Cable Compliance: Will ‘Good Enough’ Work When it Comes to Margin over Standard?
When is “just good enough” really good enough – especially when it comes to enterprise networks?
If a network is experiencing problems (dropped links, bottlenecks or slow connections), minimally compliant cable – cable that’s deemed “just good enough” – can sometimes be the culprit, creating a weak link in the chain.
No one wants a cabling system that can barely support current application requirements – let alone what future applications will demand. The typical cable infrastructure (layer 0) has a lifecycle of 25 years or longer – which means it will also have to support technologies and applications that we aren’t even thinking about today.
Minimally compliant cables aren’t designed to meet the speed and power demands of today’s technology and applications. Imagine the implications of cable compliance as technology demands continue to grow.
Lower-tier cables tend to cut it close when it comes to passing cable compliance requirements. Instead of offering ample margin, they run as close to the edge as possible in terms of performance parameters, with little or no margin to spare.
1. Return Loss
Cable return loss margin indicates the difference between the cable’s measured return loss and the maximum return loss level allowed per the standards.
A cable with return-loss margin above the standard reduces the amount of work the physical layer (PHY) inside your equipment must put forth to keep connection links going.
When cable compliance is higher than what the standard requires in terms of return loss, reliance on digital signal processing is reduced and network reliability is improved. This also leads to less reliance on PHY echo cancellation algorithms, which synthesize echo and subtract it from incoming signals to (hopefully) remove echo.
2. Near-End Crosstalk (NEXT)
Cable NEXT margin indicates the difference between the cable’s measured NEXT and the maximum NEXT level allowed per the standards.
Similar to a cable with a return-loss margin above the standard, a cable with a NEXT margin above the standard also means that the cable relies less on digital signal processing of the PHY.
Less reliance on the computational power of the PHY translates to more reliable data transmission, more uptime and lower power consumption.
3. Insertion Loss
Cable insertion loss margin indicates the difference between the cable’s measured insertion loss and the maximum insertion loss level allowed per standards; the higher the margin, the better the cable performance.
Cutting it close when it comes to cable insertion loss margin doesn’t leave much wiggle room for cable temperature levels to rise without experiencing negative impacts.
Minimally compliant cables may pass the performance requirement of 20 degrees C, but problems will occur as soon as the cable gets warmer as a result of increased ambient temperature or the addition of PoE loads.
4. Pair Balance (TCL)
Pair balance is impacted by the cable’s design and manufacturing process. It’s measured via a TCL (transverse conversion loss) test, which is performed by the manufacturer. The test measures mode conversion within a pair at one end by measuring common mode signal returned on the same pair after injecting a differential mode signal onto it. The smaller the signal returned, the better the pair balance.
TCL levels indicate a cable’s noise immunity and its ability to provide adequate performance in noisy environments (noise from neighboring cables or external sources). A TCL margin above standard ensures additional noise immunity and reduces performance issues associated with external noise sources.
5. Connectivity Design
Finally, the performance of connectivity (the mated plug/jack connection) matters! Even if you have a cable with return loss, NEXT, insertion loss and TCL margin all above standard, a poor connector can drag down system performance.
RJ45 plugs and jacks are inherently unbalanced because of the split pair and capacitive and inductive coupling between the contacts in the plug and jack, as well as connector compensation design. The method of compensation needs to compensate not only for pair-to-pair crosstalk, but also the balance within and between pairs.
Investing in System Margin Above Standard
Investing in cable that meets or exceeds standards ensures excellent information capacity and high power-delivery efficiency so you don’t have to worry about infrastructure integrity.
The network will perform as expected, supporting new technologies and applications at the speeds they’re designed for while also providing fast connections and increasing productivity for network users.