Streaming Consciousness onFiber Testing

Quilt Meeting June 22, 2004

Jerry Sobieski

Mid-Atlantic Crossroads

Fiber Testing• Perspective!

– Fiber is just one part of overall system• Modulation rates• Laser characteristics• Receiver characteristics• Distance requirements• Fiber types and interfaces

– Must test to specifications designed into the system• High transmission speeds and longer fiber spans make testing and verification

much more critical than most Quilt engineers have ever had to deal, with even just a few years ago.

– WAN logistics make it far more time consuming– Performance depends upon total optical charactization

• Fiber (types, distances, etc)• Equipment (e.g. OADMs, DCMs, etc)

Fiber Characterization• Testing prior to placing in service:

– Measure end to end distance• Verify splice conformance and identify [poor] cross-connects• Identify high reflectance points

– Attenuation by segment• Different fiber types exhibit different loss

– Measure each fiber:• Both directions• At both 1310 nm and 1550 nm (assuming only SM fibers)

– Dispersion• These days we should measure both Chromatic Dispersion and Polarization

Mode Dispersion• WAN segments may need DCF – how much depends on application

specifics (WDM? Laser types? Fiber type? Distance?)

Equipment:• Field optical testset platform which supports multiple modules

(e.g. Exfo FTB400)– Optical Time Domain Reflectometer (OTDR) [module]

• Used often for repair verification so make it small and portable

– Chromatic Dispersion module/testset• OC48 and higher speed interfaces vary dramatically

– Polarization Mode Dispersion module/testset• Should have this for 10gig (or higher) WAN segments

– Optical Spectrum Analyzer (OSA)• Required for WDM systems• Useful for non-WDM problem resolution as well

• Prices have dropped dramatically if you use E-bay– E.g. $35,000 OSA (circa2001) recently spotted for $3000.– Vendors buying up used gear to get it off market

Equipment• Cleaning

– Testing is pointless on dirty fiber– Cletop (or equivalent) fiber termination cleaner (for

male components such as SC/FC/LC connectors)– Swabs (for female components such as bulkhead

connectors and ports)– Handheld fiber inspection microscope (male

components)– Fiber port camera for female ports– Compressed air canisters for blowing out components

Equipment• How do you know when the fiber is usable?• Test specs and equipment to measure it.

– BERT boxes• Spirent, IXIA have good relationships with our community• Very useful tools for verifying both Bit Error Rates and layer2/3 packet handling

– Should always BERT new circuits for 24 hours or more

• Specs– BER=10-10 as measured at the [Spirent/Ixia] interface is one picked bit

every second (at 10gig)– BER=10-14 is a blip every 3 hours

• If the testgear sees it, then FEC equipped interfaces are seeing it much more often - may be indicative of bigger problems

• Most networks will view this as acceptable, but some high end applications may not (a picked bit that gets thru can cause havoc)

Personnel

• Optical Engineers are things we must develop. – Metro and regional fiber networks designed for very

high performance DWDM systems require significantly different engineering specializations than campus networks.

• We need to hire more junior engineers and train them for metro/regional networking requirements

– Hiring these skills is expen$ive and difficult

• Existing senior engineers are both over-subscribed and expensive – filling the pipeline with new blood will help control these costs over the long term, and provide the breadth and scope of skills we need to architect, engineer, contract, deploy, operate, and maintain the new infrastructure.