copyright © 2002 terabeam corporation. all rights reserved. 1 predicting availability what is link...

Copyright © 2002 Terabeam Corporation. All rights reserved. 1

Predicting AvailabilityWhat is Link Availability?Predicting AvailabilityWhat is Link Availability?

• 5 Nines = 99.999% = Down 5 min / year

• 4 Nines = 99.99% = Down 53 min / year

• 3 Nines = 99.9% = Down 8.75 hrs / year

• 99.8% = Down 17.5 hours per year

The Primary Driver of FSO Availability is Weather

Link availability is the percentage of time over a year that the an FSO link will be operational.


• Difference between the optical power received in clear air versus the minimum power level required for a given error rate.

• Expressed in terms of “dB”– 30dB of margin = 1 part in 1,000 required– 50dB of margin = 1 part in 100,000 required

• Typical error rate 1e-9 (1 in a billion)– 1e-12 reduces margin by approximately 1 dB– 1e-6 increases margin by approximately 1 dB

Predicting AvailabilityPart 1: Clear Air Link MarginPredicting AvailabilityPart 1: Clear Air Link Margin


Predicting AvailabilityPart 2: Weather AttenuationPredicting AvailabilityPart 2: Weather Attenuation

• Curves based upon surface visibility

• Seattle 99.99 attenuation = >212 dB/km

• Seattle 99.9 attenuation = 98 dB/km

• Denver 99.9 attenuation = 40 dB/km

• Phoenix 99.9 attenuation = <5 dB/km


Predicting Availability

The Hard Part – Atmospheric Attenuation Curve


The Hard Part – Atmospheric Attenuation CurveThe Inputs

1. Visibility information from nearby airport weather stations• 100m visibility corresponds to 128 dB/km at 1550nm• 400m visibility corresponds to 27 dB/km at 1550nm

2. Cloud ceiling information3. Geographic location of airport vs. installation location4. Urban heat island effects

The Output• A four dimensional atmospheric model

– Latitude– Longitude– Altitude– Time

Visibility Sensor


Description Visibility Loss

Dense Fog 40-70 m 392-220 dB/km

Thick Fog 70-250 m 220-58 dB/km

Moderate Fog 250-500 m 58-28.2 dB/km

Light Fog 500-1000 m 28.2-13.4 dB/km

Thin Fog 1-2 km 13.4-6.3 dB/km

Haze 2-4 km 6.3-2.9 dB/km

Light Haze 4-10 km 2.9-1.03 dB/km

Clear 10-20 km 1.03-0.45 dB/km

Very Clear 20-50 km 0.45-0.144 dB/km

Extremely Clear 50-150 km 0.144-0.03 dB/km

Visibility of 1 football field ~ 130 dB/kmVisibility of 1 football field ~ 130 dB/km

Predicting AvailabilityExamples of VisibilityPredicting AvailabilityExamples of Visibility


Seattle-Boeing Field, 99.9% Visibility for Worst, Best and Average Months, 1982-98

0500

100015002000

25003000

35004000

Janu

ary

Feb

ruar

y

Mar

ch

Apr

il

May

June July

Aug

ust

Sep

tem

ber

Oct

ober

Nov

embe

r

Dec

embe

r

Month

99

.9%

Vis

ibili

ty (

me

ters

)

worst month best month average month

Predicting AvailabilityAirport Surface Visibility DataPredicting AvailabilityAirport Surface Visibility Data

• Visibility measured at 550nm

September

• Best – 3600m

• Average – 400m

• Worst – 200m


0 20 40 60 80 100 120 140 160 180 200

Surface

30

60

90

120

150

180

Heig

ht

AG

L (

m)

Attenuation (dB/km), 99.9% Availability

Stockholm, Sweden, 1982-97

Predicting AvailabilityCloud Ceiling ImpactPredicting AvailabilityCloud Ceiling Impact


Predicting AvailabilityAttenuation Vs. Percentage Time Occurrence

Predicting AvailabilityAttenuation Vs. Percentage Time Occurrence Three Altitudes in Seattle

At 99.8 Availability

• Surface = 60 dB/km

• 30th fl = 85 dB/km

• 52nd fl = 105 dB/km

A link capable of operating at 50 dB/km

• Surface = 99.78%

• 30th fl = 99.72%

• 52nd fl = 99.58%


Installation Characteristics:1. 1550nm Gigabit Ethernet link (1.25 Gbps)2. Automatic pointing and tracking3. 5 dB windows at each end4. 400m range5. 10m Altitude

Budget:Transmit Power 1000 mW 30 dBReceive Sensitivity (-36 dBm) 36 dBGeometric Loss w/o fog at 0.4 km -2.0 dBWindow attenuation (2 x 5.0 dB) -10.0 dBMispoint Loss -1.0 dBTotal Optical System Losses -9.0 dBTotal Remainder for Weather 44.0 dB

Therefore, the maximum allowed weather attenuation is:44 dB/ 0.40 km = 110 dB/km

Predicting AvailabilityPutting It All Together – A Link Budget

Predicting AvailabilityPutting It All Together – A Link Budget


•Best Year = 99.995

•Average Year = 99.94

•Worst Year = 99.66


Final Result: Link Weather Final Result: Link Weather AvailabilityAvailability


Final Result: Link Weather Final Result: Link Weather AvailabilityAvailability


0

50

100

150

200

250

300P

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Las

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Hon

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Sin

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Syd

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(LA

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99

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dB

/km

)

Predicting Availability99.9% Attenuation MarginsPredicting Availability99.9% Attenuation Margins

Attenuation margin (dB/km) required for 99.9% availability - City by City

Notes:Data derived from surface visibility data (altitude effects not included) and Kruse formulaSource: Terabeam Weather Group, Jan 2001


Predicting AvailabilityVariability w/ Location: Washington, DC

Predicting AvailabilityVariability w/ Location: Washington, DC

Washington National

Dulles Relative link footprints

99.7

99.8

99.9

99.799.8

99.9


Ne

w Y

ork

0m

2000m

4000m

6000m

Se

attle

De

nve

r

Da

llas

Mia

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Ph

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Predicting AvailabilityReal World 99.9% FSO Ranges

Predicting AvailabilityReal World 99.9% FSO Ranges


Eye SafetyThe Eye’s Response to Laser Light

Eye SafetyThe Eye’s Response to Laser Light• Cornea

– Wavelengths above 1400 nm almost completely absorbed by the cornea and not transmitted to the retina

• Retina

– Wavelengths below 1400 nm (close to visible light) focused onto the retina, so power levels must be lower to ensure safety

• Maximum Permissible Exposure (MPE) limits established by ANSI

Retina

Cornea


Eye SafetyLaser Standards OrganizationsEye SafetyLaser Standards Organizations

Organization Jurisdiction What they classify

CDRHCenter for Devices & Radiological Health

United States;

Part of the FDA

Product safety(labeling, installation, etc.)

ANSIAmerican National Standards Institute

United States;

Recognized by OSHA

User safety(maximum permissible exposure)

IECInternational Electrotechnical Commission

Much of the world;

Generally associated with the CE Mark

Product and user safety


Eye SafetyLaser Safety StandardsEye SafetyLaser Safety Standards

Class One

Eye-Safe (all conditions) aided I 1 1

Eye-Safe w/o Optical Aids unaided -- 1 1 M

Class Two

(Visible only 400 to 700 nm)

< 0.25 sec (eye aversion) aided II 2 2

< 0.25 sec unaided -- 2 2 M

Class Three “a” or “R”

Minor Hazard aided IIIa (visible only) 3a 3 R

(5 times Class 1) unaided -- 3a --

any IIIb 3 b 3 B

Class Four

Eye Hazard any IV 4 4

ViewingCondition

Class Three “b” - Eye Hazard

• Most FSO systems are Class 1 or 1M


Eye SafetyStandards and FSO UseEye SafetyStandards and FSO Use

• Class 1 systems can be installed in Unrestricted locations

• Class 1M systems can be installed in Restricted areas

• Class 3B and above only in Controlled locations


• “Sprinkler head” extensions of fiber

• Closure of SONET/SDH metro rings

• Spatial diversity

• Emergency communications

• Data outsourcing/mirroring/SANS

• Wireless backhaul

Applications & Network Integration Emerging FSO UsesApplications & Network Integration Emerging FSO Uses


Applications & Network IntegrationDeploymentsApplications & Network IntegrationDeployments

1 Single customer access

Multi-tenant building

Campus connection

Diverse lateral

Backhaul or ring closure

Point-to-point connection2

3

4

5

6

23

4

5

6

5

1

and more…

• Mobile network extensions• Mobile network backhaul• Spatial diversity


Jersey City ManhattanHudson River

Merrill Lynch Office Merrill Lynch Office

Merrill Lynch Office

2.6 km

1.8 km

1.6 km

• Merrill Lynch urgently needed additional connectivity to three locations.

• Terabeam installed Gig-E FSO units to build a ring topology to back up the SONET network

• Installation was completed within 7 days of first call

Applications & Network IntegrationDisaster Recovery – After 9/11Applications & Network IntegrationDisaster Recovery – After 9/11


Applications & Network IntegrationHybrid SolutionsApplications & Network IntegrationHybrid Solutions

Automatic protection switching between FSO, Millimeter Wave, and/or terrestrial fiber can approach 99.999% availability

FSO

RF

Copper or Fiber


Applications & Network Integration

Hybrid Solutions: Non-Correlated Failures

Applications & Network Integration

Hybrid Solutions: Non-Correlated Failures

C O 2

C O 2

O 3

O 2

O 2

H O2

H O2

H O2

H O , C O2 2

H O2

H O2

H O2

D R IZ Z L E (0 .2 5 m m /h r)

M illimeter

10 GHz3 cm

0.1 dB/Km

1 dB/Km

10 dB/Km

100 dB/Km

1,000 dB/Km

100 GHz3 mm

1 THz0.3 mm

10 THz30 m

100 THz3 m

1,000 THz0.3 m

Submillimeter Infrared Visible

H E AV Y R A IN (2 5 m m /h r)

V is ib i lity 5 0 m F O G (0 .1 g /m )3

E X C E S S IV E R A I N (1 5 0 m m /h r)

MMW (60 GHz)

FSO (30-400 THz)


Applications & Network IntegrationFree-Space & 60 GHz MMW Hybrids

Applications & Network IntegrationFree-Space & 60 GHz MMW Hybrids

FSO 60 GHz Radio

Weather Works well in rain Works well in fog

Licensing Unlicensed Unlicensed

Interference No interference Minimal interference

Range 20m – 4 km 20m – 1.2 km

Mounting Options

Indoor, outdoor Outdoor


The Future of FSOFSO TodayThe Future of FSOFSO Today

• The high bandwidth of fiber with the speed and ease of installation of wireless

• Unlicensed all over the world due to its inherent resistance to interference

• Highly secure and safe

• Allows through the window connectivity and single customer service

• Fundamentally compliments fiber by accelerating the first and last mile


The Future of FSOWhat’s on the Horizon?The Future of FSOWhat’s on the Horizon?

• All optical – “Fiber through the air”

• Lighter, smaller units

• “Innocuous” form factors (e.g., a pane of glass acting as a receive element)

• Fundamentally the cheapest way to cross the street at 100 Mbps

• Can be used to provision big bandwidth almost everywhere

– Where fiber can’t offer an adequate ROI

– Where 99.9 is acceptable

– To the home?


Thank YouThank You

copyright © 2002 terabeam corporation. all rights reserved. 1 predicting availability what is link...

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