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QFX5120 Network Cable and Transceiver Planning
Pluggable Transceivers and Direct Attach Cables Supported on QFX5120 Switches
QFX5120 switches support SFP, SFP+, SFP28, QSFP+, and QSFP28 transceivers. They also support direct attach cables. You can find the list of transceivers supported on QFX5120 switches and information about those transceivers at the following pages:
QFX5120-32C—Hardware Compatibility Tool page for QFX5120-32C
QFX5120-48T—Hardware Compatibility Tool page for QFX5120-48T
QFX5120-48Y—Hardware Compatibility Tool page for QFX5120-48Y
QFX5120-48YM—Hardware Compatibility Tool page for QFX5120-48YM
We recommend that you use only optical transceivers and optical connectors purchased from Juniper Networks with your Juniper Networks device.
If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.
The Gigabit Ethernet transceivers installed in QFX5120 switches support digital optical monitoring (DOM): You can view the diagnostic details for these transceivers by issuing the operational mode CLI command show interfaces diagnostics.
Cable Specifications for QSFP+ and QSFP28 Transceivers on QFX5120 Switches
The 40GbE QSFP+ and 100GbE QSFP28 transceivers used in QFX5120 switches use 12-ribbon multimode fiber crossover cables with MPO/UP, MPO/UPC, or MPO/APC socket connectors. The fiber can be either OM3 or OM4. We do not sell these cables.
To maintain agency approvals, use only a properly constructed, shielded cable.
Ensure that you order cables with the correct polarity. Vendors refer to these crossover cables as key up to key up, latch up to latch up, Type B, or Method B. If you are using patch panels between two QSFP+ ports, ensure that the proper polarity is maintained through the cable plant.
Table 1: QSFP+ and QSFP28 MPO Cable Signals
Table 2: QSFP+ and QSFP28 MPO Fiber-Optic Crossover Cable Pinouts
How to Calculate the Fiber-Optic Cable Power Budget for QFX Series Switches
Calculate the fiber-optic data link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at the worst-case levels.
To calculate the worst-case estimate for the fiber-optic
cable power budget (
PB) for the link:
- Determine values for the link's minimum transmitter power
PT) and minimum receiver sensitivity (
PR). For example, here, (
PT) and (
PR) are measured in decibels, and decibels are referenced to 1 milliwatt (dBm):
PT= –15 dBm
PR= –28 dBm
See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.
- Calculate the power budget (
PB) by subtracting (
PR) from (
–15 dBm – (–28 dBm) = 13 dBm
How to Calculate the Fiber-Optic Cable Power Margin for QFX Series Switches
Calculate the fiber-optic data link's power margin when planning
fiber-optic cable layout and distances to ensure that fiber-optic
connections have sufficient signal power to overcome system losses
and still satisfy the minimum input requirements of the receiver for
the required performance level. The power margin (
PM ) is the amount of power available after
attenuation or link loss (
LL) is subtracted from
the power budget (
When you calculate the power margin, you use a worst-case analysis
to provide a margin of error, even though all the parts of an actual
system do not operate at worst-case levels. A power margin (
PM ) greater than zero indicates
that the power budget is sufficient to operate the receiver and that
it does not exceed the maximum receiver input power. This means the
link will work. A power margin (
PM) that is zero or negative indicates insufficient power
to operate the receiver. See the specification for your receiver to
find the maximum receiver input power.
Before you calculate the power margin, calculate the power budget. See How to Calculate the Fiber-Optic Cable Power Budget for QFX Series Switches.
To calculate the worst-case estimate for the power margin
PM) for the link:
- Determine the maximum value for link loss (
LL) by adding estimated values for applicable link-loss factors; for example, use the sample values for various factors as provided in Table 3 (here, the link is 2 km long and multimode, and the power margin (
PM) is 13 dBm).
Estimated Link Loss Value
Sample Link Loss Calculation Values
Higher-order mode losses
Modal and chromatic dispersion
Multimode—None, if the sum of bandwidth and distance is less than 500 MHz/km
This example assumes five connectors. Loss for five connectors: 5 (0.5 dBm) = 2.5 dBm.
This example assumes two splices. Loss for two splices: 2 (0.5 dBm) = 1 dBm.
This example assumes the link is 2 km long. Fiber attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.
This example assumes the link is 2 km long. Fiber attenuation for 2 km: 2 km (0.5 dBm/km) = 1 dBm.
Clock Recovery Module (CRM)
For information about the actual amount of signal loss caused by equipment and other factors, see your vendor documentation for that equipment.
- Calculate the (
PM) by subtracting (
LL) from (
PB– LL = PM
13 dBm – 0.5 dBm [HOL] – 5 x (0.5 dBm) – 2 (0.5 dBm) – 2 km (1.0 dBm/km) – 1 dB [CRM] = PM
13 dB m – 0.5 dBm – 2.5 dBm – 1 dBm – 2 dBm – 1 dBm = PM
PM = 6 dBm
The calculated power margin is greater than zero, indicating that the link has sufficient power for transmission. Also, the power margin value does not exceed the maximum receiver input power.
Refer to the specifications for your receiver to find the maximum receiver input power.