Fiber at Home? Fiber Wall Plate? How to/Practicality/Cost Questions.

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Terry Kennedy

Well-Known Member
Jun 25, 2015
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New York City
www.glaver.org
LR over short distance are not a good idea. Pretty sure it won't work.
It works fine, and is supported by the spec (as opposed to "out of spec, but happens to work"). If you have a port that will let you see both the thresholds and actual values, you can confirm this. For example:
Code:
           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Transmit Power     Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
---------  -----------------  ----------  ---------  ---------  ---------
Gi1/0/2     -5.6                 0.0        -0.5       -10.0      -11.0

           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Receive Power      Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
-------    -----------------  ----------  ---------  ---------  ---------
Gi1/0/2    -13.0                 1.0         0.0       -28.2      -30.0
As you can see, the maximum transmit level before going out-of-spec is -0.5 dB. The receiver warning threshold is 0.0dB, so you have half a dB of headroom. Even if you hit the alarm thresholds, that would be transmit at 0.0dB and receive at 1.0dB.

With -ER (40km) and -ZR (80km) parts you will need attenuators.

This is -ER:
Code:
           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Transmit Power     Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
---------  -----------------  ----------  ---------  ---------  ---------
Te4/0/1      2.2                 8.0         4.0        -4.7       -8.7

           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Receive Power      Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
-------    -----------------  ----------  ---------  ---------  ---------
Te4/0/1     -7.9                 3.0        -1.0       -15.8      -19.8
And this is -ZR:
Code:
           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Transmit Power     Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
---------  -----------------  ----------  ---------  ---------  ---------
Te1/1        2.2                 5.9         2.9        -1.0       -5.0

           Optical            High Alarm  High Warn  Low Warn   Low Alarm
           Receive Power      Threshold   Threshold  Threshold  Threshold
Port       (dBm)              (dBm)       (dBm)      (dBm)      (dBm)
-------    -----------------  ----------  ---------  ---------  ---------
Te1/1      -18.7                -3.0        -7.0       -27.2      -31.5
NOTE: These are examples from transceivers in actual use. Different transceivers will have different calibration points and thresholds, but these samples should give people a general idea.

There are 15km and 20km -LR parts available, as well as -ZR+ (100km, 120km) parts. The extended range -LR parts may be able to be overloaded with short cables. The extended range -ZR+ parts will definitely overload, just like the -ER and -ZR parts.