A cable test report measures some parameters and calculates the rest. Wiremap, length, insertion loss, return loss, NEXT and the time parameters are measured; ACR-F, PSACR-F, ACR-N and PSACR-N are ratios calculated from them. Knowing which is which tells you what a failure means before you read a value.
Four Families, and Why the Family Matters
Family | Parameters | What a failure points to |
|---|
Connectivity | Wiremap, length | Installation and termination errors |
|---|
Transmission loss | Insertion loss, return loss | Length, materials, impedance control, workmanship |
|---|
Ratios and crosstalk | NEXT, PS-NEXT, ACR-F, PSACR-F, ACR-N | Termination quality and cable quality, in different proportions |
|---|
Time | Propagation delay, delay skew | Run length and cable batch consistency |
|---|
Balance and alien | TCL, ELTCTL, CDNEXT, CMRL, ANEXT, PSANEXT | Construction quality, and how cables were installed alongside each other |
|---|
Measured, calculated, or not required
Not all of these are measured. Wiremap, length, insertion loss, return loss, NEXT and the time parameters are measurements. ACR-F, PSACR-F, ACR-N and PSACR-N are calculated, so when one fails the fault is in an input, and chasing the ratio itself is wasted effort.
Wiremap — The One That Says Nothing About Performance
Wiremap is the connectivity test: every conductor must reach the correct pin at both ends, with no opens, shorts, crossed or split pairs, and the shield checked where one exists. Length comes from the same section, measured per pair by TDR, against 90 meters for a permanent link and 100 meters for a channel.
It is the only parameter here that is not a statement about signal quality. A link can pass wiremap and fail everything else, which is why a wiremap-only tester is not certification. It cannot tell you whether the link will carry a signal, only that the conductors go where the drawing says.
Insertion Loss — The One Length Sets
Insertion loss measures the signal power at the far end against the signal power at the beginning, in decibels. Three things move it: gauge, where 23 AWG loses less than 24 AWG over the same distance; construction, where stranded conductors carry 20 to 50 percent more loss than solid copper of the same length; and temperature, since limits are specified adjusted for 20 °C.
Excessive length is the most common cause of failure, followed by poorly terminated connectors adding loss of their own. Insertion loss is largely a design outcome, so a surprise failure usually means the run is longer than the drawing claims, or the cable is not what it was sold as.
Return Loss — The One Terminations Hide
Return loss measures the reflections caused by impedance changes along the link, in decibels. Every departure from a uniform 100-ohm path — a poor crimp, a crushed section, a sharp bend — reflects energy back toward the transmitter instead of sending it onward. It is measured from both ends on every pair across 1 to 100 MHz, and the report should name the worst pair, the frequency, and the limit at that frequency.
This is the parameter most likely to pass on a bench and fail after installation, because its faults come from handling. A cable coiled in a box has no reflections. The same cable pulled around a tight corner and terminated in a hurry does.
NEXT and PS-NEXT — The Ones Terminations Decide
Pairs are twisted so noise arrives equally on both conductors and the receiver cancels it. NEXT is what happens when that fails between pairs: unwanted coupling from one pair onto another, measured at the same end as the transmitter.
Because NEXT is a difference in signal strength between a disturbing pair and a disturbed pair, a larger number means less crosstalk and is more desirable — the opposite of insertion loss. It varies sharply with frequency, so it is measured across a range, typically 1 to 100 MHz, and the report must state the frequency with the value.
PS-NEXT is the same idea summed: the combined crosstalk from all three other pairs onto the measured pair, the condition that matters for any scheme using all four pairs at once, including Gigabit Ethernet and 10GBASE-T. It runs about 3 dB below the worst-case NEXT at each end, so it rarely fails alone, and because it is calculated from NEXT, fixing the NEXT failure fixes PS-NEXT automatically.
Termination quality dominates both, because the connector and punch-down are where the twist is opened. Cable quality matters far less.
Which end each parameter is measured at
ACR-F — The Ratio That Is Not a Measurement
ACR-F is attenuation to crosstalk ratio at the far end, and it is where reports lose people, because it is not a measurement. It is calculated by subtracting the disturbing pair’s insertion loss from the far-end crosstalk that pair induces in an adjacent pair. It was formerly called ELFEXT, before the naming was aligned with ISO terminology.
Because it is a ratio of two measurements, a failure tells you the relationship degraded, not which side moved. The practical asymmetry is worth knowing: an ACR-F failure usually points at the cable rather than the termination. A short link with excellent terminations can still fail if the cable’s own far-end crosstalk is poor, which makes ACR-F the parameter that catches off-spec or counterfeit cable most reliably.
Propagation Delay and Delay Skew — Two Different Questions
Propagation delay is the time a signal takes to travel from one end of the link to the other, measured per pair in nanoseconds. Field testers measure it at 10 MHz, as required by ANSI/TIA-1152 and by ISO/IEC 11801. Category 5e UTP typically runs a little under 5 ns per meter against a worst-case allowance of 5.7 ns per meter, and most structured wiring standards expect a maximum horizontal delay of 570 ns, while a Cat 6A channel is commonly quoted at 555 ns over 100 meters.
Delay skew is a different question: the difference between the propagation delay on the fastest and slowest pairs. Because each pair has its own twist rate, the pairs do not arrive together, which matters for schemes that use all four pairs at once. Well-built cabling holds skew under 50 ns over a 100-meter link; under 25 ns is excellent, and 45 to 50 ns is marginally acceptable.
The diagnostic contrast is the point of putting them together. Excessive propagation delay has only one cause: the cable is too long. Skew does not. It points at mixed cable batches in one run, or a pair damaged during the pull.
Alien Crosstalk — The One That Is Not on the Mandatory List
Alien crosstalk is unwanted coupling from one balanced twisted-pair component, channel or permanent link to another — cable-to-cable rather than pair-to-pair. It is the most significant transmission parameter for 10GBASE-T, and it depends on how close adjacent cables and connectors are, cable length, twist density, EMI and the hardware between them.
Two facts are routinely assumed rather than checked. Alien crosstalk is not on the list of parameters ANSI/TIA-1152 requires to be reported. The standard provides annex methods usable on installed Cat 6A cabling, and commercial Level IIIe testers can run them, but it takes two sets of testers with a communications link between them, and it has to be written into the specification. The second: it comes from differential coupling, so it is not worsened by common-mode noise from motors, transformers or lighting.
Margin Is Not the Same as Value
Most people read the pass and stop. The number worth reading is the margin.
Margin against value
Every parameter reports a worst-case margin and a worst-case value. Worst-case margin is where the result came closest to the limit line, which is the one to care about. Worst-case value is where the raw value was worst overall, without reference to the limit. Because a tester searches for both across all pairs and pair combinations, the two can fall on different pairs entirely.
A margin of 4 dB is meaningfully better than a margin of 1 dB. A pass at 1 dB deserves a second look: the link works and has almost nothing left.
What Actually Moves the Numbers
Length dominates insertion loss and propagation delay. Termination quality — twist opened up at the connector and punch-down — dominates NEXT and PS-NEXT. Handling such as crushing, sharp bends and over-tensioned pulls appears in return loss. Construction and batch show up in insertion loss, ACR-F and skew. Temperature shifts insertion loss away from the 20 °C basis the limits assume. And the specified test limit decides the verdict.
One layout detail is easy to miss: keeping at least 5 meters between a consolidation point and the outlet improves NEXT and PS-NEXT.
FAQ
Does a passing report prove my link will run 10GBASE-T? It proves the link met every limit in the selected test limit at the time of testing. It does not prove alien crosstalk performance unless that was specified and tested, because it is not among the parameters ANSI/TIA-1152 requires.
Why does my report show a pass but the link drops packets? Read the margins rather than the verdict. A worst-case margin near 1 dB on return loss or NEXT describes a link with no headroom, and such links fail intermittently under load.
Are TCL and ELTCTL always reported? No. Depending on the limit, a report may also carry balance parameters — TCL, equal level TCL (ELTCTL), common mode to differential mode NEXT (CDNEXT) and common mode return loss (CMRL) — describing how well the cable keeps differential signals differential. They appear only when the limit calls for them, so their absence is not evidence they passed.
Procurement Checklist
- Name the test limit in the specification, not just the cable category.
- Require the full ANSI/TIA-1152 parameter set, and state separately whether alien crosstalk is required.
- Require worst-case margin as well as pass or fail, with the offending pair and frequency.
- Set a minimum acceptable margin where the application is not forgiving.
- Confirm the tester’s accuracy level matches the category: Level IIe for Cat 5e, Level III for Cat 6, Level IIIe for Cat 6A, and that calibration is current.
- On a modular plug terminated link, specify the correct far-end adapter so the plug sits inside the measurement.
- Require the report per link, with the limit printed on it.
The Short Version
Measured: wiremap, length, insertion loss, return loss, NEXT, propagation delay, delay skew. Calculated: ACR-F, PSACR-F, ACR-N, PSACR-N. Not on the mandatory list: alien crosstalk, which is an annex method you have to ask for.
Insertion loss and propagation delay fail because of length. NEXT and PS-NEXT fail because of termination. Return loss fails because of handling and impedance control. ACR-F fails because of the cable. Skew fails because of mixed batches or a damaged pair. Read the margin, not the pass.
The Values Only Mean Something Against a Named Limit
Every number on a report is compared against a limit somebody selected, and the same link can pass one limit and fail another. We supply the cable side of that measurement: horizontal and patch constructions whose published performance is stated per construction and per test limit, with the test documentation to match.
Sources
- Belden, "What ANSI/TIA-1152 Says About Category 6A Testing" (Al Greiner) — the definitional wording for wiremap, insertion loss, length, NEXT, PSNEXT, ACRF, PSACRF, return loss, propagation delay and delay skew; the statement that alien crosstalk is not on the ANSI/TIA-1152 list of parameters to report and is an annex method requiring two testers with a communications link; tester accuracy levels IIe, III and IIIe for Cat 5e, Cat 6 and Cat 6A; calibration guidance — https://www.belden.com/blog/ansi-tia-1152-and-cat-6a-testing
- Fluke Networks, "Cable Testing 101: How to Read the Details of Your LinkWare PC Report" — the reported parameter set including ACR-N and PSACR-N; the balance and alien parameters that appear depending on the test limit (TCL, ELTCTL, CDNEXT, CMRL); the distinction between worst-case margin and worst-case value and the fact that they may fall on different pairs — https://www.flukenetworks.com/blog/cabling-chronicles/series-101-how-read-details-your-linkware-pc-report
- SCP, "Electrical Parameters for Category Cables" — insertion loss dependence on gauge with 23 AWG against 24 AWG and stranded against solid at 20 to 50 percent more loss; the 20 °C basis; margin defined as the difference between measured and permitted loss; NEXT and PS-NEXT definitions, the 1 to 100 MHz range and PS-NEXT about 3 dB below worst-case NEXT; return loss from both ends across 1 to 100 MHz; ACR-F derived by subtracting the disturbing pair’s insertion loss from the far-end crosstalk it induces; ANEXT definition, its dependence on cable proximity, length, twist density, EMI and hardware, and its insensitivity to common-mode noise; propagation delay measured at 10 MHz, typical under 5 ns per meter with 5.7 ns per meter worst case, the 570 ns maximum horizontal delay and the statement that excessive propagation delay has only one cause; delay skew under 50 ns with under 25 ns described as excellent and 45 to 50 ns as marginally acceptable; length limits of 90 meters permanent link and 100 meters channel measured by TDR — https://scpcat5e.com/electrical-parameters-for-category-cables/
- Cable Test Shop, "Category 6A Test Parameters: NEXT, PSACR, ELFEXT, and More" — the Cat 6A permanent link figures quoted here, being approximately 27.9 dB for NEXT and 25.5 dB for PS-NEXT at 500 MHz, approximately 555 ns propagation delay for a 100-meter channel and a 50 ns delay skew limit; the observation that ACR-F failures point to cable quality rather than termination quality; the note that TIA renamed ELFEXT to ACR-F to align with ISO terminology — https://cabletestshop.com/blog/cat6a-test-parameters-explained/
- Cabling Installation & Maintenance, "Category 6 performance requirements, and then some" — the note that NEXT loss performance improves with at least 5 meters between the consolidation point and the telecommunications outlet connector, with a similar note for PSNEXT loss, and the channel testing alternative — https://www.cablinginstall.com/standards/cabling-standards/article/16464962/category-6-performance-requirements-and-then-some
- Fluke Networks Knowledge Base, "ANSI/TIA-1152: Twisted-Pair Field Testing Standard" — the Level IIIe and Level 2G accuracy levels and the analyzers that meet them — https://www.flukenetworks.com/knowledge-base/applicationstandards-articles-copper/ansitia-1152-twisted-pair-field-testing-standard
