Rethinking

Rethinking "Plug and Play" and Testing

By: Kent Goldsmith | Engineer Manager

 

At CABLExpress, we believe in the philosophy that you should Respect Layer One®. In fact, it pretty much drives our whole existence!

With that in mind, we realized that maybe we all need to re-think the term “plug and play.” This terminology is a cabling industry buzzword that implies simplicity with fiber optic connectivity infrastructure. 

Testing... testing...

Many fiber optic links consist of a backbone trunk frequently terminated with an MPO-style connector on both ends. This is then connected to an MPO to LC fiber optic cassette module on both ends. The fiber optic jumpers on both ends of the module then connect directly to equipment. 

Even though this is considered a “plug and play” system, we still need to test it to verify functionality. A channel test is the best way to accomplish this. This test will show the true loss from active device to active device. It is often referred to as end-to-end attenuation testing.

Meeting industry standards

Most attenuation testers are already programmed with the industry standard losses but mistakes can be made if the tester is not used properly and with the correct settings. Typically for a 10G link, the loss budget is 2.6dB. There are different loss budgets associated with different transmission speeds and protocols (Ethernet vs. Fibre Channel).

The industry standard loss for an MPO mated pair (two MPOs connected to each other) is 0.7dB maximum. The standard loss for an LC mated pair (two LCs connected to each other) is 0.5dB maximum.

The link described above has two LC mated pairs and two MPO mated pairs.

So we must add them up to see that the end-to-end attenuation will be 2.4dB maximum. This total does not include the attenuation within the fiber itself. However, this attenuation is very low and does not significantly add to the overall link attenuation unless the link is very long.

A typical building (intrabuilding) link is usually not more than 300 meters (984ft). The attenuation for 50um OM4 fiber at 850nm is 3.5dB per kilometer or 1000m. So a 300 meter link would fall at around 1dB for loss within the fiber.  In our scenario, if we add the 1dB of loss within the fiber and the total losses of the four mated pairs in the link we get 2.5dB maximum for the link. This meets the industry standard loss budget of 2.6dB for a 10G link.

Keep 'em clean

To ensure minimal loss, it is also very important to clean all connectors before mating them. The best practice is to clean and inspect, but if you don’t have the time or the equipment to effectively inspect the endfaces of your fiber optic connectors, then it is acceptable to just clean them. A one click cleaner is the best and fastest way to accomplish this in the field.

There are a number of factors to keep in mind when ensuring your links meet loss budgets. Sometimes “plug and play” requires a little more forethought than you might expect.