How to accelerate your cabling system approvals Adrian Young Fluke Networks November, 2013 Singapore
Objectives for this session Resolve field failures on the spot Look at real world examples of fault resolution Ways to avoid common field failures
Twisted Pair Failures
NEXT failures What is typically done today Press TEST again Change the limit to Channel, hope no one notices Use a 5 metre patch cord, makes the NEXT look better Re-terminate the connector Try a different vendors connector Try a different tester What should be done Use time domain analysis, if available
Time Domain Xtalk (TDX) Not possible to convert the entire frequency Doing so would result in a noisy unusable trace = Only part of the frequency band is converted
Assumption NEXT measurement always runs parallel to limit line With Category 6A, turned out not to be the case
Assumption NEXT measurement always runs parallel to limit line With Category 6A, turned out not to be the case
Assumption NEXT measurement always runs parallel to limit line With Category 6A, turned out not to be the case Analysis band Good margin
Incorrect assumption As a result, issues that only occurred at the higher frequencies could not be identified Red lines - approximate acceptable performance of connections (jacks)
New TDX algorithm Identify the frequency of interest Closest point to the limit line X
New TDX algorithm Convert some of the frequencies before and after into the time domain X
New TDX algorithm A NEXT issue can be identified at any frequency Red lines - approximate acceptable performance (jacks)
New vs. Old TDX Comparison Old TDX New TDX
TDX in action NEXT fails Worst pair combination = 3,6-4,5
TDX in action NEXT fails switch to the time domain for 3,6-4,5 Connections are typically - Less than 35 % Events in the cable are typically - Less than 10% Questionable cross connect @ 15.5 m
Return Loss failures What is typically done today Press TEST again Change the limit to Channel, hope no one notices Use a 5 metre patch cord, may make the Return Loss look better Re-terminate the connector Try a different vendors connector Try a different tester What should be done Use time domain analysis, if available
Traditional TDRs Time Domain Reflectometers Inject a pulse into a pair Measure the response in the time domain Signal Injected Spreading of pulse caused by dispersion Signal Received Event Distance
Traditional TDRs Time Domain Reflectometers Inject a pulse into a pair Measure the response in the time domain Signal Injected Spreading of pulse caused by dispersion Signal Received Two events Distance As with an Optical Time Domain Reflectometer closely spaced events can be missed
Alternative TDR approach Using an Inverse Fourier Transform (math), you can convert from the frequency domain (MHz) to the time domain (Metres). Significant Impedance Anomalies = Allows you to see where the impedance anomalies are that caused Return Loss issues
Alternative TDR approach However, using a IDFT still results in dispersion Frequency Domain Time Domain
New TDR approach Use advanced mathematic algorithms Compensator Frequency Domain Time Domain
Return Loss fails TDR in action #1 Failing at lower frequencies - suggests a cable issue All four pairs on top of each other - suggests water in the cable
Return Loss fails TDR in action #1 Cable anomalies are typically - Less than 0.8 % Water in the cable - anomalies are > - 6% Anomaly of -9.3% @ 50.1 m
Return Loss fails TDR in action #2 Failing at lower frequencies - suggests a cable issue
TDR in action #2 Return Loss fails Cable anomalies are typically - Less than 0.8% - Multiple anomalies exceeding 0.8% here - Suggests damaged cable 0.8% - 0.8%
1000BASE-T would not work In this recent example, one of several now, the link kept dropping back to 100BASE-TX The link was tested end to end for compliance to ISO/IEC Class E A And showed a PASS with good margins
1000BASE-T would not work The link was retested with the addition of TCL: Transverse Conversion Loss ELTCTL: Equal Level Transverse Conversion Transfer Loss TCL and ELTCTL are mandated for lab testing, not field testing in both ANSI/TIA and ISO/IEC standards May wish to use as a troubleshooting tool
Common Fibre Failures
Negative loss Stop setting a reference through a bulkhead adapter? Fixed input port Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss
Negative loss Using an SC to LC adapter is the same as setting a reference through a bulkhead adapter not allowed LC SC
3 Jumper Reference Allowed in ISO/IEC 14763-3 In the field this does not work, you end up with negative loss results or optimistic results Expect this method to go away with the revision of ISO/IEC 14763-3
1 Jumper Reference Requires interchangeable adapters on the input port X
Do this! The 1 Jumper Reference reduces uncertainty Required by many vendors for warranty testing
Ensuring correct reference Field tester manufacturers are starting to include instructional animations in the field testers Here the technician is trying to set a 2 Jumper Reference
Fails @ 1550 nm, not 1310 nm If the 1550 nm loss is greater than the 1310 nm loss, you have either a crack or bend in the fiber Normally found in The back of the connector The splice tray at the splice protector VFL or OTDR required to locate it
Trouble shoot using an OTDR What is an OTDR? Optical Time Domain Reflectometer Allows you to look down the fibre link In reality, it is a box that sits in a cupboard that no one knows how to use
New generation of OTDRs Automatic interpretation of OTDR traces Minimal training / supervision
Real world example Problem is with cassette
Real world example Cassette at far end was replaced resolved in minutes
Real world example Cassette at far end was replaced resolved in minutes
Avoiding issues
Build a reference link Copper testing Anchor it down so it s performance does not change Test it and document it Consider batch testing your reels Lay out > 30 m (100 ft) and terminate it Test it If it is marginal now, it is not going to get better when you install it
Fiber testing You MUST test your reels 100% Quick termination using Mechanical splice or Bare fiber adapter OTDR (Length test) the cable Any breaks will result in a shorter length than expected Mechanical Splice
Questions? Thank you for your time harry.potter@flukenetworks.com