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Should You Be Worried About Bending A Fiber Cable?

September 28, 2016

Fiber wires lose light no matter what. They have a db/km loss rate, this is subject matter we have covered in my other blog on Split Ratio & Budget Light Loss.

But, did you know your bend radius could affect the db loss of a fiber cable?

There is a lot of engineering, research and development that goes into building fiber network hardware. Today I'm talking about passive fiber network TAPs and the bend radius of a fiber cable.

Light freqency


Typical Electronic Frequency in HZ = is 1/ wavelength. In Fiber the Frequency (f) equation is the speed of light in fiber (v) /wavelength (A). The average speed of light in a fiber is around *2.14 X 10 -8 m/seconds.

  • Note this will cary with different fiber but is an acceptable average.
  • Frequency A is a higher frequency than frequency B which has a longer wavelengths.
  • An interesting fact - the frequency of a signal (light or photon flow) stays the same in the air or in a fiber.


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Bend Loss Factors

Bend loss occurs when the fiber cable bends is tighter than the cable's maximum bend tolerance. Bending loss can also occur on a smaller scale from such factors as:

  • Sharp curves of the fiber core
  • Displacements of a few millimeters or less, caused by buffer or jacket imperfections
  • Poor installation practice

Microbending: losses are due to microscopic fiber deformations in the core-cladding interface caused by induced pressure on the glass.

Microbending

 

Macrobending: losses are due to physical bends in the fiber that are large in relation to fiber diameter. 

Macrobending

Attenuation due to macrobending increases with wavelength (ie. greater at 1550nm at 1310nm)


The signal still can get through but loss is still an issue - light is power. Light distortion = power loss. This hurts your optical budge.

In other words, if you have your fibers wrapped too tightly inside your network tools – you could be losing a lot more db than you thought, affecting the distance the data can travel with integrity.

Second, if the bend is too great, there will be stress placed on the cladding that may cause micro cracks, allowing leakage over time, as well as excess stress on the connectors, also causing misalignment that can cause further drops in db.

Our passive fiber TAPs have been designed and factory tested (read 'Born in the USA: The Story of Garland Network TAPs') eliminating any tight bend radius issues. We did not want to have a small compact design that would require tight fiber bends, increasing the risk of db loss as well as sharp curves that can occur in the manufacturing and assembly process.

Looking to add fiber TAPs to your next deployment, but not sure where to start? Join us for a brief network Design-IT consultation or demo. No obligation - it’s what we love to do!

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Heartbeats Packets Inside the Bypass TAP

If the inline security tool goes off-line, the TAP will bypass the tool and automatically keep the link flowing. The Bypass TAP does this by sending heartbeat packets to the inline security tool. As long as the inline security tool is on-line, the heartbeat packets will be returned to the TAP, and the link traffic will continue to flow through the inline security tool.

If the heartbeat packets are not returned to the TAP (indicating that the inline security tool has gone off-line), the TAP will automatically 'bypass' the inline security tool and keep the link traffic flowing. The TAP also removes the heartbeat packets before sending the network traffic back onto the critical link.

While the TAP is in bypass mode, it continues to send heartbeat packets out to the inline security tool so that once the tool is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the tool is ready to go back to work. The TAP will then direct the network traffic back through the inline security tool along with the heartbeat packets placing the tool back inline.

Some of you may have noticed a flaw in the logic behind this solution!  You say, “What if the TAP should fail because it is also in-line? Then the link will also fail!” The TAP would now be considered a point of failure. That is a good catch – but in our blog on Bypass vs. Failsafe, I explained that if a TAP were to fail or lose power, it must provide failsafe protection to the link it is attached to. So our network TAP will go into Failsafe mode keeping the link flowing.

Glossary

  1. Single point of failure: a risk to an IT network if one part of the system brings down a larger part of the entire system.

  2. Heartbeat packet: a soft detection technology that monitors the health of inline appliances. Read the heartbeat packet blog here.

  3. Critical link: the connection between two or more network devices or appliances that if the connection fails then the network is disrupted.

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