Calculating Your Insertion Loss Budget
Calculating an Insertion Loss Link Loss budget isn’t a new topic. However, tolerances of Insertion Loss (IL) and Maximum Attenuation Allowance have become more important as the speed of data transmissions have grown throughout the years. All of these values are standards driven, available in ANSI/TIA-568-C.0 for performance and test requirements, and ANSI/TIA-568-C.3 for standards on fiber and connectors
As an example, a 10 Gb/s fiber link in the data center over OM4 could easily reach 400m with a handful of mated pairs (defined as connector to patch panel, connector to cassette, or even splices with certain parameters for fiber type (ex, MMF) diameter (µm), wavelength (nm), maximum attenuation (dB/km), and modal bandwidth-length (MHz-km).
With most data centers having 10 Gb/s uplinks in the rear view, and quickly surpassing 40 Gb/s, and now into 100 Gb/s and 400 Gb/s on the near horizon, there is less room for error for distance and performance as there was when data transmission speeds were ‘lower’. Also, as data centers are physically getting larger, leaf-spine networks are sprawling, and lossless transport is needed for storage services, link channel design is a necessity. With the service life of the average fiber cable plant at around 20 years, a small amount of additional IL/attenuation at 40 Gb/s will make a gigantic difference in fiber application reach when speeds are approaching 400 or 800 Gb/s and beyond.
The How – Testing the Link Per Standards
ANSI/TIA-568-C-0 provides the Link Attenuation Allowance Calculation below:
Link Attenuation Allowance (dB) = Cable Attenuation Allowance (dB) + Connector Insertion Loss Allowance (dB) + Splice Insertion Loss Allowance (dB)
Where: Cable Attenuation Allowance (dB) = Maximum Cable Attenuation Coefficient (dB/km) × Length (km) Connector Insertion Loss Allowance (dB) = Number of Connector Pairs × Connector Loss Allowance (dB) Splice Insertion Loss Allowance (dB) = Number of Splices × Splice Loss Allowance (dB)
Example: Cable Attenuation Allowance = Max Cable Attenuation Coefficient (Example: 3.5dB/Km @ 850nm) x Length (.2Km) x # of Connector Pairs (2) x Connector Pair Loss Allowance (0.5dB)
Connector Insertion Loss 0.5dB x (ex: 2 connectors of Optimized IL Cassettes) = 1.0dB
Link Attenuation Allowance = 0.7dB Cable Attenutation Allowance + 1.0dB (Connector Insertion Loss Allowance) = 1.7dB Link Attenuation for a 200m Trunk with (2) Optimized IL Cassettes
Note: This is considered a ‘worst case scenario’ per ANSI/TIA-568-C-0 standards-based values, which many contractors/installers will design with to ensure reach and performance of the intended application. The reality is most manufacturers components exceed the IL values for the intended performance category, Panduit included.
Application Requirements vs Testing to Standards
The issue with field testing is that the test value only provides a PASS/FAIL acknowledgement. This result gives no assurance that your intended application will provide the reach distance necessary to deliver data from end to end. As an example, the below image shows the distance with Loss Budget calculations. For 16Gb/s Fibre Channel using OM4, you can expect 150m @ 1.0dB connector loss, while 2.4dB loss will give about 50m of distance. While a PASS may have been seen from meeting loss budgets per standards, if the expectation was to get greater than 150m @ 1.0dB loss, the only way to achieve this is now to lower the connector loss by moving to a greater performance option (for example, Standard IL to Optimized IL or Ultra IL performance).
Design, design, design, and ensure you’re futureproofing yourself. While Standard Insertion Loss/ Standard Performance components may be sufficient today, remember you’re building for 15-20 years down the road. Servers come and go, as do switches, but does your cable plant? How are these calculations done?
As you can see having to re-calculate values based on distance, IL changes based on the performance levels of the fiber and the rest of the channel components, and adding additional connectors complicates these calculations immensely. This is why Panduit has simplified this by providing an online Link Loss Calculator.
Note: As mentioned above, while these application reaches and distances are based on standards, the expectation is of better distances/performance in real-world implementation, assuming all installation standards for cleaning, bend radius, and OTDR testing is followed.
To view Panduit’s online Link Loss Calculator, with Application Reach Tables, visit the Panduit Online Link Loss Calculator, and try it for yourself!