# Presentation: 945661

## Predicting AvailabilityWhat 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

- 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 Availability****Part 1: Clear Air Link Margin**

## Predicting AvailabilityPart 2: Weather Attenuation

**Predicting Availability****Part 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 Inputs**
- 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
- Cloud ceiling information
- Geographic location of airport vs. installation location
- Urban heat island effects
**The Output**
- A four dimensional atmospheric model
- Latitude
- Longitude
- Altitude
- Time

- Visibility Sensor

## Predicting AvailabilityExamples of Visibility

- Visibility of 1 football field ~ 130 dB/km

**Predicting Availability****Examples of Visibility**

## Predicting AvailabilityAirport Surface Visibility Data

**Predicting Availability****Airport Surface Visibility Data**

- Visibility measured at 550nm

- September
- Best – 3600m
- Average – 400m
- Worst – 200m

## Predicting AvailabilityCloud Ceiling Impact

**Stockholm, Sweden, 1982-97**

**Predicting Availability****Cloud Ceiling Impact**

## Predicting AvailabilityAttenuation Vs. Percentage Time Occurrence 

**Predicting Availability****Attenuation 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%

## Predicting AvailabilityPutting It All Together – A Link Budget 

- 1550nm Gigabit Ethernet link (1.25 Gbps)
- Automatic pointing and tracking
- 5 dB windows at each end
- 400m range
- 10m Altitude
**Budget:**
- Transmit Power 1000 mW                                           30 dB
- Receive Sensitivity (-36 dBm)                                     36 dB
- Geometric Loss w/o fog at 0.4 km	 -2.0 dB
- Window attenuation (2 x 5.0 dB)	 -10.0 dB
- Mispoint Loss	-1.0 dB
- _Total Optical System Losses            __	__-9.0 dB_
- Total Remainder for Weather	44.0 dB
- Therefore, the maximum allowed weather attenuation is:
**44 dB/ 0.40 km = 110 dB/km**
**	**
**	****	****	****	**

**Predicting Availability****Putting It All Together – A Link**** ****Budget**** **

## Predicting AvailabilityFinal Result:  Link Weather Availability 

**Best Year**
-  = 99.995
**Average Year**
-  = 99.94
**Worst Year **
-  = 99.66

**Predicting Availability****Final Result:  Link Weather Availability**** **

## Predicting Availability99.9% Attenuation Margins

**Predicting Availability****99.9% 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 formula
- Source: Terabeam Weather Group, Jan 2001

## Predicting AvailabilityVariability w/ Location: Washington, DC

- Washington National

- Dulles

*Relative* link footprints

## Predicting AvailabilityReal World 99.9% FSO Ranges 

**Predicting Availability****Real World 99.9% FSO Ranges**** **

## Eye SafetyThe 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

## Eye SafetyLaser Standards Organizations

**Eye Safety****Laser Standards Organizations**

| Organization | Jurisdiction | What they classify |
| --- | --- | --- |
| CDRH
Center for Devices & Radiological Health | United States;
Part of the FDA | Product safety(labeling, installation, etc.) |
| ANSI
American National Standards Institute | United States;
Recognized by OSHA | User safety(maximum permissible exposure) |
| IEC
International Electrotechnical Commission | Much of the world;
Generally associated with the CE Mark | Product and user safety |

## Eye SafetyLaser Safety Standards

**Eye Safety****Laser Safety Standards**

- Most FSO systems are Class 1 or 1M

## Eye SafetyStandards 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

- Closure of SONET/SDH metro rings
- Spatial diversity
- Emergency communications
- Data outsourcing/mirroring/SANS
- Wireless backhaul

**Applications & Network Integration ****Emerging FSO Uses**

## Applications & Network IntegrationDeployments

**1**

**Single customer access**

**Multi-tenant building**

**Campus connection**

**Diverse lateral**

**Backhaul or ring closure**

**Point-to-point connection**

**2**

**3**

**4**

**5**

**6**

***and more...***
**Mobile network extensions**
**Mobile network backhaul**
**Spatial diversity**

## Applications & Network IntegrationDisaster Recovery – After 9/11

- 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 Integration****Disaster Recovery – After 9/11**

## Applications & Network IntegrationHybrid 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 

**MMW (60 GHz)**

## Applications & Network IntegrationFree-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 FSOFSO 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 FSOWhat’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 You