Testing Optical Fiber Links in Premises Networks — November 20001 AA BBB A B A Horizontal Segment...

Testing Optical Fiber Links in Premises Networks — November 2000 1

A A

BB B

A

B

A

Horizontal Segment

Backbone Segment

Optical Fiber Link

WorkArea

Outlet

MainPatchPanel

Testing Optical Fiber Links

Noyes Fiber Systems

In Premises Networks


Outline

• Optical Fiber Links — Overview • Parameters — What should I test?• Industry Standards — Which should I use?• Test Equipment — What do I need?• Procedures

– Light source and power meter– Certification test set– OTDR– Troubleshooting


Optical Fiber Links and Link Segments

Optical Fiber Links and Link Segments

TIA-568 defines an optical fiber link segment as:

“… the cable, connectors, and splices between two optical fiber patch panels.”


Optical Fiber Link Segment

AdapterConnector

Patch panel or outlet

Optical Fiber

Patch panel

Splice

A B


Optical Fiber Links

• In structured cabling systems, links may include horizontal and backbone segments.

• All links defined in TIA-568 are duplex (one fiber for each direction of transmission).

• Optical fiber channels include the patch cords that connect equipment to each end of every link.


Horizontal and BackboneLink Segments

Horizontal Segment

Backbone Segment

Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room

Horizontal Patch Panel

Telecom Closet

Splice


Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room


Telecom Closet

Splice

Link

Link vs. ChannelChannel

Which Do I Certify ?Fiber patch cords add negligible loss (and NO CROSS-TALK!). So in fiber

optic networks, unlike CAT5/6 networks, you certify the link not the

channel.


TIA-568 Link — Detailed View

SpliceOutlet Horizontal

Patch Panel

MainPatch Panel“NIC”

(Network Interface Card in a PC)

Rx

Tx

Network Equipment(Hub, switch, etc.)

Rx

Tx

Horizontal Segment

Backbone Segment

Link

PatchCord

PatchCord

PatchCord

A

B

A

B B

A

B

A

B

A A

B

A

Channel


TIA-568 Link Polarity

• TIA-568 defines a duplex (2-fiber) system with patch cord “plugs” and wall or panel “jacks.”

• Every plug and jack has an A and B side:

Plug

A-side: OUTPUT

B-side: INPUT

Jack

A-side: INPUT

B-side: OUTPUT

A

BPatch Cord Link Segment

A

B


TIA-568 Link Polarity (cont.)• Every plug and jack must mate A to A and B to B. • Every link segment and patch cord must have one “flip” from

A to B and B to A.

Rx

Tx

Equipment Link (1 Flip)

Patch Cord (1 Flip)

EquipmentPatch Cord (1 Flip)

A

B

A

B

A

B

A

B

A

B

A

B

Rx

TxB

A

B

A

Patch PanelJacks

Patch CordPlugs

Patch CordPlugs

EquipmentJacks

EquipmentJacks


ParametersParameters


Fiber Parameters Include …

• Attenuation (insertion loss per km)• Bandwidth (LED and laser) • Insertion loss caused by bending• Group Index of Refraction (GIR) • … and more.


Connector Parameters Include …

• Insertion loss • Return loss (reflectance) • Loss over temperature and humidity• Loss increase after “N” connection cycles• … and more.


Typical Fiber Optic Field Measurements

• Link Certification – Insertion loss– Length– OTDR trace

• Troubleshooting– Equipment output power – Link insertion loss – Link continuity (flash light or red laser)– Link fault-locating (red laser or OTDR)


What Is Not Typically Measured in the Field

• Bandwidth — fiber bandwidth is measured at the factory and not impacted by installation practices.

• Return Loss — optical return loss (reflection) does not significantly impact LAN transceivers (but can impact telco equipment and so is measured in telco/CATV networks).

• Cross-talk — Cross-talk is never a fiber optic problem!


Power and Insertion Loss — What You Really Need to Know

• Power is normally expressed in dBm:PdBm = dB relative to one milliwatt = 10 log10 (Pwatts/1 mW)

• Insertion loss in dB is the difference between input and output power, when both powers are expressed in dBm.

• “Attenuation” is fiber insertion loss in dB/km.• The insertion loss of passive components, such

as optical fiber and connectors, is always positive.


Fiber Insertion Loss Example

1 km of optical fiber

PIN = - 20 dBm POUT = - 23 dBm

Insertion Loss = PIN - POUT

= -20 dBm - (-23) dBm

= 3 dB

Attenuation = 3 dB/km.


Connection Insertion Loss Example

PIN = - 20 dBm POUT = - 20.75 dBm

Optical Fiber Connection (mated connector pair)

Insertion Loss = PIN - POUT

= -20 dBm - (-20.75) dBm

= 0.75 dB


PIN (watts) / POUT (watts) Insertion Loss (dB)

1:1 (no loss) 0 dB

2:1 3 dB

4:1 6 dB

10:1 10 dB

100:1 20 dB

1 000:1 30 dB

10 000:1 40 dB

Insertion Loss as a Ratio

• Insertion Loss (dB) = 10 x Log [ PIN (watts) / POUT (watts) ]


What Is Optical Return Loss?

• Fiber optic link optical return Loss, or ORL, expressed in dB, is the difference between input and reflected power, when both powers are expressed in dBm.

PIN = - 20 dBm

PREFL = - 45 dBmOptical Fiber Link

Optical Return Loss = PIN – PREFL

= -20 dBm - (-45) dBm

= 25 dB


Optical Return Loss (cont.)

• The ORL of an event, such as a connection, is measured using an OTDR as “reflectance”. – To make things complicated, reflectance in dB, is the negative of

ORL in dB.

• 10Mb/s, 100 Mb/s, and even Gigabit Ethernet systems are not very sensitive to reflection so the ORL of premises network links is not normally measured.

• In the future, however, field measurement of ORL in premises networks may become more important because of 10 Gigabit Ethernet and higher rate systems.


What About Bandwidth?

• High bandwidth fiber has low dispersion.

High bandwidth Fiber

Pulses In Pulses Out

Low bandwidth Fiber

Pulses In Pulses Out


Bandwidth (cont.)

• Bandwidth is an important fiber parameter.• Bandwidth is expressed in units of MHz “dot” km, for

example 500 MHzkm (not MHz “per” km)• Bandwidth may also be specified as a guaranteed operating

distance for a given bit rate, for example “Gigabit Ethernet guaranteed to 1000 meters”

• Because bandwidth is not impacted by installation practices it is not normally measured in the field.

• However, it is a critical to specify bandwidth or guaranteed operating distance when ordering optical fiber cable.


StandardsStandards


Fiberoptic Standards

• There are two types of fiber optic standards:

Application Standardssuch as:

10Base-FL100Base-FX

FDDIATM

Fibre Channel1000Base-SX and LX

Cabling Standardssuch as:

TIA-568-B* (North America)ISO 11801 (International)

EN 50173 (European)

* Replaced TIA-568-A in 2000.


Example Cabling Standard: TIA-568-B

• TIA-568-B specifies the following maximum values on 62.5 m multimode fiber in backbone links: – Fiber attenuation at 850 nm: 3.50 dB/km*– Fiber attenuation at 1300 nm: 1.50 dB/km– Loss per connection (mated pair): 0.75 dB– Loss per splice (mechanical or fusion): 0.3 dB

* In TIA-568-A, max. fiber attenuation at 850 nm was 3.75 dB/dm


Example Application Standard:Gigabit Ethernet

• IEEE 802.3z (Gigabit Ethernet) specifies the following maximum values on 62.5 m, 200 MHz-km multimode optical fiber links when using 850 nm (SX) sources:– Insertion loss: 2.60 dB– Distance: 275 m


Standards (cont.)

• There are only a few cabling standards• In North America, TIA-568-B is the primary

commercial building cabling standard. • But there are many applications standards

including: 10, 100, and 1000 Mb/s Ethernet, FDDI, ATM, Fibre Channel and more.

• And new application standards like 10 Gb/s Ethernet are in development.


Which standard(s) should I use?

• It is very possible for a link to meet the requirements of a cabling standard, like TIA-568, and not meet the requirements of a high-speed application like Gigabit Ethernet.

• Therefore, every optical fiber link should meet the applicable cabling standard and the toughest application standard it must support.


TIA-568-B vs. GBE Example

• Referring to the earlier link example assume:– connector specs: 0.6 dB loss per connection– fusion splice loss: 0.1 dB– fiber specs: 62.5 um, 200 MHzkm, 3 dB/km– horizontal segment length: 90 M– backbone segment length: 150 M

• Does this link meet TIA-568-B and will it support 1000Base-SX (850 nm) ?


Example (cont.)

Outlet

Rx Tx Rx Tx

Certification Test Set (Main Unit)

Certification Test Set (Remote Unit)

HorizontalPatch Panel

Splice

MainPatch Panel

A A

BB B

A A

B

0.6 dB 0.6 dB 0.6 dB 0.6 dB

90 m 150 m

0.1 dB

HorizontalSegment

BackboneSegment


Example (cont.)

• TIA-568-B requirements are met:– Horiz. length = 90 M (90 M max)– Horiz. Loss = 1.47* dB (2 dB max.)– BB length = 150 m (2000 m max.)– BB fiber attenuation = 3 dB/km (3.50 dB/km

max.)– BB connector loss = 0.6 dB (0.75 dB max.)– BB splice loss: = 0.1 dB (0.3 dB max)

– Total link loss: = 3.22** dB (4.33*** dB max.)* Horizontal segment loss = 0.09 km x 3 dB/km + 2 x 0.6 dB = 1.47 dB

** Total link loss = 1.47 dB + 3 dB/km x .15 km + 2 x .6 + .1 = 3.22 dB*** TIA-568-B limit = 2 dB + 3.50 dB/km x .15 km + 2 x .75 + .3 = 4.33 dB


Example (cont.)

• But not all 1000Base-SX requirements are met:

– Link length = 90 m + 150 m

= 240 m (275 m max.)

– Link loss = 0.24 km x 3 dB/km + 4 x 0.6 dB + 0.1 dB

= 0.72 dB + 2.5 dB

= 3.22 dB (2.60 dB max.)


Example (cont.)

• Could this link support 1000Base-SX?

– Yes, by using lower-loss connectors.

• For example by using connectors with an average loss of 0.4 dB then:

– Total link loss = 0.72 dB + 4 x 0.4 dB + 0.1 dB

= 0.72 + 1.7 dB

= 2.42 dB (2.60 dB max.)


Important Conclusion:

• Multimode fiber links may have to exceed the requirements of TIA-568-B in order to support high speed applications like Gigabit Ethernet.

FUTURE SHOCK:10 Gigabit and even 100 Gigabit Ethernet are being

discussed by the standards bodies. So high-bandwidth fiber, low-loss connectors, and good installation practices

will be even more critical in the future.


Test EquipmentTest Equipment


Basic Test Kit

• Light source — 850/1300 nm LED source may be used to measure insertion loss on multimode and singlemode links found in premises networks.

• Optical power meter — Measures optical power and optical fiber insertion loss.

• Microscope — 200x recommended to inspect connector polish and cleanliness

• Flashlight — to check continuity on multimode fiber links (will not work well on singlemode fiber)


Additional Test Equipment

• Certification Test Set – Fastest way to certify duplex optical fiber links.– Measures loss, length, and provides PASS/FAIL results– Very useful in high fiber count installations.

• OTDR (Optical Time-Domain Reflectometer) – Generates a baseline trace.– Very useful fault-locator.– Only way to measure events such as connections and splices.

• Visible (red) laser– Very useful troubleshooter—highlights breaks and bad connectors.– Highlights bends in singlemode fibers.– Check continuity on multimode or singlemode fibers.


Using an Optical Fiber Scope

Ferrule Scratch goes near the core!

Fiber

Core(singlemode)

Dirt particles


Using an Optical Fiber Scope (cont.)

Core(multimode)

Fiber

Ferrule

Body oil(don’t touch

the connector end-face!)


Setting Up Your Light Source and Optical Power Meter

• Turn on light source and optical power meter and allow them to warm-up per User’s Guide.

• Set reference (typically once per day):– Attach clean Tx jumper to source– Connect other end of Tx jumper to meter.– Set reference level.

• Disconnect Tx jumper from optical power meter (Do NOT remove jumper from light source!)


Light Source / Power Meter (cont.)

• Check jumpers:– Attach the Rx jumper to power meter– Connect the Tx and Rx jumpers using an adapter.– Verify loss is less than or equal to a typical connection

loss (e.g. 0.4 dB)

• Attach light source and meter to opposite ends of the fiber link under test (see diagram).

• Measure loss in dB • Repeat for other fibers … keep connectors clean!


One-Jumper Reference Method

Light Source Optical PowerMeter

0 dB

1) Set reference

Tx Rx

Tx jumper

Tx Rx

Rx jumper

Optical PowerMeter

Light Source

2) Check jumpers

0.4 dB

Adapter


Measuring Optical Fiber Link Loss

-22 dBm-20 dBm Outlet

Tx Rx

Light Source Optical PowerMeter


Splice

MainPatch Panel

A A

BB B

A A

B

2 dB

HorizontalSegment

BackboneSegment


Using a Certification Test Set

• Attach clean Tx jumpers to Main and Remote• Connect the other end of each Tx jumper to the Rx

port on the other unit.• Set reference (typically once per day). • Check jumpers.• Set up Auto Test rule.• Connect Main and Remote to the link under test.• Test and store results (two fibers per Auto Test).


One-Jumper Reference Method

Rx Tx Rx Tx

Main Unit Remote Unit

MainTx Jumper

RemoteTx Jumper

1) Set reference

0 dBm

Rx Tx Rx Tx


2) Check jumpers

0.4 dBm

RemoteRx JumperMain

Rx Jumper

Adapters


Certifying (Loss + Length)

Outlet

Rx Tx Rx Tx



Splice

MainPatch Panel

A A

BB B

A A

B

2dB 2dB 240 mPASS

HorizontalSegment

BackboneSegment

-20 dBm-22 dBm

-22 dBm -20 dBm

240 m


Using an OTDRTo Generate a Baseline Trace

• Turn on OTDR and allow it to warm-up per User’s Guide.

• Attach launch cable to OTDR port and receive cable to far-end of fiber link under test– Both must have the same fiber type as link under test.

• Set wavelength, pulse width, range, number of averages, etc. – Or, use automatic setup features of the OTDR

• Run test, save trace, move to next fiber


Using an OTDR

ReceiveCable

(Fiber box)

OTDR

SMMM

LaunchCable

(Fiber Box)

Work AreaOutlet


Splice

MainPatch Panel

A A

BB B

A A

B

HorizontalSegment

BackboneSegment

(to generate a baseline trace)


Example OTDR Trace

0

0 25050 100 150 200

-2

-1

-3

-4

-5

RelativePower(dB)

Link Loss ( 2.1 dB)

One Connection(Loss 0.4 dB)

Splice(Loss 0.1 dB)

LaunchCable

Term.Cable

Horiz.Seg.

BackboneSegment

Two Connections (Loss 0.8 dB)

Distance (m)

A BLink Length ( 130 m)


Why is an OTDR So Useful?

• Because it can:– Generate a baseline trace– Measure link insertion loss* and length,– Measure event insertion loss, return loss (reflectance),

and location (connections and splices)– Fault locate

* However a light source and optical power meter are the most accurate tools for measuring insertion loss.


Troubleshooting a failed fiber link

• Measure equipment output power.• Verify connectivity using a visual fault

identifier (also called a VFI or red laser). • Measure end-to-end link loss.• Fault-locate using an OTDR:

– Generate a trace.– Look for breaks, or events with excessive loss– Compare with baseline trace if available


Example Fault:(Fiber break)

Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room


Telecom Closet

Splice

Break

Link Failure Alarm !


Measure Transmitter Output Level

(Using an Optical Power Meter)

Network Equipment

Outlet

Main Patch Panel


Telecom Closet

Splice

Optical Power Meter (OPM)

Equipment output levelslook okay.

- 8 dBm


Verify Connectivity(Using a VFI or “red laser”)

NOTE: A VFI or “red laser” generates visible light at about 650 nm.

Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room


Telecom Closet

SpliceNo light seenat link output.Visual Fault

Identifier(VFI)


Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room


Telecom Closet

Splice

Light Source

LowOpticalPowerMeter

or … Verify Connectivity(Using a light source and power meter)


Fault-Locate (Using an OTDR)

OTDR

MM

Network Equipment

Work Area

Outlet

Main Patch Panel

Equipment Room


Telecom Closet

Splice

LaunchCable

ReceiveCable


OTDR Trace Showing Break at 120 m

0

0 25050 100 150 200

-2

-1

-3

-4

-5

RelativePower(dB)

Distance (m)

A B

BaselineTrace

New Trace

Distance to fault ( 120 m)

Fault !


Questions?

Testing Optical Fiber Links in Premises Networks — November 20001 AA BBB A B A Horizontal Segment...

Documents

Transcript of Testing Optical Fiber Links in Premises Networks — November 20001 AA BBB A B A Horizontal Segment...