OBS Systems

• 8ee* t# fin* the n#n-catastr#phic pr#%le!sin OBS syste!s

- Ena%le the functi#nality #f err#r-free

asse!%ly n#*es c#!%ine* with tuna%le

c#!pensat#r - 2aintain the accurate #ffset ti!e

- L#cate an* !easure the *ist#rti#n #f payl#a*

an* c#ntr#l pac$ets

- Supp#rt pr#t#c#l-in*epen*ent W,2 transp#rt - #solate !ifferent !egra!ing effects


19/31

;mpai!ment- < ecu!it'-=a!e outin

• Present network : very few variables (i.e. # of hops

are !se" to "etermine the ro!tin table altho!h thereare several variables on the physical state

• $!t!re networks: ,onito! te canne *uait' an% ink secu!it'

an% up%ate te !outin ook-up tabescontinua'

;n te !outin %ecisions ensu!e tat' Cannes aciee acceptabe &

' Neto!k aciees su++icient t!ansmission an%p!otection capacit'

' >iest p!io!it' %ata is t!ansmitte% on te st!onestan% most secu!e inks


20/31

+estigial Si*e%an* Optical 7iltering

• 7ilter -/ 6 (.@ > '.5) ×%it-rate ( %0+

• 7ilter *etuning f 6 (. > .@) × %0

7reuency

-/

f +SB-


21/31

40+Gb)"

23 Data

?-9

?-@

+

Di"per"ion

+

O"& i%e (p"

0 50 100 1500.0

0.5

1.0

1.5

i%e (p"0 50 100 150

0.0

0.5

1.0

1.5

∆t

,onito! Cock ase

' ;soate CD +!om ,D e++ects

' 9o cost

. &!' )*' Dec.' +,,+

#ite!e%spect!um

&nti!ecanne

#ite!e%spect!um

' Time %ea' ( t ) beteen to ? sinas is a +unction o+ CD' its can be !ecoe!e% +!om eite! pa!t o+ te spect!um


22/31

P2, 2#nit#ring echniues

, 4euires high- spee*

*e3ices (*e!#nstrate*f#r ' %/s 4C signal)

, Affecte* %y #ther

*ist#rti#n s#urces

D "an %e integrate*with electr#nic

euali0ati#n

A.

Eye #pening!easure!ent

B.

47 spectru!analysis

D 8# high spee* electr#nics

D ,epen*s #nly #n P2,

D Bit-rate in*epen*ent

D


23/31

Outline


Impairments




24/31

4esearch #als(Generously Suorte! 0y #ntel)

• Si!ulate an @ @ switch with fee*%ac$ %uffering

• ,eter!ine the #pti!al nu!%er #f input/#utput p#rts an* *elay lines

• Si!ulate *elay lines ha3ing recirculati#n capa%ility

• In3estigate the effect #f ran*#! %urst si0e

Control nit

8

2

8 D 2 6 @

Switch

,elay Lines

,ata Burst

Lines

"#ntr#l Line

Burst

(8D2) = (8D2)

"#ntr#l Pac$et

Optical 7i%er

,elay Lines

Opti!al 8u!%er #f Input P#rts an*


25/31

Opti!al 8u!%er #f Input P#rts an*

,elay Lines

h r # u g h p

u t E f f i c i e n c y

• (9F) setup gi3es a higher thr#ughput than a (9) an* (95) setup

• Is this scala%le t# a switch with !#re nu!%er t# p#rts G

L#a*

(9)

(9F)

(95)

Buffere*

Bufferless

(9)

(9)

(9)

(892) (8 input *ata lines 2 *elay lines)(H9')

(H9)

#finputp#rts

'st Buffer

J%ytes

5n* Buffer

J%ytes

Fr* Buffer

J%ytes

th Buffer

J%ytes

F . @ '

. @ ' -

. ' - -

H ' - - -

Buffer Si0e

h h t Effi i L * f


26/31

hr#ughput Efficiency 3s. L#a* f#r

,ifferent 2a=i!u! Burst Si0es

L#a*

h r # u g h p u t E f f i c i e n c y

• he thr#ughput efficiency *ecreases with increase in %urst si0e.

• Buffer si0e 6 !a=. %urst si0e9 F %uffers f#r 9F case.

2a=i!u! 6 ' J%ytes

%urst si0e

2a=i!u! 6 ' J%ytes

%urst si0e

2a=i!u! 6 5 J%ytes

%urst si0e

2a=i!u! 6 5 J%ytes

%urst si0e

Eff t f A**i B ff


27/31

Effect #f A**ing Buffers #n

hr#ughput Efficiency

• hr#ughput efficiency *#es n#t increases with the nu!%er

#f *elay lines

• 7#r an @ = @ switch9 it is %eneficial t# ha3e 5 #r F *elay lines

I n c r e a

s e i n

h r # u g h p u

t E f f i c i e n c y

' Buffer

5 Buffers

F Buffers

Bufferless

Buffers

(9 ) Switch

L#a*


28/31

h r # u g h

p u t E f f i c i e n c y

L#a*

hr#ughput Efficiency f#r 4ecirculati#n

• With F recirculati#ns the thr#ughput efficiency #f appr#=i!ately

@K can %e achie3e*.

• th recirculati#n increases the thr#ughput %y #nly >'K.

' 4#un* rip

5 4ecirculati#ns

F 4ecirculati#ns

4ecirculati#ns

' 4ecirculati#ns

Bufferless

(9 F) Switch

Increase in hr#ughput Efficiency


29/31

L#a*

' Buffer

5 Buffers

F BuffersF Buffers with 5

recirculati#ns

F Buffers with F

recirculati#ns

Bufferless

I n c r e a s e i n

h r # u g h p u

t

E f f i c i e n c y

Increase in hr#ughput Efficiency

with Buffers an* 4ecirculati#n

• F Buffers an* F recirculati#ns increase the thr#ughput efficiency

%y 5H K

• hr#ughput efficiency *#es n#t increase linearly with nu!%er #f*ela lines


30/31

• (9F) c#nfigurati#n pr#3i*es higher thr#ughput than

#ther c#nfigurati#ns.

• >5K increase in thr#ughput efficiency is #%taine* with

F %uffers an* recirculati#ns.

• 8u!%er #f *elay lines sh#ul* %e li!ite* t# 5 #r F9 as the

thr#ughput *#es n#t increase !uch with an increase in

nu!%er #f *elay lines.

• -U1, …, the fi0er !elay line has loss, …, otical a"lifiers

a!! noise, an!, … recirculations can !egra!e the ayloa!.

Jey Buffer 4esults f#r @@ Switch

S


31/31

Summary

• Degradation effects including CD, PMD,

nonlinearities should be addressed in OBS.

• Fast monitoring can help the long-term stabilityand robustness of a OBS network.

• Optical buffers enable enhanced OBS

functionality.

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