In Part 1 of our three-part Fiber Jumper series, we discussed the differences between single mode fiber and various multi-mode standards. We’re back for Part 2 of our three-part Fiber Jumper series and ready to dive into cable variations, and what they all mean.
Rules of the Road: Simplex and Duplex
Simplex is quite simple; it’s one single fiber, like a single lane road. When you’re connecting bidirectional transceivers, a single fiber is all you need! You’d actually be surprised by how many connections can be sent simultaneously over a single fiber; with DWDM you can use the standard 40 channel grouping for 20 connections (20 transmits and 20 receive channels). Simplex can also be used in testing when you’re connecting a standard transceiver to itself.
Duplex is the most common jumper; essentially duplex is two lanes bonded together. One lane is for transmit and one lane is for receive, like a two-way street.
Stay in Your Lane: 12- and 24-Lane Options and Assignments
For transceivers such as some QSFPs, you will have 4 transmitting fibers and 4 receiving fibers with 4 unused in-between them. They are typically a bundle of fibers in a single fiber jacket. These can get involved, though. Depending on how you’re using them, you want each end’s fibers to line up in a specific order.
- Method A (Direct): Lane 1 on side A maps to Lane 1 on side B and so forth. In structured fiber solutions, you’ll occasionally see this.
- Method B (Cross): Lane 1A connects to Lane 12B, Lane 2A connects to Lane 11B and so forth. This is so that the transmit on one side lines up with the receive on the other. When you’re connecting one transceiver to another, this is where it’s at!
- Method C (Cross Pair): This one is a bit unusual as it crosses pairs. 1 to 2, 2 to 1, 3 to 4, 4 to 3, and so on. Criss-cross, apple sauce! This is typically used in structured fiber environments where the multicore fiber bundles are carrying signals used by traditional two lane transceivers.
Like 12-lane, there are applications that call for bundles of fibers in larger numbers. The A and B methods are valid here as well, but you may see other less traditional assignments, too.
Road Trippin’: Jackets for Every Environment
Fiber jackets determine what environments they are suitable for. The right rating for the job helps strike the right balance of safety and economy.
- PVC is the most basic. If these burn they will release some noxious smoke.
- Riser PVC is intended for vertical and horizontal runs in facilities with contained HVAC systems. If they burn, they do release noxious smoke, but not as much as unqualified PVC.
- Plenum is an airspace meant to circulate air. It’s also the rating for a fiber that isn’t going to poison you if it burns. It might still be smokey, but if you’re running through ductwork, Plenum-rated fibers are a must.
- Lastly, Low Smoke Zero Halogen (LSZH), is non-halogenated and flame retardant, emits limited smoke, and no halogen when exposed to high sources of heat, e.g. flame. LSZH reduces the amount of toxic and corrosive gas emitted during combustion, and is typically used in poorly ventilated areas.
Sure there are more variants of common fiber lanes and jacket types (armored jumpers are really cool!), but we’ll leave those off for now, and next time we’ll discuss the what and why of different fiber connectors. In the meantime, if you are ready to talk to an optics expert about your fiber needs, you can start chatting live with them now!