Fiber Optic Patch Cords and Connectors

Introduction

So the role of any network cable is to connect devices, right? They transmit data to allow the devices to communicate, and more and more often, they also transmit electricity to power the device as well.

Patch cords, specifically, provide a temporary link between multiple devices or other cables It’s considered temporary because it can easily connected and disconnected (REMOVE UTP CABLE), which no one appreciates.

In this lab we’re going to take a close look at patch cords and their connectors. As we saw in the previous episode, they can be used to build simple—but complete—fiber optic networks. So this is a great place to start as we develop the lab.

!!! tip

Address term cord vs cable

Tools and Materials Needed

Step 1: Examine the UTP Patch Cord

I had to take our tiny network here offline to talk about patch cords we’ve been using to enable my laptop to connect to the router.
Examine the UTP patch cord from E1, and review its components and common roles in networks.
- Components
  - Copper strands
  - Coating (color-coded)
  - Boot
  - Crimping
- Roles
  - Internet WAN link
  - Switch links to PCs, cameras, or Wi-Fi radios
  - PoE delivery

Step 2: Examine the Fiber Optic Patch Cords

Review its components and compare/contrast to the UTP patch cord. - Review components - 9um SM fiber and 125um cladding - 250um primary buffer coating - 900um tight buffer coating - PVC jacket and labeling - Ferrule - Crimp - Boot - Review roles - Internet WAN link - Switch links to PCs, cameras, or Wi-Fi radios - Non-conductive, so no PoE, but dielectric nature has advantages too - There are composite cables that can carry electric with fiber. - Discuss durability and damage prevention

Step 3: Identify and Examine the Types of Optical Fibers and Connectors

Duplex LC-UPC OM4 cords
Although it looks similar to the previous cord and has the same LC-UPC connector, it’s using MM fiber instead of SM. For a variety of reasons, I prefer SM over MM, but we’ll get to that in a minute.
Duplex LC-UPC OM5 cords
MM colors for boots and connectors (mention FOCIS), speeds
Simplex SC-UPC OS2 cords
Simplex SC-APC OS2 cords
Simplex LC-UPC to ST-UPC OS2 cords
Simplex LC-UPC to FC-UPC OS2 cords
Now that we’ve covered the general role of patch cords, as well as the common types of cables and connectors used, we’ll wrap things up with a few considerations for deciding which patch cords to use.

Step 4: Consider Singlemode vs Multimode Tradeoffs

One of the first things to consider is which type of fiber to use for each cable: singlemode or multimode?

As you build out your lab, this becomes an increasingly important question. I’ll cover this topic more in-depth in a later episode, but for now, here are some rules of thumb.

Rule #1: Determine your distance requirements.** Both SM and MM can go further than TP, but SM can go way further than MM. In your lab, this is generally not a problem, but if you plan to simulate cable plants over 1Km, like I will, SM is needed. Be careful because there are multiple versions of both MM and SM, each with important characteristics!
Rule #2: Determine your device requirements.** Devices can also define constraints on your cabling decisions based on their transceiver specifications. Historically, because most ISP and DC cabling is shorter and MM fiber and transceivers were cheaper, devices standardized on MM. That’s beginning to change as device costs come down while speeds are increasing, and now network designers see long-term advantage of SM cable plants, however. You can find transceivers that will operate with both MM and SM fiber, giving you flexibility. But as always, study your tech specs carefully!
Rule #3: Determine your fiber application requirements.** Depending on your overall lab plans and network needs, which fiber you use will constrain how you can then use it. If you’re experimenting with attenuation, for example, SM generally has lower loss than MM. One of my objectives is to study WDM with my lab, and for that, SM—specifically G652—is the best choice.

Step 5: Consider Connector Choice Tradeoffs

Next up is considering which type of connector to use for your cable. We’ve reviewed some of the most common options in this episode: an SC or LC form factor, and a UPC or APC polish. Here the options can get a bit more complicated, but the same evaluation process for fiber is useful.
In this case, distance isn’t really an factor, but your device and application requirements still define your constraints.
Transceivers in ISP and DC environments are still generally LC-UPC, so that is straightforward. Between devices, however, such as in patch panels, you might want to consider your port density and rack space constraints, as well as overall cable management standards.
PON networks, however, utilize SC-APC for much of the ISP and OSP. APC has reduced attenuation, and SC form factors are easier to handle, so the application determines the connector.
In any case, remember that you have flexibility through the use of mixed-connector cables as well as adapters within the cable plant to implement the right connector at each termination point.
As a note, there are many other specialized connectors that have their advantages, such as multi-fiber MPOs and highly compact MDCs. I plan to cover some of these later in the lab.

Step 6: Consider Buy-vs-Build Tradeoffs of Patch Cords

Before we wrap up, I wanted to quickly talk about the question of “buy vs build.” Going back to our original UTP patch cords, many people are comfortable making these out of the components: bulk UTP cable, connector boots, and RJ-45s. They can be made on-demand, can be more economical, and made to the exact lengths you need. - So what about fiber? At a high-level, all of those advantages for making your own patch cords apply. But it is more complicated due to skills, tools, and materials needed for preparing and terminating the cables. As a result, most experienced technicians would not recommend it. - There are impressive advances in mechanical connectors and splice-on-connectors, and I’d like to explore this later in the lab, but I personally recommend you purchase your patch cords whenever possible. I certainly do!

Conclusion

We now covered the roles, types, and tradeoffs of fiber patch cords. In some cases there are no easy or right answers on what option to use. In each case, research your requirements; understand your distance, device, and application constraints; and be consistent in your design. And above all, use your lab to experiment and learn all you can. That’s what it’s for!

!!! question

So what patch cords do you use and why?

In the next lab in this series, we’ll take a look at fiber optic connectors and adapters, which will allow us to interconnect patch cords between our devices. This is where the fun really begins.

Again, if you’re new to fiber optics and like what you saw here, head over to the FOA website and check out their Fiber U courses and textbooks.