Testing Optical Fiber Links In Premises Networks Noyes Fiber Systems Horizontal Segment Backbone Segment A A A A Work Area Outlet Main Patch Panel B B B B Optical Fiber Link Testing Optical Fiber Links in Premises Networks — November 2000

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 Testing Optical Fiber Links in Premises Networks — November 2000

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.” Testing Optical Fiber Links in Premises Networks — November 2000

Optical Fiber Link Segment Adapter Connector Optical Fiber Splice A B Patch panel or outlet Patch panel Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

Horizontal and Backbone Link Segments Horizontal Segment Backbone Segment Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Testing Optical Fiber Links in Premises Networks — November 2000

Link vs. Channel Which Do I Certify ? Channel Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Link 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. Testing Optical Fiber Links in Premises Networks — November 2000

TIA-568 Link — Detailed View Channel Link Patch Cord Horizontal Segment Patch Cord Backbone Segment Patch Cord “NIC” (Network Interface Card in a PC) Rx Tx A Network Equipment (Hub, switch, etc.) Rx Tx A A A A A A Splice B B B B B B Main Patch Panel Outlet Horizontal Patch Panel Testing Optical Fiber Links in Premises Networks — November 2000

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 B Patch Cord Link Segment Testing Optical Fiber Links in Premises Networks — November 2000

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) A B Patch Panel Jacks Patch Cord Plugs Equipment Jacks Testing Optical Fiber Links in Premises Networks — November 2000

Parameters Testing Optical Fiber Links in Premises Networks — November 2000

Fiber Parameters Include … Attenuation (insertion loss per km) Bandwidth (LED and laser) Insertion loss caused by bending Group Index of Refraction (GIR) … and more. Testing Optical Fiber Links in Premises Networks — November 2000

Connector Parameters Include … Insertion loss Return loss (reflectance) Loss over temperature and humidity Loss increase after “N” connection cycles … and more. Testing Optical Fiber Links in Premises Networks — November 2000

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) Testing Optical Fiber Links in Premises Networks — November 2000

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! Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

Fiber Insertion Loss Example PIN = - 20 dBm POUT = - 23 dBm 1 km of optical fiber Insertion Loss = PIN - POUT = -20 dBm - (-23) dBm = 3 dB Attenuation = 3 dB/km. Testing Optical Fiber Links in Premises Networks — November 2000

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 Testing Optical Fiber Links in Premises Networks — November 2000

Insertion Loss as a Ratio Insertion Loss (dB) = 10 x Log [ PIN (watts) / POUT (watts) ] 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 Testing Optical Fiber Links in Premises Networks — November 2000

Why Use dBm to Express Power ? dBm is a convenient unit to express the small power levels used in fiber optic communication systems: Power (watts) Power (dBm) 0.1 W + 20 dBm 0.01 W + 10 dBm 0.001 W (1 mW) 0 dBm 0.1 mW - 10 dBm 0.01 mW - 20 dBm 0.001 mW - 30 dBm 0.000 1 mW - 40 dBm 0.000 01 mW - 50 dBm Testing Optical Fiber Links in Premises Networks — November 2000

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 dBm Optical Fiber Link Optical Return Loss = PIN – PREFL = -20 dBm - (-45) dBm = 25 dB Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

What About Bandwidth? High bandwidth fiber has low dispersion. Pulses In Pulses Out Low bandwidth Fiber Pulses In Pulses Out Testing Optical Fiber Links in Premises Networks — November 2000

Bandwidth (cont.) Bandwidth is an important fiber parameter. Bandwidth is expressed in units of MHz “dot” km, for example 500 MHzkm (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. Testing Optical Fiber Links in Premises Networks — November 2000

Standards Testing Optical Fiber Links in Premises Networks — November 2000

Cabling Standards such as: Application Standards such as: Fiberoptic Standards There are two types of fiber optic standards: Cabling Standards such as: TIA-568-B* (North America) ISO 11801 (International) EN 50173 (European) * Replaced TIA-568-A in 2000. Application Standards such as: 10Base-FL 100Base-FX FDDI ATM Fibre Channel 1000Base-SX and LX Testing Optical Fiber Links in Premises Networks — November 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 Testing Optical Fiber Links in Premises Networks — November 2000

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 Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

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 MHzkm, 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) ? Testing Optical Fiber Links in Premises Networks — November 2000

Horizontal Patch Panel Example (cont.) Horizontal Patch Panel Main Patch Panel Outlet Splice A A A A 0.1 dB B B B B Rx Tx Tx 0.6 dB 0.6 dB 0.6 dB 0.6 dB Rx 90 m 150 m Horizontal Segment Backbone Segment Certification Test Set (Main Unit) Certification Test Set (Remote Unit) Testing Optical Fiber Links in Premises Networks — November 2000

TIA-568-B requirements are met: 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 Testing Optical Fiber Links in Premises Networks — November 2000

But not all 1000Base-SX requirements are met: 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.) Testing Optical Fiber Links in Premises Networks — November 2000

Could this link support 1000Base-SX? 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.) Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

Test Equipment Testing Optical Fiber Links in Premises Networks — November 2000

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) Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

Using an Optical Fiber Scope Ferrule Scratch goes near the core! Dirt particles Fiber Core (singlemode) Testing Optical Fiber Links in Premises Networks — November 2000

Using an Optical Fiber Scope (cont.) Ferrule Fiber Core (multimode) Body oil (don’t touch the connector end-face!) Testing Optical Fiber Links in Premises Networks — November 2000

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!) Testing Optical Fiber Links in Premises Networks — November 2000

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! Testing Optical Fiber Links in Premises Networks — November 2000

One-Jumper Reference Method Tx Rx Rx jumper Optical Power Meter Light Source 2) Check jumpers 0.4 dB Adapter Light Source Optical Power Meter 0 dB 1) Set reference Tx Rx Tx jumper Testing Optical Fiber Links in Premises Networks — November 2000

Measuring Optical Fiber Link Loss Outlet Tx Rx Light Source Optical Power Meter Horizontal Patch Panel Splice Main Patch Panel A B 2 dB Horizontal Segment Backbone Segment -20 dBm -22 dBm Testing Optical Fiber Links in Premises Networks — November 2000

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). Testing Optical Fiber Links in Premises Networks — November 2000

One-Jumper Reference Method Rx Tx Main Unit Remote Unit Main Tx Jumper Remote 1) Set reference 0 dBm Rx Tx Main Unit Remote Unit 2) Check jumpers 0.4 dBm Remote Rx Jumper Main Adapters Testing Optical Fiber Links in Premises Networks — November 2000

Certifying (Loss + Length) 240 m Outlet Rx Tx Main Unit Remote Unit Horizontal Patch Panel Splice Main Patch Panel A B 2dB 2dB 240 m PASS Horizontal Segment Backbone Segment -20 dBm -22 dBm -22 dBm -20 dBm Testing Optical Fiber Links in Premises Networks — November 2000

Using an OTDR To 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 Testing Optical Fiber Links in Premises Networks — November 2000

(to generate a baseline trace) Using an OTDR (to generate a baseline trace) Work Area Outlet Horizontal Patch Panel Splice Main Patch Panel A B Horizontal Segment Backbone Segment Launch Cable (Fiber Box) Receive Cable (Fiber box) OTDR SM MM Testing Optical Fiber Links in Premises Networks — November 2000

One Connection (Loss  0.4 dB) Two Connections (Loss  0.8 dB) Example OTDR Trace Link Length ( 130 m) A B One Connection (Loss  0.4 dB) -1 Launch Cable -2 Horiz. Seg. Two Connections (Loss  0.8 dB) Link Loss ( 2.1 dB) Relative Power (dB) Splice (Loss  0.1 dB) -3 Term. Cable Backbone Segment -4 -5 50 100 150 200 250 Distance (m) Testing Optical Fiber Links in Premises Networks — November 2000

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. Testing Optical Fiber Links in Premises Networks — November 2000

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 Testing Optical Fiber Links in Premises Networks — November 2000

Example Fault: (Fiber break) Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Link Failure Alarm ! Break Testing Optical Fiber Links in Premises Networks — November 2000

Measure Transmitter Output Level (Using an Optical Power Meter) Optical Power Meter (OPM) Equipment output levels look okay. - 8 dBm Network Equipment Outlet Main Patch Panel Horizontal Patch Panel Telecom Closet Splice Testing Optical Fiber Links in Premises Networks — November 2000

Verify Connectivity (Using a VFI or “red laser”) Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Visual Fault Identifier (VFI) No light seen at link output. NOTE: A VFI or “red laser” generates visible light at about 650 nm. Testing Optical Fiber Links in Premises Networks — November 2000

or … Verify Connectivity (Using a light source and power meter) Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Light Source Low Optical Power Meter Testing Optical Fiber Links in Premises Networks — November 2000

Fault-Locate (Using an OTDR) Network Equipment Work Area Outlet Main Patch Panel Equipment Room Horizontal Patch Panel Telecom Closet Splice Launch Cable Receive Cable OTDR MM Testing Optical Fiber Links in Premises Networks — November 2000

OTDR Trace Showing Break at 120 m Distance to fault ( 120 m) Fault ! 250 50 100 150 200 -2 -1 -3 -4 -5 Relative Power (dB) Distance (m) A B Baseline Trace New Trace Testing Optical Fiber Links in Premises Networks — November 2000

Questions? Testing Optical Fiber Links in Premises Networks — November 2000